Cardiac Resynchronization Therapy (CRT), commonly known as biventricular pacing, is a specialized treatment for certain patients with heart failure. It is designed to correct the abnormal electrical conduction in the heart that causes its chambers to beat out of sync. This lack of coordination, especially between the left and right ventricles, leads to inefficient blood pumping and worsening heart failure symptoms.
Recognizing the types of cardiac resynchronization therapy is important for most of the patient. CRT does not cure heart failure but helps the heart pump more efficiently, improves symptoms, enhances exercise capacity, and reduces hospitalizations. It is typically recommended for patients with moderate to severe heart failure, a low ejection fraction (≤ 35%), and evidence of electrical dyssynchrony on ECG, most commonly a wide QRS complex (≥ 130 ms), particularly in the presence of left bundle branch block (LBBB).
Cardiac resynchronization is accomplished through a surgically implanted device, and there are different types and techniques based on the patient’s needs and clinical scenario.
Types of Cardiac Resynchronization Therapy
- Cardiac Resynchronization Therapy with Pacemaker (CRT-P)
This is the basic form of cardiac resynchronization. A CRT-P device is a specialized pacemaker designed to stimulate both the right and left ventricles simultaneously, thereby resynchronizing their contractions. The system includes three leads: one placed in the right atrium, another in the right ventricle, and a third lead threaded through the coronary sinus to pace the left ventricle from the outside. The CRT-P is suitable for patients with symptomatic heart failure, reduced ejection fraction, and wide QRS complexes, especially those in sinus rhythm without a history of life-threatening arrhythmias. The goal of CRT-P is to improve cardiac efficiency, reduce symptoms like fatigue and breathlessness, and enhance the patient’s quality of life. The surgery is minimally invasive and is performed under local anesthesia with sedation. The leads are positioned via veins and the device is implanted under the skin, usually below the collarbone. - Cardiac Resynchronization Therapy with Defibrillator (CRT-D)
CRT-D combines the benefits of CRT pacing with the lifesaving capability of an implantable cardioverter-defibrillator (ICD). It is indicated for patients who qualify for CRT but also have a high risk of sudden cardiac death due to ventricular arrhythmias. The device can deliver pacing therapy to coordinate heartbeats and, if needed, provide high-voltage shocks to correct dangerous arrhythmias. This version includes all three leads as in CRT-P, with the addition of defibrillation capability in the right ventricular lead. The CRT-D is preferred in patients with ischemic cardiomyopathy, previous cardiac arrest, or episodes of sustained ventricular tachycardia. While it offers a broader spectrum of protection, CRT-D is generally more expensive, requires closer monitoring, and may be associated with a slightly higher complication rate due to the complexity of the device. - Epicardial Lead Placement for CRT
In some patients, placing the left ventricular lead through the coronary sinus (transvenous route) is technically challenging or unsuccessful due to venous anomalies, scar tissue, or previous cardiac surgeries. In such cases, surgeons may opt for an epicardial approach. During this procedure, the left ventricular lead is placed directly on the outer surface of the heart via a small surgical incision in the chest (thoracotomy or mini-thoracotomy). Epicardial lead placement requires general anesthesia and is more invasive than traditional CRT implantation, but it offers a reliable alternative when transvenous access is not feasible. It is also used in pediatric patients or in those undergoing concomitant heart surgery. The outcome is generally good, with excellent lead stability and pacing thresholds. - His-Bundle Pacing (HBP) for Resynchronization
His-bundle pacing is an emerging technique that directly stimulates the His-Purkinje system, the heart’s native electrical pathway to achieve physiological ventricular activation. Unlike traditional CRT, which stimulates the ventricles from outside, HBP activates them from within their natural conduction system, often resulting in more synchronized contraction. HBP can be especially useful in patients with narrow QRS or atypical conduction patterns who do not qualify for traditional CRT. It can also be considered in patients who did not respond to conventional CRT or where coronary sinus lead placement failed. Although technically more demanding, HBP offers the advantage of more natural electrical conduction and may reduce the need for biventricular pacing in selected cases. - Left Bundle Branch Area Pacing (LBBAP)
LBBAP is a newer form of conduction system pacing that involves placing the lead deep into the interventricular septum to capture the left bundle branch directly. This method overcomes some limitations of His-bundle pacing, such as lead dislodgment and high pacing thresholds. LBBAP offers a promising alternative for achieving resynchronization in patients with left bundle branch block or non-responders to CRT. This technique is still being studied and refined but is showing high success rates in restoring synchronized ventricular contraction. It is often performed by experienced electrophysiologists using advanced mapping and imaging tools. - Hybrid CRT Surgery
In some complex cases such as patients with congenital heart disease, multiple lead failures, or extensive scarring, a hybrid approach may be used. This involves combining surgical techniques (epicardial lead placement) with transvenous methods or using mapping tools to optimize lead positioning. These surgeries are individualized and require collaboration between cardiac surgeons and electrophysiologists.Hybrid CRT approaches are generally reserved for patients who have not responded to conventional CRT, have failed multiple lead attempts, or require customized lead configurations. While more invasive, they provide critical options for restoring synchrony in otherwise intractable cases.
- Upgrade from Conventional Pacemaker or ICD to CRT :-
Some patients already have a traditional pacemaker or ICD and develop worsening heart failure or new signs of dyssynchrony. In such cases, an upgrade to a CRT device may be indicated. This involves replacing the existing device with a CRT-P or CRT-D and adding a left ventricular lead if not already present.Upgrading to CRT is an important strategy for patients who were initially stable but have shown clinical deterioration, particularly with reduced left ventricular function and widened QRS. This procedure is typically done under local anesthesia and has been shown to improve outcomes in appropriately selected patients.
Conclusion
Cardiac resynchronization therapy has transformed the management of heart failure in patients with electrical dyssynchrony. It works by restoring coordinated contraction between the heart’s ventricles, thereby improving the heart’s efficiency, reducing symptoms, and prolonging life. The choice of CRT type, whether CRT-P, CRT-D, epicardial, or conduction system pacing depends on the individual’s cardiac anatomy, underlying rhythm, arrhythmic risk, and response to previous therapies.
While traditional CRT with a transvenous lead system remains the gold standard, newer approaches like His-bundle pacing and left bundle branch area pacing are redefining what’s possible in resynchronization therapy. For patients who don’t respond to conventional methods or present unique anatomical challenges, surgical epicardial or hybrid techniques offer viable alternatives.
With careful patient selection, expert surgical or electrophysiological execution, and long-term follow-up, cardiac resynchronization surgery significantly improves both quality and length of life for heart failure patients. As technology evolves and experience grows, more patients are likely to benefit from these life-enhancing and life-saving procedures.
