Cardiac Resynchronization Therapy (CRT) is a device-based treatment for certain types of heart failure. It involves implanting a specialized device to help the heart pump blood more effectively. CRT aims to improve the heart’s pumping efficiency, which can be compromised when its chambers do not beat in a coordinated manner. The therapy helps alleviate symptoms and enhance the overall well-being of patients.
How Cardiac Resynchronization Therapy Works
Cardiac Resynchronization Therapy addresses electrical dyssynchrony, a condition where the heart’s lower chambers, the ventricles, contract out of sync. When the ventricles do not pump together, the heart’s ability to move blood forward is reduced, leading to heart failure symptoms.
A CRT device consists of a pulse generator and three thin wires called leads. One lead is placed in the right atrium, an upper chamber, and another in the right ventricle. The third lead is threaded through a vein on the outside of the left ventricle, usually via the coronary sinus, to stimulate this chamber.
The device sends precisely timed electrical impulses to both the right and left ventricles, prompting them to contract simultaneously. This coordinated contraction, known as biventricular pacing, restores a more synchronized pumping action, improving the heart’s overall pumping efficiency.
Some CRT devices, known as CRT-D devices, also include the functionality of an implantable cardioverter-defibrillator (ICD). These can deliver an electrical shock to correct dangerously fast heart rhythms. A CRT-P device, by contrast, provides only the pacing function without the defibrillator component.
Identifying Candidates for CRT
Cardiologists evaluate several factors to determine if a patient is a suitable candidate for Cardiac Resynchronization Therapy. Patients have moderate to severe heart failure symptoms despite receiving optimal medical therapy. This often corresponds to New York Heart Association (NYHA) functional classes II to IV, reflecting limitations in daily activities.
A primary diagnostic metric is the Left Ventricular Ejection Fraction (LVEF), which measures the percentage of blood pumped out of the left ventricle with each beat. For CRT, patients have a reduced LVEF, often at or below 35%, indicating impaired pumping function of the main pumping chamber.
The heart’s electrical conduction system is also examined through an electrocardiogram (ECG). A Left Bundle Branch Block (LBBB) is a common indicator of electrical dyssynchrony. LBBB appears as a wide QRS complex on the ECG, signifying a delay in the electrical activation of the left ventricle. This delay contributes to the uncoordinated ventricular contraction that CRT aims to correct.
The Implantation Procedure
Implanting a CRT device is a minimally invasive procedure. It is typically performed in a cardiac catheterization lab or an operating room. Patients usually receive local anesthesia to numb the area near the collarbone, along with sedation.
A small incision is made in the upper chest, often below the left collarbone. Through this incision, the physician guides the three leads (thin, insulated wires) through a vein and into the heart chambers. Real-time X-ray imaging, called fluoroscopy, is used to precisely guide the leads to their intended positions within the right atrium, right ventricle, and along the outside of the left ventricle via the coronary sinus.
Once the leads are securely in place, they are connected to the pulse generator, which is then placed in a small pocket created under the skin in the chest. The device is thoroughly tested to ensure it is functioning correctly and programmed to the patient’s specific needs. Finally, the incision is closed with stitches or surgical adhesive, and a sterile dressing is applied to the site.
Life After CRT Implantation
Following a CRT implantation, patients typically have a short hospital stay. During the initial recovery period, patients are advised to limit movement of the arm on the side of the implant to prevent the leads from shifting. Proper wound care for the incision site is also explained to prevent infection.
Long-term management involves regular follow-up appointments to monitor the device’s function and battery status. These visits typically occur every six months or annually, where a healthcare provider uses a programmer to check the device’s performance and make any necessary adjustments to its settings. The battery in a CRT device is designed to last for several years, often between 8 to 10 years.
When the battery approaches depletion, a simpler procedure is performed to replace only the pulse generator, usually leaving the existing leads in place if they are still functioning well. Patients should carry a device identification card and inform all healthcare providers about their implant. While most household appliances are safe, it is advisable to avoid strong magnetic fields and discuss MRI compatibility with their doctor, as many newer devices are MRI-conditional.
With effective CRT, many patients experience significant improvements in their heart failure symptoms, including reduced shortness of breath and fatigue, and an enhanced ability to perform daily activities. This therapy often leads to an improved quality of life and can contribute to better long-term outcomes for individuals with heart failure.