Effects of dipyridamole on cardiac and systemic haemodynamics: real-time three-dimensional stress echo beyond regional wall motion

Dose-consistent dynamic SPECT

BACKGROUND

Coronary flow reserve (CFR) values measured by dynamic SPECT systems are typically consistent with other modalities (e.g., PET). However, large discrepancies are often observed for individual patients. Positioning of the region-of-interest (ROI), representing the arterial input function (AIF) could explain some of these discrepancies. We explored the possibility of positioning the ROI in a manner that evaluates its consistency with patient-based injected radiotracer doses.

METHODS

Dose-consistent dynamic SPECT methodology was introduced, and its application was demonstrated in a twenty-patient clinical study. The effect of various ROI positions was investigated and comparison to myocardial perfusion imaging was performed.

RESULTS

Mean AIF ratios were consistent with the injected dose ratios for all examined ROI positions. Good agreement (> 80%) between total perfusion deficit and CFR was found in the detection of obstructive CAD patients for all ROIs considered. However, for individual patients, significant dependence on ROI position was observed (altering CFR by typically 30%). The proposed methodology's uncertainty was evaluated (~ 7%) and found to be smaller than the variability due to choice of ROI position.

CONCLUSION

Dose-consistent dynamic SPECT may contribute to evaluating uncertainty of CFR measurements and may potentially decrease uncertainty by allowing improved ROI positioning for individual patients.

A case report of dipyridamole stress-induced ST depression progressing to ST-elevation myocardial infarction despite intravenous aminophylline: steal, spasm, or something else?

BACKGROUND

Dipyridamole stress is commonly used for myocardial perfusion imaging and is generally safe. Myocardial ischaemia can occasionally occur and is classically thought to be due to coronary steal as a result of redistribution of flow away from collateral dependent myocardium. Although ischaemia more commonly presents as electrocardiographic (ECG) ST depression and angina, ST-elevation myocardial infarction may occur as a very rare complication.

CASE SUMMARY

We report a case of a patient who developed chest pain and ST depression during dipyridamole infusion. The pain persisted despite intravenous aminophylline with new inferior ST elevation soon after. Coronary angiography showed subtotal right coronary artery occlusion with no collateral supply. The symptoms and ECG changes resolved after percutaneous coronary intervention.

DISCUSSION

Coronary steal may not fully account for our patient's presentation given the failure of aminophylline and absent angiographic collaterals. Vasospasm may be triggered by dipyridamole and can directly cause ischaemia or provoke rupture of an unstable plaque. Augmentation of cardiac energetics during vasodilator stress may also play a role.

Prediction of long-term ischemic events by noninvasively assessed coronary flow reserve

BACKGROUND

Coronary flow reserve (CFR) by adenosine echocardiography in left anterior descending (LAD) or posterior descending coronary arteries may predict clinical outcome.

METHODS

We used models accounting (Cox's model) or not (logistic regression and neural network) for time to event and either considered (forced models) or not (stepwise logistic regression and neural network models) all among 21 covariates to predict 1-year composite events after LAD CFR.

RESULTS

There were 553 consecutive patients with coronary artery disease (CAD): 89 patients had also posterior descending CFR. During 1-year follow-up 328 patients were event-free, 35 had composite ischemic events and 190 underwent short-term revascularization. LAD and posterior descending CFR (respectively, 1.53 ± 0.83, N = 225 and 1.84 ± 0.80, N = 42) were significantly (P < 0.0001) lower in patients with events (or with revascularization following CFR measurement) than in those without (respectively, 3.13 ± 0.84, N = 328, and 2.53 ± 0.72, N = 47). Using LAD CFR as a continuous covariate, by both forced Cox's and logistic regression, coefficients (t values, respectively, -14.11 and -10.19) were significant (both P < 0.00001) to predict outcome. Global predictive accuracies by neural network, adopting a receiver operating characteristic areas under the curve (ROC) assessment, were excellent (>0.91) and the role of LAD CFR among predictors was overwhelming. Other indices of myocardial ischemia and the presence of coronary stenoses or previous infarction did not modify the multivariable predictive role of LAD CFR. When patients with revascularization were discounted, the LAD CFR predictive role was the same.

CONCLUSIONS

Thus, adenosine echocardiography-based LAD CFR predicts 1-year composite ischemic events in patients with CAD, independent of the multivariable model adopted. Posterior descending CFR also has a role.