Cardiac arrest while swimming: long QT syndrome type 1 — case discussion

Presentation

Practice case (not a real patient). A 17-year-old boy collapses during a competitive swimming race. Bystanders start CPR, and an automated external defibrillator delivers one shock for VF; he regains consciousness before reaching hospital. He takes no regular medicines and has no previous symptoms. His echocardiogram shows a structurally normal heart. ESC 2022 gives a separate set of recommendations for the evaluation of sudden cardiac arrest survivors.^[1]

Step 1 — At presentation

Discussion:

• ESC 2022: in SCA survivors, collection of blood samples at presentation is recommended for potential toxicology and genetic testing (Class I, Level B).^[1]
• ESC 2022: sodium channel blocker testing and exercise testing are recommended in SCA survivors without a clear underlying cause (Class I, Level B).^[1]

Step 2 — Read the ECG

Repeated 12-lead ECGs over the next days show a QTc of 500 ms.^[1]

• ESC 2022: LQTS is diagnosed with either a QTc of 480 ms or more in repeated 12-lead ECGs, with or without symptoms, or an LQTS diagnostic score above 3 (Class I, Level C); his QTc alone meets the first criterion.^[1]
• ESC 2022 names exercise as the gene-specific trigger for LQT1 and strenuous swimming as an LQT1 trigger to avoid, so his collapse while swimming points to LQT1.^[1]

Step 3 — Genetic testing

Discussion:

• ESC 2022: in clinically diagnosed LQTS, genetic testing and genetic counselling are recommended (Class I, Level C); AHA/ACC/HRS 2017 gives the same advice (COR I, LOE B-NR).^[1][2]
• ESC 2022: genetic screening identifies a mutation in 75% of LQTS cases, and three main genes account for 90% of positively genotyped cases.^[1]
• ESC 2022: genetic testing and counselling on its potential consequences should be undertaken by an expert multidisciplinary team (Class I, Level C); CSANZ 2011 asks for testing in a specialised cardiac genetic clinic or clinical genetics service where family management and genetic counselling can be offered.^[1][4]

The test finds a pathogenic KCNQ1 variant.^[1]

• ESC 2022 lists KCNQ1 as the undisputed gene for LQT1.^[1]

Step 4 — Protect him from the next arrest

Discussion:

• ESC 2022: ICD implantation in addition to beta-blockers is recommended in LQTS patients with cardiac arrest (Class I, Level B); survivors of a cardiac arrest have a high risk of recurrence even on beta-blockers (14% within 5 years on therapy).^[1]
• AHA/ACC/HRS 2017: in patients with a cardiac channelopathy and SCA, an ICD is recommended if meaningful survival of greater than 1 year is expected (COR I, LOE B-NR).^[2]
• ESC 2022: beta-blockers, ideally non-selective (nadolol or propranolol), are recommended in LQTS with documented QT prolongation to reduce the risk of arrhythmic events (Class I, Level B).^[1]
• ESC 2022 general measures in LQTS: avoid QT-prolonging drugs (crediblemeds.org), avoid and correct electrolyte abnormalities, and avoid genotype-specific triggers for arrhythmias (Class I, Level C), which for LQT1 includes strenuous swimming.^[1]

Step 5 — Living with the ICD

Discussion:

• AHA/ACC/HRS 2017: appropriate ICD therapy for VF or fast VT is reported in 8% to 33% of channelopathy patients, while inappropriate shocks and device complications are reported in 8% to 35%.^[2]
• To minimise inappropriate shocks, AHA/ACC/HRS 2017 says concurrent beta blockers in LQTS and CPVT, optimal device programming and appropriate lead selection are necessary.^[2]
• AHA/ACC/HRS 2017: patients on a beta blocker should have ongoing monitoring of changes in QTc over time and of the adequacy of beta blockade with exertion.^[2]

Step 6 — His family

His parents and a 14-year-old sister ask whether they need tests. AHA/ACC/HRS 2017 calls clinical screening of first-degree relatives of patients with inherited arrhythmia syndromes crucial to identifying affected family members.^[2]

• ESC 2022: when a Class IV or V variant has been identified in a living or deceased individual with a condition that carries a risk of VA and SCD, genetic testing of first-degree and symptomatic relatives and obligate carriers is recommended (Class I, Level C).^[1]
• AHA/ACC/HRS 2017: in first-degree relatives of patients with a causative mutation for LQTS, genetic counselling and mutation-specific genetic testing are recommended (COR I, LOE B-NR).^[2]
• AHA/ACC/HRS 2017: approximately 10% to 36% of genotype-positive patients with LQTS have a QTc of 440 ms or less, most commonly in LQT1, so a normal ECG in a relative does not settle the question.^[2]
• ESC 2022: relatives with a mutation but without QT prolongation still receive a diagnosis of LQTS, and beta-blockers should be considered in patients with a pathogenic mutation and a normal QTc interval (Class IIa, Level B).^[1]

Step 7 — Sport

Discussion:

• ESC 2022: athletes diagnosed with a cardiovascular disease associated with SCD are managed according to current guidelines for sports eligibility (Class I, Level C).^[1]
• AHA/ACC/HRS 2017: many athletes who are on therapy for inherited disorders or have ICD implants are able to participate in athletics, depending on the nature and severity of the disease and with appropriate precautions and counselling about potential residual risks.^[2]
• ESC 2020 sports guideline: participation in competitive sports (with or without an ICD) is not recommended in individuals with LQTS and prior cardiac arrest or arrhythmic syncope (Class III, Level C), and ICD implantation does not constitute clearance for intensive or competitive sports.^[9]
• AHA/ACC 2025 takes a different line: in competitive athletes with previously symptomatic LQTS who are under expert assessment and supervision, competitive sport is reasonable with shared decision-making after risk assessment, education and guideline-directed therapies; in LQTS, including LQT1, competitive swimming and diving can be considered with precautions (supervision by someone trained in CPR, a preference for pools rather than open water, access to an AED).^[10]
• AHA/ACC 2025 also asks that competitive athletes with a channelopathy are assessed by a cardiologist with expertise in cardiac channelopathies, with shared decision-making.^[10]

Learning points

• A QTc of 480 ms or more in repeated 12-lead ECGs diagnoses LQTS under ESC 2022 (Class I, Level C).^[1]
• After a cardiac arrest in LQTS, an ICD in addition to beta-blockers is recommended (ESC 2022, Class I, Level B).^[1]
• Strenuous swimming is an LQT1 trigger to avoid (ESC 2022).^[1]
• After cardiac arrest in LQTS, ESC 2020 does not recommend competitive sport, with or without an ICD (Class III, Level C). AHA/ACC 2025 frames its LQTS consideration for previously symptomatic athletes under expert assessment and supervision: competitive sport is reasonable with shared decision-making after risk assessment, education and guideline-directed therapies.^[9][10]
• In first-degree relatives of a patient with a causative LQTS mutation, genetic counselling and mutation-specific genetic testing are recommended (AHA/ACC/HRS 2017, COR I, LOE B-NR).^[2]