Wearable health technology, particularly smartwatches, has revolutionized personal health monitoring by enabling continuous, non-invasive tracking of various physiological parameters. The potential applications of these devices in cardiology are extensive, but it is crucial to validate their accuracy against established medical-grade devices.

The Apple Watch Series 9 (Apple, USA) exemplifies the capabilities of modern smartwatches, offering a wide range of health tracking features. These include heart rate monitoring, detection of irregular heart rhythms suggestive of atrial fibrillation, electrocardiogram recording, blood oxygen level measurement, and comprehensive mobility metrics (including VO2 max, six-minute walk distance, walking speed, step length, double support time, and walking asymmetry). Many of these parameters are highly relevant for cardiovascular patients, potentially aiding in disease progression monitoring and adverse event prediction. However, there is a lack of comprehensive validation studies for these devices in specific cardiovascular disease populations.

This investigator-initiated, prospective observational study will consist of two phases: a training phase which involves 50 participants and a prospective validation phase which involves 20 participants. The study aims to validate smartwatch-based assessments using medical-grade devices and techniques. The study will focus on adult patients with congenital heart disease, pulmonary hypertension, heart failure, and coronary artery disease, as well as athletes undergoing cardiovascular assessment. By comparing smartwatch data with established clinical measurements, we seek to determine the reliability and potential clinical utility of these wearable devices in diverse cardiovascular contexts. Anonymized smartwatch data collected during the two phases will be published to a publicly registry to facilitate further research. This research will help bridge the gap between consumer-grade wearable technology and clinical practice in cardiology.

This study is investigator-initiated, prospective observational study and will consist of two phases: a training phase and a prospective validation phase.

Training Phase (First Phase) 50 participants will undergo comprehensive baseline assessments and continuous physiological monitoring with the smartwatch. Data collected during this phase will be anonymized and exported to a public open-source training model.

At Visit 1 of the first phase, Comprehensive demographic and clinical data will be collected from each participant, Clinical Management System (CMS), Electronic Patient Record (ePR), and Clinical Data Analysis and Reporting System (CDARS) of the Hospital Authority in Hong Kong. This will include age, sex, height, weight, body mass index, and detailed medical history focusing on cardiovascular conditions. Information about current medications and smoking status will also be recorded. Additionally, participants will undergo a baseline clinical examination, including blood pressure measurement, heart rate, and a 12-lead electrocardiogram.

VO2max Participants will undergo a conventional cardiopulmonary exercise test (CPX) to determine their maximal oxygen uptake (VO2max) at Visit 1. This test will be conducted in a controlled clinical setting under the supervision of cardiologists. Participants will exercise on a treadmill while their respiratory gas exchange is measured using a metabolic cart. The exercise intensity will be gradually increased until the participant reaches volitional exhaustion or predetermined safety criteria are met. The highest oxygen uptake value achieved during the test will be recorded as the VO2max. Participant will concurrently be wearing the investigational smartwatch for pre- and post-SaO2 and VO2max assessment. This gold-standard measurement will serve as the reference for validating the smartwatch's continuous VO2max estimation.

6-Minute walk distance The 6-minute walk distance will be assessed in a hospital setting at Visit 2 of the first phase under the supervision of a research staff. Participants will be instructed to walk as far as possible in six minutes along a predetermined course, typically a straight hallway. The total distance walked will be measured and recorded. During the test, the research nurse will monitor the participant's heart rate, blood oxygen saturation, and perceived exertion at regular intervals. Participant will concurrently be wearing the investigational smartwatch for pre- and post-SaO2 and VO2max assessment.

Oxygen saturation During the follow-up period of the first phase, participants will be provided with a medical-grade pulse oximeter for home use. They will be instructed to measure their oxygen saturation once daily throughout the one-week study period. Measurements should be taken at approximately the same time each day, preferably in the morning after waking and before any strenuous activity. Participants will record their oxygen saturation readings in a provided log. These daily measurements will serve as reference points for validating the continuous oxygen saturation data collected by the smartwatch.

Prospective Validation Phase (Second Phase) 20 participants will undergo similar assessments, with the primary aim of validating the smartwatch's measurements against medical-grade devices. Data collected during this phase also will be anonymized and exported to a public open-source training model.

At the Visit of the second phase, Comprehensive demographic and clinical data will be collected from each participant, Clinical Management System (CMS), Electronic Patient Record (ePR), and Clinical Data Analysis and Reporting System (CDARS) of the Hospital Authority in Hong Kong. This will include age, sex, height, weight, body mass index, and detailed medical history focusing on cardiovascular conditions. Information about current medications and smoking status will also be recorded. Additionally, participants will undergo a baseline clinical examination, including blood pressure measurement, heart rate, and a 12-lead electrocardiogram.

VO2max Participants will undergo a conventional cardiopulmonary exercise test (CPX) to determine their maximal oxygen uptake (VO2max) at Visit 1. This test will be conducted in a controlled clinical setting under the supervision of cardiologists. Participants will exercise on a treadmill while their respiratory gas exchange is measured using a metabolic cart. The exercise intensity will be gradually increased until the participant reaches volitional exhaustion or predetermined safety criteria are met. The highest oxygen uptake value achieved during the test will be recorded as the VO2max. Participant will concurrently be wearing the investigational smartwatch for pre- and post-SaO2 and VO2max assessment. This gold-standard measurement will serve as the reference for validating the smartwatch's continuous VO2max estimation.

Inclusion Criteria:

• Age 20 to 70 years old
• Ability to provide informed consent
• History of the following cardiovascular conditions:
• Adult congenital heart disease
• Pulmonary hypertension
• Heart failure
• Coronary artery disease
• Athletes undergoing cardiovascular assessment

Exclusion Criteria:

• Contraindication for undergoing physical exertion including cardio-pulmonary exercise testing (CPX) and 6-minute walk test (6MWT)
• Pregnancy
• Known allergy to components of the investigational product

Patients having adult congenital heart disease or pulmonary hypertension, heart failure or coronary artery disease, or are athletes undergoing cardiovascular assessment