Doppler Contrast Echocardiography

The advent and evolution of 2D echocardiography with Doppler gave a new dimension to the evaluation of valvular heart disease (VHD) and noninvasive cardiovascular hemodynamics. Extending from basic M-mode evaluation to the more sophisticated Doppler techniques, the way one looks at the valve anatomy and physiology has changed significantly. Doppler echocardiography has become the everyday tool for diagnosing valve pathology and for the serial evaluation of VHD (van de Brink et al, 1991). Despite significant technical advancements in image quality, spatial and temporal resolution, suboptimal image quality has not been entirely eliminated. Often due to body habitus (both obesity and markedly underweight individuals), chronic obstructive lung diseases or mechanically ventilated patients, 2D echocardiography suffers from poor signal to noise ratio (SNR). In these circumstances, the spectral Doppler signals are also weak due to high acoustic impedance. Harmonic imaging, power Doppler, low mechanical index pulsing and contrast echocardiography (CE) are some of the methods to improve image quality (Allen MR et al, 1999; Kitzman DW et al, 2000). Gramiak and Shah, often considered pioneers in the use of contrast agents, demonstrated the use of indocyanine dye to improve visualization of cardiac chambers (Gramiak & Shah, 1969). Several authors have compared the application of contrast use against second harmonic imaging in assessing endocardial definition and proven its superiority (Kornbluth M et al, 2000). The American Society of Echocardiography (ASE) has recommended the use of contrast for the purposes of improving endocardial visualization in all subjects with >2 suboptimal contiguous wall segments, to reduce interpreter’s variability and augment accuracy (Mulvagh SL et al, 2008). They also recommend using contrast agents to diagnose pathologic conditions that occur predominantly in the left ventricular (LV) apex, since this near-field region is better visualized after CE. This would include diseases such as apical variant of hypertrophic cardiomyopathy, isolated left ventricular noncompaction, apical thrombus and left ventricular aneurysm or pseudoaneurysm. Contrast agents have also been used for enhancing the spectral Doppler signals required for evaluation of LV diastolic function, cardiovascular hemodynamic assessment, and comprehensive valvular analysis. Despite these standard national guidelines and recommendations, it has been estimated that <1% of warranted patients ever receive contrast. These authors believe that CE is underutilized across the globe. In this chapter, we focus our attention to one particular use of contrast agents-the augmentation of continuous