Second-Degree Atrioventricular Block—Reply

Abstract

In Reply We thank Littmann for his comments on our Challenges in Clinical Electrocardiography.1 He asserts that the patient’s rhythm strip is consistent with Mobitz type I atrioventricular (AV) block and that this is important for understanding the cardiac events surrounding the patient’s death. We acknowledge that this is a challenging rhythm strip to perfectly discern owing to the low quality of the implantable loop recording and some ambiguous findings. On close analysis, Littmann has isolated an instance (strip II) in which it does appear that the PR interval prolongs and then shortens before and after a blocked P wave. Thus, we agree that this particular portion of the rhythm strip is most consistent with Mobitz I, which may be owing to the effect of fentanyl on the AV node via vagal tone. However, in another instance (strip I), the PR and RR intervals are constant and preserved through blocked P waves, which is consistent with infranodal block and Mobitz II. Given evidence of extant infranodal conduction disease by virtue of a wide QRS complex, the very long PR interval, both left and right bundle branch blocks on prior electrocardiograms, and the patient’s history of syncope, this patient has substrate for infranodal block as well. In other words, a patient can have features consistent with both Mobitz I (nodal) and Mobitz II (infranodal) second degree block, as the rhythm strip suggests in this case. Identify all potential conflicts of interest that might be relevant to your comment. Conflicts of interest comprise financial interests, activities, and relationships within the past 3 years including but not limited to employment, affiliation, grants or funding, consultancies, honoraria or payment, speaker's bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued. Err on the side of full disclosure. If you have no conflicts of interest, check "No potential conflicts of interest" in the box below. The information will be posted with your response. Not all submitted comments are published. Please see our commenting policy for details.