Chapter 5: Rhythm, Part 1

Question 1

Arrhythmia meaning

Answer 1

Abnormal rhythm (meaning without rhythm)

Question 2

Rhythm of all automaticity foci

Answer 2

All pace with regular rhythm

Question 3

Sinus arrhythmia

Answer 3

• present in humans at all times
• not a true arrhythmia
• because the autonomic system causes barely detectable rate changes in sinus pacing that relate to the phases of respiration (normal minimal variations in SA node pacing rate in association with phases of respiration)

Question 4

Autonomic system effect in respiration that causes sinus arrhythmia

Answer 4

• inspiration activate sympathetic stimulation of the SA node = slight increase in HR during inspiration
• parasympathethetic inhibtion of the SA = slight decrease in pacing rate

Question 5

Importance variability of sinus rhythm -what does it indicate

Answer 5

-absence of this variability = indicator of increased mortality 0 particularly after infarction

Question 6

Three conduction pathways in the right atrium

Answer 6

Internodal pathways

• course from SA to AV noe
• Anterior, Middle and Posterior Internodal tracts

Question 7

Bachman’s bundle

Answer 7

Originates in the SA node an distributes depolarization to the left atrium

Question 8

What produces the P wave on the ECG

Answer 8

Depolarization of the atrial myocardium

Because depolarization passes too rapidly thrugh the atrial conduction system and therefore oes not record on ECG

Question 9

PQ interval

Answer 9

• pause between atrial depolarization and AV node depolarization because conduction of depolarization slows within the AV node
• during this delay blood from the atria passes into the ventricles
• horizontal baseline on the ECG

Question 10

What produces the QRS complex no ECG

Answer 10

Depolarization of the ventricular myocardium
(depolarization passing through the purkinje fibers of the ventricular conduction system is too weak to record on ECG = concealed conduction)

Question 11

From the purkinje fibers where does the depolarization travel

Answer 11

To the endocardial surface of the ventricular myocardium

Question 12

Left to right depolarization of the septum - why, in what sequence

Answer 12

• Occurs before the rest of the venricular myocardium depolarizes
• because the left bundle branch produces fine terminal filaments while the right bundle branch does not

Question 13

Ventricular contraction on the ECG

Answer 13

Begins and ends during the QT interval

Question 14

Repolarization of Purkinje fibers (T vs. U wave)

Answer 14

• takes longer than ventricular repolarization
• end of T wave makrs the end of ventricular repolarizatin but repolrization of Purkinje occurs a bit later - beyond end of T wave can sometimes see small hump = U wave

Question 15

Irritable automaticity focus -characteristics

Answer 15

• may suddenly pace rapidly

- emergency rate 150-250 per minute is approximately the same for foci of all levels

Question 16

Categories of arrhythmias

Answer 16

1) Irregular rhythms
2) Escape
3) Premature beats
4) Tachy-arrhythmias

Question 17

Types of irregular rhythms

Answer 17

1) Wandering pacemaker
2) Multifocal atrial tachycardia
3) Atrial fibrilation

Question 18

Irregularly irregular

Answer 18

Irregular chaotic rhythm with no predictable recurring pattern

Question 19

Entrance block/parasystolic automaticity foci

Answer 19

• type of malfunctioning of automaticity foci
• any incoming depolarization is blocked - protecting them from passive depolarization b any other source
• by being insensitive to passive depolarization cannot be overdrive -suppressed
• when a automaticity focus has entrance block = parasystolic (the focus paces but can’t be over-drived suppresed)

Question 20

Wandering pacemaker

Answer 20

An irregular rhythm produced by the pacemaker activity wandering from the SA node to nearby atrial automaticity foci
So the cycle lengths vary and P wave morphology (shape) varies as the pacemaking center moves

Question 21

Multifocal atrial tachycardia

Answer 21

• rhythm experienced by patients with chornic obstructive pulmonary disease
• heart rate > 100 per minute
• P waves of various shapes because three + atrial foci are involved
• because atria are developing resistance to overdrive suppression (signs of parasystole) - no single focus achieves pacemaking dominance so all pace together