Effect of systemic blood pressure on microcollateral circulation evaluated by real-time contrast echocardiography

BACKGROUND

In acute myocardial infarction, residual collateral-derived myocardial blood flow (CBF) within the ischemic area is one of the major determinants of infarct size. Management of systemic blood pressure (sBP) related to maintain collateral circulation is still difficult. The aim of this study was to reveal the influence of sBP on the rescue of area at risk by collateral circulation.

METHODS

Real-time myocardial contrast echocardiography just after the onset of complete occlusion of the left circumflex coronary artery was performed in collateral-rich open-chest dogs. The video intensity of the ischemic area was evaluated during the occlusion and the CBF (A x beta) was calculated from a replenishment curve: y = A (1 - e(-beta t)). To analyze the effect of sBP on the collateral circulation, sBP was altered by infusion of nitroglycerin or etilefrine hydrochloride. To evaluate the defect size (%DS), every end-systolic myocardial contrast echocardiography image after left circumflex coronary artery occlusion was converted into binary images using custom offline software.

RESULTS

The %DS increased and CBF slightly decreased at low sBP. The %DS decreased and CBF increased at high sBP. At excessively high sBP, %DS increased and CBF decreased again.

CONCLUSION

Real-time myocardial contrast echocardiography, which is a useful noninvasive method to evaluate the collateral perfusion quantitatively, has a crucial role in the decision of patient treatment and management strategy of acute myocardial infarction.

Impact of the Coronary Flow Reduction at Rest on Myocardial Perfusion and Functional Indices Derived from Myocardial Contrast and Strain Echocardiography

BACKGROUND

The severity of the coronary flow reduction that corresponds to myocardial perfusion and functional abnormalities remains unclear. We estimated the impact of various severities of flow-limiting coronary stenosis at rest on myocardial perfusion and functional indices from myocardial contrast echocardiography and tissue strain imaging and characterized the relationship between both the indices.

METHODS

Four levels of flow-limiting stenoses (slight, mild, moderate, severe) of the left circumflex coronary artery were examined in 10 open-chest dogs. In the left circumflex coronary artery area, plateau videointensity and time to plateau (TP) of the replenishment curve from myocardial contrast echocardiography were calculated for perfusion analysis, and peak systolic strain and postsystolic strain index (PSI) from tissue strain imaging were measured for functional analysis.

RESULTS

Plateau videointensity and peak systolic strain tended to decrease with increased severity of stenosis, although these differences did not reach the level of statistical significance. TP and PSI were significantly increased in the context of moderate (>or=30-<50%) and severe (>or=50%) flow reduction when compared to baseline values (TP, moderate 1.69 +/- 0.20 and severe 1.77 +/- 0.25 vs baseline 0.93 +/- 0.17, P < .01, respectively; PSI, moderate 0.96 +/- 0.15 and severe 1.28 +/- 0.32 vs baseline 0.59 +/- 0.18, P < .05 and P < .01, respectively). Further, TP and PSI were positively correlated with flow reduction (r = 0.81 and r = 0.84, P < .0001, respectively), and PSI was positively correlated with TP (r = 0.72, P < .0001).

CONCLUSIONS

In contrast to conventional indices, such as plateau videointensity and peak systolic strain, novel indices, such as TP and PSI, were both able to detect 30% or greater coronary flow reduction at rest.