Chapter 5 Cardiac Abnormalities

Question 1

Based on the lead II, identify characteristics of normal sinus rhythm

Answer 1

1) the frequency of QRS complexes is approximately 1/s, indicating a normal beating rate
2) the QRS complex shape is normal for lead II and its duration is less than 120ms (rapid depolarization of the ventricles)
3) each QRS complex is preceded by a P wave (SA nodal origin)
4) the PR interval is less than 200ms
5) QT interval is less than half of the R-to-R interval
6) no extra P waves (means no AV block)

Question 2

physiological result of the tachycardia? and that of bradycardia?

Answer 2

Tachycardia : limit the diastolic time for ventricular filling
Bradycardia : fail to support sufficient cardiac output or reduce stroke volume due to the decreased coordination of myocyte contraction

Question 3

When does supraventricular tachycardia occur?

Answer 3

When the atria are abnormally excited and drive the ventricles at a very rapid rate.

Question 4

2 mechanisms for supra ventricular tachycardia

Answer 4

1. The atrial region (outside the SA node) was irritated and begin to fire rapidly to take over the pacemaker function.
   This abnormal pacemaker region is called an ectopic focus
2. atrial conduction is altered and a single wave of excitement does not die out but continually travels around some abnormal atrial conduction loop. This activity may drive the atria and AV node at a very high frequency (RE-entry phenomenon)

Question 5

Atrial flutter?

Answer 5

tachycardia of atrial origin where a large re-entrant pathway drives the atria at very fast rates (250-300bpm)
ventricular rate is fixed ratio of atrial rate (2:1 , 4:1)

Question 6

first degree AV block?

Answer 6

slow conduction through the AV node
Longer PR interval (>0.2s)
At normal heart rates, physiologically normal

Question 7

second degree AV block?

Answer 7

some, but not all, atrial impulse are transmitted through AV node to the ventricle.
The problem is slower than normal conduction
Atrial rate is faster than ventricular rate

Question 8

How does a stenotic valve induce cardiac muscle hypertrophy?

Answer 8

When a valve does not fully open, the chamber upstream of the valve has to develop more pressure. This pressure work will increase muscle thickness.

Question 9

How does a insufficient valve lead to chamber dilation?

Answer 9

The regurgitant blood flow makes additional volume.

Question 10

What are the two different ways supraventricular tachycardia can occur? (think… focus)

Answer 10

1) Ectopic focus - Area out side of the SA node which can be irritated and then rapidly fire and take over the pacemaker function.
2) Re-entry phenomenom - This is when a single wave of conduction does not die out as normally, but instead has continual acticity in the conduction loop

Question 11

Where in the heart do conduction blocks occur?

Answer 11

AV node

Question 12

What occurs in a first degree AV block?

Answer 12

slow conduction (long PR interval)

Question 13

What occurs in a second degree AV block?

Answer 13

Some but not all atrial impulses are transmitted through the AV node. (Some QRSs have P waves and some don’t)

Question 14

What occurs in a third degree AV block?

Answer 14

No atrial impulses make it through the node, but the ventricles take over the pacemaker role (results in completely independent P waves and QRSs).

Question 15

What is the physiological reason that some people with AFIB can tolerate it? aka, how do they compensate?

Answer 15

Atrial contraction only plays a minor role in ventricular filling, therefore it may not affect some people at rest

Question 16

What is postextrasystolic potentitation?

Answer 16

The volume of blood ejected by a PVC is less than normal, and most PVCs are followed by a compensatory pause which has a larger than normal stroke volume.

Question 17

Does aortic stenosis result in a high or low pulse pressure?

Answer 17

low