Background-Ultrasound can cause microbubble destruction. If microbubbles are administered as a continuous infusion, then their destruction within the myocardium and measurement of their myocardial reappearance rate at steady state will provide a measure of mean myocardial microbubble velocity. Conversely, measurement of their myocardial concentration at steady state will provide an assessment of microvascular cross-sectional area. Myocardial blood flow (MBF) can then be calculated from the product of the two. Methods and Results-Ex vivo and in vitro experiments were performed in which either flow was held constant and pulsing interval (interval between microbubble destruction and replenishment) was altered, or vice versa. In vivo experiments were performed in 21 dogs. In group 1 dogs (nϭ7), MBF was mechanically altered in a model in which coronary blood volume was constant. In group 2 dogs (nϭ5), MBF was altered by direct coronary infusions of vasodilators. In group 3 dogs (nϭ9), non-flow-limiting coronary stenoses were created, and MBF was measured before and after the venous administration of a coronary vasodilator. In all experiments, microbubbles were delivered as a constant infusion, and myocardial contrast echocardiography was performed using different pulsing intervals. The myocardial video intensity versus pulsing interval plots were fitted to an exponential function: yϭA(1Ϫe Ϫ␤t ), where A is the plateau video intensity reflecting the microvascular cross-sectional area, and ␤ reflects the rate of rise of video intensity and, hence, microbubble velocity. Excellent correlations were found between flow and ␤, as well as flow and the product of A and ␤. Conclusions-MBF can be quantified with myocardial contrast echocardiography during a venous infusion of microbubbles.This novel approach has potential for measuring tissue perfusion in any organ accessible to ultrasound. (Circulation. 1998;97:473-483.)

Both bolus injection and continuous infusion provide quantitative assessment of relative stenosis severity. Compared with bolus injection, continuous infusion also allows quantification of MBF and data acquisition without attenuation of any myocardial bed.

AimsCT calcium scoring (CTCS) and CT cardiac angiography (CTCA) are widely used in patients with stable chest pain to exclude significant coronary artery disease (CAD). We aimed to resolve uncertainty about the prevalence of obstructive coronary artery disease and long-term outcomes in patients with a zero-calcium score (ZCS).Methods and resultsConsecutive patients with stable cardiac symptoms referred for CTCS or CTCS and CTCA from chest pain clinics to a tertiary cardiothoracic centre were prospectively enrolled. In those with a ZCS, the prevalence of obstructive CAD on CTCA was determined. A follow-up for all-cause mortality was obtained from the NHS tracer service. A total of 3914 patients underwent CTCS of whom 2730 (69.7%) also had a CTCA. Half of the patients were men (50.3%) with a mean age of 56.9 years. Among patients who had both procedures, a ZCS was present in 52.2%, with a negative predictive value of 99.5% for excluding ≥70% stenosis on CTCA. During a mean follow-up of 5.2 years, the annual event rate was 0.3% for those with ZCS compared with 1.2% for CS ≥1. The presence of non-calcified atheroma on CTCA in patients with ZCS did not affect the prognostic value (P = 0.98).ConclusionIn patients with stable symptoms and a ZCS, obstructive CAD is rare, and prognosis over the long-term is excellent, regardless of whether non-calcified atheroma is identified. A ZCS could reliably be used as a ‘gatekeeper’ in this patient cohort, obviating the need for further more expensive tests.

Aims The aim of this investigation was to evaluate echocardiographic parameters of cardiac function and in particular right ventricular (RV) function as a predictor of mortality in patients with coronavirus disease‐2019 (COVID‐19) pneumonia. Methods and Results This prospective observational study included 35 patients admitted to a UK district general hospital with COVID‐19 and evidence of cardiac involvement, that is, raised Troponin I levels or clinical evidence of heart failure during the first wave of the COVID‐19 pandemic (March–May 2020). All patients underwent echocardiography including speckle tracking for right ventricular longitudinal strain (RVLS) providing image quality was sufficient (30 out of 35 patients). Upon comparison of patients who survived COVID‐19 with non‐survivors, survivors had significantly smaller RVs (basal RV diameter 38.2 vs 43.5 mm P = .0295) with significantly better RV function (Tricuspid annular plane systolic excursion (TAPSE): 17.5 vs 15.3 mm P = .049; average RVLS: 24.3% vs 15.6%; P = .0018). Tricuspid regurgitation (TR) maximal velocity was higher in survivors (2.75 m/s vs 2.11 m/s; P = .0045) indicating that pressure overload was not the predominant driver of this effect and there was no significant difference in left ventricular (LV) ejection fraction. Kaplan–Meier and log‐rank analysis of patients split into groups according to average RVLS above or below 20% revealed significantly increased 30‐day mortality in patients with average RVLS under 20% (HR: 3.189; 95% CI: 1.297–12.91; P = .0195). Conclusion This study confirms that RVLS is a potent and independent predictor of outcome in COVID‐19 patients with evidence of cardiac involvement.

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