Real-time myocardial contrast echocardiography for pharmacologic stress testing: is quantitative estimation of myocardial blood flow reserve necessary?

BACKGROUND: Little is known about the diagnostic accuracy of quantitative real-time myocardial contrast echocardiography (MCE) as an adjunct to stress testing. This study was performed to evaluate the agreement between MCE and technetium 99m-sestamibi single photon emission computed tomography (SPECT) for detection of perfusion defects and to investigate whether quantitative assessment of myocardial perfusion can increase the diagnostic value of MCE.
METHODS: MCE was performed at rest and during peak adenosine stress in 50 unselected patients undergoing SPECT imaging. Concordance between the 2 methods was assessed using kappa statistics. MCE images were analyzed quantitatively, measuring peak intensity (A) and maximal rise of signal intensity (beta). Myocardial blood flow reserve was estimated by calculating the ratios of A(adenosine)/A(baseline) (A reserve), beta(adenosine)/beta(baseline) (beta reserve), and A x beta(adenosine)/A x beta(baseline) (A x beta reserve).
RESULTS: Visual analysis of MCE agreed well with SPECT (kappa = 0.67) with sensitivity of 64%, specificity of 97%, and overall accuracy of 87%. Quantitative analysis showed that peak signal intensity A significantly increased under adenosine stress in SPECT-normal segments (2.6 +/- 1.9 vs 3.0 +/- 1.6 dB, P <.0001), tendencially decreased in reversible (3.0 +/- 2.0 vs 2.4 +/- 1.2 dB, P =.07) and remained unchanged in fixed (0.9 +/- 0.9 vs 0.8 +/- 0.9 dB) defects. beta Increased markedly under adenosine in normal segments (0.4 +/- 0.4 vs 1.4 +/- 1.3, P <.0001) but not in segments with reversible or fixed defects. Receiver operating characteristic showed that beta reserve and A x beta reserve, but not A reserve, are sensitive parameters for detecting perfusion defects with areas under the curve of 0.84, 0.85, and 0.61, respectively. Cut-off values of 1.9 and 2.3, respectively, for beta and A x beta reserve yielded sensitivity rates of 79% and 80%, specificity rates of 75% and 78%, and overall accuracy rates of 76% and 79%, respectively.
CONCLUSION: Quantitative estimation of myocardial blood flow reserve by MCE parameters corresponds to the evaluation of myocardial perfusion by nuclear imaging and can increase the sensitivity but not the overall accuracy of contrast echocardiography.