Coronary flow reserve in stress-echo lab. From pathophysiologic toy to diagnostic tool

Abstract

The assessment of coronary flow reserve by transthoracic echocardiography has recently been introduced into clinical practice with gratifying results for the diagnosis of left anterior descending artery disease simultaneously reported by several independent laboratories. This technological novelty is changing the practice of stress echo for 3 main reasons. First, adding coronary flow reserve to regional wall motion allows us to have - in the same sitting - high specificity (regional wall motion) and a high sensitivity (coronary flow reserve) diagnostic marker, with an obvious improvement in overall diagnostic accuracy. Second, the technicalities of coronary flow reserve shift the balance of stress choice in favour of vasodilators, which are a more robust hyperemic stress and are substantially easier to perform with dual imaging than dobutamine or exercise. Third, the coronary flow reserve adds a quantitative support to the exquisitely qualitative assessment of wall motion analysis, thereby facilitating the communication of stress echo results to the cardiological world outside the echo lab. The next challenges involve the need to expand the exploration of coronary flow reserve to the right and circumflex coronary artery and to prove the additional prognostic value - if any - of coronary flow reserve over regional wall motion analysis, which remains the cornerstone of clinically-driven diagnosis in the stress echo lab.

Figure 1

Schematic representation of coronary flow velocity profile obtained with tranthoracic Doppler of distal left anterior descending coronary artery : in diastole the flow velocity is higher than in systole.

Figure 2

Relationship between the true increments of the flow signal obtained with the currently available imaging techniques. Modified from Gould KL, ref.1. On the abscissa are represented different narrowing of the coronary vessel.

Figure 3

Visualization of left main and bifurcation of left anterior descending coronary artery and circumflex assessed by transesophageal approach. The color-Doppler trace the flow inside the proximal tract of left coronary artery Left: the Pulsed wave Doppler highlights the typical biphasic flow velocity coronary pattern

Figure 4

Artist's drawing illustrating transducer beam orientations to the left anterior descending coronary artery (LAD) with the corresponding echocardiographic images of the mid-distal tract of LAD color flow.

Figure 5

The classical ischemic cascade, triggered by coronary vasospasm and/or epicardial stenosis. The various markers are usually ranked according to a well-defined time sequence.

Figure 6

The alternative ischemic cascade, triggered by microvasculature dysfunction. The various markers are a different time sequence in comparison with the classical ischemic cascade.

Figure 7

Imaging and projections for transthoracic imaging of right coronary and posterior descending coronary arteries.