REVIEW OF THE PUBLISHED LITERATURE WITH MCE USED FOR WALL MOTION EVALUATION
The use of rest MCE in the context of chest pain was evaluated in different studies either or both for WM and MP assessments. The studies that evaluated only MP were not included in our review.
Rinkevich et al. 1 studied the MCE in predicting events in pts with CP who presented to the ED with non ST-elevation at the ECG; in particular they analysed 1017 pts, assessing both regional WM and MP with MCE in addition to the standard ECG evaluation, with a mean follow-up of 7.7 months. Considering only rest WM data, which is the main purpose of the current review, 43 pts with normal WM had events and 249 events (85% of all events) took place in patients with rest WM abnormalities assessed with contrast.
On the multivariable Cox regression analysis, history of hypertension (P=0.028), ECG (P=0.0001), WM (P<0.0001), and MP (P<0.0001) were significant predictors of cardiac events. Abnormal WM increased the risk of events by five-fold when compared with normal WM (95% CI: 3.4–7.2), whereas abnormal MP increased the risk by only twofold
when compared with normal MP (95% CI: 1.5–2.7).
They concluded that early assessment of WM (and MP) on MCE added significant diagnostic and prognostic value to routine evaluation in pts presenting to the ED with suspected cardiac CP and no ST-segment elevation. There was no standard (without contrast) echocardiography included in the standard clinical comparison control, so that MCE for rest WM assessment was compared to clinical assessment and ECG only. Furthermore, Troponin assessment was not included in the study.
Tong et al. 2 compared WM and MP analysis with modified TIMI risk score (mTIMI, which is TIMI score not including troponin levels) in 957 pts presenting to the ED with CP and a nondiagnostic ECG. Cumulative pts outcomes were determined at three time points: early (within 24 hours), intermediate (up to 30 days), and late (>30 days). On the basis of their mTIMI or TIMI scores, pts were categorized as either low (score<2), intermediate (score of 3 or 4), or high (score >5) risk. The mTIMI score was unable to discriminate between intermediate- compared to high-risk pts at any follow-up time point, whereas only 2 of 523 pts with normal WM had an early primary event. WM evaluation provided incremental prognostic value over mTIMI scores for predicting intermediate and late events. But it should be emphasized that rest MCE WM was not assessed with very low mechanical index imaging but rather with harmonic low mechanical index, which has lower yield to detect WM abnormalities compared with very low mechanical index imaging. The full TIMI score could not improve upon these results at any follow-up time point.
Wei et al. 3 enrolled 1166 pts (cohort 1) with a validation cohort (cohort 2) of 720 pts; all pts presented to ED with CP lasting 30 minutes or more and there wasn’t any ST-segment elevation on the ECG. Wall motion (WM) and myocardial perfusion (MP) were separately assessed by MCE. Any abnormality or ST changes on ECG (odds ratio [OR] 2.5; 95% confidence interval [CI], 1.4-4.5, P = 0.002, and OR 2.9, 95% CI, 1.7-4.8, P < 0.001, respectively), abnormal WM with normal MP (OR 3.5, 95% CI, 1.8-6.5, P < 0.001), and abnormal WM with abnormal MP (OR 9.6, 95% CI, 5.8-16.0, P < 0.001), so that either or both WM and MP were found to be significant multivariate predictors of nonfatal myocardial infarction or cardiac death. Apparently, there was no comparison between WM assessed with MCE and without contrast, so that in this well-conducted study, there remains the clinical question whether contrast WM assessment is superior or not to standard WM assessment without contrast.
Kalvaitis et al. 4 explored the effect of time delay of the use of MCE in the ED. In particular 957 pts were enrolled, they presented to ED with CP and no ST-elevation at the ECG and were divided into 4 quartiles depending on the time between their last episode of CP and the MCE evaluation. Pts in quartile I had MCE during ongoing CP (time delay of 0 minutes). The time delays in quartiles II, III, and IV were 54 ± 44, 213 ± 54, and 556 ± 184 minutes, respectively (P < 0.001). In each quartile, pts with normal WM had the lowest incidence of events, whereas those with both abnormal WM and MP had the highest incidence of events. Pts with abnormal WM but normal MP had an intermediate event rate. They concluded that timing of MCE did not affect the ability to predict event rate at 24 hours in pts with CP. Again, it should be emphasized that rest MCE WM was not assessed with very low mechanical index imaging but rather with harmonic low mechanical index, which has lower capability to detect WM abnormalities compared with very low mechanical index imaging.
Wyrick et al. 5 analysed the cost-efficiency of MCE in 957 pts presenting to ED with CP and no ST-elevation at the ECG, but this analysis is most probably conducted on the same patient cohort studied by Kalvaitis et al,4 so we did not include it in our review.
Finally, Porter et al. 6 compared patient outcome after stress real-time MCE (RTMCE), using very-low mechanical index, versus conventional stress echo with low mechanical index and harmonic imaging (CSE). Outpatient and inpatient subjects admitted for chest pain with normal or equivocal troponin were referred for dobutamine or exercise stress echocardiography were prospectively randomized to either RTMCE or CSE. Definity contrast was used for CSE only when endocardial border delineation was inadequate (63% of studies). 2014 pts were evaluated with a mean follow-up of 2.6 years. An abnormal RTMCE was more frequently observed than an abnormal CSE at peak stress (p < 0.001), and more frequently resulted in revascularization (p = 0.004). Resting WM abnormalities were also more frequently seen with RTMCE (p < 0.01), and were an independent predictor of death/nonfatal MI (p = 0.005) for RTMCE, but not CSE. This is a signal that RTMCE, as now supported by European and American guidelines,7,8 is superior to standard contrast-echocardiography-using higher mechanical index (0.2-0.4) and harmonic imaging- to detect mild WM abnormalities.