A patient's ECG recording shows a very long P-R interval. What is the cause of this abnormal wave pattern?
The P wave marks the time of atrial depolarization and the QRS complex signals ventricular depolarization. Between those two events the AV node was excited and the action potential was spread through the conducting tissue to the ventricular myocardium. A prolonged P-R interval signifies an unusually slow conduction through the AV node and conducting system, possibly due to insufficient blood flow (ischemia).
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