Cardiac Resynchronization Therapy (CRT) is an advanced treatment for individuals with heart failure whose heart chambers are not contracting in a coordinated manner. This therapy uses a specialized device, often called a biventricular pacemaker, to restore a synchronized pumping action. The goal of CRT is to improve the heart’s efficiency, boost its ability to pump blood, and ultimately reduce the debilitating symptoms associated with advanced heart failure.
Understanding the Mechanism: How CRT Works
The effectiveness of Cardiac Resynchronization Therapy centers on correcting ventricular dyssynchrony, a condition common in advanced heart failure. In a healthy heart, the electrical signal causes the lower chambers, or ventricles, to contract simultaneously. In heart failure, an electrical conduction delay—often seen as a wide QRS complex on an electrocardiogram—causes the right and left ventricles to contract out of sync. This uncoordinated movement significantly reduces the heart’s pumping efficiency and overall blood output.
CRT addresses this problem through biventricular pacing, delivering electrical impulses to both ventricles at the same moment. The CRT device uses three leads, or insulated wires, positioned in the heart’s chambers to achieve this simultaneous stimulation. By precisely timing the delivery of these impulses, the device forces the right and left ventricles to contract together.
This resynchronized contraction immediately improves the mechanical function of the heart. The coordinated action increases the volume of blood pumped with each beat, leading to improved cardiac output. Over time, this mechanical advantage can lead to “reverse remodeling,” where the heart muscle structure improves, and the left ventricle’s size and function become closer to normal.
Who Needs CRT? Identifying Eligible Patients
Patient selection for CRT is highly specific and guided by clinical criteria. Patients must typically have moderate to severe heart failure symptoms, categorized as New York Heart Association (NYHA) functional class II, III, or ambulatory class IV. This means their daily activities are significantly limited by symptoms such as fatigue or shortness of breath.
A defining factor is a severely reduced Left Ventricular Ejection Fraction (LVEF), which must be 35% or less, indicating poor pumping function. An electrocardiogram must also show evidence of an electrical delay, specifically a wide QRS complex, usually measuring 120 milliseconds or more. The strongest indication for CRT is the presence of a wide QRS complex, particularly if it is 150 milliseconds or greater, along with a Left Bundle Branch Block (LBBB) pattern.
The presence of LBBB is a strong predictor of a positive response to CRT. Patients with LBBB generally show the greatest benefit, including significant improvements in survival and a reduction in heart failure hospitalizations. Before a CRT device is considered, patients must have been receiving optimal medical therapy for heart failure for at least three months.
The Implantation Procedure and Device Components
The CRT system consists of a pulse generator and three insulated wires known as leads. The pulse generator is a small metal case containing the battery and computer circuitry for monitoring the heart’s rhythm and delivering timed electrical impulses. This unit is typically implanted just beneath the skin in the upper chest, usually below the collarbone.
The procedure is minimally invasive, generally performed in a catheterization laboratory under local anesthesia and light sedation. The leads are inserted into a major vein near the collarbone and guided to the heart’s chambers using X-ray imaging. One lead is placed in the right atrium, another in the right ventricle, and the third is threaded through the coronary sinus to reach the outside surface of the left ventricle.
Once the leads are positioned optimally, they are tested to ensure they can sense the heart’s electrical activity and deliver pacing impulses effectively. The leads are then connected to the pulse generator, which is secured in its pocket under the skin. The entire procedure typically takes a few hours, and most patients require a short hospital stay for monitoring afterward.
Life After CRT: Management and Follow-Up
Following implantation, patients can typically resume most normal activities within a few days to weeks, though full benefits develop gradually. While some patients feel immediate improvement, the heart’s structural changes, or reverse remodeling, often take several months to become fully apparent. A reduction in symptoms and an increase in functional capacity are common outcomes within the first six months.
Long-term management involves regular monitoring to ensure the device is functioning optimally and pacing settings are correct. These checks are performed periodically, either in-person at a clinic or through remote monitoring systems. The battery life of a CRT device typically ranges from five to ten years and requires replacement when depleted.
Patients must be mindful of strong electromagnetic fields, including industrial equipment and certain medical procedures, which can temporarily interfere with the device’s function. Many newer CRT systems are designed to be compatible with Magnetic Resonance Imaging (MRI), allowing access to this diagnostic tool under specific safety conditions. Patients should discuss the specific model with a cardiologist to understand all necessary precautions.