Evaluating equivocal left main stenosis with fractional flow reserve – not all daughter vessels are created equally

Fractional flow reserve (FFR) evaluation of intermediate left main coronary artery (LMCA) stenosis has been validated in clinical decision-making. However, the size of the daughter vessel, in which the FFR transducer is placed and the amount of myocardium it subtends, has received less attention. We present a case that demonstrates the importance of transducer location, size of the daughter vessel and the amount of subtended myocardium in evaluation of LMCA stenosis, pointing out potential pitfalls.