Invited Commentary

Abstract

In myocardial contrast echocardiography (MCE), microscopic particles of gas-filled aqueous shells, which cause ultrasound reflections far stronger than those made by the native circulatory system, are injected intravenously. These microbubbles traverse the pulmonary circulation in sufficiently high concentration to cause contrast enhancement in the left ventricle [1Lang R.M. Mor-Avi V. Clinical utility of contrast-enhanced echocardiography.Clin Cardiol. 2006; 29: I-15-25Google Scholar]. Combined with other advancements in ultrasound imaging technologies, such as harmonic imaging and accelerated intermittent imaging, which improve the detection of contrast agents, MCE has been clinically used in the diagnosis and prognosis of coronary artery disease by assessing coronary artery flow and flow reserve [1Lang R.M. Mor-Avi V. Clinical utility of contrast-enhanced echocardiography.Clin Cardiol. 2006; 29: I-15-25Google Scholar, 2Caiati C. Montaldo C. Zedda N. Bina A. Illiceto S. New noninvasive method for coronary flow reserve assessment: contrast-enhanced transthoracic second harmonic echo Doppler.Circulation. 1999; 99: 771-778Crossref PubMed Scopus (297) Google Scholar, 3Mulvagh S.L. Foley D.A. Aeschbacher B.C. Klarich K.W. Seward J.B. Second harmonic imaging of intravenously administered echocardiographic contrast: visualization of coronary arteries and measurement of coronary blood flow.J Am Coll Cardiol. 1996; 27: 1519-1529Abstract Full Text PDF PubMed Scopus (122) Google Scholar]. Miyagawa and colleagues [4Miyagawa S. Masai T. Fukuda H. et al.Coronary microcirculatory dysfunction in aortic stenosis: myocardial contrast echocardiography study.Ann Thorac Surg. 2009; 87: 715-719Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar] report on the use of MCE to assess microcirculatory dysfunction before and after aortic valve replacement (AVR) in 22 patients with isolated moderate or severe AS. Compared with the contrast intensity (CI) of the ventricular cavity, the CI of the subendocarial region was −18.46 dB in patients with AS, versus −11.8 dB and −12.68 dB in controls, thereby demonstrating significantly reduced myocardial blood flow. Post-AVR, subendocardial blood flow improved to −13 dB and −12.7 dB at 2 weeks and 1 year, respectively. Subepicardial blood flow did not change post-AVR. It is known [5Hildick-Smith D.J.R. Shapiro L.M. Coronary flow reserve improves after aortic valve replacement for aortic stenosis: an adenosine transthoracic echocardiography study.J Am Coll Cardiol. 2000; 36: 1889-1896Abstract Full Text Full Text PDF PubMed Scopus (100) Google Scholar, 6Rajappan K. Rimoldi O.E. Camici P.G. Bellenger N.G. Pennell D.J. Sheridan D.J. Functional changes in coronary microcirculation after valve replacement in patients with aortic stenosis.Circulation. 2003; 107: 3170-3175Crossref PubMed Scopus (173) Google Scholar] that it is the hyperemic MBF (post-adenosine or dipyrimadole) and not the resting MBF that is increased after AVR. Because coronary vasodilator reserve (CVR) is the ratio of hyperemic to resting MBF, CVR increases post-AVR. Also, CVR improved before ventricular mass regression was completed, suggesting an important role for diastolic perfusion time improvement with AVR. Herein lies the major criticism of this study. The MBF is mainly diastolic in nature, and calculations of CVR are based on diastolic flows or flow velocity. The authors, on the other hand have used end-systolic measurements of MBF. The relevance as well as the significance of end-systolic MBF measurements will remain controversial. It would have been desirable if the authors had compared MCE with other modalities such as positron emission tomography to assess MBF. However, the use of MCE has many advantages in comparison with routine echocardiography as previously mentioned. The authors are to be commended for this ingenious use of MCE. If indeed it can reliably measure CVR in AS patients, it would be very interesting to follow asymptomatic patients with AS by MCE to see if CVR measurements correlate with development of symptoms or the need for surgery. Coronary Microcirculatory Dysfunction in Aortic Stenosis: Myocardial Contrast Echocardiography StudyThe Annals of Thoracic SurgeryVol. 87Issue 3PreviewThe aims of this study were to quantify the microcirculatory dysfunction in aortic stenosis (AS) and to measure the changes in transmural perfusion after aortic valve replacement (AVR), using quantitative myocardial contrast echocardiography. Full-Text PDF