Devices

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These articles provide education to enhance your healthcare partnership. All treatment decisions should involve your healthcare team. Use this knowledge to have informed discussions, not replace medical care.

In Brief

Two implantable devices are used in heart failure, and they do entirely different things. One — the implantable defibrillator — is a safety net that does nothing day to day but stands ready to stop a sudden, life-threatening heart rhythm before it becomes fatal. The other — cardiac resynchronization therapy — re-coordinates a heart whose ventricles have fallen out of electrical step, and can make a person feel better while helping the pump recover. Neither treats heart failure the way the medications of Article 6 do, and neither is a substitute for them: a device is always an addition to medication, never a replacement. The idea that ties the article together is that each device solves one specific problem — the defibrillator addresses the risk of sudden death from an electrical rhythm; resynchronization addresses a coordination problem in how the heart contracts. Whether a device helps is not settled by the ejection fraction alone. It depends on the whole picture — a person’s rhythm history, the pattern on their heart tracing, their other risks, and how far medication has already improved the heart. This article explains what each device does, and who does and does not stand to benefit.

Two Devices, Two Different Jobs

It is easy to lump “heart failure devices” together, but the two most important ones solve different problems. The implantable defibrillator addresses the risk of dying suddenly from an electrical rhythm disturbance. Cardiac resynchronization therapy addresses a mechanical inefficiency in how a damaged heart contracts. One protects against a sudden, potentially fatal event; the other improves the coordination of the pump. Knowing which problem a device solves is central to understanding when it helps.

And running through both is a principle worth stating before the details: these devices are added on top of the four core medications, never in place of them. When a device is planned purely as a precaution — before any dangerous rhythm has ever happened — medication is generally established first, and heart function re-checked, before implanting. When someone has already survived a dangerous rhythm, or the situation is urgent, the pathway is different.

The Implantable Defibrillator (ICD): A Safety Net Against Sudden Death

A weakened heart is more electrically unstable than a healthy one. Scarred or stressed heart muscle can suddenly break into a dangerous, potentially lethal rhythm — ventricular tachycardia or ventricular fibrillation, in which the pumping chambers race or quiver instead of pumping effectively — and within minutes, without intervention, this can cause sudden cardiac death. It is one of the ways heart failure can cause death, and it can occur in someone who otherwise feels stable.

An implantable cardioverter-defibrillator (ICD) is the answer to that specific danger. Implanted under the skin, usually with wires (leads) that run into the heart, it continuously monitors the rhythm and does nothing at all — until it detects one of those dangerous rhythms. Then, depending on the rhythm and the device’s programming, it may use a sequence of rapid pacing impulses — called antitachycardia pacing — that can stop some fast rhythms painlessly, without a shock, or it may deliver a shock to reset the heart. It functions purely as a safety net. It does not help the heart pump, does not relieve breathlessness, and does not slow the disease. Much of the time a person is unaware of it, and its value lies in an event that may never occur.

Doctors distinguish two situations. In secondary prevention — a person who has already survived a cardiac arrest or a dangerous sustained arrhythmia — the case for an ICD is strong, because the danger has already proven itself. In primary prevention — someone at high risk who has not yet had such an event — the decision rests on statistics. The landmark trials found that in people with a substantially reduced ejection fraction, an ICD reduced the risk of death — by roughly a quarter in a broad heart failure population with an ejection fraction of 35 percent or below,[2] and by roughly a third in people with a prior heart attack and severely reduced function.[3] Both figures describe the effect across large groups in the trials, not a fixed promise for any one person — and the higher someone’s own risk, the more a defibrillator stands to help.

An important qualification applies here, though. Much of that evidence comes from an era before today’s four-pillar medication, and one large, more recent trial in people whose heart failure was not caused by coronary disease — a group called non-ischemic cardiomyopathy (heart-muscle weakness from another cause) — found that an ICD did not significantly reduce overall deaths on top of modern therapy — even though it did reduce sudden arrhythmic deaths specifically. Subsequent analyses suggested that age and competing causes of death may shape who benefits most, with greater apparent benefit in younger patients.[4] The lesson underneath matters: a defibrillator prevents only one mode of death — a sudden lethal rhythm. If a person’s greatest threat is the pump gradually giving out, preventing the arrhythmic death may not lengthen overall survival, because another mode of death takes its place. As medication has grown better at preventing sudden death, the added protection a defibrillator offers has narrowed in some groups, and the decision has become more individualized than automatic.

An ICD has real downsides, too. Its shocks can be painful and frightening. And not every therapy it delivers is appropriate: a device can occasionally treat a rhythm that was not in fact a lethal ventricular arrhythmia, or fire because of a sensing problem — though modern programming has substantially reduced this. In very advanced heart failure, where death is more likely to come from the pump giving out than from a sudden arrhythmia, a defibrillator — which guards only against sudden arrhythmic death — may offer little.

Cardiac Resynchronization Therapy (CRT): Re-coordinating the Squeeze

The second device solves a different problem entirely. In a healthy heart, an electrical signal sweeps across the pumping chambers so their walls contract together in one coordinated squeeze. In some people with heart failure, that signal is delayed — usually seen on the electrocardiogram as a widened QRS (the electrical signature of the ventricles activating) with a pattern called left bundle branch block. When that happens, different regions of the ventricles contract at different times rather than as one coordinated pump, working against each other and wasting an already-weakened heart’s effort. This is electrical dyssynchrony.

Cardiac resynchronization therapy (CRT) — also called biventricular pacing — corrects it. Using specially positioned pacing leads, the device re-times the contraction so the ventricles work together again, restoring the coordination the disease took away. Unlike the defibrillator, CRT can produce benefits a person can feel: in appropriately selected patients, it eases symptoms, improves exercise capacity, raises the ejection fraction, and reduces both hospitalizations and death.[5][6] It is one of the few interventions that can make a failing heart pump measurably better rather than merely slowing its decline.

The key limitation is that CRT only helps hearts that have this coordination problem. Benefit is strongest in symptomatic heart failure with a markedly prolonged QRS — especially the left-bundle-branch-block pattern — and becomes less certain as the QRS narrows, or as the tracing looks less like that classic pattern. In people whose QRS is narrow — whose ventricles are already contracting in a coordinated way — CRT offers no benefit and, in a trial that tested it, was associated with harm.[7] Resynchronizing a heart that is not out of sync does not help; it can hurt. This is why the electrocardiogram, not the ejection fraction alone, is central to deciding who is a candidate — alongside symptoms, rhythm, and how much pacing a person is expected to need. And even when the criteria are met, not everyone improves to the same degree.

CRT is often combined with a defibrillator in a single implanted unit. A resynchronization device on its own is called CRT-P (the P for pacing); combined with a defibrillator, it is CRT-D. The choice between them is not automatic — it depends on whether a person is also expected to benefit from defibrillation, which is a separate question from whether they benefit from resynchronization. The two functions remain distinct, chosen for two separate reasons.

What Having a Device Involves

Getting a device is a procedure, and like any procedure it carries some risk. Around the implant itself, the main ones are bleeding or a pocket of blood (hematoma), a small chance of a collapsed lung (pneumothorax) from placing the leads, and a lead shifting out of position early on and needing repositioning. Over the longer term, leads can occasionally fail, devices and leads are sometimes subject to manufacturer recalls, and — for defibrillators — shocks can be delivered inappropriately or leave a lasting emotional mark. Afterward, the device is checked periodically, often remotely from home. When the battery nears depletion, the generator is replaced in a smaller procedure; how long it lasts varies by device and by how much therapy it delivers. Two practical points are worth raising with the care team: short-term driving restrictions can apply after an ICD or a shock, and an MRI is not simply off-limits — many modern systems can be scanned under specified conditions, but the device team needs to know the exact system and coordinate the scan. None of these are reasons to refuse a device that is truly needed; they are part of the honest picture — and part of why a device is worth having only when it is likely to help.

A word on infection. The most serious device complication is infection. It is uncommon, but it must be taken seriously, because once an implanted system is infected, antibiotics alone usually cannot clear it, and treatment often means removing the whole system — device and leads. That removal is a specialized procedure carried out by experienced teams.[8] What matters most for a person living with a device is catching infection early: redness, swelling, warmth, or drainage around the device pocket, a wound that is not healing, or an unexplained fever all warrant prompt assessment.

Who Does Not Need a Device

This part matters as much as any other, and it is easy to overlook. Devices are powerful, invasive, and permanent, and they are not for everyone with heart failure. Several situations make a device unnecessary, inappropriate, or less likely to help.

People whose heart recovers enough on medication that a preventive defibrillator is no longer needed. This is the most important case, and it follows directly from Article 6. When a defibrillator is being considered purely to prevent a first dangerous rhythm, the decision leans heavily on the ejection fraction — and the four core medications can lift that number substantially over months. So a heart that would have qualified before treatment can recover enough that, when it is measured again later, it no longer needs the device. This is exactly why guidelines call for a stretch of optimized medication and a fresh ejection-fraction measurement before a preventive defibrillator goes in.[1] How long to wait is not one fixed number: it depends on why the ejection fraction is low — a newly diagnosed cardiomyopathy, a recent heart attack, recent procedures to restore blood flow, and other potentially reversible causes each carry their own timeline. The principle is simple: a device is not rushed in before medication has had a fair chance, so that hardware is not implanted in a heart that would have recovered.

People with a narrow QRS being considered for CRT. As above, without electrical dyssynchrony there is nothing for resynchronization to fix, and it should not be used.[1][7]

People with very advanced heart failure and limited life expectancy. When the disease has progressed to the point that death is expected from the failing pump itself, a defibrillator that guards only against sudden arrhythmic death may add little, and the decision shifts toward comfort and goals of care — the subject of Article 12. For someone already living with a defibrillator, this is also the point at which many people choose to have its shocking function turned off, so that it does not deliver distressing shocks during a natural death. This is done noninvasively, through the device’s programming, and the pacing functions can often stay on. One point is worth stating plainly, because families often misunderstand it: turning off the shocks is not a cause of death, and it is widely recognized as ethically and legally different from assisted dying. It removes one specific intervention, nothing more — and it is a conversation worth having openly with the care team.

Underlying all of this is a principle worth naming. Modern medical therapy can improve heart function enough that some people no longer meet the criteria for a primary-prevention defibrillator once they are reassessed — but the larger point is not simply that fewer people need devices. It is that device benefit depends on the individual: the cause of the cardiomyopathy, the ECG pattern, competing risks, age, and expected survival all shape whether a device will help this person. The right question is never “does the rule allow a device,” but “will this particular person benefit” — a judgment for a specialist team, individualized to the person in front of them.

A Device Is an Addition, Never a Replacement

Neither device treats heart failure the way the four core medications do. The defibrillator does nothing for the failing pump; it only stands guard. Resynchronization helps a specific electrical problem, but it does not replace the medicines that slow the disease. Both are built to sit on top of optimized medication, added to address a specific residual risk — sudden death — or a specific mechanical problem — dyssynchrony — that the pills alone do not cover.

A device is therefore never a reason to stop, skip, or neglect the medications. The person with an ICD still needs their four pillars; the person with CRT still needs them too. The device handles one narrow job; the medicine does the rest. Understanding that division of labor is what keeps a device in its proper place.

One practical safety note. Every person with a defibrillator should know their device team’s shock plan in advance, because plans vary. In many, a single shock followed by complete recovery warrants prompt contact with the device team; repeated shocks, or a shock accompanied by persistent symptoms — chest pain, severe breathlessness, or fainting — require emergency care. The specifics belong in a plan made with the care team before they are ever needed.

Questions Worth Asking If a Device Is Proposed

Because these are major, permanent decisions, a few plain questions help make them clear:

• Which problem is this device meant to solve for me — the risk of sudden death, a coordination problem, or both?
• What is my expected benefit as an individual — not just whether I technically qualify?
• Has my medication been fully optimized, and my ejection fraction re-measured, before deciding?
• If my heart has been recovering on medication, do I still need this — or is it worth waiting and re-checking?
• What are the specific risks for me, and what will living with it involve — checks, battery changes, and the small chance of infection?

Clinical Bottom Line

Two devices matter in heart failure, and they do different jobs. The implantable defibrillator is a silent safety net against sudden death from a lethal rhythm; it does not relieve symptoms or slow the disease. Its benefit is clearest in people whose heart was damaged by coronary disease or a heart attack; when the weakness comes from another cause, whether it helps depends more on the individual — their arrhythmia risk, their age, and what else threatens their health. Cardiac resynchronization therapy re-coordinates a heart contracting out of step — its benefit strongest with a markedly wide QRS and left bundle branch block, less certain as the pattern moves away from that, and capable of harm in a narrow QRS. For planned primary-prevention decisions, medication generally comes first: because the four core drugs can restore a weakened heart, some people who once qualified for a defibrillator no longer need one after their medication is optimized and their ejection fraction re-measured. Above all, neither device is a generic treatment for a weak heart. Each solves one specific problem, and whether it helps depends on the person’s phenotype and competing risks — not simply on crossing an ejection-fraction threshold. A device is always an addition to medication, never a replacement.

What Comes Next

This article covered the devices that support the heart. Article 9 turns to what happens when standard treatment — medication and devices together — is no longer enough: advanced heart failure, and the options of heart transplant and mechanical circulatory support (left ventricular assist devices). How candidacy is assessed, what each option involves, and how these decisions are made.

Key Terms

Implantable cardioverter-defibrillator (ICD): A device implanted under the skin that continuously monitors the heart’s rhythm and delivers pacing or a shock to stop a lethal arrhythmia; a safety net against sudden death that does not relieve symptoms or treat the pump.

Ventricular tachycardia / ventricular fibrillation: Dangerous, fast heart rhythms arising in the pumping chambers — tachycardia rapid and organized, fibrillation chaotic; if sustained, either can cause sudden cardiac death.

Sudden cardiac death: Death from an abrupt loss of heart function due to a lethal arrhythmia; one of the ways heart failure can kill without warning.

Primary prevention: Implanting a defibrillator in a high-risk person who has not yet had a life-threatening arrhythmia.

Secondary prevention: Implanting a defibrillator in a person who has already survived a cardiac arrest or dangerous arrhythmia.

Antitachycardia pacing: A sequence of rapid pacing impulses an ICD can deliver to stop certain fast ventricular rhythms painlessly, without a shock.

Ischemic vs non-ischemic cardiomyopathy: Heart muscle weakness caused by prior coronary disease or heart attack (ischemic) versus other causes (non-ischemic); the distinction affects how much a defibrillator helps.

Cardiac resynchronization therapy (CRT): Also called biventricular pacing; a device that re-times the ventricles to contract together, correcting electrical dyssynchrony and improving the pump in selected patients. A resynchronization device alone is CRT-P; combined with a defibrillator, it is CRT-D.

Electrical dyssynchrony: A delay that makes different regions of the ventricles contract at different times rather than as one coordinated pump, reducing efficiency; the problem CRT is designed to fix.

QRS: The part of the electrocardiogram representing the ventricles’ electrical activation; a wide QRS suggests the signal is delayed and the contraction may be out of sync.

Left bundle branch block: A specific pattern of delayed electrical conduction, seen as a wide QRS, that marks the pattern most likely to benefit from CRT.

References

1. Heidenreich PA, Bozkurt B, Aguilar D, et al. 2022 AHA/ACC/HFSA Guideline for the Management of Heart Failure: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2022;145:e895–e1032. https://doi.org/10.1161/CIR.0000000000001063
2. Bardy GH, Lee KL, Mark DB, et al. Amiodarone or an Implantable Cardioverter–Defibrillator for Congestive Heart Failure (SCD-HeFT). N Engl J Med. 2005;352(3):225–237. https://doi.org/10.1056/NEJMoa043399
3. Moss AJ, Zareba W, Hall WJ, et al. Prophylactic Implantation of a Defibrillator in Patients with Myocardial Infarction and Reduced Ejection Fraction (MADIT-II). N Engl J Med. 2002;346(12):877–883. https://doi.org/10.1056/NEJMoa013474
4. Køber L, Thune JJ, Nielsen JC, et al. Defibrillator Implantation in Patients with Nonischemic Systolic Heart Failure (DANISH). N Engl J Med. 2016;375(13):1221–1230. https://doi.org/10.1056/NEJMoa1608029
5. Bristow MR, Saxon LA, Boehmer J, et al. Cardiac-Resynchronization Therapy with or without an Implantable Defibrillator in Advanced Chronic Heart Failure (COMPANION). N Engl J Med. 2004;350(21):2140–2150. https://doi.org/10.1056/NEJMoa032423
6. Cleland JGF, Daubert JC, Erdmann E, et al. The Effect of Cardiac Resynchronization on Morbidity and Mortality in Heart Failure (CARE-HF). N Engl J Med. 2005;352(15):1539–1549. https://doi.org/10.1056/NEJMoa050496
7. Ruschitzka F, Abraham WT, Singh JP, et al. Cardiac-Resynchronization Therapy in Heart Failure with a Narrow QRS Complex (EchoCRT). N Engl J Med. 2013;369(15):1395–1405. https://doi.org/10.1056/NEJMoa1306687
8. Baddour LM, Epstein AE, Erickson CC, et al. Update on Cardiovascular Implantable Electronic Device Infections and Their Management: A Scientific Statement From the American Heart Association. Circulation. 2010;121(3):458–477. https://doi.org/10.1161/CIRCULATIONAHA.109.192665

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