Heart failure and pacemaker or defibrillator:
when they may be needed

Article written and reviewed by Dr Luca Moretti

Pacemakers, implantable defibrillators, and cardiac resynchronization are not the same thing. A traditional pacemaker is mainly used to correct excessively slow heartbeats or conduction disorders; an ICD detects and treats potentially life-threatening ventricular arrhythmias; CRT coordinates ventricular contraction when electrical activation is abnormal.
In heart failure, the choice depends on ejection fraction, ECG, type of heart disease, symptoms, response to treatment, and risk of sudden death. A low EF alone does not automatically mean that a device should be implanted.

The three main functions are:

• pacemaker: prevent excessively slow heart rates and treat certain conduction disorders;
• ICD: terminate ventricular tachycardia or ventricular fibrillation to prevent sudden death;
• CRT: resynchronize ventricular contraction when electrical activation is dyssynchronous;
• CRT-D: combine resynchronization and defibrillator function in the same system.

Indications are established after optimizing pharmacological treatment of heart failure, except in situations in which pacing or resynchronization must be planned earlier.

Pacemaker, ICD, and CRT: what is different

A conventional pacemaker sends small electrical impulses when the heart is beating too slowly or conduction between the atria and ventricles is impaired. It is not implanted simply because a person has heart failure: there must be an indication related to rhythm or conduction.
However, in some patients with reduced ventricular function, prolonged right ventricular pacing alone can worsen the synchronization of contraction. For this reason, when a high pacing burden is expected, a resynchronization strategy may be preferred.

An ICD has a different purpose. It continuously monitors the rhythm and, if it detects dangerous ventricular tachycardia or ventricular fibrillation, can deliver rapid pacing or a shock to terminate it. Its main purpose is to prevent sudden arrhythmic death, not to directly improve breathlessness or pumping strength.
CRT, by contrast, stimulates both ventricles in a coordinated manner and can improve mechanical function in patients in whom slowed electrical conduction, especially left bundle branch block, causes dyssynchrony.

When an ICD defibrillator may be needed

An ICD is strongly indicated for secondary prevention in people who have survived a ventricular arrhythmia that caused hemodynamic instability, when there is no reversible cause and there is a reasonable expectation of survival with good functional status for more than one year.
Primary prevention instead concerns people who have not yet had a lethal arrhythmia but have a sufficiently high risk.

According to the 2026 ESC guidelines, an ICD is recommended in patients with symptomatic HFrEF in NYHA class II-III, ischemic etiology, and EF no higher than 35% despite at least three months of optimal foundational therapy, provided that at least 40 days have elapsed since any myocardial infarction and expected survival is more than one year with good functional status.
In nonischemic forms with the same criteria, an ICD should be considered, but the average benefit may be less marked and the decision requires particular attention to age, comorbidities, and the competing risk of nonarrhythmic death.

When CRT resynchronization can improve heart failure

CRT is most useful when the heart not only has reduced function but also contracts dyssynchronously because of an electrical conduction abnormality. The key ECG finding is QRS duration and, above all, the presence of left bundle branch block.
The strongest 2026 ESC indication concerns symptomatic patients with HFrEF, EF no higher than 35%, sinus rhythm, left bundle branch block, and a QRS duration of at least 150 milliseconds despite optimal therapy: in this group CRT improves symptoms and reduces hospitalizations and mortality.

CRT may also be considered with a QRS duration of 130-149 ms in the presence of left bundle branch block and in some patients with non-LBBB morphology, especially when QRS is at least 150 ms. Conversely, it is not recommended in heart failure with QRS below 130 ms in the absence of another pacing indication.
The 2026 ESC guidelines also allow CRT, in selected patients with HFrEF, LBBB, QRS of at least 150 ms, and EF no higher than 35%, to be planned at the same time as foundational therapy is started, while still reassessing EF before implantation.

CRT-P or CRT-D: why not everyone receives the same device

Resynchronization can be delivered by a device with pacing function only, CRT-P, or by a system that also includes a defibrillator, CRT-D. The choice depends on the risk of ventricular arrhythmias, the etiology of the heart disease, age, comorbidities, and patient preferences.
A young person with ischemic heart disease and a high risk of sudden death may have a different benefit-risk balance from an older person with multiple comorbidities and low arrhythmic risk but a clear indication for resynchronization.

People who already have a pacemaker or ICD may also, in some circumstances, be candidates for an upgrade to CRT. The 2026 ESC guidelines indicate that an upgrade should be considered in patients with EF no higher than 35% who develop worsening heart failure despite optimal therapy and have a substantial burden of right ventricular pacing.

Why a complete assessment is needed before implantation

A device can provide substantial benefit, but it also involves an invasive procedure, possible complications, periodic follow-up, and, in the case of an ICD, the possibility of appropriate or inappropriate therapies. For this reason, the decision should not be reduced to an EF threshold read from an echocardiogram.
The cardiologist considers the cause of heart failure, duration of optimal therapy, likelihood that EF will improve, ECG findings, presence of myocardial scar, previous arrhythmias, age, frailty, coexisting diseases, and the patient's expectations.

In particular, an ICD for primary prevention is not recommended within the first 40 days after a myocardial infarction and is not indicated in patients in NYHA class IV with refractory symptoms who are not candidates for CRT, ventricular assist device, or transplantation. In patients with advanced heart failure, the strategy must therefore be incorporated into an overall assessment of goals of care.

Frequently asked questions about pacemakers, ICDs, and CRT

Does an ejection fraction of 35% mean that a defibrillator is needed?
Not automatically. For primary prevention, the 2026 ESC guidelines also consider ischemic or nonischemic cause, symptoms, at least three months of optimal therapy, time elapsed since any myocardial infarction, expected survival with good functional status, and patient preferences.

What is the difference between a pacemaker and a defibrillator?
A pacemaker mainly treats excessively slow heart rates or conduction disorders. An ICD recognizes and treats potentially life-threatening ventricular arrhythmias. Some resynchronization devices can also include a defibrillator function.

What is CRT in heart failure?
CRT is cardiac resynchronization therapy. It stimulates the ventricles in a coordinated way to correct electrically dyssynchronous contraction and, in selected patients, can improve symptoms and cardiac function and reduce hospitalizations and mortality.

Can someone with left bundle branch block be a candidate for CRT?
They may be if other criteria are also present. In the 2026 ESC guidelines, the strongest indication concerns symptomatic patients with HFrEF, EF no higher than 35%, sinus rhythm, left bundle branch block, and QRS duration of at least 150 ms despite optimal therapy.

Does a defibrillator improve the heart's pumping strength?
An ICD by itself is mainly intended to prevent sudden death from ventricular arrhythmias and is not designed to increase pumping function. CRT, on the other hand, can improve synchronization and cardiac function in appropriate patients.