Wearable defibrillators in myocarditis: patient selection and outcomes

Myocarditis, an inflammatory disease of the heart muscle often triggered by viral infection, can leave patients vulnerable to life-threatening ventricular arrhythmias during the acute and recovery phases. For individuals whose left ventricular function is depressed but may recover, deciding between immediate implantable cardioverter-defibrillator placement and a watchful waiting strategy remains a clinical challenge. Wearable cardioverter-defibrillators have emerged as a practical bridge, offering continuous rhythm monitoring and the capacity to deliver a rescue shock when sustained ventricular tachycardia or fibrillation occurs.

In Australia, where specialised cardiac services concentrate in metropolitan centres but patients are distributed across vast distances, the appeal of a non-invasive device that can be worn at home is particularly strong. Patients in regional towns of New South Wales or Queensland can be discharged with remote telemetry rather than remaining in tertiary hospitals in Sydney or Brisbane. Out-of-hospital follow-up aligns with Medicare-supported ambulatory cardiology and reduces the burden on already stretched inpatient beds.

The therapeutic rationale rests on a critical window. Many cases of inflammatory cardiomyopathy show meaningful recovery of ejection fraction within three to six months under guideline-directed medical therapy. Permanent defibrillators implanted too early may later be unnecessary, exposing patients to lifelong device-related complications. The wearable option aims to fill that window without committing to an indwelling device prematurely.

Pathophysiology of arrhythmia risk in inflammatory cardiomyopathy

Acute myocarditis produces a substrate rich in electrically unstable tissue. Myocyte necrosis, interstitial oedema, and infiltrating lymphocytes create heterogeneous conduction, lowering the threshold for re-entrant circuits. Autonomic imbalance and heightened catecholamine sensitivity during the early inflammatory phase further predispose patients to polymorphic ventricular tachycardia and ventricular fibrillation. Tools such as repolarisation alternans at the bedside to risk stratification offer clinicians a non-invasive window into electrical vulnerability, particularly when used in conjunction with heart rate variability metrics and T-wave morphology analysis.

The severity of ventricular dysfunction on admission remains the strongest single predictor of arrhythmic events. Patients presenting with an ejection fraction below 35% during the index admission carry substantially higher risk of sudden cardiac death in the first weeks, even when biomarkers and haemodynamic status appear to be improving. Conversely, those with preserved ejection fraction rarely experience malignant arrhythmias, although subtle subclinical inflammation detected by cardiac magnetic resonance imaging can occasionally be associated with electrical instability.

Risk stratification therefore demands a multimodal approach. Cardiac MRI with late gadolinium enhancement, ambulatory Holter monitoring, signal-averaged ECG, and assessment of repolarisation behaviour all contribute incremental information. The goal is to identify patients whose arrhythmic risk justifies bridging protection while avoiding unnecessary device use in those likely to recover spontaneously.

Mechanism and practical operation of the wearable defibrillator

A wearable cardioverter-defibrillator consists of two main components: a chest harness containing sensing electrodes and defibrillation pads, and a small monitoring unit worn at the waist or on a shoulder strap. The system continuously analyses the surface ECG, distinguishing true ventricular arrhythmias from motion artefact, loose lead contact, or supraventricular tachyarrhythmias. When the device detects a sustained rhythm above a programmed rate threshold and confirms ventricular origin through morphology matching, it charges and prompts the patient with vibration and audible alarms before delivering a biphasic shock.

Modern devices record every episode, including treated and untreated events, and transmit encrypted rhythm strips to a secure cloud platform accessible to the treating team. Australian clinicians commonly pair this with home visits by cardiac nurses and scheduled telehealth reviews funded through Medicare's chronic disease management items. The data flow supports timely decisions about escalation, prolonged monitoring, or transition to an implanted system.

Device algorithm refinements have reduced inappropriate shocks substantially over the past decade, although noise from chest hair, perspiration, or ill-fitting garments can still trigger false alarms. Patient education on electrode placement, daily self-check routines, and garment care is essential. Most Australian centres now embed a structured teaching session before discharge, often delivered by a cardiac rehabilitation nurse who follows the patient across the early recovery weeks.

Selecting the right candidate for wearable protection

Not every patient with inflammatory cardiomyopathy requires external defibrillation. Clinicians typically reserve wearable devices for those with a left ventricular ejection fraction of 35% or less during the acute phase, syncope or documented non-sustained ventricular tachycardia during hospitalisation, and a reasonable expectation of recovery that justifies deferring permanent implantation. Patients with advanced heart failure requiring inotropic support or those listed for transplantation are usually steered toward definitive surgical options.

Conversely, wearable defibrillators are not appropriate for individuals unable to operate the device, those with cognitive impairment, or patients with limited life expectancy from non-cardiac disease. Pregnancy, while not an absolute contraindication, requires careful discussion because the safety profile of defibrillation shocks to the fetus has not been firmly established. Body habitus also matters; the standard garment accommodates a range of chest circumferences, but extreme body shapes may not achieve reliable electrode contact.

Australian consensus statements adapted from international guidelines encourage a heart-team approach, including input from arrhythmology, heart failure, and imaging specialists. In tertiary centres in Melbourne and Perth, formal myocarditis multidisciplinary meetings have been established to streamline decisions about wearable bridging, catheter ablation candidacy, and timing of implantable cardioverter-defibrillator placement.

Evidence base and reported clinical outcomes

The prospective registry data from the United States and Europe have shaped current understanding, showing appropriate shock rates of roughly 1 to 2% during the typical three-month wearing period in broadly defined cardiomyopathy populations. Subgroup analyses focused on myocarditis suggest comparable or slightly higher event rates, particularly within the first 30 days after diagnosis when inflammation remains active. The majority of treated episodes occur during daily activities rather than sleep, reflecting the role of catecholamine surges and exertion as triggers.

Left ventricular function improvement occurs in roughly half of patients wearing the device, with most recovery seen between weeks six and twelve. Among those whose ejection fraction normalises, the wearable is usually removed without progression to permanent implantation, sparing patients from unnecessary procedures. A smaller group fails to recover, and timely transition to an implantable cardioverter-defibrillator becomes appropriate. Registry follow-up also captures the rare but sobering presentation of acute electrical storm management considerations when malignant arrhythmias cluster despite intervention.

Real-world Australian experience echoes international findings. Single-centre audits from the Royal Brisbane and Women's Hospital and Westmead in western Sydney have reported low inappropriate shock rates and high patient adherence when supported by structured nursing follow-up. Importantly, no randomised trial has yet compared wearable bridging to early implantation in myocarditis specifically, so decisions continue to draw on observational data and clinical judgement.

Living with the device and supporting adherence

Adherence remains the most practical challenge. Patients wear the device continuously except during bathing, but in warm Australian summers, skin irritation and heat-related discomfort prompt some to remove the garment more often than recommended. Choosing lightweight cotton underlayers, positioning air conditioning thoughtfully, and rotating electrode sites help mitigate these problems. Sleep disturbance from audible alarms and bulk under nightwear is a common complaint, and cardiac nurses routinely counsel patients on practical adjustments.

Returning to physical activity requires structured guidance. Once the acute inflammatory phase has settled and biomarkers have normalised, supervised exercise testing protocols can help clinicians confirm safety before clearance for work, driving, or recreational sport. Most Australian rehabilitation programmes incorporate graded walking, light resistance training, and education about warning symptoms during the wearing period.

Psychological impact deserves explicit attention. Many patients describe heightened anxiety during the wearing period, particularly after any alarm event. Connecting them with peer support groups, including state-based affiliates of the Heart Foundation, and arranging regular contact with their cardiology team can ease the emotional load. Returning to work is generally feasible, although those in occupations involving heavy lifting, contact sports, or operating heavy machinery may need temporary role modification.

Culturally safe care matters across Australia's diverse population. For Aboriginal and Torres Strait Islander patients, partnering with Aboriginal Health Workers and ensuring access to culturally appropriate cardiac rehabilitation improves engagement with wearable monitoring. Multilingual resources and telehealth interpreters in languages such as Mandarin, Vietnamese, and Arabic support patients from migrant backgrounds in Sydney and Melbourne.

The wearable cardioverter-defibrillator represents a thoughtfully timed intervention rather than a permanent solution. When used for the right patient during the right window, it can prevent sudden death without committing individuals to a lifelong implanted device. As Australian clinicians continue to refine selection criteria and embed shared decision-making, the goal remains clear: protect vulnerable patients through the acute phase, identify those whose hearts recover, and avoid unnecessary long-term hardware. Explore the latest themed collection and clinical resources at the Journal of Arrhythmia to deepen your approach to wearable defibrillator use in myocarditis care.