Healthy and Active, but Getting Fatigued

ANSWER

The correct interpretation of this ECG includes sinus bradycardia with marked sinus arrhythmia and junctional escape beats with sinus arrest. An intraventricular conduction defect is also present. 

Sinus bradycardia is indicated by the normal PQRST complexes at a rate of less than 60 beats/min. A marked sinus arrhythmia is ­evidenced by more than one pause (between third and fourth beats and seventh and eighth beats on the lead I rhythm strip) on the ECG. 

Sinus arrest occurs when the sinus node fails to conduct (absence of P wave during the interval of the pause). A normal QRS complex without a preceding P wave indicates a junctional escape beat. Finally, an intraventricular conduction defect is documented by a QRS duration ≥ 110 ms in the absence of a right or left bundle branch block.