atrioventricular blocks

Question 1

first degree AV block

Answer 1

• rate: depends on sinus node rate - 1st deg is delay in conduction above to bundle branches that can occur w several underlying rhythms
• regularity: regular
• early/late beats: none
• P wave morphology: uniform
• A/V ratio: 1:1
• PR interval: consistent long PR interval, > 200ms
• QRS duration and morphology: < 120ms
• QT interval: < 1/2 preceding R-R interval
• causes: cardiomyopathy, ischemia, injury to AV node, valvular do, digitalis toxicity, mechanical injury to AV node or junctional tissue
• concerns: no major concerns - but watch for progression to further block development
• treatments: not required

Question 2

second degree AV block type I, Mobitz Type I, Wenckebach

Answer 2

• rate: depends on underlying SA node rhythm and pattern of block
• regularity: regular atrial rate, ventricular rhythm irregular
• early/late beats: dropped beats (P waves not followed by QRS)
• P wave morphology: uniform
• A/V ratio: > 1:1
• PR interval: progressively prolonged PR intervals
• QRS duration and morphology: < 120 ms
• QT interval: < 1/2 preceding R-R interval
• causes: inferior MI, cardiomyopathies, digitalis toxicity, valvular disease
• concerns: hemodynamic threat based on HR - indiv sx vary; watch for progression
• treatments: based on sx of bradycardia (dec CO) - inc transcutaneous pacing, atropine, dopamine/epi (like other bradycardias)

*note: permanent pacemaker may be indicated if persistent

Question 3

second degree AV block type II, Mobitz II, classic

Answer 3

• rate: usually slow (depending on SA node rate)
• regularity: makes ventricular rhythm irregular majority of the time - occasionally can be in patterns hen ventricular rhythm is regular
• early/late beats: dropped beats
• P wave morphology: identical
• A/V ratio: > 1:1
• PR interval: consistent long PR intervals; some P waves have no assoc QRS complexes
• QRS duration and morphology: < 120 ms
• QT interval: < 1/2 preceding R-R interval
• causes: worsening ischemia/injury to AV node/junctional tissue by injury or ischemia, cardiomyopathy, valve disease, dig toxicity
• concerns: bradycardia is common; pts often progress to complete heart block
• treatments: based on presence of sx

Question 4

third degree - complete heart block

Answer 4

• rate: usually slow
• regularity: both atrial/ventricular rhythms are regular
• early/late beats: dropped P waves
• P wave morphology: identical; P waves and QRS complexes don’t correlate
• A/V ratio: > 1:1
• PR interval: not consistent when present (P waves and QRS complexes don’t correlate)
• QRS duration and morphology: duration can be narrow or wide (see examples in packet)
• QT interval: < 1/2 preceding R-R interval
• causes: untreated dig toxicity, worsening ischemia/injury, cardiomyopathy, valvular disease, mechanical trauma to AV node
• concerns: hemodynamic compromise can occur bc of slow HR and loss of atrioventricular synchrony; common PEA (second example in packet)
• treatments: based on sx - transcutaneous pacing is 1st choice, as there is no communication b/w SA node and ventricle and speeding up SA node will not be beneficial/has been known to further slow down ventricular response