Implantable Cardioverter-Defibrillator Decisions in Nonischemic Cardiomyopathy

Implantable cardioverter-defibrillators (ICDs) remain an important strategy for preventing sudden cardiac death in selected patients with nonischemic cardiomyopathy. The decision, however, has become more individualised as contemporary heart-failure therapy, cardiac magnetic resonance imaging, genetic testing and newer device technologies have changed risk assessment.

Updated guidance requires more than a single left ventricular ejection fraction (LVEF) measurement. Clinicians should consider symptoms, duration of guideline-directed medical therapy (GDMT), myocardial fibrosis, arrhythmic history, genotype, competing mortality, device complications and the patient’s preferences. These principles are particularly relevant in Australia, where access to advanced imaging, electrophysiology services and device follow-up varies between metropolitan and regional settings.

Who should be considered for primary prevention

For many adults with nonischemic dilated cardiomyopathy, a primary-prevention ICD is considered when LVEF remains at or below 35%, the patient has New York Heart Association (NYHA) class II or III symptoms, and they are receiving stable, evidence-based heart-failure therapy. A meaningful expectation of survival with acceptable functional status for more than one year is essential. The device should reduce the risk of sudden death without becoming disproportionate to the person’s overall prognosis.

Medical treatment should generally be optimised before implantation, unless the patient has sustained ventricular tachycardia, ventricular fibrillation or another urgent indication. This period commonly includes an angiotensin receptor–neprilysin inhibitor or an angiotensin-converting enzyme inhibitor, evidence-based beta-blocker, mineralocorticoid receptor antagonist and sodium-glucose cotransporter 2 inhibitor. Diuretic therapy controls congestion but does not substitute for disease-modifying treatment.

The usual reassessment interval is around three months after optimisation, although timing must reflect the cause and trajectory of cardiomyopathy. Recovery may take longer in newly diagnosed disease, myocarditis, tachycardia-mediated cardiomyopathy or peripartum cardiomyopathy. A persistently depressed LVEF after appropriate treatment strengthens the case for an ICD, while substantial reverse remodelling may remove the indication.

Why ejection fraction is only part of the decision

The benefit of prophylactic ICD therapy is not uniform across all patients with a low LVEF. The DANISH trial showed a reduction in sudden cardiac death among patients with nonischemic systolic heart failure, but the overall mortality benefit was less clear, particularly in older adults with substantial competing risks. Age, frailty, renal disease, pulmonary disease and recurrent hospitalisation should therefore be included in shared decision-making.

Cardiac magnetic resonance imaging can identify late gadolinium enhancement, which often represents replacement fibrosis and is associated with ventricular arrhythmia risk. A scar pattern, even when LVEF is moderately reduced, may support closer rhythm surveillance or specialist discussion. Conversely, absence of detectable fibrosis does not eliminate risk and should not override a clear clinical indication.

Genetic information can further refine assessment. Lamin A/C, filamin C, desmin, phospholamban and certain desmosomal variants may be associated with malignant ventricular arrhythmias at LVEF values above the conventional threshold. A family history of sudden death, unexplained syncope or multiple affected relatives warrants a structured inherited-cardiomyopathy assessment and, where appropriate, cascade testing.

Secondary prevention and high-risk phenotypes

A survivor of cardiac arrest caused by ventricular fibrillation or haemodynamically unstable sustained ventricular tachycardia generally has a strong secondary-prevention indication, provided the event was not due to a fully reversible cause. Electrolyte disturbance, acute myocarditis, drug toxicity, severe hypoxia and transient ischaemia must be investigated before attributing the event to an enduring arrhythmic substrate.

Unexplained syncope in a patient with cardiomyopathy deserves particular attention. It may represent intermittent ventricular tachycardia, advanced atrioventricular block or a non-arrhythmic process. Ambulatory monitoring, an implantable loop recorder, electrophysiology testing and cardiac imaging can be selected according to the phenotype rather than applied routinely.

Arrhythmia mechanisms are not interchangeable. Reflex syncope and functional bradycardia may require a different pathway from ventricular arrhythmia prevention; the discussion of cardioneuroablation strategies illustrates why the underlying mechanism should be established before committing a patient to an ICD or pacemaker strategy.

Choosing between an ICD, CRT-D and other systems

Cardiac resynchronisation therapy with defibrillation (CRT-D) should be considered when reduced LVEF coexists with suitable electrical dyssynchrony, particularly a left bundle branch block and a prolonged QRS duration. In patients with LVEF at or below 35%, sinus rhythm and a QRS of at least 150 milliseconds with left bundle branch block, the expected benefit is generally greatest. CRT can improve symptoms, ventricular function and hospitalisation risk while providing defibrillation capability.

The choice between CRT-D and CRT-P depends on sudden-death risk, age, comorbidity, patient values and the likelihood of meaningful response. A conventional transvenous ICD may be appropriate when pacing is unnecessary. A subcutaneous ICD can reduce transvenous lead-related complications in selected patients, but it cannot provide chronic bradycardia pacing, antitachycardia pacing or CRT.

A wearable cardioverter-defibrillator may be used as a temporary bridge in carefully selected situations, such as newly diagnosed cardiomyopathy, active myocarditis or a waiting period after device extraction. It is not a routine replacement for a permanent ICD. Adherence, skin tolerance, alarm burden and the patient’s capacity to respond to alerts must be assessed.

Balancing device benefits and complications

An ICD can deliver life-saving therapy, but inappropriate shocks, lead malfunction, infection, venous obstruction and psychological distress are clinically important. Programming should use contemporary evidence-based detection intervals and therapies that reduce unnecessary shocks. Medication review, treatment of atrial fibrillation and correction of reversible triggers can further reduce inappropriate therapy.

Lead placement also has longer-term haemodynamic consequences. Transvenous leads crossing the tricuspid valve can contribute to lead-related tricuspid regurgitation, especially when there is leaflet impingement, entanglement or progressive right-sided remodelling. The practical considerations in lead-related tricuspid regurgitation are relevant when selecting a device system and planning future lead interventions.

Infection prevention should include careful patient preparation, antibiotic prophylaxis, pocket management and avoidance of unnecessary reintervention. When extraction is required, referral to an experienced centre is important. Patients should receive clear information about wound care, driving restrictions, electromagnetic interference, remote monitoring and what to do after a shock.

Australian practice and access considerations

Australian decision-making takes place across a mixed public and private health system. Patients in Sydney, Melbourne, Brisbane, Perth and Adelaide commonly have access to tertiary electrophysiology services, cardiac MRI and inherited-cardiomyopathy clinics, while people in regional and remote communities may require coordinated travel, telehealth and local cardiology support. The Royal Flying Doctor Service and regional referral networks can be important for urgent assessment, although follow-up after implantation still needs a reliable local plan.

The local device market includes transvenous, subcutaneous and CRT systems supplied by major international manufacturers. Device selection should be based on clinical need, MRI compatibility, lead performance, programming capability and service support rather than brand familiarity. Australia’s Therapeutic Goods Administration regulates devices, while public hospitals and private insurers operate within different procurement and funding arrangements.

Medication access also influences the timing of ICD assessment. Angiotensin receptor–neprilysin inhibitors, mineralocorticoid receptor antagonists and sodium-glucose cotransporter 2 inhibitors may involve Pharmaceutical Benefits Scheme criteria, dose titration and affordability considerations. Documenting the therapy actually tolerated, rather than simply listing prescribed medicines, helps an electrophysiology team judge whether the cardiomyopathy has received an adequate period of GDMT.

Patients should receive advice that reflects Australian circumstances, including driving rules set by Austroads, long-distance travel between appointments and the availability of remote monitoring. A person living in regional New South Wales or northern Queensland may need a device clinic capable of reviewing transmissions without repeated metropolitan travel. Clear escalation pathways are especially important after shocks or alerts.

Shared decisions and follow-up after implantation

Shared decision-making should explain the likely reduction in sudden death, the chance of receiving appropriate therapy, and the possibility that an ICD will not improve breathlessness or prevent progressive pump failure. Some patients prioritise longevity, while others place greater value on avoiding shocks, procedures or future hospitalisation. Advance care planning should be discussed before a crisis, including the option of deactivating shock therapy when goals of care change.

Follow-up includes wound review, interrogation, battery surveillance, lead assessment, arrhythmia review and continued heart-failure management. Remote monitoring can identify atrial arrhythmias, lead abnormalities and fluid-related signals between clinic visits, but it does not remove the need for clinical review. Device therapies should be investigated promptly, with attention to whether a shock was appropriate, inappropriate or part of an electrical storm.

At generator replacement, the original indication should be reassessed rather than automatically renewed. LVEF may have improved, the patient’s age and comorbidity may have changed, or the balance between benefit and procedural risk may be different. Conversely, prior appropriate ICD therapy, persistent fibrosis or a high-risk genetic diagnosis may support continued protection even after partial recovery of ventricular function.

Apply these principles through a multidisciplinary pathway involving heart-failure specialists, electrophysiologists, imaging experts, genetic services, nurses and the patient’s general practitioner. Clinicians and researchers can use the Journal of Arrhythmia’s peer-reviewed evidence and educational resources to refine local protocols, support informed conversations and improve equitable access to ICD care across Australia.