A biventricular pacemaker, also known as cardiac resynchronization therapy (CRT), is a type of pacemaker used to treat heart failure. It helps coordinate the pumping of the left and right ventricles of the heart. Some biventricular pacemakers also have a built-in implantable cardioverter-defibrillator (ICD). An ICD monitors the heart rhythm and can deliver electric shocks to restore a normal rhythm if a dangerous arrhythmia occurs. So some biventricular pacemakers have defibrillator capabilities, while others do not.
What is a biventricular pacemaker?
A biventricular pacemaker is a special type of pacemaker used for cardiac resynchronization therapy (CRT). It helps coordinate the contraction of the heart’s lower chambers (the ventricles).
In heart failure, the ventricles may not contract at exactly the same time. This uncoordinated pumping reduces the heart’s efficiency. A biventricular pacemaker uses leads in the right atrium and both ventricles to pace the heart. This resynchronizes the ventricles and improves pumping ability.
Biventricular pacemakers are used in people with moderate to severe heart failure who have electrical conduction delays. These delays cause the ventricles to contract asynchronously. Symptoms improved by CRT include shortness of breath, fatigue, and edema.
Main components of a biventricular pacemaker
– Pulse generator – The pacemaker itself. It contains the battery and generates electrical impulses.
– Atrial lead – Senses atrial activity and paces the right atrium if needed.
– Right ventricular lead – Senses right ventricular activity and paces the right ventricle.
– Left ventricular lead – Paces the left ventricle to resynchronize contraction with the right.
What is an implantable cardioverter-defibrillator (ICD)?
An implantable cardioverter-defibrillator (ICD) is a device implanted under the skin to monitor heart rhythm and deliver therapy if needed. An ICD has two main functions:
1. Pacemaker
It can act as a pacemaker, delivering small electrical impulses to make the heart beat if the heart rate is too slow.
2. Defibrillator
More importantly, an ICD can act as a defibrillator. It monitors the heart continuously for dangerous arrhythmias, especially ventricular tachycardia and ventricular fibrillation. If one of these lethal heart rhythms occurs, the ICD quickly delivers a high-energy electric shock to reset the heart to a normal rhythm. This prevents sudden cardiac death.
ICDs are used in people at high risk of dangerous arrhythmias, such as those who have had a prior cardiac arrest or have heart failure at risk of sudden death. They provide 24/7 monitoring and life-saving defibrillation if needed.
Do biventricular pacemakers have defibrillators?
Some biventricular pacemakers have a built-in ICD, while others do not. There are pros and cons to each option:
Biventricular pacemaker with ICD
Advantages:
– Provides resynchronization pacing to improve heart failure symptoms
– Also protects against sudden cardiac death if dangerous heart rhythm occurs
Disadvantages:
– More complex procedure to implant
– Higher risk of complications like infection
– May require replacement sooner due to larger battery requirements
Biventricular pacemaker without ICD
Advantages:
– Simpler implantation procedure
– Lower risk of complications
– Longer lasting battery life
Disadvantages:
– No protection against sudden cardiac death
– Patient may need separate ICD implanted later
Whether a biventricular pacemaker also needs an ICD depends on the patient’s specific condition and needs. Those at high risk for sudden cardiac death benefit from the ICD functions. For others, resynchronization pacing alone may be sufficient.
Who needs a biventricular pacemaker with defibrillator?
Guidelines generally recommend a biventricular pacemaker with defibrillator capabilities (CRT-D) for these patients:
– Those with mild to severe heart failure symptoms (NYHA class II-IV)
– Left ventricular ejection fraction 35% or less
– Expected to live more than 1 year
Patients who meet these criteria have heart failure at significant risk of lethal ventricular arrhythmias. The CRT functions improve their heart failure symptoms, while the ICD protects against sudden cardiac death.
A biventricular pacemaker without defibrillator may be sufficient for patients with heart failure who are not at high arrhythmia risk. This includes patients with:
– NYHA class I or II symptoms
– Ejection fraction over 35%
– Other reasons for lowered sudden death risk
For these patients, resynchronization pacing helps improve heart function but the risk of arrhythmia may not be high enough to warrant an ICD.
What is the procedure for implanting a biventricular pacemaker with defibrillator?
Implanting a CRT-D device is a more complex procedure than a standard pacemaker, given the extra hardware. The steps involve:
1. Insertion of leads
Three transvenous leads are inserted through the veins, one into the right atrium, right ventricle, and a third lead into a vein branch to pace the left ventricle.
2. Positioning of leads
Fluoroscopy imaging guides proper positioning of the leads. The left ventricular lead is maneuvered until it paces and resynchronizes the ventricles effectively.
3. Connection to ICD generator
The leads are connected to the ICD pulse generator, which is placed under the skin, usually below the left collarbone.
4. Testing synchronization and defibrillation
The implanting physician tests the CRT pacing effects and ability of the ICD to sense arrhythmias and deliver appropriate therapy.
5. Closure of incisions
Finally, the incisions are closed and the skin is sutured back together. A sterile dressing is applied.
The procedure takes 2-4 hours with the patient under sedation or general anesthesia. There is usually a 1-2 day hospital stay afterwards for monitoring.
What are the potential complications of implanting a biventricular pacemaker with defibrillator?
Implanting a CRT-D device has several risks and possible complications including:
Infection
– Occurs in 1-7% of patients
– Treated with antibiotics, or may require removal of entire system
Bleeding
– May accumulate around the pacemaker pocket or heart
– Usually resolves on its own
Pneumothorax
– Air in the chest cavity causing lung collapse
– Requires insertion of a chest tube
Cardiac tamponade
– Blood accumulates around the heart compressing it
– Emergency drainage of the fluid is needed
Lead displacement
– Lead may detach from the heart requiring repositioning
Vascular complications
– Damage to veins used to insert leads
Procedural complications occur in 4-12% of cases, more often than with a standard pacemaker given the complexity of the system.
What is the typical battery life of a biventricular pacemaker with defibrillator?
The battery life of a CRT-D device varies based on use of the pacing functions versus defibrillation shocks:
– **Pacing alone:** Average battery life is 5-7 years
– **Frequent shocks:** Battery life may be only 2-3 years
Frequent ventricular tachycardia and fibrillation treated with shocks from the ICD quickly drain battery life. Less frequent defibrillation allows longer battery duration.
Factors affecting battery life include:
– Pacing rate – Faster pacing uses more energy
– Percent pacing – More pacing drains battery faster
– Shocks delivered – More shocks deplete battery quickly
– Lead impedance – Higher resistance uses more energy
The device can be reprogrammed to extend battery life if needed. Ultimately when the battery is depleted, the whole CRT-D system needs replacement.
How often does a biventricular pacemaker with defibrillator require replacement?
The generator battery is the main factor determining replacement frequency. On average:
– **Pacing-only system** – May last 7-10 years before battery depletion
– **Frequent shocks** – May require replacement in as little as 2-3 years
Signs the battery is running down include:
– Decreased pacing capacity and longevity
– Reduction in shock strength and energy delivery
– Battery indicator states replacement needed
Routine follow-up can detect a low battery to schedule device replacement before complete depletion. Otherwise, sudden battery depletion could leave the patient without needed pacing or defibrillation.
What is the process for replacing a biventricular pacemaker with defibrillator when the battery runs down?
Replacing a CRT-D system involves:
1. Removal of old pulse generator
The old generator is detached from the leads and taken out through the incision.
2. Testing lead integrity
The leads are tested to ensure they are functional and securely attached to the heart. Good leads may be left in place.
3. Insertion of new generator
The new CRT-D generator is connected to the leads and placed in the pocket below the collarbone.
4. Testing new system
The new generator’s pacing and ICD functions are confirmed. Threshold testing ensures appropriate rhythm detection and therapy.
5. Closing incision
The incision is closed with sutures or surgical glue. A dressing is applied.
The patient usually stays in the hospital overnight and is monitored before discharge. Anti-inflammatory medication helps with post-op soreness.
Conclusion
Some biventricular pacemakers include implantable cardioverter-defibrillator (ICD) capabilities, while others do not. Those at high risk for sudden cardiac death benefit from having the ICD functions to quickly treat dangerous ventricular arrhythmias. For other patients, resynchronization pacing without defibrillation may be adequate. Implanting the CRT-D system is more complex than a standard pacemaker and has higher procedural risks. But it provides life-saving benefits for those requiring both therapies. Routine follow-up helps detect when generator replacement is needed, typically 5-7 years on average.
