Imaging of the posterior descending coronary artery. The last frontier in echocardiography

Non-invasive color Doppler imaging of the left anterior descending coronary artery has been described, but imaging of the posterior descending coronary artery (PD) has never been reported. The aim of this paper was to describe color Doppler imaging and flow reserve of the PD, regardless of its origin from the right or circumflex coronary artery, in different settings such as acute myocardial infarction or coronary stenting.

A C256 Acuson Sequoia ultrasound system connected to a standard 3.5 MHz transducer was used. Neither a contrast agent nor harmonic or power Doppler imaging was used. However, the Nyquist limit of color Doppler was reduced to 12 cm/s. Patients were examined in the apical 2-chamber view, with the coronary sinus ostium imaged in the short axis until a diastolic flow signal close to the epicardial layer was detected. Pulsed Doppler confirmed an anterograde, doming systolic and monophasic decrescendo diastolic flow. Adenosine was intravenously infused at the standard dose of 140 microg/kg/min over 90 s in order to elicit maximal microcirculatory dilation. The resting and hyperemic peak diastolic flow velocities were measured and the coronary flow reserve was calculated as the ratio between hyperemic and resting peak diastolic flow velocities.

This simple bedside technique provided crucial information about several important issues: 1) arterial patency after thrombolysis; 2) evaluation of the physiologic impact of a coronary stenosis, with implications on the detection of a critical stenosis; 3) reperfusion imaging of perforating branches after myocardial infarction; 4) post-stent assessment of coronary flow reserve.

This paper shows, for the first time, that non-invasive imaging of the PD by non-contrast transthoracic Doppler is feasible and that the coronary flow reserve is measurable even in critical conditions. More studies are needed to assess the feasibility of PD imaging in different clinical settings and the potential benefit of contrast agents in improving the evaluation of coronary flow.