A biventricular pacemaker is a type of implantable pacemaker designed to treat heart failure. This type of therapy becomes necessary when the two lower chambers of the heart, the ventricles, do not pump in unison. A biventricular pacemaker helps the ventricles to contract more efficiently. This type of pacing is called cardiac resynchronization therapy (CRT).

Biventricular pacemakers are relatively new. Previous pacemakers were used to pace only the right side of the heart. They were usually inserted when the heart beat too slowly (bradycardia). By contrast, biventricular pacemakers pace both the right and left sides of the heart simultaneously. The device is also designed to pace the major pumping chamber (the left ventricle) from 2 different sites simultaneously. This helps the left ventricle pump blood more efficiently by synchronizing the contraction of different segments of the failing left ventricle. These pacemakers do not increase heart rate unless needed when the heart rate slows below a certain level.

Biventricular pacemakers are manufactured either as “stand alone” devices, or with built-in implantable cardioverter defibrillator (ICD). Approved by the U.S. Food and Drug Administration in May 2002, studies have shown that an ICD with biventricular may reduce mortality by up to 40 percent in patients with heart failure, as well as improve quality of life.

Like standard pacemakers and defibrillators, a biventricular pacemaker may be implanted in the patient’s chest during a minor surgery or in conjunction with open heart surgery. Once implanted, patients will have regular checkups with a physician to make sure the biventricular pacemaker is working properly.

A biventricular pacemaker is a type of implantable pacemaker designed to treat heart failure. This type of therapy becomes necessary when the two lower chambers of the heart, the ventricles, do not pump together. A biventricular pacemaker helps both ventricles to contract more efficiently. This type of pacing is also called cardiac resynchronization therapy (CRT).

Biventricular pacemakers are relatively new. Previous pacemakers were used to pace only the right side of the heart. They were usually used when the heart beat too slowly. By contrast, biventricular pacemakers pace both the right and left sides of the heart. They do not increase heart rate, but rather stimulate the left and right ventricles simultaneously. This helps the left ventricle pump blood more efficiently.

Biventricular pacemakers may be combined with an implantable cardioverter defibrillator (ICD). This is for heart failure patients felt to be at high risk of sudden cardiac death due to some types of abnormal heart rhythms (arrhythmias).

Heart failure is a chronic condition that affects more than 5 million Americans. Heart failure describes a situation in which the heart fails to pump enough blood to meet the body’s needs. It often occurs in patients whose hearts have been weakened or damaged by a heart attack or other conditions. Patients may experience breathlessness, fluid buildup in the limbs and severe fatigue.

When the heart is working properly, both of its lower chambers (ventricles) pump at the same time and in sync with the pumping of the two upper chambers (atria). This pumping is stimulated by an electrical charge that originates in a portion of the right atria called the sinoatrial node, or SA node. The impulse first spreads through the atria, stimulating them to contract. Then it passes through the atrioventricular node, or AV node, and moves into the ventricles through two specialized paths called the left and right bundle branches. Under normal circumstances, the bundle branches stimulate both ventricles to contract at the same time.

Up to 40 percent of heart failure patients, however, have disturbances in the conduction of electrical impulses to the ventricles (e.g., bundle branch block or intraventricular conduction delay). As a result, the left and right ventricles are activated at different times. When this happens, the left ventricle and the right ventricle do not contract simultaneously. In addition, different segments within the left ventricle may contact at different times resulting in dissipation of function and  a reduction of the heart’s efficiency as a pump. The heart typically responds by beating faster and dilating. This results in a vicious cycle of further dilation, constriction of the vessels in the body, salt and water retention, and further worsening of heart failure.

Patients who have heart failure and who may be candidates for biventricular pacing can be diagnosed with an electrocardiogram, which will demonstrate whether they have a bundle branch block or intraventricular conduction delay. These conduction delays do not respond to antiarrhythmics or other drugs.

A biventricular pacemaker can help by sending tiny electrical signals simultaneously to the left ventricle and to the right ventricle. By stimulating both ventricles (biventricular pacing), the device makes the walls of the right and left ventricles pump together again. In addition, activation of the left ventricle simultaneously from different sites results in improving the efficiency of the heart and increases its output. The heart is thus resynchronized, pumping more efficiently while causing less wear and tear on the heart muscle itself. This is why biventricular pacing is also referred to as cardiac resynchronization therapy (CRT).

Like a pacemaker or defibrillator, the biventricular pacemaker consists of three parts:

The generator is a small box, usually about 2 inches wide and 3 ounces in weight. Some generators are even smaller, measuring 1 inch in diameter and weighing about half an ounce. They are battery-powered, and most use lithium batteries that last for five to 10 years. When the battery runs out, the entire generator is replaced. The generator is responsible for generating the electric impulses that pace the heartbeat.

Attached to the generator are leads, or wires, which carry the electrical impulses from the generator.

At the tip of each lead is a tiny device called an electrode that delivers the necessary electrical impulses to the heart. Thus, the electric impulses are created by the generator, carried by the leads and delivered by the electrodes to the heart.

There are three main differences between a biventricular pacemaker and a standard pacemaker:

• The biventricular pacemaker has an additional wire (lead) that paces the left ventricle in addition to the standard pacemaker leads, which pace the right ventricle and right atrium.
  
  
• Biventricular pacemakers are specifically designed to treat heart failure, whereas pacemakers treat cardiac conditions that involve bradycardia (an abnormally slow heart rate).
  
  
• Standard pacemakers have been in use for nearly 40 years. Biventricular pacemakers began receiving FDA approval in 2001. The combined biventricular pacemaker/ICD was FDA approved in 2002.

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.

Insertion of the device can be performed as minor surgery, or it can take place during an open heart surgery.

If it is performed as minor surgery, it is an inpatient procedure in a hospital. The night before the procedure, patients will be asked to sign a consent form and stop eating or drinking after midnight. Certain medications may need to be reduced or stopped temporarily, so patients should discuss their medication schedules with their cardiologist before surgery. Patients may be asked to remove dentures, jewelry, nail polish and/or glasses.

The insertion site will be cleaned and shaved, and the patient will be given a local anesthetic to numb the area. Heart rate and blood pressure will be monitored during the procedure.

Once the incision area has been numbed, a small incision is made in the chest wall just below the collarbone. A pocket is formed under the skin. The patient may feel pulling, but there should be no pain.

Wires can be placed through the subclavian vein and/or cephalic vein, which can be easily accessed from the pocket under the skin. The first wire is threaded through the vein to the right ventricle, and a second wire is threaded to and attached to the right atrium. A third wire is implanted into the left ventricle, a somewhat more complicated procedure. This wire passes through the right atrium into a vein called the coronary sinus, which drains the heart of oxygen–poor blood, and then placed into a lateral branch to pace the left ventricle.

The most common complication during transplantation is the inability to successfully place the left ventricular pacing lead. In about 10 percent of patients, implantation is unsuccessful.

The procedure generally lasts two to five hours. After it is over, patients are usually admitted to the hospital overnight. During this time, a Holter monitor may be worn to monitor the heart’s rhythm. After release from the hospital, regular checkups are necessary to evaluate the function of the pacemaker.

Alternative surgical implantation procedures are available, including endoscopic and even a robotically assisted approach. Both approaches are currently being explored.

Risks associated with biventricular pacemaker insertion are similar to those for standard pacemakers. However, biventricular pacemakers carry some unique risks, especially problems with implanting the lead on the left ventricle. Some of these complications can be reduced by using a surgical approach as opposed to minimally invasive techniques.

As with all implanted devices, there is a risk of:

Approximately 1 to 2 percent of individuals with an ICD or pacemaker develop infection. Infections caused by an implanted device cannot be cured by antibiotics and require the device’s removal. 

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following biventricular pacemaker-related questions:

1. Will this affect my medication schedule?
   
   
2. Will any improvement in my condition be immediate?
   
   
3. How long will it take for me to notice improvements?
   
   
4. Will this change my schedule of office visits, or require any special monitoring?
   
   
5. Does this reduce my chances of someday needing a heart transplant?
   
   
6. Am I a candidate for a combined CRT/ICD device? If so, what are the risks of inappropriate ICD firing, and what will it feel like?
   
   
7. If my ICD fires, will it affect the CRT device?
   
   
8. Is it possible that I can begin an exercise program, or will this affect my current exercise program?
   
   
9. What are the first symptoms of complications?
   
   
10. If I think I'm experiencing side effects, should I go straight to the emergency room, or can I wait for a normal office visit?