Ambulatory External Wearable Defibrillator Use After Myocardial Infarction

The period immediately after myocardial infarction (MI) presents a difficult balance between arrhythmic risk and therapeutic uncertainty. Ventricular tachycardia or ventricular fibrillation may occur while the myocardium is electrically unstable, yet left ventricular ejection fraction (LVEF) can improve substantially after reperfusion, optimal medical therapy, and remodelling. An implantable cardioverter-defibrillator (ICD) placed too early may therefore expose patients to an invasive device without providing the expected survival benefit.

An ambulatory external wearable cardioverter-defibrillator (WCD) offers temporary protection during this interval. It continuously monitors the electrocardiogram through surface electrodes and can deliver a shock for a detected life-threatening ventricular rhythm. The device is removable and does not require surgery, making it attractive as a bridge while clinicians reassess ventricular function and complete treatment planning.

The post-MI evidence is less decisive than the technology’s intuitive appeal. A WCD can terminate selected malignant arrhythmias, but its effectiveness depends on appropriate patient selection, consistent wear, rapid response to alarms, and access to follow-up care. A prescription should therefore be part of a structured risk-management plan rather than an automatic response to a low ejection fraction.

For Australian clinicians, the decision also involves practical questions about device access, hospital funding, geography, patient work, driving, and continuity of care. These issues are especially important when a patient is discharged from a metropolitan centre such as Sydney or Melbourne to a regional community, or when follow-up involves long travel across Queensland, Western Australia, or the Northern Territory.

Why The Early Post-MI Window Matters

Sudden cardiac death risk is concentrated during the early recovery phase after an infarction, particularly in patients with extensive myocardial injury, persistent LVEF reduction, heart failure, recurrent ischaemia, or ventricular arrhythmias. Revascularisation may restore blood flow without immediately normalising electrical stability. Scar formation, autonomic disturbance, inflammation, and heterogeneous conduction can all support re-entry and ventricular tachyarrhythmia.

However, LVEF measured in hospital is not necessarily the patient’s long-term baseline. Improvement may occur over several weeks with complete revascularisation, beta-blockade, mineralocorticoid receptor antagonists, angiotensin receptor-neprilysin inhibition where appropriate, sodium-glucose cotransporter 2 inhibition, and treatment of congestion. This explains why primary-prevention ICD implantation is generally deferred for a defined period after MI and revascularisation, provided there is no separate indication for immediate secondary prevention.

The distinction between primary and secondary prevention is central. A patient who survives sustained ventricular tachycardia or ventricular fibrillation not attributable to a reversible cause may require an ICD pathway rather than relying on a WCD. By contrast, a patient with an LVEF of 30% soon after an uncomplicated infarct may be considered for temporary protection while the heart recovers and the indication for an implanted device becomes clearer.

What The Clinical Evidence Shows

The pivotal randomised study was the VEST trial, which enrolled patients with recent MI and LVEF of 35% or less. Participants were assigned to guideline-directed medical therapy with or without a WCD during the early post-discharge period. In intention-to-treat analysis, the primary endpoint of arrhythmic death was not significantly reduced. All-cause mortality showed a nominal reduction, but this was a secondary outcome and should be interpreted cautiously.

Adherence was a major limitation. Participants wore the device for a median of approximately 18 hours per day, leaving clinically meaningful periods without protection. Some alarms were not treated as intended, and inappropriate shocks, discomfort, skin irritation, and sleep disruption affected acceptability. Observational and per-protocol analyses have suggested benefit among patients who wear the device reliably, but these analyses are vulnerable to selection and healthy-adherer bias.

Current guideline positions consequently support selective rather than routine use. European and North American guidance generally allows a WCD to be considered for carefully chosen patients with transiently high risk, while emphasising that evidence for routine early post-MI deployment remains limited. Australian practice should interpret these recommendations alongside local cardiology protocols, availability of electrophysiology review, and the funding arrangements of the treating service.

A useful review process should document the clinical reason for prescribing the device, the anticipated duration, the target date for repeat echocardiography, and the criteria for escalation. Clinicians preparing a manuscript, audit, or local protocol can also consult the journal’s submission guidance when presenting outcomes from wearable defibrillator programs.

Selecting Patients And Setting Expectations

The strongest rationale for a WCD usually involves a temporary but substantial risk that is not yet suitable for permanent ICD implantation. Examples may include a markedly reduced LVEF early after MI, incomplete or staged revascularisation, recurrent non-sustained ventricular tachycardia, extensive anterior infarction, or a period in which an ICD decision must be delayed for clinical reasons. These factors should be considered together rather than treated as a checklist.

A complete assessment should include the infarct territory, reperfusion result, residual coronary disease, haemodynamic stability, heart failure status, renal function, electrolyte disturbances, medication optimisation, and prior arrhythmia history. Reversible contributors such as hypokalaemia, hypomagnesaemia, ischaemia, hypoxia, and medication effects should be corrected. Thyroid disease may also complicate rhythm management, and the discussion of thyroid dysfunction and atrial fibrillation illustrates why broader endocrine and arrhythmic assessment can matter.

Before discharge, patients and carers need practical training. They should know how to wear the garment, charge and maintain the monitor, respond to vibration and audible alarms, avoid unnecessary removal, and contact emergency services after an appropriate shock. In Australia, that means calling Triple Zero (000) for suspected ongoing emergency symptoms rather than waiting for a device review. The patient should also understand that a WCD does not prevent infarction, replace secondary prevention, or remove the need for urgent assessment of chest pain or syncope.

Follow-up should be scheduled before the patient leaves hospital. Repeat echocardiography is commonly planned after the relevant recovery interval, with earlier review if there is recurrent arrhythmia, worsening heart failure, syncope, or poor tolerance. Device data can reveal wear time and recorded events, but it should complement, not replace, clinical review.

Applying The Strategy In Australian Practice

Access to WCD therapy in Australia may vary between public hospitals, private hospitals, insurers, and individual supplier arrangements. The device is not a routine item supplied through the Pharmaceutical Benefits Scheme, so clinicians should establish who will provide it, how costs are covered, and whether technical support is available before prescribing. Local electrophysiology services may have different approval pathways, particularly outside major centres.

Geography can influence safety. A patient discharged in Melbourne may have straightforward access to a device clinic and repeat imaging, whereas someone returning to a regional town in northern Queensland or Western Australia may face long travel and fewer electrophysiology appointments. Telehealth, coordinated echocardiography, and clear communication with the local cardiologist can reduce gaps. For remote patients, the plan should account for unreliable mobile coverage, transport limitations, and the time required to reach an emergency department.

Climate and daily routines also affect adherence. Heat, perspiration, and skin irritation may be particularly troublesome in tropical Queensland or the Northern Territory, while manual work, sport, and frequent garment removal can reduce protection in any state. Patients should receive practical advice about hygiene, replacement garments, charging, and what to do during bathing. Device-specific instructions must take priority because models and supplier policies differ.

Driving advice requires individual assessment and should follow current Austroads guidance and relevant state or territory requirements. A shock, syncope, documented ventricular arrhythmia, or medication change may affect licensing independently of the WCD itself. Clinicians should record the advice given and explain that wearing a device does not automatically make driving permissible.

Reassessment, De-Implementation, And Research Priorities

The WCD should have a defined endpoint. At reassessment, the team should review LVEF, symptoms, heart failure therapy, coronary status, arrhythmia recordings, shocks, adherence, and patient preferences. If ventricular function improves and no sustained ventricular arrhythmia has occurred, the device may be discontinued. If LVEF remains severely reduced despite appropriate therapy, an ICD may become appropriate after guideline-defined waiting periods and shared decision-making.

A shock should trigger urgent specialist evaluation, even when the patient feels well. Stored electrograms require expert review to distinguish true ventricular tachycardia or fibrillation from supraventricular tachycardia, oversensing, noise, or artefact. Recurrent alarms without appropriate therapy may indicate a technical problem, poor electrode contact, or a rhythm that needs a different management strategy.

Research should focus on identifying the subgroup most likely to benefit, rather than simply expanding use. Better risk models could combine LVEF with infarct size, cardiac magnetic resonance scar, autonomic markers, premature ventricular complexes, non-sustained ventricular tachycardia, renal disease, and clinical frailty. Studies should also measure quality of life, sleep, anxiety, caregiver burden, cost, and equitable access across metropolitan and rural Australia.

For an open-access electrophysiology community, transparent reporting of wear time, inappropriate alarms, shocks, discontinuation, funding arrangements, and post-device outcomes is essential. Registries from Australian hospitals could help clarify whether results from overseas trials translate to local populations and healthcare pathways.

A WCD can be a valuable bridge for a carefully selected post-MI patient, but it is not a universal substitute for evidence-based timing of ICD implantation. The safest approach combines early risk assessment, optimised medical therapy, education, reliable follow-up, and a documented plan for reassessment. Clinicians and researchers can strengthen this field by sharing real-world Australian data and publishing practical protocols through the Journal of Arrhythmia.