How is VSD a complication of MI?

The question is: Isn't VSD a congenital defect? So how come it is a complication of MI?

The pathogenesis is: MI --> rupture of intraventricular septum as a complication of the MI --> new VSD (ventricular septal defect).

Robbins lists three types of myocardial rupture:

1. Rupture of the ventricular free wall --> haemopericardium --> cardiac tamponade (usually fatal)
2. Rupture of intraventricular septum --> new VSD and L to R shunt
3. Papillary muscle rupture --> mitral regurgitation.