Patients hospitalized with cardiovascular disease require timely detection of clinical deterioration to prevent adverse outcomes. Standard inpatient care relies on intermittent nursing vital-sign measurements performed every 4 to 8 hours, which can miss hemodynamic or arrhythmic events occurring between measurements. This trial evaluates whether digital wearable-based monitoring - wireless continuous measurement of vital signs and electrocardiography with a real-time alerting system - reduces major adverse cardiovascular events (MACE) compared with standard intermittent monitoring in patients hospitalized for cardiovascular disease. The trial uses a stepped-wedge cluster-randomized design in which four inpatient ward zones (clusters) are sequentially transitioned from standard care to wearable monitoring over five periods.

Study design: This is a prospective, stepped-wedge cluster-randomized, open-label trial with blinded endpoint adjudication, designed to test the superiority of wearable-based monitoring over standard care.

Unit of randomization: The unit of randomization is the inpatient ward zone (cluster), not the individual patient. Four clusters (ward zones 121A, 121B, 122A, and 122B at Yongin Severance Hospital) participate. The trial comprises five periods (one baseline period plus four step periods), each lasting five months. In period 1 all four clusters operate under standard care; thereafter, one cluster per period transitions to the wearable-monitoring intervention in a computer-generated random order, until all clusters are in the intervention state in period 5. Once a cluster transitions to the intervention state it remains so until the end of the trial.

Intervention: Patients admitted to a cluster operating in the intervention state receive continuous wearable monitoring (thynC Inpatient Monitoring System: continuous ECG, heart rate, respiratory rate, oxygen saturation, and body temperature with a real-time central alerting system) in addition to standard care. Patients admitted to a cluster operating in the control state receive standard care (intermittent nursing vital-sign measurement every 4 to 8 hours).

Outcome and follow-up: The primary outcome is the composite incidence of MACE within 6 months. Each participant is followed for 6 months from admission. Total study duration is approximately 36 months (25 months of enrollment, 6 months of follow-up after the last enrolled patient, and 5 months of analysis). Patients and care providers are not masked to allocation; the primary and major secondary endpoints are adjudicated by an independent committee blinded to cluster allocation and study period.

Inclusion Criteria:

Adults aged 20 years or older

• Hospitalized for cardiovascular disease, with at least one of: acute coronary syndrome; chronic coronary syndrome; acute heart failure (NYHA class III-IV or acute decompensated heart failure); arrhythmia (atrial fibrillation, ventricular tachycardia, complete AV block, or other clinically significant arrhythmia); peripheral arterial or aortic disease; post-cardiovascular-procedure observation (PCI, CABG, valve surgery, or electrophysiology study); or thromboembolic disease
• Able to provide written informed consent
• Able to wear the wearable monitoring device

Exclusion Criteria:

• Hemodynamically unstable shock (sustained systolic blood pressure < 90 mmHg requiring vasopressors; cardiogenic shock; septic shock)
• Planned or current intensive care unit admission
• Within 24 hours after cardiopulmonary resuscitation
• Physical condition precluding device wearing (bilateral upper-limb amputation; severe skin lesion, burn, or open wound at the device site; known allergy to device materials)
• Severe cognitive impairment or delirium precluding informed consent Extracorporeal membrane oxygenation (ECMO) or intra-aortic balloon pump (IABP) in use
• Continuous renal replacement therapy (CRRT) in use (patients on CRRT may participate if hemodynamically stable and device wearing is technically feasible)
• Unable to communicate in Korean for study explanation and the consent process
• Previously enrolled in this study (re-admitted patients are not re-enrolled; each participant is enrolled only at the first admission)
• Considered inappropriate for participation by the investigator

Open-label for participants and care providers. The primary and major secondary endpoints are adjudicated by an independent endpoint adjudication committee blinded to cluster allocation and study period.