Restoration of electrical diastole with bi-ventricular pacing.

Cardiac resynchronization therapy (CRT) has been shown to improve quality of life, increase cardiac output, enhance functional class, and reduce mortality in patients with cardiomyopathy and mechanical dyssynchrony. For pacemaker-dependent patients, the addition of a left ventricular (LV) lead most often leads to a reduction of QRS morphology of 30%, compared with right ventricular pacing alone. We report a 70-year-old man with a history of ischaemic dilated cardiomyopathy (LVEF, 0.15) and high-grade AV block, who underwent implantation of dual-chamber ICD 8 years prior to presentation. He subsequently developed symptoms of progressive congestive heart failure and chronic orthostatic intolerance associated with baseline sustained hypotension (SBP 1⁄4 75 mmHg). He was referred for an upgrade to a CRT ICD system with the implantation of an LV lead. The patient’s electrolytes, including potassium, were within normal limits. His baseline rhythm was normal sinus rhythm with highgrade AV block and atrial sensing and 100% right ventricular pacing (Panel A). Electrocardiogram demonstrated a markedly prolonged QRS interval of .500 ms without discernable electrical diastole. An epicardial LV lead was placed into a lateral tributary of the coronary sinus, and bi-ventricular pacing was established. Electrocardiogram obtained during normal sinus rhythm with atrial sensing and bi-ventricular pacing (Panel B) demonstrated a remarkable reduction in QRS duration and the restoration of electrical diastole. Systolic blood pressure increased to 100 mmHg and orthostatic intolerance resolved.