Characteristic feature of the ECG is ?: (A) Progressive lengthening of PR interval till a beat is dropped., (B) Slurred QRS complex, (C) Irregular heart rate and premature ventricular beats, (D) Shortened ST interval
Answer is A. Mobitz type I second-degree A V block (A V Wenckebach block) is characterized by progressive PR interval prolongation prior to block of an atrial impulse.