Approximately 20 to 30 percent of heart failure patients have disturbances in the conduction of electrical impulses to the lower chambers (ventricles) of the heart. The most common cause of this disturbance is left bundle branch block, a condition in which the electrical signals do not travel through the ventricles as they are supposed to.  As a result, the left and right ventricles are activated at different times. Biventricular pacemakers do not increase heart rate, but rather stimulate the left and right ventricles simultaneously. This enables the left ventricle to pump blood more efficiently. The device also has the cabability to pace the heart if the heart rate slows below a certain level. 

A biventricular pacemaker may be recommended when a patient has all of the following characteristics:

Studies have shown that biventricular pacemakers may also benefit older patients. The mean age of insertion, according to one study, was 65 years of age. However, benefits of biventricular pacing have been observed in patients up to 75 years old.

In addition, a number of studies have been conducted to see if other patients might benefit from cardiac resynchronization therapy (CRT). Patients who might benefit, but who are not routinely recommended for CRT, include patients with right branch bundle block, Class II NYHA heart failure and atrial fibrillation. CRT in any of these situations remains experimental, and data are inconclusive.

Despite their potential for improvement, however, a significant number of patients do not respond to CRT therapy. Researchers estimate that up to one-third of patients will not benefit, as measured by an improvement in NYHA class. To some degree, this may reflect issues with patient selection, and researchers are working to developing guidelines that would help physicians better select people who would benefit from CRT.

Among some patients, a combined biventricular pacemaker/implantable cardioverter defibrillator (ICD) may be recommended. These are patients who are at risk for sudden cardiac death or have a history of ventricular tachycardia or ventricular fibrillation. Among these patients, combined ICD and CRT therapy has been shown to improve outcomes. Special combination devices have been developed that prevent the ICD from firing inappropriately in response to electrical pacing.

Patients who already have an ICD may be able to “upgrade” to the combined biventricular pacemaker/ICD if they develop heart failure (or if heart failure symptoms become more severe). Nonrandomized studies have been completed that indicate patients with atrial fibrillation and bundle branch blocks with severe heart failure may also benefit from biventricular pacing. Though the data are preliminary, they appear promising.

Similarly, studies are being conducted to see if certain heart failure patients with a standard pacemaker would benefit from “upgrading” to a biventricular pacemaker. In approximately 8 to 15 percent of heart failure patients, pacemakers are implanted to treat bradycardia, or abnormally slow heartbeats. These patients, however, are at increased risk for death or urgent heart transplantation due to pump failure. Researchers are studying whether this pump failure is caused by dyssynchrony of the right and left ventricles and whether a biventricular pacemaker might help. 

Various methods have been described to select patients who are likely to respond to this therapy. In addition to criteria described above, echocardiography and related techniques may provide further help in predicting a good reponse. Patients who demonsterate dyssynergy (difference in onset of contraction) among different left ventricular segments are likely to improve with this type of pacing, because this will result in uniform contractions within the same heart chamber. Associated techniques include M mode echocardiography, strain rate imaging and tissue Doppler imaging. Some recent studies have suggested that MRI may also be useful for this purpose.