Bedside Assessment of Left Ventricular Emptying Using Contrast-Enhanced Handheld Ultrasound: A Pilot Study

Abstract

Accurate bedside assessment of left ventricular emptying as measured by left ventricular ejection fraction (LVEF) and regional contractility can significantly impact the care of patients with a variety of suspected cardiac conditions. Handheld ultrasound has been shown to outperform standard physical examination in diagnosing left ventricular systolic dysfunction, but it can be limited by poor ultrasound windows, especially in acute care settings.1Testuz A. Muller H. Keller P.F. Meyer P. Stampfli T. Sekoranja L. et al.Diagnostic accuracy of pocket-size handheld echocardiographs used by cardiologists in the acute care setting.Eur Heart J Cardiovasc Imaging. 2013; 14: 38-42Crossref PubMed Scopus (61) Google Scholar, 2Melamed R. Sprenkle M.D. Ulstad V.K. Herzog C.A. Leatherman J.W. Assessment of left ventricular function by intensivists using hand-held echocardiography.Chest. 2009; 135: 1416-1420Abstract Full Text Full Text PDF PubMed Scopus (173) Google Scholar In this pilot study we examined the feasibility of contrast-enhanced handheld ultrasound examination in the bedside assessment of left ventricular emptying. We conducted a prospective, blinded observational study comparing unenhanced ultrasound with contrast-enhanced ultrasound examination using a handheld device (VScan, General Electric, Wauwatosa, WI) for the assessment of left ventricular emptying. Study patients were recruited from the inpatient cardiology service or cardiac intensive care unit. Study patients were identified in the echocardiography laboratory if they met standard criteria for the use of an ultrasonic enhancing agent for endocardial border definition (inability to visualize two or more consecutive segments) and had undergone contrast-enhanced comprehensive echocardiography.3Porter T.R. Mulvagh S.L. Abdelmoneim S.S. Becher H. Belcik J.T. Bierig M. et al.Clinical applications of ultrasonic enhancing agents in echocardiography: 2018 American Society of Echocardiography Guidelines Update.J Am Soc Echocardiogr. 2018; 31: 241-274Abstract Full Text Full Text PDF PubMed Scopus (180) Google Scholar All study subjects were recruited and examined within 24 hours of the comprehensive echocardiography. The study was approved by the Mount Sinai Institutional Review Board, and all patients provided informed consent. Left ventricular emptying assessed by biplane planimetry LVEF and regional wall motion abnormalities as interpreted by an attending cardiologist on contrast-enhanced comprehensive echocardiography were used as the gold standard. The examinations were performed by three independent blinded observers, cardiology fellows with an equivalent level of training: >1 year training in clinical cardiology including at least 4 weeks of formal training in echocardiography. Initially, the nonenhanced ultrasound examination was conducted by the observer, and findings were recorded by the research personnel at bedside using a standardized questionnaire. Subsequently, an ultrasonic enhancing agent was injected intravenously, and the observer conducted contrast-enhanced examination to confirm or refute the initial findings. Commercially available ultrasonic enhancing agents were used in this study (Definity, Lantheus Medical Imaging; Optison, GE Healthcare) not exceeding the manufacturer recommended maximal dosing. The interpretation confidence by the observer was assessed using a three-point confidence scale (1 = low, 2 = moderate, 3 = high). The handheld device was not equipped with contrast-specific settings; therefore, all examinations were conducted using regular settings with a mechanical index of 0.8 at the used depth. McNemar's test was used for comparing categorical variables. Confidence scores were compared using generalized estimating equation for repeated measures (SAS 9.4, Cary, NC). The study population consisted of 30 patients with a mean age of 67 (median, 69; range, 44-85) years, mean body mass index of 32 (median, 31; range, 22-59) kg/m2, and 73% men. Based on comprehensive echocardiography, 17 patients (57%) had abnormal left ventricular emptying (LVEF < 50%), 14 patients (47%) had moderate or severe left ventricular systolic dysfunction (LVEF < 40%), six patients (20%) had severe left ventricular systolic dysfunction (LVEF < 30%), and 24 patients (80%) had regional wall motion abnormalities. The mean LVEF was 43% (SD = 14%). Contrast-enhanced handheld ultrasound correctly identified any abnormal left ventricular emptying in 88% of patients compared with 65% by unenhanced ultrasound (P = .22); similarly, it identified moderate or severe left ventricular systolic dysfunction in 71% of patients compared with 43% by unenhanced ultrasound (P = .13). Contrast-enhanced handheld ultrasound correctly identified wall motion abnormalities in 83% of patients, compared with 71% by unenhanced ultrasound (P = .38). Use of echocardiographic contrast significantly improved the confidence of interpretation by observers as shown on Figure 1. This is a single-center feasibility pilot study recruiting a limited number of patients. Using regular, high mechanical index handheld ultrasound settings for contrast-enhanced imaging has inherent limitations due to rapid microbubble destruction and apical swirling, which limit optimal chamber opacification and endocardial definition. In conclusion, contrast-enhanced handheld ultrasound offers promise in accurate immediate bedside assessment of left ventricular emptying. Future studies using point-of-care ultrasound devices with contrast-specific, low mechanical index settings should further explore this approach.