[Concept of critical stenosis in cardial surgery].

When stenosis of a large artery reaches about 75% of its lumen blood flow distal to obstruction abruptly falls and ceases to play decisive role for the region it supplies. This region survives due to opening of collaterals. This allows to cross-clamp coronary artery for 20-30 minutes and to create distal anastomosis during aorto-coronary venous or mammary coronary artery bypass grafting without artificial circulation. Another example is mitral stenosis. There exists a critical value of an orifice area (1 cm2 or 25% of the lumen) when abrupt decompensation develops. Similar cut off values of inflow (nourishing) vessel stenoses can be demonstrated in other regions of cardiovascular system. Thus conception of a 'critical stenosis' is universal for the arterial part of circulation and finds wide application in clinical practice.