Contrast echocardiography in critical care: echoes of the future? A review of the role of microsphere contrast echocardiography

Echocardiography is an important diagnostic modality in the critical care setting. It is a safe, non-invasive bedside investigation that provides important cardiac structural, functional and haemodynamic information. However, in up to 25% of scans, the images are non-diagnostic, which can have a significant impact on patient diagnosis and management. Contrast echocardiography, using contrast microspheres coupled with contrast-specific ultrasound imaging modalities, overcomes many of the limitations that cause suboptimal echocardiograms in the critical care environment. These microspheres are haemodynamically inert and have the same intravascular rheology as red blood cells. By using the differential oscillating properties of myocardium and microspheres, contrast echocardiography can enhance the blood pool myocardial interface, thus improving endocardial definition. Consequently, this technique can be used to improve the accuracy, feasibility and reproducibility of transthoracic echocardiography. The technique is well accepted and indicated for improving the image quality in suboptimal scans, and for the assessment of global and regional left ventricular (LV) function and LV ejection fraction. It also has a significant role to play in enhancing LV morphology (for conditions such as apical hypertrophic cardiomyopathy, pseudoaneurysm and non-compaction), assessing intracardiac masses and evaluating LV thrombus. Contrast echocardiography is of benefit in various clinical settings, particularly the critical care setting. Here it can salvage a non-diagnostic transthoracic echocardiogram, thus avoiding an alternative, more invasive investigation, while remaining a truly bedside, non-invasive investigative procedure. Future applications for contrast echocardiography could include use as a perfusion modality, enhancement of three-dimensional echocardiography, and targeted delivery of gene therapy.