This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
Wenckebachk phenomenon is defined as - 
Select and explain. 
A. Progressive lengthening of PR, B. Slurred QRS complex, C. Irregular hea rate & permature ventricular beats, D. Shoened ST intervals
A: Progressive lengthening of PR
Answer: A: Progressive lengthening of PR 
Explanation: wenkebach phenomenon is the progressive lengthening of PR i nterval seen in mobitz type 1 AV block. Ref Harrison 20th edition pg 1436