Introduction

Cardiac Resynchronization Therapy (CRT), also known as biventricular pacing, is an advanced and effective treatment for select patients with heart failure. This therapy is designed to improve the heart’s efficiency and reduce the symptoms of heart failure by correcting electrical dyssynchrony, a condition in which the heart’s chambers beat out of sync. While traditional treatments like medications can ease symptoms and slow the progression of heart failure, they often fall short when electrical conduction abnormalities are at the root of the problem. That’s where CRT steps in as a game-changer. Understanding what is cardiac resynchronization therapy is crucial for patients considering this treatment.

Heart failure affects millions of individuals worldwide and significantly impairs the quality of life, especially when the ventricles the heart’s main pumping chambers fail to contract in a coordinated manner. CRT uses a specialized pacemaker device to restore synchrony between the left and right ventricles, helping the heart pump blood more effectively. This treatment has been shown to improve survival rates, reduce hospitalizations, and enhance the quality of life for patients who meet the criteria.

What is Cardiac Resynchronization Therapy?

Cardiac Resynchronization Therapy is a medical procedure that involves implanting a device under the skin, similar to a pacemaker, that sends timed electrical signals to the heart’s ventricles to help them beat in a more coordinated way. The goal is to correct the delay in ventricular contraction seen in certain types of heart failure, especially in patients with wide QRS complexes on ECG (electrocardiogram), typically caused by left bundle branch block (LBBB).

In a healthy heart, electrical impulses travel in a precise manner that causes the chambers to contract in a synchronized rhythm. In some heart failure patients, especially those with reduced left ventricular ejection fraction (LVEF ≤ 35%) and prolonged QRS duration (≥130–150 ms), these impulses are delayed or disrupted. This causes the ventricles to contract out of sync, leading to inefficient pumping of blood. CRT restores coordination, significantly improving the heart’s function.

How CRT Works
The CRT system typically consists of a small, battery-powered device implanted under the skin near the collarbone. Three insulated wires (leads) are threaded through veins and attached to specific areas of the heart:

One lead is positioned in the right atrium, the upper chamber that receives blood from the body.
A second lead is placed in the right ventricle, the lower chamber that pumps blood to the lungs.
The third lead is guided through the coronary sinus vein and positioned on the outer surface of the left ventricle.

Once in place, the device delivers tiny electrical impulses to both the left and right ventricles, ensuring they contract together in a synchronized fashion. This “resynchronization” improves the heart’s pumping efficiency, reduces symptoms like fatigue and breathlessness, and can lead to improved survival.

CRT Device Types
There are two primary types of CRT devices, chosen based on the patient’s risk of life-threatening arrhythmias:

CRT-P (Cardiac Resynchronization Therapy – Pacemaker) :-
This device delivers synchronized pacing to the heart but does not have defibrillation capability. It is used in patients who require resynchronization but are not at high risk of sudden cardiac arrest.
CRT-D (Cardiac Resynchronization Therapy – Defibrillator) :-
This device combines biventricular pacing with an implantable cardioverter-defibrillator (ICD), which can deliver shocks if a life-threatening arrhythmia such as ventricular tachycardia or fibrillation occurs. It is recommended for patients with both heart failure and a high risk of sudden cardiac death.

Procedure Overview
CRT implantation is typically performed under local anesthesia with conscious sedation. The surgeon accesses a central vein and threads the three leads into the heart under X-ray guidance. Once positioned, the leads are connected to the CRT device, which is placed beneath the skin near the collarbone.

The procedure generally takes 2 to 3 hours, followed by a short hospital stay. After implantation, the device is tested and programmed to meet the patient’s individual pacing needs. Most patients experience gradual improvement in symptoms over the following weeks and months.

Follow-Up and Monitoring
After CRT implantation, regular follow-up is necessary to monitor device performance and heart function. Device checks are done in-person or remotely using telemetry systems. Medications for heart failure are usually continued alongside CRT. In some cases, echocardiograms or other imaging tests are repeated to evaluate the improvement in heart function.

Patients are advised on activity restrictions immediately following the procedure and are typically able to return to normal activities within a few weeks. Device battery life lasts 5–8 years, after which replacement is needed through a minor surgical procedure.

Limitations and Challenges
While CRT is a highly effective therapy, it is not without limitations. Some patients may not respond to the treatment, especially if they have significant scar tissue, narrow QRS complexes, or non-specific conduction abnormalities. Lead placement challenges, infection risks, and device-related complications, though rare, can also occur.

Ongoing research into newer pacing techniques like His-bundle pacing (HBP) and left bundle branch area pacing (LBBAP) aims to offer more physiologic alternatives and improve response rates in difficult cases.

Conclusion

Cardiac Resynchronization Therapy is a revolutionary advancement in the management of select heart failure patients who suffer from ventricular dyssynchrony. By electrically synchronizing the heart’s chambers, CRT helps the heart pump blood more effectively, relieves symptoms, reduces hospitalization, and improves survival. It is especially beneficial in those with reduced ejection fraction, prolonged QRS duration, and persistent heart failure symptoms despite optimal medical therapy.

The therapy involves implantation of a device that paces both ventricles simultaneously, and it comes in two main forms CRT-P and CRT-D tailored to the patient’s arrhythmic risk. Though not a cure for heart failure, CRT can transform the outlook for many patients, restoring not only cardiac function but also independence and hope.

With ongoing advancements in device technology, implantation techniques, and patient selection criteria, CRT continues to play a vital role in contemporary heart failure care. Understanding what CRT is and how it works empowers patients to make informed decisions about their treatment and work collaboratively with their healthcare team toward better outcomes.