Dear Editor,
Left bundle branch block (LBBB) is a block in the conduction pathway of the left bundle branch found in 0.06%–0.1% of the population and is associated with increased mortality.[1] It is present in > 30% of heart failure patients and is commonly found in patients with cardiomyopathy. It is diagnosed as QRS duration ≥ 120 ms, dominant S wave in V1, broad monophasic R wave and absent Q waves in lateral leads, and R wave peak time > 60 ms in leads V5–6. The R wave in the lateral leads may be either “M shaped,” notched, monophasic, or an RS complex. We report a case of resolution of incomplete LBBB upon induction of general anesthesia, followed by intermittent rate-dependent reappearance of LBBB.
A 77-year-old female, known hypertensive for 10 years, controlled on medications was posted for lumbar spine fixation. On preoperative evaluation, she was found to have incomplete LBBB (LBBB morphology, but QRS duration <120 ms) [Figure 1a] with metabolic equivalents >4 and normal echocardiographic findings. In the operation theater, standard preinduction monitors were applied including electrocardiogram (ECG), noninvasive blood pressure, and pulse oximeter. Patient had a heart rate (HR) of 94 beats/min and blood pressure 146/84 mmHg. The patient was induced using the standard protocol. Post-intubation, the morphology of ECG turned from LBBB to normal. Multiple episodes of change in ECG morphology from LBBB to normal and vice versa were observed intermittently [Figure 1b]. The reappearance of LBBB was always associated with an increase in the HR, but without any hemodynamic instability.
Figure 1.
(a) Pre-operative ECG of the patient showing Left Bundle Branch morphology, (b) Patient monitor showing intra-operative heart rate intermittent appearance and disappearance of Left bundle branch block morphology
Transient resolution of LBBB after induction of anesthesia has already been reported.[2] This was attributed to the aberrant conduction of supraventricular electrical signals under anesthesia. Resolution of LBBB has been reported after preoxygenation even before the induction of anesthesia.[3] Chronic LBBB might precondition the myocardium, and preoxygenation meets the increased myocardial demand, hence resolving LBBB.
The rate-dependent LBBB can be explained by the concept of the critical HR described by Costantini.[4] Change in HR by even 1 beat/min from the critical HR could lead to appearance/disappearance of LBBB. Maintenance of adequate depth of anesthesia and analgesia becomes of utmost importance in such patients. Hence, the sudden resolution of LBBB under general anesthesia and the rate-dependent change to sinus morphology can be a normal variation, albeit any new onset of LBBB should warrant urgent management and should be screened with echocardiography. (class I indication, American Heart Association guidelines).
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
References
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