Maulik Shah

Predictive Value of the Index of Microcirculatory Resistance in Patients With ST-Segment Elevation Myocardial Infarction

OBJECTIVES The objective of this study is to evaluate the predictive value of the index of microcirculatory resistance (IMR) in patients undergoing primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI). BACKGROUND Despite adequate epicardial artery reperfusion, a number of patients with STEMI have a poor prognosis because of microvascular damage. Assessing the status of the microvasculature in this setting remains challenging. METHODS In 29 patients after primary PCI for STEMI, IMR was measured with a pressure sensor/thermistor-tipped guidewire. The Thrombolysis In Myocardial Infarction (TIMI) myocardial perfusion grade, TIMI frame count, coronary flow reserve, and ST-segment resolution were also recorded. RESULTS The IMR correlated significantly with the peak creatinine kinase (CK) (R = 0.61, p = 0.0005) while the other measures of microvascular dysfunction did not. In patients with an IMR greater than the median value of 32 U, the peak CK was significantly higher compared with those having values <or=32 U (3,128 +/- 1,634 ng/ml vs. 1,201 +/- 911 ng/ml, p = 0.002). The IMR correlated significantly with 3-month echocardiographic wall motion score (WMS) (R = 0.59, p = 0.002) while the other measures of microvascular function did not. The WMS at 3-month follow-up was significantly worse in the group with an IMR >32 U compared with <or=32 U (28 +/- 7 vs. 20 +/- 4, p = 0.001). On multivariate analysis, IMR was the strongest predictor of peak CK and 3-month WMS. The IMR was the only significant predictor of recovery of left ventricular function on the basis of the percent change in WMS (R = 0.50, p < 0.01). CONCLUSIONS Compared to standard measures, IMR appears to be a better predictor of microvascular damage after STEMI, both acutely and in short term follow-up.

Prognostic Value of the Index of Microcirculatory Resistance Measured After Primary Percutaneous Coronary Intervention

Background— Most methods for assessing microvascular function are not readily available in the cardiac catheterization laboratory. The aim of this study is to determine whether the Index of Microcirculatory Resistance (IMR), measured at the time of primary percutaneous coronary intervention, is predictive of death and rehospitalization for heart failure. Methods and Results— IMR was measured immediately after primary percutaneous coronary intervention in 253 patients from 3 institutions with the use of a pressure–temperature sensor wire. The primary end point was the rate of death or rehospitalization for heart failure. The prognostic value of IMR was compared with coronary flow reserve, TIMI myocardial perfusion grade, and clinical variables. The mean IMR was 40.3±32.5. Patients with an IMR >40 had a higher rate of the primary end point at 1 year than patients with an IMR ⩽40 (17.1% versus 6.6%; P=0.027). During a median follow-up period of 2.8 years, 13.8% experienced the primary end point and 4.3% died. An IMR >40 was associated with an increased risk of death or rehospitalization for heart failure (hazard ratio [HR], 2.1; P=0.034) and of death alone (HR, 3.95; P=0.028). On multivariable analysis, independent predictors of death or rehospitalization for heart failure included IMR >40 (HR, 2.2; P=0.026), fractional flow reserve ⩽0.8 (HR, 3.24; P=0.008), and diabetes mellitus (HR, 4.4; P<0.001). An IMR >40 was the only independent predictor of death alone (HR, 4.3; P=0.02). Conclusions— An elevated IMR at the time of primary percutaneous coronary intervention predicts poor long-term outcomes.

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 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 (IMRapp), which does not adjust for collateral flow, and the true IMR (IMRtrue), 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 IMRtrue (mean difference=0.8±11.7, P=0.675). IMRapp was higher pre-PCI compared with post-PCI (mean difference=10.0±14.5, P<0.001). IMRapp was higher than IMRtrue (mean difference=9.3±14.2, P<0.001), and the difference between the IMRapp and IMRtrue became greater with decreasing fractional flow reserve and increasing coronary wedge pressure. Pre-PCI fractional flow reserve correlated modestly with IMRapp (r=−0.33, P=0.03), but not IMRtrue (r=0.26, P=0.10). Conclusions— Coronary microcirculatory resistance is independent of functional epicardial stenosis severity when collateral flow is taken into account.

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.

First US experience following FDA approval of the ABBOTT vascular bioresorbable vascular scaffold for the treatment of coronary artery disease

Drug eluting stents are considered the “gold standard” for the percutaneous treatment of coronary artery disease. Recent publications have suggested that a reasonable alternative, in well selected cases, may be the ABSORBTM bioresorbable vascular scaffold (BVS) stent.

Impingement of Left Main Ostium After Device Occlusion of Paravalvular Leak Post-Transcatheter Aortic Valve Replacement

An 83-year-old woman presented with recurrent heart failure 2 months after transcatheter aortic valve replacement (TAVR) with a Sapien 23-mm valve (Edwards Lifesciences, Irvine, California). Echocardiography demonstrated severe paravalvular leak (PVL). A 6-F multipurpose guide was advanced across

Response to Letter Regarding Article, “Prognostic Value of the Index of Microcirculatory Resistance Measured After Primary Percutaneous Coronary Intervention”

We thank Dr Poullis for his interest in our article. The index of microcirculatory resistance (IMR) is not a ratio like coronary flow reserve but is defined as pressure divided by flow during maximal hyperemia and therefore is a measure of the minimal achievable microvascular resistance. We and others have published articles on the clear relationship between IMR and cardiac biomarker elevation in the setting of ST-segment–elevation myocardial infarction.1–3 These studies have demonstrated that patients with higher IMR values immediately after primary percutaneous intervention for ST-segment–elevation myocardial infarction have higher levels of cardiac biomarkers, greater degrees of microvascular dysfunction on noninvasive imaging, and less recovery of left ventricular function over time. Measuring IMR in the nonculprit vessels …