This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Split first hea sound is heard in: September 2008 
Select and explain. 
A. Mitral stenosis, B. Left bundle branch block, C. Complete right bundle branch block, D. Pulmonary hypeension
C: Complete right bundle branch block
Answer: C: Complete right bundle branch block 
Explanation: Ans. C: Complete right bundle branch block S1 is caused by the closure of the tricuspid and mitral values. Generally, the closure will be simultaneous so that a single S1 is heard, loudest at the apex. With a split S1 the closure of the two valves does not occur together. Splitting of the S1 is best heard in the tricuspid area and is not effected by respiration or other maneuvers which increase intrathoracic pressure. An split S1 by 10-30 ms is a normal phenomenon. Split S1 can be associated with pathological conditions, such a right bundle branch block.