A cardiac resynchronisation therapy-defibrillator (CRT-D) is a combined device that provides both ICD protection against life-threatening arrhythmias and biventricular pacing to resynchronise the heart’s contractions in patients with heart failure and electrical dyssynchrony.
In some patients with heart failure and a reduced ejection fraction, the left and right ventricles do not contract in a coordinated way, most commonly because of a left bundle branch block (LBBB) on the ECG. This dyssynchrony reduces the efficiency of the heart’s pumping action. CRT addresses this by pacing both ventricles simultaneously through two leads (one in the right ventricle and one placed via the coronary sinus into a vein on the back of the left ventricle), coordinating their contractions and improving cardiac output.
The addition of defibrillator function (making it a CRT-D rather than a CRT-P, which is pacing only) provides protection against ventricular fibrillation and sustained ventricular tachycardia. CRT-D is typically recommended for patients who already meet criteria for an ICD (such as cardiac arrest survivors, or patients with significantly reduced ejection fraction) and who also have heart failure with LBBB and QRS duration greater than 130ms on ECG.
CRT can produce significant improvements in symptoms, exercise capacity, quality of life, and, in suitable patients, ejection fraction. Around one-third of patients experience marked improvement and some achieve substantial recovery of heart function. The device requires specialist implantation and follow-up, including remote device monitoring.
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