Rate-related left bundle branch block and cardiac memory in a patient with bradycardia: Case report and literature review

Abstract

Rate-related left bundle branch block (LBBB) is a well-studied phenomenon. Cardiac memory is another physiologic phenomenon in which T-wave abnormalities occur in the absence of ischemia. The association between these 2 phenomena has been described in several case reports. A literature review was performed through Ovid and PubMed, where at total of 93 cases of rate-related LBBB were identified. Cases were reviewed, and data were collected on rates of appearance and disappearance as well as the presence or absence of cardiac memory. There is some overlap in the rate at which LBBB appears. Cardiac memory is associated with rate-related LBBB in several cases, but its true prevalence is unknown. Cardiac memory is a phenomenon that is well described in the literature but is often underrecognized in clinical practice. As a consequence of overlooking this phenomenon and not including cardiac memory in the differential when T-wave abnormalities are observed, patients may be subjected to unnecessary invasive diagnostic testing.

Figure 1

Electrocardiogram from admission showing normal sinus rhythm and heart rate of 60 beats per minute with a left bundle branch block

Figure 2

Electrocardiogram showing sinus bradycardia with a left bundle bunch block at a heart rate of >40 beats per minute followed by normal conduction when the heart rate drops below 40 beats per minute. Inverted T waves are now seen in leads V4 to V6

Figure 3

Electrocardiogram showing sinus bradycardia with normal conduction at a rate of 44 beats per minute. Inverted T waves present in the precordial leads are consistent with cardiac memory