Myocardial blood flow assessment in cardiac amyloidosis using myocardial contrast echocardiography

Cardiac amyloidosis (CA) patients may present with angina and coronary syndromes. Cardiac biomarkers are chronically elevated in some cases. Many proceed with coronary investigation which often reveals angiographically patent vessels. An explanation for their presentation is thought to be due to microvascular amyloid deposition resulting in microvascular dysfunction. We performed vasodilator myocardial contrast echocardiography (MCE) on a patient with CA to assess myocardial blood flow reserve (MBFR). She previously had patent epicardial coronary arteries on coronary angiography and a normal dobutamine stress echocardiogram. Real-time MCE was performed according to an established protocol using a commercial ultrasound machine and contrast agent. Images were recorded in the 3 apical views with low-power settings at a mechanical index of 0.1. Flash-impulse imaging at a high mechanical index (1.0) was performed to achieve complete myocardial bubble destruction, after which 10 end-systolic frames were recorded digitally in each view. Imaging was repeated after dipyridamole infusion. Background-subtracted plots of peak myocardial contrast intensity (representingmyocardial blood volume A) versus pulsing intervals (representing time) were constructed by QLab software to fit the monoexponential function conventional equation: y=A (1−e− t). From these plots, the slope of the replenishment curve was determined (representing myocardial blood velocity ). Per segment, the product of A and yielded rest MBF and post-dipyridamole MBFs (stress MBF), respectively. MBFR was calculated as the ratio of peak MBF to resting MBF. The results show a marked reduction in MBFR. This supports the hypothesis of microvascular dysfunction and adds to our pathophysiological understanding of this challenging condition.