Comparison of simultaneous dobutamine echocardiography and thallium-201 stress-reinjection single-photon emission computed tomography in predicting improvement of chronic myocardial dysfunction after revascularization

Twenty-four-hour thallium-201 imaging enhances the detection of myocardial ischemia and viability after myocardial infarction: a comparison study with echocardiography follow-up

BACKGROUND

To explore the value of 24 hour late Tl-201 imaging for detection of myocardial ischemia/viability after myocardial infarction.

MATERIALS AND METHODS

Thirty-eighty patients with myocardial infarction underwent immediate, 3 hour redistribution and 24-hour late imaging after intravenous injection of 5 mCi Tl-201. Image quality analysis was performed using a 4-grade model. The immediate/redistribution, redistribution/late, and immediate/late Tl-201 images were analyzed double-blinded. The capability of detection of myocardial ischemia/viability was compared between the 3 hour redistribution and the 24-hour late imaging. Thirty-two patients underwent coronary angiography and successful revascularization of stenotic coronary arteries. The relationship between the severity of coronary artery stenosis and the time to completed redistribution of myocardial perfusion defects after resting injection of Tl-201 was investigated. The sensitivity, specificity, and accuracy for predicting an improvement in function post revascularization were compared between the 24-hour late imaging and the 3-hour redistribution imaging by way of a follow-up echocardiography.

RESULTS

Three hour redistribution and 24-hour late imaging showed no significant differences in image quality according to the 4-grade model (P = 0.3580). Of 194 abnormal segments based on immediate Tl-201 imaging, redistribution imaging showed 60 reversible segments, taking up 31% (60/94), and late imaging showed 86 reversible segments, taking up 44% (86/194), with a significant difference (P = 0.0064). Of 128 severely abnormal segments, redistribution imaging showed 32 reversible segments, taking up 25% (32/128), and late imaging showed 48 reversible segments, taking up 38% (48/128), with a significant difference (P = 0.0310). Of 66 mildly abnormal segments, redistribution imaging showed 28 reversible segments, taking up 42% (28/66), and late imaging showed 38 reversible segments, taking up 58% (38/66), with no significant difference. Twenty-four hour late imaging showed an additional 30 reversible segments, taking up 22% (30/134) among 134 abnormal segments based on the immediate Tl-201 imaging, which did not improve on 3-hour redistribution imaging. The coronary arteries supplying the reversible segments detected by the 24-hour late imaging were more severe in diameter stenosis than those supplying the reversible segments detected by the 3-hour redistribution imaging. The sensitivity, specificity, and accuracy for predicting the functional improvement after the revascularization were 93% and 83%, 80% and 78%, 86% and 78%, respectively, by the 24-hour late imaging and the 3-hour redistribution imaging correspondingly, with the former being superior to the latter on the basis of the evaluation results of 9.90 +/- 3.62 months of follow-up echocardiography (chi = 10.8655, P = 0.0010).

CONCLUSION

Twenty-four hour late Tl-201 imaging, with satisfactory image quality, enhances the detection of myocardial ischemia/viability after myocardial infarction.

Integrated backscatter for the assessment of myocardial viability

PURPOSE OF REVIEW

Ultrasonic tissue characterization is a non-invasive diagnostic method that uses myocardial integrated backscatter analysis to determine contractile performance and myocardial viability independent of wall motion. This review discusses recent clinical findings regarding the application of ultrasonic tissue characterization for the assessment of myocardial viability.

RECENT FINDINGS

As this technique is non-invasive, ultrasonic tissue characterization can be used to predict the patency of infarct-related arteries in patients in the early stage of acute myocardial infarction. Several recent studies have shown that this technique is useful in identifying myocardial contractile reserve. The accuracy of ultrasonic tissue characterization for predicting functional recovery after coronary reperfusion is comparable to dobutamine echocardiography and radionuclide methods. Several studies have suggested that the cyclic variation of myocardial integrated backscatter reflects myocardial viability rather than contractile reserve. The cyclic variation of integrated backscatter is associated with myocardial viability confirmed by the integrity of the microvasculature identified by contrast echocardiography. In addition, the cyclic variation of integrated backscatter better reflects myocardial viability confirmed by the integrity of cellar metabolism than contractile reserve.

SUMMARY

Ultrasonic tissue characterization with integrated backscatter is a useful non-invasive method that can provide unique information for the assessment of myocardial viability.

Sensitive detection of myocardial viability in chronic coronary artery disease by ultrasonic integrated backscatter analysis

BACKGROUND

Myocardial viability is not synonymous with contractile reserve and identifiable in a significant percentage of dysfunctional myocardial segments without contractile reserve. The usefulness of ultrasonic tissue characterization by the phase-corrected magnitude of cyclic variation of integrated backscatter (MVIB) in chronic coronary artery disease is not fully validated. Thus, whether MVIB predominantly reflects the contractile reserve or myocardial viability of chronically dysfunctional myocardium was determined.

METHODS

The MVIB of severely dysfunctional interventricular septum or posterior wall was measured in 34 consecutive patients with previous myocardial infarction. Dobutamine stress echocardiography and fluorine-18 fluorodeoxyglucose positron emission tomography were used as the standards of contractile reserve and myocardial viability, respectively.

RESULTS

Among 44 dysfunctional segments, only 15 were judged as having contractile reserve and 29 were judged as not by dobutamine stress echocardiography, whereas 26 segments showed myocardial viability using fluorine-18 fluorodeoxyglucose positron emission tomography and 18 did not. MVIB was greater in segments with than in those without contractile reserve (4.7 +/- 2.2 vs -1.4 +/- 4.9 dB, P < .0001), but there was considerable overlap between the groups. On the other hand, MVIB of segments with and without myocardial viability (4.1 +/- 2.6 vs -4.3 +/- 3.3 dB, P < .0001) was distinctly different and predicted myocardial viability with a sensitivity of 92% and a specificity of 94%.

CONCLUSIONS

For patients with chronic coronary artery disease, MVIB better reflects myocardial viability than it does contractile reserve. Ultrasonic tissue characterization, in concordance with fluorine-18 fluorodeoxyglucose positron emission tomography, is a sensitive method for detecting myocardial viability.

Use of pharmaceuticals in noninvasive cardiovascular diagnosis

A number of pharmaceuticals are employed as diagnostic agents for cardiovascular diseases. Four groups of agents are reviewed here: 1) vasoactive substances employed as adjuncts to physical maneuvers in diagnosis of structural heart disease; 2) vasodilators used to produce heterogeneity of coronary flow; 3) sympathomimetic agents simulating the effects of exercise on the heart for the purpose of detection of coronary artery stenosis; and 4) ultrasonic contrast agents used to enhance myocardial imaging for the assessment of segmental wall motion. In the first group are amyl nitrate, a vasodilator, and methoxamine and phenylephrine, both vasopressors. The vasodilators of the second group are dipyridamole and adenosine. When combined with scintigraphic perfusion imaging or with echocardiographic assessment of segmental wall motion, these agents can detect single- or multiple-vessel coronary artery disease with sensitivity and specificity comparable to submaximal exercise. They are especially useful for preoperative risk assessment before noncardiac surgery. The sympathomimetic agents of the third group, dobutamine and arbutamine, increase myocardial contractility and heart rate, and dilate the peripheral vasculature. As with the vasodilators, when combined with nuclear or echocardiographic techniques they are equivalent to exercise in detection of coronary disease. They are especially useful in patients with bronchospastic disease and for assessment of myocardial viability. Agents from groups 2 and 3 have acceptable side-effect and safety profiles. The last group reviewed includes echocardiographic contrast agents that, in this investigative setting, are employed to enhance detection of segmental wall motion when used with agents from groups 2 and 3.