Coronary microcirculatory dysfunction can be assessed by positive dicrotic wave and amplitude index on resting distal coronary pressure waveform, a newly developed index.

Aims: Some lesions have high resting distal coronary pressure/aortic pressure (Pd/Pa) despite low fractional flow reserve (FFR). This study aimed to assess microcirculatory dysfunction as a possible basal mechanism. Methods and results: Patients were grouped into two according to coffee intake (caffeine 222 mg) before coronary angiography. Through an adenosine-induced Pd/Pa decrease, amplitude index was calculated by dividing the difference between the highest pressure after the inflection point and the minimal diastolic pressure by the pulse pressure on the Pd waveform. In 130 coronary lesions (caffeine group, n = 69; non-caffeine group, n = 61) from 113 patients, the amplitude index through the adenosine-induced Pd/Pa decrease in all lesions was 0.54 ± 0.11 at resting Pd/Pa and 0.44 ± 0.12 at FFR (P < 0.0001). The positive dicrotic wave distribution on a maximal hyperaemia (FFRnicr)-resting Pd/Pa graph was analysed. In lesions with FFRnicr <0.80 on the FFRnicr-resting Pd/Pa graph, the resting Pd/Pa was divided into three zones based on Pd/Pa values: high-remaining, intermediate, and low. The high-remaining zone had a higher amplitude index than the intermediate zone (0.60 ± 0.09 vs. 0.48 ± 0.12; P < 0.005); the low zone lesions had no inflection point (no amplitude index). The high-remaining zone correlated with a larger positive dicrotic wave than the intermediate zone (94 vs. 30%; P < 0.005). Most lesions in the high-remaining zone corresponded to the caffeine group. Conclusion: In severe coronary stenosis, a high-remaining resting Pd/Pa with a high amplitude index or a positive dicrotic wave on the resting Pd waveform suggests microcirculatory dysfunction, such as insufficient arteriolar dilation reactive to myocardial ischaemia. Registration: UMIN000046883.

Saline-induced Pd/Pa ratio predicts functional significance of coronary stenosis assessed using fractional flow reserve.

AIMS: Fractional flow reserve (FFR), assessed using distal coronary pressure/aortic pressure (Pd)/(Pa) ratio, functionally evaluates coronary stenosis. An assessment method without vasodilators would be helpful. A single intracoronary bolus of saline decreases Pd because of the speculated low-viscosity effect. We hypothesised that saline-induced Pd/Pa ratio (SPR) could functionally evaluate coronary stenosis. This study aimed to test the accuracy and utility of SPR for predicting FFR ≤0.80. METHODS AND RESULTS: In 137 coronary lesions with over 50% angiographic diameter stenosis, SPR was assessed using an intracoronary bolus of saline (2 mL/s) for five heartbeats (SPR-5) and three heartbeats (SPR-3). FFR was obtained after intravenous adenosine infusion (140 µg/kg/min). There was a strong correlation between FFR and SPR-5 or SPR-3 (R=0.941 and R=0.933, respectively). Receiver operating characteristic (ROC) curve analysis demonstrated good accuracy (86.3%) for SPR-5, with a cut-off of ≤0.84 for predicting FFR ≤0.80 (area under ROC curve 0.96, specificity 94.3, sensitivity 79.9). Thirty-three lesions (24%) were located in the "grey zone" (SPR 0.83-0.88). No complications were observed in 673 SPR measurements. CONCLUSIONS: SPR may accurately predict FFR and can limit adenosine use to one in four lesions. Further studies are needed to confirm the validity of SPR.