Short left main coronary artery causing dynamic left ventricular outflow tract obstruction and new onset left bundle branch block

Left bundle branch block can be seen in conditions like aortic stenosis, extensive coronary artery disease, primary disease of the cardiac electrical conduction system, dilated cardiomyopathy, Lyme disease; it is also associated with short left main coronary artery and dynamic left ventricular outflow tract obstruction. While the former is caused by the shearing force on septal branches of the left anterior descending artery, the latter is related to either Venturi effect in hypertrophic cardiomyopathy or effect of systolic anterior motion caused by abnormal geometric relationship of papillary muscle and the mitral apparatus. A 50-year-old male, former smoker with a history of dyslipidemia, presented with shortness of breath and exertional chest pain. After clinic review, he was thought to have stable angina, electrocardiogram, and echocardiography were normal and lifestyle modification was advised. Patient had some improvement, but represented seven months later with worsening of symptoms. Repeat electrocardiograph showed a new onset left bundle branch block, with short left main coronary artery on coronary angiogram and dynamic left ventricular outflow tract obstruction in stress echocardiography, with a gradient of 40 mmHg. Short left main coronary artery is a rare cause of left bundle branch block, and it should be considered when evaluating patients with new onset left bundle branch block without hypertrophic cardiomyopathy.