Invasive and non-invasive assessment of ischaemia in chronic coronary syndromes: translating pathophysiology to clinical practice

Figure 1. Illustration of inverse relationship between accuracy and ease of use for physiological indices of coronary circulatory evaluation. CT, computed tomography; FFR, fractional flow reserve; iFR, instantaneous wave-free ratio; Pd/Pa, resting distal to aortic pressure ratio; QFR, quantitative flow reserve.

Figure 2. The relationship between flow velocity and pressure drop across a diseased coronary segment is unique to its severity and morphology. The figure depicts the curves across three illustrative stenoses of differing grades of severity and shows how this relationship forms the basis of all invasive physiological parameters used in clinical practice. CFR, coronary flow reserve; FFR, fractional flow reserve; hSR, hyperaemic stenosis resistance; NHPR, non-hyperaemic pressure ratio; PH, hyperaemic pressure; PR, resting pressure; VH, hyperaemic velocity; VR, resting velocity.

Figure 3. Guide to performing coronary physiology measurements using pressure, Doppler, and thermodilution wires. ECG, electrocardiogram; FFR, fractional flow reserve; IC, intracoronary; IV, intravenous; NHPR, non-hyperaemic pressure ratio; Pd/Pa, resting distal to aortic pressure ratio.

Figure 4. Illustration of different phases of cardiac cycle for evaluating non-hyperaemic indices. Pd/Pa (resting average distal pressure [Pd] divided by average aortic pressure [Pa]) is the average Pd/Pa during the entire cardiac cycle. Instantaneous wave-free ratio is the average Pd/Pa during the latter 75% of diastole, excluding the terminal 5 ms. Diastolic pressure ratio is the average Pd/Pa during the entire diastole. Diastolic pressure ratio is Pd/Pa during the wave-free period. Resting full-cycle ratio is the lowest mean Pd/Pa ratio during the entire cardiac cycle. Diastolic hyperaemia-free ratio is the average Pd/Pa during the period between Pa less than mean Pa ending at systole.

Figure 5. Coronary haemodynamic evaluation with dual sensor coronary wire. (A) Coronary pressure and thermodilution. (B) Coronary pressure and Doppler.

Figure 6. Comprehensive assessment of suspected chronic coronary syndrome. Complex coronary artery disease refers to serial stenoses, left main stem stenosis, or coronary artery disease in the presence of impaired left ventricular function. Under these circumstances, utilization of combined flow and pressure-derived physiology indices can assist tailored management strategy. Patients with substrate suggestive of NOCAD should be considered for endothelium-independent microvascular function assessment by coronary flow measurement(s). CFR, coronary flow reserve; CMD, coronary microvascular dysfunction; FFR, fractional flow reserve, hMR, hyperaemic microvascular resistance; hSR, hyperaemic stenosis resistance; ic, intracoronary; IMR, index of microvascular resistance; NOCAD, non-obstructive coronary artery disease, PW, pressure wire.