Abstract Body (Do not enter title and authors here): Background:
Ultrafast ultrasound or High Frame Rate (HFR) myocardial contrast echocardiography (MCE) due to its high temporal resolution (>1000 frames/sec) can reduce noise and improve perfusion assessment. We hypothesised that quantitative HFR MCE is superior to quantitative conventional MCE in evaluating patients with obstructive coronary artery disease (OCAD).

Methods:
25 consecutive eligible patients consisting of 20 patients (pts) with high pre-test probability (PTP) and 5 with low PTP for OCAD underwent rest and stress perfusion imaging with conventional and HFR MCE during intravenous infusion of a commercially used microbubbles at rest and following vasodilator stress. All patients with high PTP for OCAD also underwent invasive coronary angiography. Quantitative analysis of myocardial perfusion at rest and stress was performed using the time-intensity curve with both conventional and HFR MCE and were correlated with coronary angiography. Myocardial blood flow reserve (MBFR) was derived (MBFR<2.0 was considered reduced).

Results:
Of the 20 pts with high PTP, 18 pts demonstrated 27 vascular territories with OCAD on coronary angiography. Of these 27 vascular territories with OCAD, HFR MCE identified 25 (93%) vascular territories with reduced MBFR compared to 22 (81%) by conventional MCE (p 0.22). Of the 12 normal vascular territories in 4 pts with low PTP, HFR MCE identified 7 (58%) vascular territories as normal vs 5 (42%) by conventional MCE (p 0.41). Accuracy for the detection of OCAD by HFR vs conventional MCE were 32/39 (83%) vs 27/39 (69%) respectively (p 0.18).
However, the number of segments with low MBFR detected by HFR MCE in pts with OCAD was significantly higher 92 (73%) compared to 83 (66%) by conventional MCE (p 0.02). Furthermore, hyperaemic MBF was significantly lower with HFR vs conventional MCE (0.8 +/- 0.1 SD vs 1.6 +/- 0.3 SD respectively, p 0.03).
Interobserver variability by two different physicians from randomly selected 7 patients involving 21 vascular territories (13 OCAD and 8 territories in low PTP pts) demonstrated concordance of 94%, and 100% for HFR vs conventional MCE respectively for the correct identification of normal and abnormal MBFR.

Conclusion:
In the first study in humans with suspected OCAD, quantitative Ultrafast MCE was similar to conventional MCE for the detection of OCAD but was superior in identifying the extent and intensity of inducible myocardial ischemia which has both therapeutic and prognostic implications.