Lecture 8: Cardiac Arrhythmias

Question 1

Tachycardia

Answer 1

• fast heart rate >100 beats/min

causes: increased body temp, sympathetic stimulation, toxic conditions

Question 2

Endogenously mediated tachycardia

Answer 2

aka Exercise: HR increases, cardiac output increases, filling time reduced but stroke-volume does not fall

• sympathetic stim increases contractility, maintaning SV
• systolic interval is reduced allowing for more diastolic filling time
• sympathetic stim and skeletal muscle pump increase venous return to maintain ventricular filling

Question 3

Pathologically mediated tachycardia

Answer 3

• HR increases, but cardiac output (CO) decreases
• mean arterial pressure decreases and activates sympathetic NS, which is too late and can’t compensate
• no muscle pump to increase venous return

*positive feedback system w/ bad ending

Question 4

Bradycardia

Answer 4

-slow heart rate

Question 5

Respiratory type of sinus arrhythmia

Answer 5

spillover signals: from medullary respiratory center in vasomotor center during inhaling/exhaling cycles

-these signals alternately increase and decrease number of impulses transmitted through symp and vagus nerves to heart

Question 6

Sinoatrial block

Answer 6

Characteristics:

• sudden cessation of P waves
• resultant standstill of atria
• ventricles pick up new rhythm, usually from AV node
• rate of QRS is slowed but otherwise unaltered

Question 7

Atrioventricular block

Answer 7

Causes:

• ischemia of AV node of AV bundle fibers through coronary insufficiency
• compression of AV bundle by scar tissue of calcified portions
• inflammation of AV node or bundle
• extreme stim of heart by vagus nerves

Question 8

Incomplete AV block (first degree)

Answer 8

• when P-R interval increases > 0.20 sec

- increases in length with slower heart beat and decreases with faster heart beat

Question 9

Incomplete AV block (second degree)

Answer 9

• when P-R interval increases > 0.25 - 0.45 sec
• Atrial P wave is present but QRS-T wave may be missing, resulting in dropped beats of ventricle
• 2 P waves : 1 QRS-T complex rhythm or other variations may develop

Question 10

Complete AV block

Answer 10

• ventricles establish own signal (usually AV node)
• no relation between rate of P-waves and QRS-T complexes
• highly variable duration
• after AV conduction ceases, ventricles may not beat for 5 - 30 sec
• periodic fainting spells called “Stokes-Adams syndrome”
• ventricular escape may be due to Purkinje system acting as ectopic pacemaker

Question 11

Partial intraventricular block

Answer 11

“electric alternans”

-alternation in amplitude of P waves, QRS complexes, and T waves

Question 12

Premature contractions

Answer 12

contractions occurring out of sequence

caused by ectopic foci: local ischemic areas, calcified plaques, irritation of conduction system/nodes