Abstract
BackgroundDiagnosis of significant coronary artery disease (CAD) and acute coronary artery occlusion in ICU can be difficult, and an inappropriate intervention is potentially harmful. Myocardial contrast perfusion echo (MCPE) examines ultrasound contrast intensity replenishment curves in individual myocardial segments measuring peak contrast intensity and slope of return as an index of myocardial blood flow (units = intensity of ultrasound per second [dB/s]). MCPE could possibly serve as a triage tool to invasive angiography by estimating blood flow in the myocardium. We sought to assess feasibility in the critically ill and if MCPE could add incremental value to the clinical acumen in predicting significant CAD.MethodsThis is a single-centre, prospective, observational study. Inclusion criteria were as follows: adult ICU patients with troponin I > 50 ng/L and cardiology referral being made for consideration of inpatient angiography. Exclusion criteria were as follows: poor echo windows (2 patients), known ischaemic heart disease, and contrast contraindications. Seven cardiologists and 6 intensivists blinded to outcome assessed medical history, ECG, troponin, and 2D echo images to estimate likelihood of significant CAD needing intervention (clinical acumen). Clinical acumen, quantitative MCPE, and subjective (visual) MCPE were assessed to predict significant CAD.ResultsForty patients underwent MCPE analysis, 6 (15%) had significant CAD, and median 11 of 16 segments (IQR 8–13) could be imaged (68.8% [IQR 50–81]). No adverse events occurred. A significant difference was found in overall MCPE blood flow estimation between those diagnosed with significant CAD and those without (3.3 vs 2.4 dB/s, p = 0.050). A MCPE value of 2.8 dB/s had 67% sensitivity and 88% specificity in detecting significant CAD. Clinical acumen showed no association in prediction of CAD (OR 0.6, p = 0.09); however, if quantitative or visual MCPE analysis was included, a significant association occurred (OR 17.1, p = 0.01; OR 23.0, p = 0.01 respectively).ConclusionsMCPE is feasible in the critically ill and shows better association with predicting significant CAD vs clinical acumen alone. MCPE adds incremental value to initial assessment of the presence of significant CAD which may help guide those who require urgent angiography.
Highlights
Diagnosis of significant coronary artery disease (CAD) and acute coronary artery occlusion in ICU can be difficult, and an inappropriate intervention is potentially harmful
Angiography was performed in 22 patients (55%)
Normal non-invasive studies led to the decision not to proceed with angiography in the remaining 18 patients: normal follow-up echo in 11 (28%), normal CT coronary angiogram in 3 (8%), and normal MRI perfusion study in four (10%)
Summary
Diagnosis of significant coronary artery disease (CAD) and acute coronary artery occlusion in ICU can be difficult, and an inappropriate intervention is potentially harmful. Echo contrast agents (e.g. Definity) are microbubbles of inert gas surrounded by a stabilizing shell (e.g. perflutren carbon) typically 1–8 μm in diameter These bubbles are injected into the venous system and are small enough to pass through the pulmonary microvasculature to pass into the systemic circulation. This allows for the labelled use of this agent for left ventricle (LV) opacification to improve detection of thrombus, regional wall motion abnormalities, accurate ejection fraction estimation, etc. This feature can be used to an advantage by applying a burst of high-intensity ultrasound for a short period of time; bubbles are destroyed; and through analysing the ‘replenishment’ rate, as contrast bubbles trickle back in to the myocardial circulation, perfusion can be assessed [5] (see Fig. 1)
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