An early proof-of-concept of cardiac resynchronization therapy.

Almost 50 years ago, we published detailed hemodynamic findings in a patient with heart failure and intermittent left bundle branch block. Delayed intraventricular conduction was consistently accompanied by an increased duration of left ventricular (LV) isometric contraction, a drop in systolic blood pressure, a rise in heart rate, and a drop in cardiac output. To our knowledge, this observation provided the first ever evidence that delayed mechanical LV contraction was associated with deterioration, and return to a normal pre-ejection phase with improvement in LV function.