Trastuzumab-Induced Cardiomyopathy and Intermittent Left Bundle Branch Block.

Trastuzumab-induced cardiomyopathy is a known complication of its use in breast cancer treatment, but it remains mostly asymptomatic and often reversible. Non-myopathic cardiac complications have been rarely reported with trastuzumab. These include left and right bundle branch block, arrhythmias and sinus node dysfunction. We report a case of a 52-year-old female breast cancer patient with trastuzumab-induced asymptomatic intermittent left bundle branch block recurring nearly a year after the initial diagnosis and resolution of trastuzumab-related cardiomyopathy.