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Cardiology
arrhythmias
long QT syndrome
A 45-year-old man presents for a health maintenance visit at an outpatient clinic. He reports experiencing occasional, brief episodes of lightheadedness, usually while under mild emotional stress, but denies syncope, chest pain, or dyspnea. His past medical history is unremarkable, and he takes no regular medications. He notes that his younger sister experienced an unexplained sudden cardiac arrest at age 30, from which she was successfully resuscitated. On physical examination, his blood pressure is 128/78 mmHg, heart rate is 62 beats/minute, and respiratory rate is 14 breaths/minute. Cardiovascular examination reveals regular rhythm with no murmurs, rubs, or gallops. A 12-lead electrocardiogram (ECG) shows a heart rate of 60 bpm, a QT interval of 500 msec, and no other significant abnormalities. An echocardiogram performed subsequently shows normal left ventricular size and systolic function, with no structural abnormalities. Given this presentation, which of the following represents the most likely diagnosis and the subsequent appropriate comprehensive management strategy?
| Lab Parameter | Value | Reference Range |
|---|---|---|
| Sodium | 138 mmol/L | 135-145 mmol/L |
| Potassium | 4.1 mmol/L | 3.5-5.0 mmol/L |
| Chloride | 102 mmol/L | 98-107 mmol/L |
| Bicarbonate | 25 mmol/L | 22-29 mmol/L |
| Glucose | 5.2 mmol/L | 3.9-6.1 mmol/L (fasting) |
| Hemoglobin | 145 g/L | 130-170 g/L |
| White Blood Cell Count | 7.5 x 10^9/L | 4.0-11.0 x 10^9/L |
| Platelets | 280 x 10^9/L | 150-450 x 10^9/L |
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