CRT and CRT-D: resynchronization therapy in heart failure

According to the EHRA patient website, in heart failure the ventricles may contract at different times instead of at the same time. This is called dyssynchrony, and it may make symptoms worse. The cause may be left bundle branch block: in it, the electrical signal reaches the left ventricle late.

The symptoms EHRA lists: shortness of breath, tiredness, dizziness, feeling your heartbeat, swelling of the ankles and legs, cough. In some severe cases where medicines are not enough, CRT may be needed. It coordinates the right and left ventricles.

CRT-P (a biventricular pacemaker) only paces. According to EHRA, it has two or three leads: in the right ventricle, the left ventricle and the right atrium. In atrial fibrillation, the atrial lead is not placed.

CRT-D is a device with three leads that delivers resynchronization together with defibrillation, meaning it can stop dangerous ventricular rhythms with a shock.

The choice depends on the risk of a dangerous arrhythmia. The specialist makes this decision together with you, because everyone's situation is different.

Three terms from the guideline, put simply:

• LVEF: shows how much blood the left ventricle pumps out with one beat.
• QRS: a wave on the ECG; its width is measured in milliseconds (ms).
• NYHA: a class showing how much heart failure limits everyday activity; the higher the number, the greater the limitation.

According to the ACC summary of the 2021 ESC/EHRA guideline, CRT is recommended in symptomatic heart failure with sinus rhythm (the heart's normal rhythm), an LVEF of 35 % or less, a QRS of 150 ms or more and left bundle branch block.

In the following situations it should be considered:

• a QRS of 130–149 ms and left bundle branch block;
• a block of another type, but a QRS of 150 ms or more;
• NYHA class III–IV, atrial fibrillation and a QRS of 130 ms or more, provided that pacing of both ventricles is ensured.

If, because of atrial fibrillation, pacing of both ventricles is not complete (less than 90–95 %), the guideline says AV junction ablation should be added. Ask your doctor about this procedure.

With CRT, a lead is also placed for the left ventricle. According to EHRA, the implantation may take longer than for a standard pacemaker; for a pacemaker, 1–2 hours is usually quoted. Many steps are the same: usually local anesthesia and a sedative, a small incision on the left side of the chest, and X-ray guidance.

Beforehand, tell the doctor about any blood clotting problems, blood-thinning medicines and allergies. According to EHRA, after a few hours of observation you are allowed home the same day or the next day, and someone must pick you up.

Another difference is the risk of infection. According to the 2021 ESC summary, infection is more common with CRT than with a standard pacemaker. A lead may also move out of place, and then a repeat operation may be needed.

In the first days, the incision may hurt and itch; keep it clean and dry. According to EHRA, most people go back to work within one or two weeks. Sources differ on arm movement: EHRA says no restriction is needed, while the NHS in the UK advises not raising the elbow above the shoulder for 4–6 weeks. Follow your own doctor's instructions.

CRT does not help everyone equally. The 2022 ESC guideline says that in people who have not benefited from CRT and who have frequent extrasystoles of the same type, ablation or antiarrhythmic medicines should be considered.

According to patient guides, if your temperature rises above 38.5 °C, if there is redness or swelling over the device, fluid leaking from the incision, or if dizziness or shortness of breath gets worse, tell your doctor right away.

Sources differ, so follow your doctor's schedule. EHRA: the first check at 2–12 weeks, then usually once a year. NHLBI says at least once every 6 months for an ICD.

According to NHLBI, a CRT-D is replaced about every 4 years, which is often earlier than a standard ICD. The sources give no separate figure for CRT-P. Your doctor will tell you the exact time frame. Replacement is simpler than the first implantation, and working leads are usually left in place. But according to the ACC summary of the 2021 ESC/EHRA guideline, the risk of infection is higher at replacement.