Echocardiographic, Electrocardiographic Changes and Clinical Outcomes of Patients Who Respond to Cardiac Resynchronization Therapy after One Year

BACKGROUND: Response to cardiac resynchronization therapy (CRT) is commonly assessed after 6 or 12 months. We evaluated subsequent echocardiographic changes, serial QRS duration, and clinical outcomes in patients showing delayed responses to CRT after 12 months. METHODS: Among all patients who received CRT in Seoul St. Mary's Hospital, 36 one-year survivors were enrolled. Indicators of a positive CRT response were ≥ 15% reduction in left ventricular end-systolic volume (LVESV) or ≥ 10% increase in left ventricular ejection fraction (LVEF) on any follow up echocardiogram. We defined the early responders as patients responding before one year, the late responders as patients responding after one year, and the non-responders as patients who did not respond on any follow-up echocardiogram. RESULTS: We identified 17 early responders, 10 late responders, and 9 non-responders. The late responders showed modest improvement in LVESV and LVEF at two years after CRT. QRS duration was shortened the day after CRT in all three groups. Narrowed QRS was maintained for two years in early and late responders, whereas it was continuously prolonged over time in non-responders. Incidence of all-cause death or heart failure hospitalization was comparable between early and late responders, while non-responders showed worst prognosis. CONCLUSION: Patients responding to CRT after one year show modest echocardiographic improvement but clinical outcome is similar to early responders. Shorter baseline QRS duration and long-term maintenance of QRS duration shortening are important features of the late responders to CRT.