Usefulness of myocardial parametric imaging to evaluate myocardial viability in experimental and in clinical studies

Quantitative evaluation of myocardial blush to assess tissue level reperfusion in patients with acute ST-elevation myocardial infarction: incremental prognostic value compared with visual assessment

BACKGROUND

Tissue level reperfusion gauges functional recovery in acute ischemic syndromes. However, its current clinical assessment is based upon visual interpretation of myocardial blush grade (MBG), which is operator dependent. The purpose of the study was to test whether quantification of MBG can enhance the predictive value of visual assessment for functional recovery in patients with acute ST-elevation myocardial infarction (STEMI).

METHODS

Myocardial blush grade was assessed in 124 consecutive patients with STEMI visually and quantitatively, analyzing the time course of blush intensity rise. We defined Gmax as the peak gray level intensity and Tmax as the time to peak intensity. Ejection fraction >50% at 4 to 6 months of follow-up was deemed as the primary end point for assessment of successful tissue reperfusion.

RESULTS

Ejection fraction >50% at follow-up was predicted by visual MBG with moderate sensitivity (65%) and specificity (64%). However, a cutoff value of Gmax/Tmax = 3.1/s yielded significantly higher sensitivity and specificity (91% and 96%, respectively, for both P < .01). Gmax/Tmax was the most powerful predictor of follow-up ejection fraction >50% (relative risk of 4.6 vs 3.2 for visual MBG).

CONCLUSIONS

Quantitative MBG is highly predictive for functional recovery in patients with STEMI and provides incremental prognostic value to visual assessment. Thus, this simple approach may be used to gauge reperfusion strategies in acute ischemic syndromes.

Contrast echocardiography for the assessment of myocardial viability

PURPOSE OF REVIEW

The availability of an accurate, non-invasive method for distinguishing viable from irreversibly damaged myocardium, after acute myocardial infarction or in chronic coronary artery disease, is important in clinical decision making. Such a tool would enable physicians to identify patients most likely to benefit from revascularization strategies in patients with coronary artery disease and left ventricular dysfunction. Myocardial contrast echocardiography is a new technique that utilizes acoustically active gas-filled microspheres (microbubbles), which remain exclusively in the intravascular space and allow the simultaneous assessment of global and regional myocardial structure, function, and perfusion. An increasing body of data supports its role in assessing myocardial viability and predicting the recovery of function.

RECENT FINDINGS

Myocardial contrast echocardiography accurately differentiates 'stunning' from necrosis, delineates transmural extent of infarction, predicts recovery of regional and global left ventricular systolic function in the recuperative phase, identifies patients at high risk of left ventricular remodelling, and provides incremental viability data when performed in conjunction with low-dose dobutamine echocardiography.

SUMMARY

Technological advances have positioned myocardial contrast echocardiography as a safe, practical bedside technique for the evaluation of myocardial viability. It has comparable accuracy with other non-invasive imaging techniques, such as dobutamine stress echocardiography, radionuclide scintigraphy and cardiac magnetic resonance imaging.

The potential of a new stable ultrasound contrast agent for site-specific targeting. An in vitro experiment

Microbubble-based ultrasound contrast agents can be used for specific site targeting, but demonstrate time-limited opacification. We have previously demonstrated the potential of gold-bound microtubules to provide a stable ultrasound contrast effect. Aim of the present study was to test the feasibility of gold-bound microtubules specifically to bind to human thrombi and to inflammatory activated human umbilical vein endothelial cells (HUVEC) in vitro. HUVEC were incubated with tumor necrosis factor, to induce expression of adhesion molecules. Human clots and HUVEC were incubated with biotinylated monoclonal antifibrin and anti-E-selectin antibodies, respectively. Probes were incubated with excess avidin followed by biotinylated gold-bound microtubules and by secondary Cy3-anti-beta-tubulin antibody and processed for immune fluorescence microscopy. Clots were transferred in copolymer foils filled with buffer and were ultrasonographically imaged before and after their treatment with the antifibrin antibody and with biotinylated microtubules, using a broadband harmonic transducer, transmitting and receiving at a mean frequency of 1.7 MHz and 3.2 MHz. The feasibility of specific gold-bound microtubules conjugation to antibody treated clots and HUVEC was confirmed using immune fluorescence analysis. Contrast intensities of the clots significantly increased after their treatment with antifibrin antibody and incubation with gold-bound microtubules (39 +/- 2 dB versus 26 +/- 2 dB, p < 0.001) and remained high after 20 min of ultrasound exposure (37 +/- 2 dB versus 39 +/- 2 dB, p = NS). Thus, gold-bound microtubules can specifically bind to human thrombi and to endothelial cells, providing a significant contrast effect which remains stable in the ultrasound field. This may be a promising approach to target thrombi and inflammatory active atherosclerotic plaques.