Eligible patients

This retrospective study included patients who were referred to stress echocardiography from January 2013 to February 2014 at the Karolinska University Hospital in Huddinge (The heart clinic), Sweden. This patient group was selected as the image protocol at our institution routinely involves analysis of both greyscale and contrast-enhanced images both at rest and during stress, regardless of image quality. This enables a comparison of the diagnostic outcome between greyscale and contrast-enhanced images at rest in the subset of patients beyond the current recommendations for contrast agent usage in standard echocardiography. Note that the greyscale images routinely are acquired with such quality that deformation analysis using speckle tracking is feasible during rest and stress. The image acquisition was performed with a GE Vivid E9 (GE Healthcare, Wisconsin, USA), at a transmitted frequency of 1.5–1.7 MHz. All contrast-enhanced images were acquired at a low MI index using contrast specific image sequences, such as pulse inversion. SonoVue® (Bracco Diagnostics Inc., Switzerland) (n = 187) and Optison® (GE Healthcare, Wisconsin, USA) (n = 5) were used as contrast agents.

The exclusion criteria were based on the recommendations for contrast agent usage during standard echocardiography [7, 8]. Patients were excluded if they fulfilled the criteria for contrast-enhanced echocardiography, i.e. two or more contiguous LV segments not visualized on a greyscale image or suspicion of LV structural abnormalities, such as apical hypertrophic cardiomyopathy, ventricular non-compaction, thrombus or ventricular pseudoaneurysm. Experienced echocardiographer (n = 4, 3–15 years of experience) of contrast-enhanced echocardiography visually evaluated whether patients should be included in the study or not. Additionally, patients were excluded if any apical 2 chamber (ch), 3ch or 4ch images in either greyscale or contrast mode were missing. The study protocol was approved by the regional ethical review board in Stockholm, Sweden.