Scenario: As a part of a screening regimen, a 24-hour ECG Holter was obtained on a 28-year-old healthy male firefighter. Three different time periods are shown below. The overall recording revealed a normal sinus rhythm with a heart rate range of 37–146/min. Baseline measurements included a blood pressure of 135/60 mm Hg and a body mass index of 31 kg/m2. The firefighter also successfully completed a graded exercise treadmill test using a Bruce protocol, achieving 100% of his maximum heart rate. Other than a previous history of smoking, he had no significant personal or familial medical history of cardiovascular diseases and does not take any medicine.

Second degree heart block, Type 1 (T1 and T2), Type II (T3).

The first ECG strip (T1) shows regularly irregular sinus bradycardia at rate of 42/min with second degree atrioventricular (AV) heart block Type 1 (also called...

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