How Does CRT Work?

In a healthy heart, the left and right ventricles contract at the same time, pumping blood efficiently to the lungs and the rest of the body. However, in people with heart failure, the electrical signals that coordinate the heartbeat may be delayed, causing the ventricles to beat out of sync. This can make the heart less effective at pumping blood, leading to symptoms like fatigue, shortness of breath, and fluid retention.

CRT works by delivering electrical impulses to both ventricles at the same time, or nearly at the same time, to restore proper synchronization. This coordinated contraction helps improve the efficiency of the heart and reduces the symptoms of heart failure.

Components of a CRT Device:

A CRT device is similar to a pacemaker or implantable cardioverter-defibrillator (ICD), but it has a few key differences. It consists of:

1. Pulse Generator (Device): This is the small battery-powered unit that generates electrical impulses. It’s implanted just under the skin, usually near the collarbone.
2. Leads (Wires):
   • One lead is placed in the right atrium (upper chamber of the heart).
   • One lead is placed in the right ventricle (lower chamber).
   • A third lead is placed in the left ventricle via the coronary sinus (a vein near the back of the heart). This is the critical lead for achieving synchronization between the two ventricles.

These leads carry electrical signals from the pulse generator to the heart, ensuring the ventricles beat together in a synchronized manner.

Indications for CRT:

CRT is recommended for patients with heart failure who have certain conditions:

1. Severe Heart Failure: Typically, CRT is used for patients with New York Heart Association (NYHA) class III or IV heart failure, meaning they have moderate to severe heart failure symptoms that significantly impact their quality of life.
2. Reduced Ejection Fraction: CRT is typically prescribed for people with a reduced ejection fraction (EF), meaning the heart’s pumping ability is weakened (usually an EF of 35% or less). EF measures how much blood the heart pumps with each contraction.
3. Ventricular Dyssynchrony: CRT is particularly effective for individuals with ventricular dyssynchrony, where the heart’s electrical system causes the left and right ventricles to contract out of sync. This is often seen in patients with left bundle branch block (LBBB) on an ECG.
4. Inability to Improve with Medication: CRT is often used for people with heart failure who have not responded to medications or lifestyle changes. It is used to improve symptoms and quality of life, and sometimes to help reduce hospitalizations related to heart failure.

How Is CRT Implanted?

The procedure to implant a CRT device is similar to that of a pacemaker or ICD. It is performed under local anesthesia with sedation and involves the following steps:

1. Preparation: The patient is given a sedative and local anesthesia to numb the implantation site.
2. Implantation of Leads: The leads are inserted through veins, typically via the subclavian vein, and guided to the right atrium, right ventricle, and left ventricle (via the coronary sinus).
3. Device Placement: The pulse generator is implanted just under the skin, typically near the collarbone. It is connected to the leads, which are then tested to ensure they are positioned correctly and functioning properly.
4. Testing and Adjustment: The device is tested, and its settings are programmed to optimize the synchronization of the ventricles. The procedure typically takes a few hours.
5. Post-Procedure Care: After implantation, patients may stay in the hospital for a day or two for monitoring, and most patients can resume normal activities within a few weeks.

Benefits of CRT:

CRT can significantly improve the quality of life for people with heart failure by:

1. Improving Heart Function: By restoring the synchronization of the ventricles, CRT allows the heart to pump more efficiently, increasing the amount of blood pumped to the body.
2. Relieving Symptoms of Heart Failure: Many patients experience relief from symptoms such as shortness of breath, fatigue, and swelling after CRT implantation.
3. Improving Exercise Capacity: Some patients are able to exercise more easily and engage in physical activities that were previously difficult due to heart failure.
4. Reducing Hospitalizations: By improving heart function and reducing symptoms, CRT can help reduce the number of hospital visits for heart failure-related issues.
5. Prolonging Life: In some cases, CRT has been shown to improve survival rates in patients with severe heart failure and ventricular dyssynchrony.

Risks and Complications:

As with any medical procedure, there are some risks associated with CRT implantation, including:

1. Infection: Infection at the implantation site or around the leads.
2. Lead Dislodgement: The leads can move out of place, requiring repositioning or replacement.
3. Bleeding or Bruising: At the site of the incision or where the leads are inserted.
4. Damage to Heart Tissue: Although rare, there is a risk that the leads may irritate or damage heart tissue.
5. Device Malfunction: The device could malfunction, although this is uncommon with modern CRT devices.
6. Phantom Shocks: Some patients may experience unnecessary shocks, but this can often be managed by adjusting the settings of the device.

Living with CRT:

After receiving a CRT device, most patients can lead normal, active lives. However, there are some important considerations:

1. Regular Check-Ups: Regular follow-up appointments are necessary to ensure the device is working properly. The device can often be monitored remotely, and the settings can be adjusted as needed.
2. Activity Restrictions: Patients should avoid certain activities that may interfere with the device, such as using powerful magnets, certain electrical equipment, or undergoing MRI scans without precautions.
3. Lifestyle Changes: Maintaining a heart-healthy lifestyle (e.g., a balanced diet, regular exercise, and medication adherence) is essential for managing heart failure and maximizing the benefits of CRT.
4. Battery Life: The device’s battery typically lasts 5 to 10 years, after which it will need to be replaced in a simple procedure.