13. Ventricular Arrhythmias & AV Blocks

Question 1

What are the characteristics of ventricular arrhythmias?

Answer 1

• Lack of a preceding P wave
• Wide QRS > 0.12 secs
• (in most ventricular beats) depolarization and repolarization are in opposite direction

Question 2

What defines a bundle branch block?

Answer 2

• QRS intervals greater than or equal to 0.12 sec
• IS preceded by a physiologic P wave

Question 3

What distinguishes a bundle branch block from ventricular ectopic beats? Similarities?

Answer 3

• Both feature wide QRSs
• Ventricular ectopics lack preceding P waves and usually come and go against the backdrop of a sinus rhythm

Question 4

What is the most common and least concerning ventricular arrhythmia?

Answer 4

PVCs

Question 5

What characterizes a PVC?

Answer 5

• Beat arrives early relative to background rhythm
• Lacks a preceding P wave
• QRS is wide

Question 6

What characterizes a unifocal PVC?

Answer 6

• Same configuration
• From one focus in the ventricle

Question 7

What characterizes a multifocal PVC?

Answer 7

2 configurations –> indicate 2 diff ventricular foci

Question 8

What is bigeminy? What does it look like on an ECG?

Answer 8

PVC in which every other beat is ventricular in origin

Question 9

What is trigeminy? What does it look like on an ECG?

Answer 9

Every 3rd beat is ventricular

Question 10

What are some consequences of PVCs?

Answer 10

• Very frequent PVCs may be indicative of ischemia, valve disease, or infection of the heart
• PVCs don’t benefit from full diastolic filling time and lack atrial priming –> rhythms above may impair CO or BP (esp. in older patients)

Question 11

What characterizes an idioventricular rhythm?

Answer 11

• Slow HR (below 30 bpm) b/c higher pacemakers aren’t functioning
• No P waves
• Wide QRS

Question 12

What characterizes ventricular tachycardia?

Answer 12

• Greater or equal to 3 PVCs in a row
  
  • Wide QRS
  • no P wave
• Rate > 100 bpm

Question 13

What do sustained runs of ventricular tachycardia look like? Significance?

Answer 13

First BP falls, then CO decreases –> person passes out

Question 14

What is the R on T phenomenon? What does it look like on an ECG? Significance?

Answer 14

• PVC falls on the terminal 1/2 of the T wave –> ventricle may only be partially repolarized
• Sets the stage for re-entrant, “circus” tachycardia
• May precipitate ventricular tachycardia

Question 15

What is ventricular fibrillation? Significance?

Answer 15

• Ventricles become unsynchronized b/c small populations of cells depolarize randomly
• No functional contraction occurs —> no CO
• Pre-fatal condition
  
  • Defibrillation is URGENT

Question 16

1° AV block? Nature of prob? ECG characteristics?

Answer 16

• Nature: fixed delay in AV conduction
• ECG criteria:
  
  • P:QRS ratio is still 1:1
  • PR interval > 0.20 s
  • Regular QRS

(pictured: lead V1)