Primary coronary microvascular dysfunction and poor coronary collaterals predict post-percutaneous coronary intervention cardiac necrosis

Evaluation of microcirculatory protection in percutaneous revascularisation: A stent implantation technique and device comparison

BACKGROUND

Coronary microvascular dysfunction (CMD) after percutaneous coronary intervention (PCI) is prognostically important and may also be a cause of persistent angina. The stent balloon inflation technique or material properties may influence the degree of CMD post-PCI.

METHODS

Thirty-six patients with stable angina attending for elective PCI were randomized to either slow drug eluting stent (DES) implantation technique (DES slow group): +2 atm. every 5 s., maintained for a further 30 s or a standard stent implantation technique (DES std group): rapid inflation and deflation. PressureWire X with thermodilution at rest and hyperemia and optical coherence tomography (OCT) were performed pre- and post-PCI. Combined primary endpoints were changes in index of microvascular resistance (delta IMR) and coronary flow reserve (delta CFR) following PCI. The secondary endpoints included differences in cardiac troponin I (delta cTnI) at 6 h post-PCI, Seattle angina questionnaire (SAQ) at 1, 3, 6, and 12 months and OCT measures of stent results immediately post-PCI and at 3 months.

RESULTS

Both groups were well matched, with similar baseline characteristics and OCT-defined plaque characteristics. Delta IMR was significantly better in the DES slow PCI arm with a median difference of -4.14 (95% CI -10.49, -0.39, p = 0.04). Delta CFR was also numerically higher with a median difference of 0.47 (95% CI -0.52, 1.31, p = 0.46). This did not translate to improved delta median cTnI (1.5 (34.8) vs. 0 (27.5) ng/L, p = 0.75) or median SAQ score at 3 months, (85 (20) vs. 95 (17.5), p = 0.47).

CONCLUSION

Slow stent implantation is associated with less CMD after elective PCI in patients with stable angina.

Current developments and future applications of intracoronary hemodynamics

Intracoronary hemodynamic assessment of the physiologic significance of coronary lesions improves clinical outcomes in patients with coronary artery disease. Coronary flow velocity reserve, fractional flow reserve, instantaneous wave-free ratio, and index of microcirculatory resistance utilize sensor-mounted guidewires to approximate coronary flow. Coronary flow velocity reserve and fractional flow reserve rely on pharmacologic administration of adenosine to achieve hyperemia and diagnose epicardial lesion severity. As an adenosine-free index, the instantaneous wave-free ratio utilizes a wave-free period in the mid-late diastole during which resistance is constant and low to assess lesion significance. The index of microcirculatory resistance combines hyperemic pressure measurements with thermodilution to quantify microvascular resistance. We review the physiology, clinical trials, and clinical applications of these invasive hemodynamic assessments.

Calculation of the index of microcirculatory resistance without coronary wedge pressure measurement in the presence of epicardial stenosis

OBJECTIVES

This study sought to investigate a novel method to calculate the index of microcirculatory resistance (IMR) in the presence of significant epicardial stenosis without the need for balloon dilation to measure the coronary wedge pressure (P(w)).

BACKGROUND

The IMR provides a quantitative measure of coronary microvasculature status. However, in the presence of significant epicardial stenosis, IMR calculation requires incorporation of the coronary fractional flow reserve (FFR(cor)), which requires balloon dilation within the coronary artery for P(w) measurement.

METHODS

A method to calculate IMR by estimating FFR(cor) from myocardial FFR (FFR(myo)), which does not require P(w) measurement, was developed from a derivation cohort of 50 patients from a single institution. This method to calculate IMR was then validated in a cohort of 72 patients from 2 other different institutions. Physiology measurements were obtained with a pressure-temperature sensor wire before coronary intervention in both cohorts.

RESULTS

From the derivation cohort, a strong linear relationship was found between FFR(cor) and FFR(myo) (FFR(cor) = 1.34 × FFR(myo) - 0.32, r(2) = 0.87, p < 0.001) by regression analysis. With this equation to estimate FFR(cor) in the validation cohort, there was no significant difference between IMR calculated from estimated FFR(cor) and measured FFR(cor) (21.2 ± 12.9 U vs. 20.4 ± 13.6 U, p = 0.161). There was good correlation (r = 0.93, p < 0.001) and agreement by Bland-Altman analysis between calculated and measured IMR.

CONCLUSIONS

The FFR(cor), and, by extension, microcirculatory resistance can be derived without the need for P(w). This method enables assessment of coronary microcirculatory status before or without balloon inflation, in the presence of epicardial stenosis.

Coronary microvascular dysfunction in the clinical setting: from mystery to reality

Far more extensive than the epicardial coronary vasculature that can be visualized angiographically is the coronary microcirculation, which foregoes routine imaging. Probably due to the lack of techniques able to provide tangible evidence of its crucial role, the clinical importance of coronary microvascular dysfunction is not fully appreciated. However, evidence gathered over the last several decades indicates that both functional and structural abnormalities of the coronary microvasculature can lead to myocardial ischaemia, often comparable with that caused by obstructive coronary artery disease. Indeed, a marked increase in coronary microvascular resistance can impair coronary blood flow and trigger angina pectoris, ischaemic ECG shifts, and myocardial perfusion defects, and lead to left ventricular dysfunction in patients who otherwise have patent epicardial coronary arteries. This condition--often referred to as 'chest pain with normal coronary arteries' or 'cardiac syndrome X'--encompasses several pathogenic mechanisms involving the coronary microcirculation. Of importance, coronary microvascular dysfunction can occur in conjunction with several other cardiac disease processes. In this article, we review the pathogenic mechanisms leading to coronary microvascular dysfunction and its diagnostic assessment, as well as the different clinical presentations and prognostic implications of microvascular angina. As such, this review aims to remove at least some of the mystery surrounding the notion of coronary microvascular dysfunction and to show why it represents a true clinical entity.

The index of microcirculatory resistance predicts myocardial infarction related to percutaneous coronary intervention

BACKGROUND

Periprocedural myocardial infarction (MI) occurs in a significant proportion of patients undergoing percutaneous coronary intervention (PCI) and portends poor outcomes. Currently, no clinically applicable method predicts periprocedural MI in the cardiac catheterization laboratory before it occurs. We hypothesized that impaired baseline coronary microcirculatory reserve, which reduces the ability to tolerate ischemic insults, is a risk for periprocedural MI and that the index of microcirculatory resistance (IMR) measured during PCI can predict occurrence of periprocedural MI.

METHODS AND RESULTS

Consecutive patients undergoing elective PCI of a single lesion in the left anterior descending coronary artery were recruited. A pressure-temperature sensor wire was used to measure IMR before PCI. Of the 50 patients studied, 10 had periprocedural MI. From binary logistic regression analyses of all clinical, procedural, and physiological parameters, univariable predictors of periprocedural MI were pre-PCI IMR (P=0.003) and the number of stents used (P=0.039). Pre-PCI IMR was the only independent predictor in bivariable regression analyses performed by adjusting for each available covariate one at a time (all P≤0.02). Pre-PCI IMR ≥27 U had 80.0% sensitivity and 85.0% specificity for predicting periprocedural MI (C statistic, 0.80; P=0.003). Pre-PCI IMR ≥27 U was independently associated with a 23-fold risk of developing periprocedural MI (odds ratio, 22.7; 95% CI, 3.8-133.9).

CONCLUSIONS

These data suggest that the status of the coronary microcirculation plays a role in determining susceptibility toward periprocedural MI at the time of elective PCI. The IMR can predict subsequent risk of developing myocardial necrosis and may guide adjunctive prevention strategies.

Coronary microcirculatory resistance is independent of epicardial stenosis

BACKGROUND

Recent studies show that coronary microcirculatory impairment is an independent predictor of poor outcomes in patients with cardiovascular disease. However, controversy exists over whether microcirculatory resistance, a measure of coronary microcirculatory status, is dependent on epicardial stenosis severity. Previous studies demonstrating that microcirculatory resistance is dependent on epicardial stenosis severity have not accounted for collateral flow in their measurement of microcirculatory resistance. We investigated whether the index of microcirculatory resistance is independent of epicardial stenosis by comparing the index of microcirculatory resistance (IMR) levels in patients before and after percutaneous coronary intervention (PCI).

METHODS AND RESULTS

Consecutive patients undergoing elective PCI of the left anterior descending artery were recruited. Patients who developed periprocedural myocardial infarction were excluded. A pressure-temperature sensor wire was used to measure the apparent IMR (IMR(app)), which does not adjust for collateral flow, and the true IMR (IMR(true)), which incorporates wedge pressure measurement to account for collateral flow, before and after PCI. In 43 patients, there was no difference between pre- and post-PCI IMR(true) (mean difference=0.8±11.7, P=0.675). IMR(app) was higher pre-PCI compared with post-PCI (mean difference=10.0±14.5, P<0.001). IMR(app) was higher than IMR(true) (mean difference=9.3±14.2, P<0.001), and the difference between the IMR(app) and IMR(true) became greater with decreasing fractional flow reserve and increasing coronary wedge pressure. Pre-PCI fractional flow reserve correlated modestly with IMR(app) (r=-0.33, P=0.03), but not IMR(true) (r=0.26, P=0.10).

CONCLUSIONS

Coronary microcirculatory resistance is independent of functional epicardial stenosis severity when collateral flow is taken into account.