Abstract & Commentary
Long-Term Benefits of Cardiac Resynchronization Therapy in Patients with Left Bundle Branch Block
By Edward P. Gerstenfeld, MD
Professor of Medicine, Chief, Cardiac Electrophysiology, University of California, San Francisco
Dr. Gerstenfeld does research for Biosense Webster, Medtronic, and Rhythmia Medical.
Source: Goldenberg I, et al. Survival with cardiac-resynchronization therapy in mild heart failure. N Engl J Med 2014;370:1694-1701.
The Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy (MADIT-CRT) showed that implantation of a cardiac-resynchronization therapy with a defibrillator (CRT-D) in patients with left bundle-branch block (LBBB), Class I or II congestive heart failure (CHF), and an ejection fraction < 30% was associated with a significant reduction in heart-failure events over 2.4 years. In this study, post-trial follow-up was performed in 1691 surviving patients and 854 patients enrolled in the post-trial registries. Patients were followed for a median of 5.6 years after the trial was completed.
After 7 years of follow-up, the cumulative rate of death from any cause in patients with LBBB was 29% in the implantable cardiac defibrillator (ICD) only group compared to 18% in the CRT-D group (hazard ratio in the CRT-D group, 0.59; 95% confidence interval [CI], 0.43-0.80; P < 0.001). The cumulative rate of heart failure was also significantly lower among those randomized to CRT-D. The rate of death from any cause or congestive heart failure was no different between the ICD only and CRT-D groups in those patients without LBBB. The lack of survival benefit persisted for patients with non-LBBB regardless of QRS duration < 150 ms or > 150 ms, and among patients with right bundle-branch block (RBBB). The authors concluded that early CRT-D placement in patients with mild heart failure symptoms, left ventricular systolic dysfunction, and LBBB was associated with a significantly longer long-term survival.
Commentary
Cardiac resynchronization therapy has been demonstrated to improve symptoms and heart failure hospitalization among patients with reduced ejection fraction (EF), wide QRS, and Class III CHF. The MADIT-CRT trial extended thee findings to patients with milder Class I or II CHF. The current study shows that there remains a long-term (7-year) benefit in mortality and reduced CHF hospitalizations in patients with Class I or II CHF and LBBB who receive CRT-D. However, there was no clear benefit in patients without LBBB, even in the presence of a wide QRS. Should we no longer implant biventricular devices in patients with wide QRS and non-LBBB patterns? Certainly there is little evidence in patients with RBBB that there is benefit from CRT-D. In addition, patients with non-LBBB patterns and QRS durations < 150 ms are unlikely to benefit. However, patients with a wide QRS have been shown to benefit from CRT-D in several trials enrolling patients with reduced EF and Class III CHF. Many of these patients will be undergoing ICD placement, and CRT is often the last hope before undergoing transplant evaluation. Some of these patients may benefit from CRT and there is little additional risk. In patients with reduced EF and only mild CHF, one should carefully consider the added cost and complexity of adding a left ventricular lead in patients with non-LBBB patterns. The likely reason for lack of benefit is that the latest left ventricular activation may not be in the posterolateral wall in these patients. Improved technology to allow localization of the latest region of ventricular activation is being investigated using cardiac MRI. More information on where to place the LV lead in patients with non-LBBB patterns and real-time measurement of dyssynchrony during LV lead placement may lead to improved therapy in the future. For now, one should certainly strongly recommend placement of CRT-D devices in patients with EF < 30% and LBBB, regardless of CHF class. Groups with non-LBBB patterns and mild CHF require further study.
