Repeated USMLE Questions Step 2 CK- 310

A 68-year-old man presents to the emergency room complaining of multiple episodes of fainting since he woke up today. His fainting mainly occurs when he stands up. He has a history of coronary artery disease, diabetes, high cholesterol and hypertension. He takes atenolol, metformin, lovastatin and lisinopril. On physical examination, his blood pressure is 120/75, pulse is 55/min. and irregular, heart sounds are normal and lungs are clear on auscultation.  ECG shows dropped beat after progressive lengthening of the PR interval.

What is the most likely initial diagnosis?

A- Atrial flutter

B-Atrial fibrillation

C-Mobitz type I (Wenckebach) second degree AV block

D- Mobitz type II second degree AV block

E- Third degree atrioventricular block






Answer:

ECG finding is compatible with type 1 second degree A-V block (Mobitz 1). It is characterized by progressive prolongation of P-R intervals followed by a dropped beat. In atrial flutter, ECG shows the characteristic sawtooth pattern. Atrial fibrillation shows no P waves and irregular irregularity. In the other 2 types of BBB, there is no P-R prolongation. ECG shows two or more P waves for every normal or slightly abnormal QRS complex.

The correct answer is C