Sinus bradycardia with first degree AV block

Sinus bradycardia with first degree AV block

Sinus bradycardia with first degree AV block
Sinus bradycardia with first degree AV block

Sinus bradycardia is evident from the long RR interval of 1280 ms, corresponding to a heart rate of 47 per minute. PR interval is also prolonged at about 320 msec. The combination can occur in vagotonic states or in those on beta blockers or other drugs which suppress both the sinus node and the AV node. Pure sinus node inhibitors like ivabradine cannot produce this combination. This combination is also often seen with acute inferior wall myocardial infarction.

Higher resting heart rate is a predictor of cardiovascular risk. Even small increments in heart rate over time was associated with worse prognosis [1]. In that respect, moderate sinus bradycardia may be beneficial.

First degree heart block though generally considered benign, marked prolongation with PR interval 300 ms or more can produce symptoms similar to those in pacemaker syndrome [2]. Marked first degree AV block can reduce cardiac output and may not be well tolerated, especially in patients with left ventricular dysfunction. Loss of atrial contribution to ventricular filling, shortening of diastolic filling time and diastolic mitral regurgitation may contribute to reduction of cardiac output.

In a long term follow up of 7575 person Framingham cohort, 124 had PR interval more than 200 milliseconds. In this study, prolongation of PR interval was associated with increased risk of atrial fibrillation, pacemaker implantation and all cause mortality [3].

References

  1. Rakesh Gopinathannair, Brian Olshansky. Resting sinus heart rate and first degree AV block: modifiable risk predictors or epiphenomena?Indian Pacing Electrophysiol J. 2009 Nov 1;9(6):334-41.
  2. Y H Kim, S O’Nunain, T Trouton, G Sosa-Suarez, R A Levine, H Garan, J N Ruskin. Pseudo-pacemaker syndrome following inadvertent fast pathway ablation for atrioventricular nodal reentrant tachycardia. J Cardiovasc Electrophysiol. 1993 Apr;4(2):178-82.
  3. Susan Cheng , Michelle J Keyes, Martin G Larson, Elizabeth L McCabe, Christopher Newton-Cheh, Daniel Levy, Emelia J Benjamin, Ramachandran S Vasan, Thomas J Wang. Long-term outcomes in individuals with prolonged PR interval or first-degree atrioventricular block. JAMA. 2009 Jun 24;301(24):2571-7.