Defining the coronary slow flow phenomenon.

he enigma of angina in the absence of significant epicardial coronary artery disease (CAD) has puzzled cardiologists since the advent of invasive coronary angiography. Indeed, an early paper by Likoff et al1 was entitled ‘Paradox of normal selective coronary angiograms in patients considered to have unmistakable coronary heart disease’ and described 15 women with angina, a positive exercise stress test and normal coronary angiography. This condition was later described as ‘syndrome X’ following the demonstration of myocardial lactate production during rapid atrial pacing in these patients. Investigators attributed this effort-related myocardial ischemia (and thus angina) to coronary microvascular dysfunction, although controversy still exists as to the exact mechanisms responsible for the chest pain.2,3