This is a cross-sectional observational study designed to assess the disease burden and quality of life in individuals with LQTS 2 and 3. Each participant will answer each patient-reported outcome questionnaire only once over a 6-month period. The study will enroll up to 200 participants.

The aim of the present cross-sectional observational study is to evaluate the health status and quality of life burden in patients with LQTS. The total study duration is anticipated to last for a period of up to 18 months, including up to 6 months of each individual's observation period. The observation period may be extended by up to 3 months (total 9 months). During the optional extension, data collection via myQTwave will be limited to emotional and physical symptoms survey. This prospective cohort study will collect PRO information in a cohort of patients with LQTS 2 or 3. All screened participants will be assigned a unique identifier. Eligible participants will download the myQTwave app on the Apple iPhone and Apple Watch delivered to them after enrollment.

Patient-reported outcomes will be captured via the Apple iPhone and daily health metrics (sleep, physical and Heart-related data) will be collected using the Apple Watch.

Inclusion Criteria:

1. The participant is willing and provides written informed consent to participate in this study.

2. Male or female participant of at least 18 years of age, English-speaking.

3. Confirmed genetic diagnosis of LQT2 or 3, demonstrated by one of the following:

   • Genetic testing report (pathogenic or likely pathogenic (P/LP) mutation) in KCHN2 or SCN5a genes) or,
   • A signed physician's letter confirming genetic diagnosis of LQTS 2 or 3.

4. Documented QTc ≥ 480 ms within the last year, demonstrated by one of the following:

   • 12-lead electrocardiogram (ECG), or
   • A signed physician's letter confirming an ECG demonstrating QTc value ≥ 480 ms.

5. The participant is able to operate a smartphone and a companion watch. *The number of participants with QTc between 480 and 500 ms will be limited to 50.

Exclusion Criteria:

1. Current participation in another clinical trial involving a drug or device.
2. Participants unwilling to use an iPhone or Apple Watch for the duration of the study.
3. Known diagnosis of Brugada Syndrome
4. Participants unwilling to comply with outlined procedures.

Participants will be recruited from cardiology and genetic clinics at academic and private medical centers across the United States, as well as through outreach efforts targeting individuals and families affected by inherited arrhythmia conditions. This includes engagement through community-based initiatives. The study population includes individuals with a genetically confirmed diagnosis of Long QT Syndrome type 2 or 3.