Transient Left Bundle Branch Block During the Recovery Period of A Stress Test - Transient Left Bundle Branch Block During the Recovery Period of A Stress Test - Open Access Pub

Exercise-dependent complete left bundle branch block is a rare entity.We present a case in which this phenomenon was demonstrated during the recovery period of a stress test. To the best of our knowledge such an observation has not been previously described. DOI10.14302/issn.2329-9487.jhc-12-171 A 56 year-old male with history of hypertension, hyperlipidemia, and diabetes mellitus was referred for an exercise stress test due to atypical chest pain. His medication included metformin, simvastatin and enalapril. His baseline electrocardiogram at rest was normal (Figure 1). He exercised for 10:02 minutes on a Bruce protocol, achieving 11.8 METS. The exercise was discontinued at a maximal heart rate of 142 beats per minute (bpm), (87% of his maximal predicted heart rate). After 0:12 minutes of recovery, at a heart rate of 138 bpm, complete left bundle branch block (CLBBB) developed (Figure 2 and Figure 3), which resolved after about two minutes (Figure 4). The patient was asymptomatic throughout the test, and there was no evidence of ischemic ST-T changes. Because of the appearance of CLBBB during the recovery period, he was referred for rest and stress echocardiography, which were both found to be normal. Figure 1. Normal baseline resting electrocardiogram at a heart rate of 75 bpm. Figure 2. LBBB appeared at a heart rate of 138 bpm, during the initial phase of the recovery period of the stress test. Figure 3. Complete LBBB developed during the later stages of the recovery period (115 bpm). Figure 4. Complete resolution of LBBB occurred only after 3:10 minutes of recovery. Exercise-dependent CLBBB is a relatively rare phenomenon. In the present case, we describe a patient with transient CLBBB that developed only during the recovery period of a stress test, at a sub-maximal heart rate of 138 bpm, and persisted for more than 2 minutes despite the slowing of the heart rate to 92 bpm. The classic manifestation of acceleration-dependent aberration is the appearance of aberration at a critical cycle length, followed by normalization of conduction with slowing of the heart rate. The following vagaries of acceleration-dependent aberration were previously described by Fisch C. et al 1: group I – unexpected normalization of conduction when aberration would be expected to continue and group II – unexpected appearance or persistence of aberration under conditions in which it would not be expected. In the present case, LBBB aberrancy was first noted for 2 consecutive beats at a cycle length of 400 ms. However, conduction and QRS width had unexpectedly normalized despite