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Pacemakers for CHF

The last five years have seen tremendous hope for patients with congestive heart failure (CHF) by advanced pacing therapy. Cardiac Resynchronization Therapy (CRT) is a technology that can significantly improve certain patients with advanced CHF (NYHA Class III or IV) with respect to fatigue, exercise tolerance, dyspnea and mortality. 

  • The Problem: Dyssnchrony:

    The patients with inter-ventricular conduction delay (i.e. left bundle branch block or right bundle branch block) with symptoms of CHF often have problems with timing of contraction within the walls of both ventricles. When the ventricles are not activated simultaneously, they may become dyssynchronous. Dyssynchrony degrades the efficiency of the heart's ability to pump by reducing diastolic filling time, worsening mitral regurgitation and weakening myocardial contractility independent of ejection fraction.  However, patients with reduced left ventricular function will likely be more symptomatic.

  • The Solution: Bi-Ventricular Pacing:

    Bi-Ventricular pacing has emerged as an important therapy to reverse dyssynchrony. The standard dual chamber pacemaker is designed to pace the right atrium (RA) and right ventricle (RV) on demand. This form of pacing actually causes dyssynchrony as the RV is activated before the left ventrical (LV).  By adding a third wire to the back wall of the LV, an advanced pacemaker can now control the timing of activation of both walls of the heart such that they move simultaneously together. With the aid of an echocardiogram, the pacemaker can be programmed for optimal timing. This is cardiac resynchronization therapy.

  • The Data:

    Several randomized controlled studies have been performed evaluating the efficacy of CRT. Two studies, COMPANION and Care-HF, have shown between a 19% to 36% reduction in all cause mortality with CRT patients compared to control patients on similar optimal medical therapy. Other trials confirmed significant improvements in functional class and quality of life and a reduction in hospital admissions for CHF.

  • The Patient:

    Patients who may benefit from CRT should have a QRS duration greater than or equal to 120 ms and exhibit NYHA Class III or VI CHF. There is no specific LV ejection fraction for CRT devices, however, those patients with LV EF less than or equal to 40% may further benefit from a combined CRT/defibrillator device. Future trials are ongoing to evaluate this therapy in other patient populations.

References:

COMPANION
Bristow MR, Saxon LA, Boehmer J, et al. Cardiac-resynchronization therapy with or without an implantable defibrillator in advanced chronic heart failure. N Engl J Med 2004;350:2140-2150. 

CARE-HF
Cleland JGF, Daubert J-C, Erdmann E, et al. The effect of cardiac resynchronization on morbidity and mortality in heart failure. N Engl J Med 2005;352:1539-1549. 

MUSTIC
Cazeau S, Leclercq C, Lavergne T, et al. Effects of multisite biventricular pacing in patients with heart failure and intraventricular conduction delay. N Engl J Med 2001;344:873-880.

MIRACLE ICD
Young JB, Abraham WT, Smith AL, et al. Combined cardiac resynchronization and implantable cardioversion defibrillation in advanced chronic heart failure: the MIRACLE ICD Trial. JAMA 2003;289:2685-2694.

Southcoast Physicians Group An affiliate of Southcoast Physicians Group.