Cardiac Resynchronisation Therapy (CRT)

Cardiac Resynchronization Therapy (CRT), also known as biventricular pacing, is a treatment for heart failure, particularly in patients with left ventricular dyssynchrony (i.e., when the left and right sides of the heart beat out of sync). CRT is used to improve heart function and symptoms by coordinating the timing of the heart's contractions. This therapy is delivered through a device known as a CRT pacemaker or CRT-defibrillator, which helps synchronize the electrical activity of the heart, allowing it to pump more efficiently.

Key Points:

1. Indications for CRT:

   • Heart Failure: CRT is typically indicated in patients with symptomatic heart failure (e.g., New York Heart Association (NYHA) class II to IV), particularly when the heart's ejection fraction (EF) is reduced (usually ≤35%).
   • Left Bundle Branch Block (LBBB): The therapy is often recommended in patients with LBBB or other forms of electrical dyssynchrony that impair coordinated heart contractions.
   • Sinus Rhythm: CRT is most effective in patients with normal sinus rhythm (i.e., not those with atrial fibrillation), although some devices can provide support for those with atrial arrhythmias.

2. Mechanism of Action:

   • The device has three leads: one in the right atrium, one in the right ventricle, and a third lead placed in the left ventricle via the coronary sinus. This third lead stimulates the left ventricle, which helps to restore more synchronized contraction of both the left and right ventricles.
   • By improving the synchronization of ventricular contractions, CRT can reduce symptoms of heart failure, improve exercise tolerance, and enhance the quality of life.

3. Benefits:

   • Improved Symptoms: Patients typically experience a reduction in symptoms like shortness of breath and fatigue.
   • Reduced Hospitalizations: CRT has been shown to decrease the frequency of hospital admissions related to heart failure.
   • Increased Survival: In some cases, CRT can lead to improved survival rates in patients with severe heart failure.

4. Device Types:

   • CRT-P (Pacemaker): For patients who do not have a high risk of sudden cardiac arrest.
   • CRT-D (Defibrillator): Includes a defibrillator function in addition to pacing capabilities. This is indicated for patients who are at risk for life-threatening arrhythmias like ventricular tachycardia or ventricular fibrillation.

5. Eligibility Criteria:

   • Symptoms of heart failure despite optimal medical therapy.
   • A reduced left ventricular ejection fraction (usually ≤35%).
   • Evidence of ventricular dyssynchrony, typically seen on an ECG with prolonged QRS duration (usually ≥150 ms), most often with a left bundle branch block pattern.

6. Risks and Complications:

   • Infection: As with any implantable device, there's a risk of infection.
   • Lead dislodgement: Leads may move from their optimal position, which can compromise therapy.
   • Device malfunction: The device can malfunction or fail, requiring further medical intervention.
   • Phrenic nerve stimulation: In some cases, stimulation of the diaphragm (via the lead in the left ventricle) can cause discomfort or difficulty breathing, although this can often be resolved by adjusting the device settings.

7. Follow-Up:

   • CRT devices require regular follow-up appointments to ensure they are working properly, adjust the settings as needed, and check for complications. Remote monitoring is also common to track the device’s performance.

Conclusion:

Cardiac Resynchronization Therapy is an important treatment option for patients with heart failure and electrical dyssynchrony, especially in those who have not responded well to medications. By restoring coordination between the heart's chambers, CRT improves symptoms, reduces hospitalizations, and may even improve survival in some patients. However, it is not appropriate for all heart failure patients, and careful selection based on the patient’s clinical status and rhythm is crucial.

For more and up to date info you can head on over to: Could a CRT pacemaker help my heart failure? - BHF  or BHF