Concepts for Exam #1

Question 1

What is an EKG?

Answer 1

A recording of the heart’s electrical activity.

Question 2

What is automaticity?

Answer 2

The ability to produce an electrical impulse without outside stimulation.

Question 3

What is excitability?

Answer 3

The ability to respond to an outside stimulus.

Question 4

What is conductivity?

Answer 4

The ability to transmit an electrical impulse signal from cell-to-cell.

Question 5

What are the three types of cells in the heart?

Answer 5

(1) Pacemaker cells (SA node); (2) conducting cells (includes the rest of the conduction system); and (3) myocardial cells (muscle cells of the atria and ventricles).

Question 6

What are the characteristics of pacemaker cells?

Answer 6

(1) They depolarize spontaneously; (2) they are located in the SA node; (3) they set the heart at 60-100 bpm; and (4) they are influenced by external neurohumoral input.

Question 7

What are the two types of cardiomyocyte action potential?

Answer 7

(1) Fast-response (occurring in the atria, ventricles, and purkinje fibers); and (2) slow-response (occurring in the SA and AV nodes).

Question 8

Describe the fast-response action potential:

Answer 8

Phase 4: Resting membrane potential; Phase 0: depolarization (Na+ influx); Phase 1: K+ efflux; Phase 2: plateau (Ca2+ influx/K+ efflux); Phase 3: repolarization (K+ efflux).

Question 9

How do catecholamines (epinephrine/norepinephrine) influence the pacemaker rate?

Answer 9

They increase the rate of depolarization; and increase the heart rare.

Question 10

How does acetylcholine (released during vagal stimulation) influence the pacemaker rate?

Answer 10

It decreases the rate of depolarization; and decreases the heart rate.

Question 11

Describe the process of excitation-contraction coupling:

Answer 11

A wave of depolarization stimulates the release of calcium from the sarcoplasmic reticulum; calcium allows the interaction between actin and myosin; contraction occurs.

Question 12

What are the components of the conduction pathway?

Answer 12

SA node; AV node; His bundle; left bundle branch (with anterior and posterior fascicles) and right bundle branch; purkinje fibers.

Question 13

Describe the placement of the limb leads:

Answer 13

Right arm; left arm; left leg. This creates three standard limb leads and three augmented limb leads; these six leads provide a frontal view of the heart.

Question 14

Describe the placement of the precordial (chest) leads:

Answer 14

V1: 4th intercostal, right side.
V2: 4th intercostal; left side.
V4: 5th intercostal, mid-clavicular.
V6: 5th intercostal; mid-axillary.
V3 and V5 are placed inbetween; these leads provide a transverse view of the heart.

Question 15

What are the three characteristics of an EKG waveform?

Answer 15

(1) Duration; (2) amplitude; (3) and configuration.

Question 16

Describe the normal appearance of the P-wave:

Answer 16

The direction is variable, it is always negative in aVR, and it may be biphasic in some leads; it should be rounded (not tall or wide), and preceed each QRS complex; the first half represents right atrial depolarization, and the second half represents left atrial depolarization.

Question 17

What does the P-wave look like during atrial enlargement?

Answer 17

Right Atrial Enlargement: taller than 2.5mm; initial component is tall in biphasic waves; Left Atrial Enlargement: the wave is wide and often notched; amplitude is normal or increased.

Question 18

Describe the normal appearance of the PR-interval:

Answer 18

It should be smaller than 1 large box in duration; if prolonged, it indicates first-degree heart block.

Question 19

What does the Q-wave represents, and how can you tell if it is pathologic?

Answer 19

The Q-wave represents septal depolarization; pathologic Q-waves are deep and wide (deeper than 1/3 the height of the R-wave) and they often fall straight down. These occur hours to days after an infarct, and will remain for life.

Question 20

Describe the normal appearance of the QRS complex:

Answer 20

Narrow is normal (less than 3 small boxes); large positive R-waves are seen in the left lateral and inferior leads; large negative S-waves are seen in V1 and V2. R-wave amplitude should increase throughout the precordial leads.

Question 21

What are the two reasons for a wide QRS complex?

Answer 21

(1) The impulse is being generated in the ventricles; or (2) the impulse is taking an aberrant pathway through the ventricles.

Question 22

What does a STEMI look like?

Answer 22

ST elevations of at least 1 mm in the limb leads, or 2 mm in the precordial leads; shape should be rounded, not concave (concave elevation is due to J-point notching).

Question 23

What does a normal T-wave look like?

Answer 23

The are variable in appearance; deflection is typically in the same direction as the QRS complex.

Question 24

What does a normal QT interval look like, and what determines its duration?

Answer 24

It is normally half-way between two QRS complexes; the duration is proportionate to heart rate.

Question 25

Describe the three methods for calculating heart rate:

Answer 25

(1) 300/# of large boxes between R-waves; (2) 300-150-100-75-60-50 method; and (3) multiply the number of QRS complexes in a 30-box span by 10.

Question 26

What is hypertrophy?

Answer 26

Increased muscle mass due to pressure overload (such as in chronic hypertension); typically occurs in the ventricles.

Question 27

What is enlargement?

Answer 27

Dilation of a chamber due to fluid overload; typically occurs in the atria.

Question 28

Why do hypertrophied ventricles typically progress to dilation?

Answer 28

The greater the stress, the more forceful the recoil; eventually, the stretch is so great that the elasticity is lost (occurs faster in the right ventricle because there is less muscle here).

Question 29

What is a vector?

Answer 29

A vector represents an electrical force moving through the ventricles in a particular direction.

Question 30

What is a mean vector?

Answer 30

Summation of all the vectors; the direction of the mean vector is the axis of ventricular depolarization. Axis is defined in the frontal plane only.

Question 31

What are the two signs of right ventricular hypertrophy?

Answer 31

(1) Right axis deviation; (2) poor R-wave progression.

Question 32

How can you identify poor R-wave progression?

Answer 32

The R-wave is larger than the S-wave in V1; the S-wave is larger than the R-wave in V6.

Question 33

What are the three signs of left ventricular hypertrophy?

Answer 33

(1) Left-axis deviation; (2) increased R-waves over the left ventricle; (3) increased S-waves over the right ventricle.

Question 34

What is the most important criteria for dagnosing left ventricular hypertrohy?

Answer 34

The R-wave amplitude in leads V5 or V6 plus the S-wave amplitude in V1 or V2 exceeds 7 large boxes.

Question 35

What are the two signs of secondary repolarization abnormality?

Answer 35

(1) Down-sloping ST-segment; ans (2) T-wave inversion.