Guyton Hall

Question 1

5. Which statement about cardiac muscle is most accurate? A) The T-tubules of cardiac muscle can store much less calcium than in T-tubules in skeletal muscle B) The strength and contraction of cardiac muscle depends on the amount of calcium surrounding cardiac myocytes C) In cardiac muscle, the initiation of the action potential causes an immediate opening of slow calcium channels D) Cardiac muscle repolarization is caused by opening of sodium channels E) Mucopolysaccharides inside T-tubules bind chloride ions

Answer 1

5. B) The cardiac muscle stores much more calcium in its tubular system than does skeletal muscle and is much more dependent on extracellular calcium than is the skeletal muscle. An abundance of calcium is bound by the mucopolysaccharides inside the T-tubule. This calcium is necessary for contraction depends on the calcium concentration surrounding the cardiac myocytes. At the initiation of the action potential, the fast sodium channels open first, which is followed later by opening of the slow calcium channels.

Question 2

6. A 30-year-old man has an ejection fraction of 0.25 and an end-systolic volume of 150 milimeters. What is his end-diastolic volume? A) 50 milliliters B) 100 milliliters C) 125 milliliters D) 200 milliliters E) 250 milliliters

Answer 2

6. D) The end-diastolic volume is always greater than the end-systolic volume. Multiplication of the ejection fraction by the end-diastolic volume is 50 milliliters in this problem. Therefore, the end-diastolic volume is 50 milliliters greater than the end-systolic volume and has a value of 200 milliliters.

Question 3

7. In a resting adult, the typical ventricular ejection fraction has what value? A) 20% B) 30% C) 40% D) 60% E) 80%

Answer 3

7. D) The typical ejection fraction is 60%, and lower values are indicative of a weakened heart.

Question 4

8. In which phase of the ventricular muscle action potential is the potassium permeability the highest? A) 0 B) 1 C) 2 D) 3 E) 4

Answer 4

8. D) During phase 3 of the ventricular muscle action potential, the potassium permeability of ventricular muscle greatly increases, which causes a more negative membrane potential.

Question 5

9) A 60-year-old man’s EKG shows that he has a R-R interval of 1.5 seconds at rest. Which statement best explains his condition? A) He has a fever B) He has a normal heart rate C) He has decreased parasympathetic stimulation of the S-A node D) He is a trained athlete at rest E) He has normal polarization of the S-A node

Answer 5

9. D) Heart rate is determined by the formula 60/R-R interval. The heart rate for this patient is 40 beats per minute. This heart rate is slow, which would occur in a trained athlete. A fever would increase heart rate. Excessp parasympathetic stimulation and hyperpolarization of the S-A node both decrease heart rate.

Question 6

10. Which of the following is most likely to cause the heart to go into spastic contraction? A) Increased body temperature B) Increased sympathetic activity C) Decreased extracellular fluid potassium ions D) Excess extracellular fluid potassium ions E) Excess extracellular fluid calcium ions

Answer 6

10. E) The heart goes into spastic contractions after a large increase in calcium ion concentration surrounding the cardiac myofibrils, which occurs if the extracellular fluid calcium ion concentration increases too much. An excess potassium concentration in the extracellular fluids causes the heart to become dilated because of the decrease in resting membrane potential of the cardiac muscle fibers.

Question 7

11. What happens at the end of ventricular isovolumetric relaxation? A) The A-V valves close B) The aortic valve opens C) The aortic valve closes D) The mitral valve opens E) The pulmonary valve closes

Answer 7

11. D) At the end of isovolumetric relaxation, the mitral and tricuspid valves open, which is followed by the period of diastolic filling.

Question 8

12. Which event is associated with the first heart sound? A) Closing of the aortic valve B) Inrushing of blood into the ventricles during diastole C) Beginning of diastole D) Opening of the A-V valves E) Closing of the A-V valves

Answer 8

12. E) As seen in Chapter 9, the first heart sound by definition occurs just after the ventricular pressure exceeds the atrial pressure, which causes A-V valves to mechanically close. The second heart sound occurs when the aortic and pulmonary valves close.

Question 9

13. Which condition will result in a dilated, flaccid heart? A) Excess calcium ions in the blood B) Excess potassium ions in the blood C) Excess sodium ions in the blood D) Increased sympathetic stimulation E) Increased norepinephrine concentration in the blood

Answer 9

13. B) Having excess potassium ions in the blood and extracellular fluid causes the heat to become dilated and flaccid and also slows the heart. This effect is important because of a decrease in the resting membrane potential in the cardiac muscle fibers. As the membrane potential decreases, which makes the contraction of the heart progressively weaker. Excess calcium ions in the blood and sympathetic stimulation and increased norepinephrine concentration of the blood all cause the heart to contract vigorously.

Question 10

14. A 25-year-old well-conditioned athlete weights 80 kilograms (176 pounds). During maximal sympathetic stimulation, what is the plateau level of his cardiac output function curve? A) 3 liters per minute B) 5 liters per minute C) 10 liters per minute D) 13 liters per minute E) 25 liters per minute

Answer 10

14. E) The normal plateau level of the cardiac output function curve is 13 L/min. This level decreases in any kind of cardiac failure and increases markedly during sympathetic stimulation.

Question 11

15. Which phase of the cardiac cycle follows immediately after the beginning of the QRS wave? A) Isovolumetric relaxation B) Ventricular ejection C) Atrial systole D) Diastasis E) Isovolumetric contraction

Answer 11

15. E) Immediately after the QRS wave, the ventricles begin to contract, and the first phase that occurs is isovolumetric contraction. Isovolumetric contraction occurs before the ejection phase and increases the ventricular pressure enough to mechanically open the aortic and pulmonary valves.

Question 12

16. Which of the following structures will have the slowest rate of conduction of the cardiac action potential? A) Atrial muscle B) Anterior internodal pathway C) A-V bundle fibers D) Purkinje fibers E) Ventricular muscle

Answer 12

16. C) The atrial and ventricular muscles have a relatively rapid rate of conduction of the cardiac action potential, and the anterior internodal pathway also has fairly rapid conduction of the impulse. However, the A-V bundle myofibrils have a slow rate of conduction because their sizes are considerably smaller than the sizes of the normal atrial and ventricular muscle. In addition, their slow conduction is partly caused by diminished numbers of gap junctions between successive muscles cells in the conducting pathway, causing a great resistance to conduction of the excitatory ions from one cell to the next.

Question 13

17. What is the normal total delay of the cardiac impulse in the A-V node + bundle? A) 0.22 second B) 0.18 second C) 0.16 second D) 0.13 second E) 0.09 second

Answer 13

17. D) The impulse from the S-A node travels rapidly through the internodal pathways and arrives at the A-V node at 0.03 second, at the A-V bundle at 0.12 second, and at the ventricular septum at 0.16 second. The total delay is thus 0.13 second.

Question 14

18. Sympathetic stimulation of the heart does which of the following? A) Releases acetylcholine at the sympathetic endings B) Decreases sinus nodal discharge rate C) Decreases excitability of the heart D) Releases norepinephrine at the sympathetic endings E) Decreases cardiac contractility

Answer 14

18. D) Increased sympathetic stimulation of the heart increases heart rate, atrial contractility, and ventricular contractility and also increases norepinephrine release at the ventricular sympathetic nerve endings. It does not release acetylcholine. It does cause an increased sodium permeability of the A-V node, which increases the rate of upward drift of the membrane potential to the threshold level for self-excitation, thus increasing the heart rate.

Question 15

19. If the S-A node discharges at 0.00 seconds, when will the action potential normally arrive at the epicardial surface at the base of the left ventricle? A) 0.22 second B) 0.18 second C) 0.16 second D) 0.12 second E) 0.09 second

Answer 15

19. A) After the S-A node discharges, the action potential travels through the atria, through the A-V bundle system, and finally to the ventricular septum and throughout the ventricle. The last place that the impulse arrives is at the epicardial surface at the base of the left ventricle, which requires a transit time of 0.22 second.

Question 16

20. Which condition at the A-V node will cause a decrease in heart rate? A) Increased sodium permeability B) Decreased acetylcholine levels C) Increased norepinephrine levels D) Increased potassium permeability E) Increased calcium permeability

Answer 16

20. D) The increase in potassium permeability causes a hyperpolarization of the A-V node, which will decrease the heart rate. Increases in sodium permeability will actually partially depolarize the A-V node, and an increase in norepinephrine levels increases the heart rate.

Question 17

21. Which statement best explains how sympathetic stimulation affects the heart? A) The permeability of the S-A node to sodium decreases B) The permeability of the A-V node to sodium decreases C) The permeability of the S-A node to potassium increases D) There is an increased rate of upward drift of the resting membrane potential of the S-A node E) The permeability of the cardiac muscle to calcium decreases

Answer 17

21. D) During sympathetic stimulation, the permeabilities of the S-A node and the A-V node increase. In addition, the permeability of cardiac muscle to calcium increases, resulting in an increased contractile strength. Furthermore, an upward drift of the resting membrane potential of the S-A node occurs. Increased permeability of the S-A node to potassium does not occur during sympathetic stimulation.

Question 18

22. What is the membrane potential (threshold level) at which the S-A node discharges? A) −40 millivolt B) −55 millivolt C) −65 millivolt D) −85 millivolt E) −105 millivolt

Answer 18

22. A) The normal resting membrane potential of the S-A node is −55 millivolts. As the sodium leaks into the membrane, an upward drift of the membrane potential occurs until it reaches −40 millivolts. This is the threshold level that initiates the action potential at the S-A node.

Question 19

23. Which condition at the S-A node will cause heart rate to decrease? A) Increased norepinephrine level B) Increased sodium permeability C) Increased calcium permeability D) Increased potassium permeability E) Decreased acetylcholine level

Answer 19

23. D) Increases in sodium and calcium permeability at the S-A node result in an increase in heart rate. An increased potassium permeability causes a hyperpolarization of the S-A node, which causes the heart rate to decrease.

Question 20

24. In which phase of the ventricular muscle action potential is the sodium permeability the highest? A) 0 B) 1 C) 2 D) 3 E) 4

Answer 20

24. A) Sodium permeability is highest during phase 0. Calcium permeability is highest during phase 2, and potassium is most permeable in phase 3.

Question 21

25. If the S-A node discharges at 0.00 seconds, when will the action potential normally arrive at the A-V bundle (bundle of His)? A) 0.22 second B) 0.18 second C) 0.16 second D) 0.12 second E) 0.09 second

Answer 21

25. D) The action potential arrives at the A-V bundle at 0.12 second. It arrives at the A-V node at 0.03 second and is delayed 0.09 second in the A-V node, which results in an arrival time at the bundle of His of 0.12 second.

Question 22

26. If the Purkinje fibers, situated distal to the A-V junction, become the pacemaker of the heart, what is the expected heart rate? A) 30/min B) 50/min C) 60/min D) 70/min E) 80/min

Answer 22

26. A) If the Purkinje fibers are the pacemaker of the heart, the heart rate ranges between 15 and 40 beats/ min. In contrast, the rate of firing of the A-V nodal fibers are 40 to 60 times a minute, and the sinus node fires at 70 to 80 times per minute. If the sinus node is blocked for some reason, the A-V node will take over as the pacemaker, and if the A-V node is blocked, the Purkinje fibers will take over as the pacemaker of the heart.

Question 23

27. If the S-A node discharges at 0.00 seconds, when will the action potential normally arrive at the A-V node? A) 0.03 second B) 0.09 second C) 0.12 second D) 0.16 second E) 0.80 second

Answer 23

27. A) It takes 0.03 second for the action potential to travel from the S-A node to the A-V node.

Question 24

28. What is the delay between the S-A node discharge and arrival of the action potential at the ventricular septum? A) 0.80 second B) 0.16 second C) 0.12 second D) 0.09 second E) 0.03 second

Answer 24

28. B) The impulse coming from the S-A node to the A-V node arrives at 0.03 second. Then there is a total delay of 0.13 second in the A-V node and bundle system, allowing the impulse to arrive at the ventricular septum at 0.16 second.

Question 25

29. A patient had an ECG at the local emergency department. The attending physician stated that the patient had an A-V nodal rhythm. What is the likely heart rate? A) 30/min B) 50/min C) 65/min D) 75/min E) 85/min

Answer 25

29. B) The normal rhythm of the A-V node is 40 to 60 beats per minute. Purkinje fibers have a rhythm of 15 to 40 beats per minute.

Question 26

30. Which condition at the A-V node will cause a decrease in heart rate? A) Increased sodium permeability B) Decreased acetylcholine level C) Increased norepinephrine level D) Increased potassium permeability E) Increased calcium permeability

Answer 26

30. D) An increase in potassium permeability causes a decrease in the membrane potential of the A-V node. Thus, it will be extremely hyperpolarized, making it much more difficult for the membrane potential to reach its threshold level for conduction, resulting in a decrease in heart rate. Increases in sodium and calcium permeability and norepinephrine levels increase the membrane potential, causing a tendency to increase the heart rate.

Question 27

31. When recording lead aVL on an ECG, which is the positive electrode? A) Left arm B) Left leg C) Right leg D) Left arm + left leg E) Right arm + left leg

Answer 27

31. A) By convention, the left arm is the positive electrode for lead aVL of an ECG.

Question 28

32. When recording lead II on an ECG, the right arm is the negative electrode and the positive electrode is the A) Left arm B) Left leg C) Right leg D) Left arm + left leg E) Right arm + left leg

Answer 28

32. B) By convention, the left leg is the positive electrode for lead II of an ECG.

Question 29

33. Sympathetic stimulation of the heart normally causes which condition? A) Acetylcholine release at the sympathetic endings B) Decreased heart rate C) Decreased rate of conduction of the cardiac impulse D) Decreased force of contraction of the atria E) Increased force of contraction of the ventricles

Answer 29

33. E) Sympathetic stimulation of the heart normally causes an increased heart rate, increased rate of conduction of the cardiac impulse, and increased force of contraction in the atria and ventricles. However, it does not cause acetylcholine release at the sympathetic endings because they contain norepinephrine. Parasympathetic stimulation causes acetylcholine release. The sympathetic nervous system firing increases in the permeability of the cardiac muscle fibers, the S-A node, and the A-V node to sodium and calcium.

Question 30

36. What is the normal QT interval? A) 0.03 second B) 0.13 second C) 0.16 second D) 0.20 second E) 0.35 second

Answer 30

36. E) The contraction of the ventricles lasts almost from the beginning of the Q wave and continues to the end of the T wave. This interval is called the Q-T interval and ordinarily lasts about 0.35 second.

Question 31

37. When recording lead II on an ECG, the negative electrode is the A) Right arm B) Left leg C) Right leg D) Left arm + left leg E) Right arm + left leg

Answer 31

37. A) By convention, the right arm is the negative electrode for lead II of an ECG. TMP13 p. 135

Question 32

38. When recording lead I on an ECG, the right arm is the negative electrode and the positive electrode is the A) Left arm B) Left leg C) Right leg D) Left arm + left leg E) Right arm + left leg

Answer 32

38. A) By convention, the left arm is the negative electrode for lead I of an ECG.

Question 33

39. A 65-year-old man had an ECG at a local emergency department after a biking accident. His weight was 80 kilograms (176 pounds), and his aortic blood pressure was 160/90 mm Hg. The QRS voltage was 0.5 millivolt in lead I and 1.5 millivolts in lead III. What is the QRS voltage in lead II? A) 0.5 millivolt B) 1.0 millivolt C) 1.5 millivolts D) 2.0 millivolts E) 2.5 millivolts

Answer 33

39. D) Einthoven’s law states that the voltage in lead I plus the voltage in lead III is equal to the voltage in lead II, which in this case is 2.0 millivolts.

Question 34

40. A ventricular depolarization wave, when traveling −60 degrees in the frontal plane, will cause a large negative deflection in which lead? A) aVR B) aVL C) Lead II D) Lead III E) aVF

Answer 34

40. D) Different ECG lead axes are shown in the figure. Lead III has a positive portion at 120 degrees and a negative portion at −60 degrees. Therefore, lead III has correct axes for this question.

Question 35

44. Which condition will usually result in left axis deviation in an ECG? A) Systemic hypertension B) Pulmonary valve stenosis C) Pulmonary valve regurgitation D) Rightward angulation of the heart E) Pulmonary hypertension

Answer 35

44. A) Systemic hypertension results in a left axis deviation because of the enlargement of the left ventricle. Pulmonary valve stenosis and pulmonary valve regurgitation result in an enlarged right ventricle and right axis deviation. A rightward angulation of the heart will cause a rightward shift in the mean electrical axis. Pulmonary hypertension causes enlargement of the right heart and thus causes right axis deviation.

Question 36

45. A ventricular depolarization wave, when traveling 60 degrees in the frontal plane, will cause a large positive deflection in which of the following leads? A) aVR B) aVL C) Lead I D) Lead II E) aVF

Answer 36

45. D) Lead II has a positive vector at the 60-degree angle. The negative end of lead II is at −120 degrees.

Question 37

48. Mr. Smith had an ECG at a local hospital, but his records were lost. The ECG technician remembered that the QRS deflection was large and positive in lead II and 0 in aVL. What is his mean electrical axis in the frontal plane? A) 90 degrees B) 60 degrees C) 0 degree D) −60 degrees E) −90 degrees

Answer 37

48. B) The patient has a mean electrical axis of 60 degrees because of the large deflection in lead II and zero in lead aVL. The axis of aVL is −30 degrees, which is perpendicular to lead II, and this indicates that the axis must be 60 degrees.

Question 38

50. A 55-year-old man underwent an ECG at an annual physical, and his net deflection (R wave minus Q or S wave) in standard limb lead I was −1.2 millivolts. Standard limb lead II has a net deflection of +1.2 millivolts. What is the mean electrical axis of his QRS? A) −30 degrees B) +30 degrees C) +60 degrees D) +120 degrees E) −120 degrees

Answer 38

50. D) The QRS wave plotted on lead I was −1.2 millivolts, and lead II was +1.2 millivolts, so the absolute value of the deflections was the same. Therefore, the mean electrical axis must be exactly halfway in between these two leads, which is halfway between the lead II axis of 60 degrees and the lead I negative axis of 180 degrees, which provides a value of 120 degrees.

Question 39

51. During the T-P interval in an ECG of a patient with a damaged cardiac muscle, which of the following is true? A) The entire ventricle is depolarized B) The entire ventricle is depolarized except for the damaged cardiac muscle C) About half the ventricle is depolarized D) The entire ventricle is repolarized E) The entire ventricle is repolarized except for the damaged cardiac muscle

Answer 39

51. E) During the T-P interval in a patient with a damaged ventricle, the only area depolarized is the damaged muscle. Therefore, the remainder of the ventricle is repolarized. At the J point the entire ventricle is depolarized in a patient with a damaged cardiac muscle or in a patient with a normal cardiac muscle. The area of the heart that is damaged will not repolarize but remains depolarized at all times.

Question 40

53. A 30-year-old man had an ECG at his physician’s office, but his records were lost. The ECG technician remembered that the QRS deflection was large and positive in lead aVF and 0 in lead I. What is the mean electrical axis in the frontal plane? A) 90 degrees B) 60 degrees C) 0 degree D) −60 degrees E) −90 degrees

Answer 40

53. A) Because the deflection in this ECG is 0 in lead I, the axis has to be 90 degrees away from this lead. Therefore, the mean electrical axis must be +90 degrees or −90 degrees. Because the aVF lead has a positive deflection, the mean electrical axis must be at +90 degrees.

Question 41

54. A 60-year-old woman tires easily. Her ECG shows a QRS complex that is positive in the aVF lead and negative in standard limb lead I. What is a likely cause of this condition? A) Chronic systemic hypertension B) Pulmonary hypertension C) Aortic valve stenosis D) Aortic valve regurgitation

Answer 41

54. B) The ECG from this patient has a positive deflection in aVF and a negative deflection in standard limb lead I. Therefore, the mean electrical axis is between 90 degrees and 180 degrees, which is a rightward shift in the ECG mean electrical axis. Systemic hypertension, aortic valve stenosis, and aortic valve regurgitation cause hypertrophy of the left ventricle and thus a leftward shift in the mean electrical axis. Pulmonary hypertension causes a rightward shift in the axis and is therefore characterized by this ECG.

Question 42

55. A 65-year-old patient with a heart murmur has a mean QRS axis of 120 degrees, and the QRS complex lasts 0.18 second. What is the likely diagnosis? A) Aortic valve stenosis B) Aortic valve regurgitation C) Pulmonary valve stenosis D) Right bundle branch block E) Left bundle branch block

Answer 42

55. D) A QRS axis of 120 degrees indicates a rightward shift. Because the QRS complex is 0.18 second, this indicates a conduction block. Therefore, the diagnosis that fits with these characteristics is a right bundle branch block.

Question 43

57. A 50-year-old man has been having fainting “spells” for about 2 weeks. During the episodes, his ECG shows a ventricular rate of 25 beats/min and 100 P waves per minute. After about 30 seconds of fainting, a normal sinus rhythm recurs. What is his likely diagnosis? A) Atrial flutter B) First-degree A-V block C) Second-degree A-V block D) Third-degree A-V block E) Stokes-Adams syndrome

Answer 43

57. E) This patient has a difference in the atrial rate of 100 and in the ventricular rate of 25. The 25 rate in the ventricles is indicative of a rhythm starting in the Purkinje fibers. A-V block is occurring, but it comes and goes, which is only fulfilled by Stokes-Adams syndrome.

Question 44

58. An 80-year-old man had an ECG taken at his local doctor’s office, and the diagnosis was atrial fibrillation. Which condition is likely in someone with atrial fibrillation? A) Ventricular fibrillation, which normally accompanies atrial fibrillation B) Strong P waves on the ECG C) An irregular and fast rate of ventricular contraction D) A normal atrial “a” wave E) A smaller atrial volume than normal

Answer 44

58. C) A person with atrial fibrillation has a rapid, irregular heart rate. The P waves are missing or are very weak. The atria exhibit circus movements, and atrial volume is often increased, causing the atrial fibrillation.

Question 45

59. Circus movements in the ventricle can lead to ventricular fibrillation. Which condition in the ventricular muscle will increase the tendency for circus movements? A) Decreased refractory period B) Low extracellular potassium concentration C) Increased refractory period D) Shorter conduction pathway (decreased ventricular volume) E) Increase in parasympathetic impulses to the heart

Answer 45

59. A) Circus movements occur in ventricular muscle, particularly in persons with a dilated heart or decreases in conduction velocity. High extracellular potassium and sympathetic stimulation, not parasympathetic stimulation, increase the tendency for circus movements. A longer refractory period tends to prevent circus movements of the heart, because when the impulses travel around the heart and contact the area of ventricular muscle that has a longer refractory period, the action potential stops at this point.

Question 46

60. A 50-year-old man has a blood pressure of 140/85 mm Hg and weighs 90.7 kilograms (200 pounds). He reports that he is not feeling well, his ECG has no P waves, he has a heart rate of 46 beats/min, and the QRS complexes occur regularly. What is his likely condition? A) First-degree heart block B) Second-degree heart block C) Third-degree heart block D) Sinoatrial heart block E) Sinus bradycardia

Answer 46

60. D) When a patient has no P waves and a low heart rate, it is likely that the impulse leaving the sinus node is totally blocked before entering the atrial muscle, which is called sinoatrial block. The ventricles pick up the new rhythm, usually initiated in the A-V node at this point, which results in a heart rate of 40 to 60 per minute. In contrast, during sinus bradycardia, P waves are still associated with each QRS complex. In first-, second-, and third-degree heart block, P waves are present in each of these instances, although some are not associated with QRS complex.

Question 47

65. What decreases the risk of ventricular fibrillation? A) A dilated heart B) An increased ventricular refractory period C) Decreased electrical conduction velocity D) Exposure of the heart to 60-cycle alternating current E) Epinephrine administration

Answer 47

65. B) A dilated heart increases the risk of occurrence of ventricular fibrillation because of an increase in the likelihood of circus movements. Also, if the conduction velocity decreases, it will take a longer period for the impulse to travel around the heart, which decreases the risk of ventricular fibrillation. Exposure of the heart to 60-cycle alternating current or epinephrine administration increases the irritability of the heart. If the refractory period is long, the likelihood of re-entrant type of pathways decreases, because when the impulse travels around the heart, the ventricles remain in a refractory period.

Question 48

66. Which of the following will usually result in an inverted P wave that occurs after the QRS complex? A) Premature contraction originating in the atrium B) Premature contraction originating high in the A-V junction C) Premature contraction originating in the middle of the A-V junction D) Premature contraction originating low in the A-V junction E) Atrial fibrillation

Answer 48

66. D) An inverted P wave occurs in patients with a premature contraction originating in the A-V junction. If the P wave occurs after the QRS complex, the junctional contraction started low in the A-V junction. Junctional contractions originating high in the A-V junction will have a P wave that occurs before the QRS, and likewise one originating in the middle of junction occurs during the QRS.

Question 49

69. A 60-year-old woman has been diagnosed with atrial fibrillation. Which statement best describes this condition? A) The ventricular rate of contraction is 140 beats/min B) The P waves of the ECG are pronounced C) Ventricular contractions occur at regular intervals D) The QRS waves are more pronounced than normal E) The atria are smaller than normal

Answer 49

69. A) A person with atrial fibrillation has a rapid, irregular heart rate. The P waves are missing or are very weak. The atria exhibit circus movements and often are very enlarged, causing the atrial fibrillation.

Question 50

70. What occurs after electrical shock of the heart with a 60-cycle alternating current? A) A normal arterial pressure B) A decreased ventricular refractory period C) Increased electrical conduction velocity D) A shortened conduction pathway around the heart E) Normal cardiac output

Answer 50

70. B) Ventricular fibrillation often occurs in a heart exposed to a 60-cycle alternating current. An increased conduction velocity through the heart muscle or a shortened conduction pathway around the heart decreases the probability of re-entrant pathways. A shortened ventricular refractory period increases the possibility of fibrillation. Thus, when the electrical stimulus travels around the heart and reaches the ventricular muscle that was again initially stimulated, the risk of ventricular fibrillation increases because the muscle will be out of the refractory period.

Question 51

71. A 55-year-old man has been diagnosed with StokesAdams syndrome. Two minutes after the syndrome starts to cause active blockade of the cardiac impulse, which of the following is the pacemaker of the heart? A) Sinus node B) A-V node C) Purkinje fibers D) Cardiac septum E) Left atrium

Answer 51

71. B) During a Stokes-Adams syndrome attack, total A-V block suddenly begins, and the duration of the block may be a few seconds or even several weeks. The new pacemaker of the heart is distal to the point of blockade but is usually deep in the A-V node or the A-V bundle.

Question 52

74. Which statement best describes a patient with premature atrial contraction? A) The pulse taken from the radial artery immediately after the premature contraction will be weak B) Stroke volume immediately after the premature contraction will be increased C) The P wave is never seen D) The probability of these premature contractions occurring is decreased in people with a large caffeine intake E) It causes the QRS interval to be lengthened

Answer 52

74. A) The heartbeat immediately following a premature atrial contraction weakens because the diastolic period is very short in this condition. Therefore, the ventricular filling time is very short, and thus the stroke volume decreases. The P wave is usually visible in this arrhythmia unless it coincides with the QRS complex. The probability of these premature contractions increases in people with toxic irritation of the heart and local ischemic areas.

Question 53

75. If the origin of the stimulus that causes atrial paroxysmal tachycardia is near the A-V node, which statement about the P wave in standard limb lead I is most accurate? A) The P wave will originate in the sinus node B) The P wave will be upright C) The P wave will be inverted D) The P wave will be missing

Answer 53

75. C) During atrial paroxysmal tachycardia, the impulse is initiated by an ectopic focus somewhere in the atria. If the point of initiation is near the A-V node, the P wave travels backward toward the S-A node and then forward into the ventricles at the same time. Therefore, the P wave will be inverted.

Question 54

1. What is her cardiac output in milliliters per minute? A) 2000 B) 3000 C) 4000 D) 6000 E) 7000

Answer 54

1. E) This patient has a heart rate of 70 beats per minute. The cardiac output can be determined by using the following formula: cardiac output = heart rate × stroke volume. The stroke volume can be determined from the figure, which is the volume change during the C-D segment, or 100 milliliters. By using this formula, you can determine that the cardiac output is 7000 milliliters per minute.

Question 55

2. When does the first heart sound occur in the ventricular pressure–volume relationship? A) At point B B) Between point A and point B C) Between point B and point C D) Between point C and point D E) Between point D and point A

Answer 55

2. A) During the diastolic filling phase, the mitral and tricuspid valves open and blood flows into the ventricles. At point B the isovolumic contraction phase begins, which closes the A-V valves. The closing of these valves causes the first heart sound.

Question 56

3. When does the fourth heart sound occur in the ventricular pressure–volume relationship? A) At point D B) Between point A and point B C) Between point B and point C D) Between point C and point D E) Between point D and point A

Answer 56

3. B) Between points A and B is the period of ventricular filling. The vibration of the ventricular walls makes this sound after atrial contraction forces more blood into the ventricles.

Question 57

4. What is her ventricular ejection fraction? A) 33% B) 50% C) 60% D) 67% E) 80%

Answer 57

4. D) The ejection fraction is the stroke volume/enddiastolic volume. Stroke volume is 100 milliliters, and the end-systolic volume at point D is 150 milliliters. Thus, the ejection fraction is 0.667, or in terms of percentage, 66.7%.

Question 58

34. What is her heart rate in beats per minute? A) 70 B) 78 C) 84 D) 94 E) 104

Answer 58

34. A) The heart rate can be calculated by 60 divided by the R-R interval, which is 0.86 second. This results in a heart rate of 70 beats/min.

Question 59

35. According to Einthoven’s law, if the QRS voltage in lead III is 0.4 millivolt, what is the QRS voltage in lead I? A) 0.05 millivolt B) 0.50 millivolt C) 1.05 millivolts D) 1.25 millivolts E) 2.05 millivolts

Answer 59

35. B) Einthoven’s law states that the voltage in lead I plus the voltage in lead III is equal to the voltage in lead II. In this case the voltage in lead II is 0.9 millivolt and the voltage in lead III is 0.4 millivolt. The lead I voltage is thus 0.5 (0.9 − 0.4 millivolt = 0.5 millivolt).

Question 60

41. What is the mean electrical axis calculated from standard leads I, II, and III shown in the woman’s ECG? A) −90 degrees B) −50 degrees C) −12 degrees D) +100 degrees E) +170 degrees

Answer 60

Question 61

42. What is the heart rate using lead I for the calculation? A) 70 B) 88 C) 100 D) 112 E) 148

Answer 61

42. A) The heart rate can be calculated by 60 divided by the R-R interval, which is 0.68 second. This calculation results in a heart rate of 88 beats/min.

Question 62

43. What is her likely diagnosis? A) Tricuspid valve stenosis B) Left bundle branch block C) Pulmonary valve stenosis D) Pulmonary valve insufficiency E) Aortic insufficiency

Answer 62

43. B) In the figure, the QRS width is greater than 0.12 second, which indicates a bundle branch block. Right bundle branch block is not a listed answer. The correct answer is therefore left bundle branch block.

Question 63

46. What is her heart rate? Use lead I for the calculation. A) 56 B) 66 C) 76 D) 103 E) 152

Answer 63

Question 64

47. What type of murmur is present in this patient? A) Aortic valve insufficiency B) Left bundle branch block C) Pulmonary valve stenosis D) Right bundle branch block E) Systemic hypertension

Answer 64

47. C) The right axis deviation in this patient has to occur because of a change in muscle mass in the right ventricle, which occurs in pulmonary valve stenosis. Aortic valve insufficiency and systemic hypertension will cause a left axis shift. The QRS width is not greater than 0.12 second, so the patient does not have bundle branch block.

Question 65

49. A 70-year-old woman came to a hospital emergency department because she was experiencing chest pain. Based on the ECG shown above, what is the likely diagnosis? A) Acute anterior infarction in the left ventricle of the heart B) Acute anterior infarction in the right ventricle of the heart C) Acute posterior infarction in the left ventricle of the heart D) Acute posterior infarction in the right ventricle of the heart E) Right ventricular hypertrophy

Answer 65

49. A) This patient has an acute anterior infarction in the left ventricle of the heart. This diagnosis can be determined by plotting the currents of injury from the different leads (see figure below). The limb leads are used to determine whether the infarction is coming from the left or right side of the ventricle and from the base or inferior part of the ventricle. The chest leads are used to determine whether it is an anterior or posterior infarct. When we analyze the currents of injury, a negative potential, caused by the current of injury, occurs in lead I and a positive potential, caused by the current of injury, occurs in lead III. This is determined by subtracting the J point from the TP segment. The negative end of the resultant vector originates in the ischemic area, which is therefore the left side of the heart. In lead V2, the chest lead, the electrode is in a field of very negative potential, which occurs in patients with an anterior lesion.

Question 66

52. A 50-year-old man is a new employee at ABC Software. The above ECG was recorded during a routine physical examination. What is his likely diagnosis? A) Chronic systemic hypertension B) Chronic pulmonary hypertension C) Second-degree heart block D) Paroxysmal tachycardia E) Tricuspid valve stenosis

Answer 66

52. A) Note in the figure below that the QRS complex has a positive deflection in lead I and a negative in lead III, which indicates that there is a leftward axis deviation, which occurs during chronic systemic hypertension. Pulmonary hypertension increases the ventricular mass on the right side of the heart, which gives a right axis deviation.

Question 67

56. A 60-year-old woman came to the hospital emergency department and reported chest pain. Based on the ECG tracing shown above, what is the most likely diagnosis? A) Acute anterior infarction in the base of the heart B) Acute anterior infarction in the apex of the heart C) Acute posterior infarction in the base of the heart D) Acute posterior infarction in the apex of the heart E) Right ventricular hypertrophy

Answer 67

56. D) In the figure below, the current of injury is plotted at the bottom of the graph. This is not a plot of the QRS voltages but the current of injury voltages. They are plotted for leads II and III, which are both negative, and the resultant vector is nearly vertical. The negative end of the vector points to where the current of injury originated, which is in the apex of the ventricle. The elevation of the TP segment above the J point indicates a posterior lesion. Therefore, the ECG is consistent with acute posterior infarction in the apex of the ventricle.

Question 68

61. The following ECG tracing was obtained for a 60-year- III old man who weighs 99.8 kilograms (220 pounds). Standard lead II is shown above. What is his diagnosis? A) A-V nodal rhythm B) First-degree A-V heart block C) Second-degree A-V heart block D) Third-degree A-V heart block E) Atrial flutter

Answer 68

61. B) By definition, first-degree A-V heart block occurs when the P-R interval exceeds a value of 0.20 second but without any dropped QRS waves. This ECG shows first degree block. In this figure the P-R interval is about 0.30 second, which is considerably prolonged. However, there are no dropped QRS waves. During second-degree A-V block, QRS waves are dropped.

Question 69

62. A 35-year-old woman had unusual sensations in her chest after she smoked a cigarette. Her ECG tracing is shown above. What is the likely diagnosis? A) Premature contraction originating in the atrium B) Premature contraction originating high in the A-V node C) Premature contraction originating low in the A-V node D) Premature contraction originating in the apex of the ventricle E) Premature contraction originating in the base of the ventricle

Answer 69

62. E) In the figure below, note that the premature ventricular contractions (PVCs) have a wide and tall QRS wave in the ECG. The mean electrical axis of the premature contraction can be determined by plotting these large QRS complexes on the standard limb leads. The PVC originates at the negative end of the resultant mean electrical axis, which is at the base of the ventricle. Notice that the QRS of the PVC is wider and much taller than the normal QRS waves in this ECG.

Question 70

63. What is his diagnosis? A) Normal ECG B) Atrial flutter C) A high A-V junctional pacemaker D) A middle A-V junctional pacemaker E) A low A-V junctional pacemaker

Answer 70

63. B) This patient has atrial flutter, which is characterized by several P waves for each QRS complex. This ECG has two P waves for every QRS. Notice the rapid heart rate, which is characteristic of atrial flutter.

Question 71

64. What is his ventricular heart rate in beats/min? A) 37.5 B) 60 C) 75 D) 100 E) 150

Answer 71

64. E) The average ventricular rate is 150 beats/min in this ECG, which is typical of atrial flutter. Once again notice that the heart rate is irregular because of the inability of the impulses to quickly pass through the A-V node because of its refractory period.

Question 72

67. A 65-year-old woman who had a myocardial infarction 10 days ago returned to her family physician’s office and reported that her pulse rate felt rapid. Based on the above ECG tracing, what is the likely diagnosis? A) Stokes-Adams syndrome B) Atrial fibrillation C) A-V nodal tachycardia D) Atrial paroxysmal tachycardia E) Ventricular paroxysmal tachycardia

Answer 72

67. E) The term “paroxysmal” means that the heart rate becomes rapid in paroxysms, with the paroxysm beginning suddenly and lasting for a few seconds, a few minutes, a few hours, or much longer. Then the paroxysm usually ends as suddenly as it began and the pacemaker shifts back to the S-A node. The mechanism by which this phenomenon is believed to occur is by a re-entrant circus movement feedback pathway that sets up an area of local repeated self–re-excitation. The ECG shown is ventricular paroxysmal tachycardia. That the origin is in the ventricles can be determined because of the changes in the QRS complex, which have high voltages and look much different than the preceding normal QRS complexes. This is very characteristic of a ventricular irritable locus.

Question 73

68. A 65-year-old man had the above ECG tracing recorded at his annual physical examination. What is the likely diagnosis? A) Atrial paroxysmal tachycardia B) First-degree A-V block C) Second-degree A-V block D) Third-degree A-V block E) Atrial flutter

Answer 73

68. C) Notice in this ECG that a P wave precedes each of the first four QRS complexes. After that we see a P wave but a dropped QRS wave, which is characteristic of second-degree A-V block.

Question 74

72. What is his heart rate? A) 40 beats/min B) 50 beats/min C) 75 beats/min D) 100 beats/min E) 150 beats/min

Answer 74

72. E) The heart rate can be determined by 60 divided by the R-R interval, which gives a value of 150 beats/min. This patient has tachycardia, which is defined as a heart rate greater than 100 beats/min.

Question 75

73. What is his current diagnosis? A) Sinus tachycardia B) First-degree heart block C) Second-degree heart block D) ST segment depression E) Third-degree heart block

Answer 75

73. A) The relationship between the P waves and the QRS complexes appears to be normal, and there are no missing beats. Therefore, this patient has a sinus rhythm, and there is no heart block. There is also no ST segment depression in this patient. Because we have normal P and QRS and T waves, this condition is sinus tachycardia.

Question 76

76. A 45-year-old man had the above ECG recorded at his annual physical. What is the likely diagnosis? A) Atrial paroxysmal tachycardia B) First-degree A-V block C) Second-degree A-V block D) Ventricular paroxysmal tachycardia E) Atrial flutter

Answer 76

76. A) This ECG has characteristics of atrial paroxysmal tachycardia, which means that the tachycardia may come and go at random times. The basic shape of the QRS complex and its magnitude are virtually unchanged from the normal QRS complexes, which eliminates the possibility of ventricular paroxysmal tachycardia. This ECG is not characteristic of atrial flutter because there is only one P wave for each QRS complex.

Question 77

77. A 60-year-old woman sees her physician for her annual physical examination. The physician ordered an ECG, which is shown above. What is the likely diagnosis? A) First-degree A-V block B) Second-degree A-V block C) Third-degree A-V block D) Atrial paroxysmal tachycardia E) Atrial fibrillation

Answer 77

77. E) First-, second-, and third-degree heart blocks, as well as atrial paroxysmal tachycardia, all have P waves in the ECG. However, there are usually no evident P waves during atrial fibrillation, and the heart rate is irregular. Therefore, this ECG is characteristic of atrial fibrillation.

Question 78

78. What is his heart rate? A) 105 B) 95 C) 85 D) 75 E) 37

Answer 78

78. E) This patient’s heart rate is 37 beats/min, which can be determined by dividing 60 by the R-R interval. This is characteristic of some types of A-V block.

Question 79

79. What is the likely diagnosis? A) Left bundle branch block B) First-degree A-V block C) Second-degree A-V block D) Electrical alternans E) Complete A-V block

Answer 79

79. E) This ECG is characteristic of complete A-V block, which is also called third-degree A-V block. The P waves seem to be totally dissociated from the QRS complexes, because sometimes there are three P waves and sometimes two P waves between QRS complexes. First-degree A-V block causes a lengthened P-R interval, and second-degree A-V block has long P-R intervals with dropped beats. However, this does not seem to be occurring in this ECG, because there is no relationship between the ORS waves and the P waves.