Ross McGeoch

Validation of Magnetic Resonance Myocardial Perfusion Imaging With Fractional Flow Reserve for the Detection of Significant Coronary Heart Disease

Background— Magnetic resonance myocardial perfusion imaging (MRMPI) has a number of advantages over the other noninvasive tests used to detect reversible myocardial ischemia. The majority of previous studies have generally used quantitative coronary angiography as the gold standard to assess the accuracy of MRMPI; however, only an approximate relationship exists between stenosis severity and functional significance. Pressure wire–derived fractional flow reserve (FFR) values <0.75 correlate closely with objective evidence of reversible ischemia. Accordingly, we have compared MRMPI with FFR. Methods and Results— One hundred three patients referred for investigation of suspected angina underwent MRMPI with a 1.5-T scanner. The stress agent was intravenous adenosine (140 &mgr;g · kg−1 · min−1), and the first-pass bolus contained 0.1 mmol/kg gadolinium. In the following week, coronary angiography with pressure wire studies was performed. FFR was recorded in all patent major epicardial coronary arteries, with a value <0.75 denoting significant stenosis. MRMPI scans, analyzed by 2 blinded observers, identified perfusion defects in 121 of 300 coronary artery segments (40%), of which 110 had an FFR <0.75. We also found that 168 of 179 normally perfused segments had an FFR ≥0.75. The sensitivity and specificity of MRMPI for the detection of functionally significant coronary heart disease were 91% and 94%, respectively, with positive and negative predictive values of 91% and 94%. Conclusion— MRMPI can detect functionally significant coronary heart disease with excellent sensitivity, specificity, and positive and negative predictive values compared with FFR.

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.

The index of microcirculatory resistance measured acutely predicts the extent and severity of myocardial infarction in patients with ST-segment elevation myocardial infarction.

OBJECTIVES This study investigated the relationship between the index of microcirculatory resistance (IMR) with myocardial injury and microvascular obstruction (MVO) assessed by contrast-enhanced cardiac magnetic resonance (ceCMR) imaging in a broad range of ST-segment elevation myocardial infarction (STEMI) patients undergoing emergency percutaneous coronary intervention (PCI). BACKGROUND Contrast-enhanced cardiac magnetic resonance imaging is the gold standard for assessment of microvascular obstruction (MVO), left ventricular (LV) ejection fraction, and infarct volumes in ST-segment elevation myocardial infarction (STEMI). However, ceCMR is not available acutely. The index of microcirculatory resistance is a simple invasive measure of microvascular function available at the time of emergency PCI. We investigated the relationship between IMR with myocardial injury and MVO assessed by ceCMR in STEMI patients undergoing emergency PCI. METHODS Fifty-seven patients with STEMI were included and 53 (93%) and 47 (82%) patients had complete ceCMR scans 2 days and 3 months following MI, respectively. Microvascular obstruction was defined as a dark core of hypoenhancement within the area of hyperenhanced infarct tissue 10 to 15 min following intravenous gadolinium (0.1 mmol/kg). RESULTS The median IMR (interquartile range [IQR]) was 35 (24 to 63) U. Twenty-seven patients (46%) had MVO. We found that IMR (median [IQR]) was higher in patients with MVO (38 [29 to 55] U) than in patients without MVO (27 [18 to 36] U); p = 0.003). The index of microcirculatory resistance was a negative multivariable predictor of LV ejection fraction, (p < or = 0.001) and infarct volume (p = 0.01) on the ceCMR scan 2 days after MI, and IMR was a multivariable predictor of LV ejection fraction (p = 0.028) and infarct volume (p = 0.048) at 3 months. CONCLUSIONS The index of microcirculatory resistance measured acutely was higher in patients with MVO on ceCMR, and IMR independently predicted LV function and infarct volume. This easily measured physiological parameter provides important prognostic information at the time of emergency PCI.

Bright-Blood T2-Weighted MRI Has Higher Diagnostic Accuracy Than Dark-Blood Short Tau Inversion Recovery MRI for Detection of Acute Myocardial Infarction and for Assessment of the Ischemic Area at Risk and Myocardial Salvage

Background— T2-Weighted MRI reveals myocardial edema and enables estimation of the ischemic area at risk and myocardial salvage in patients with acute myocardial infarction (MI). We compared the diagnostic accuracy of a new bright-blood T2-weighted with a standard black blood T2-weighted MRI in patients with acute MI. Methods and Results— A breath-hold, bright-blood T2-weighted, Acquisition for Cardiac Unified T2 Edema pulse sequence with normalization for coil sensitivity and a breath-hold T2 dark-blood short tau inversion recovery sequence were used to depict the area at risk in 54 consecutive acute MI patients. Infarct size was measured on gadolinium late contrast enhancement images. Compared with dark-blood T2-weighted MRI, consensus agreements between independent observers for identification of myocardial edema were higher with bright-blood T2-weighted MRI when evaluated per patient (P<0.001) and per segment of left ventricle (P<0.001). Compared with bright-blood T2-weighted MRI, dark-blood T2-weighted MRI underestimated the area at risk compared with infarct size (P<0.001). The 95% limits of agreement for interobserver agreements for the ischemic area at risk and myocardial salvage were wider with dark-blood T2-weighted MRI than with bright-blood T2-weighted MRI. Bright blood enabled more accurate identification of the culprit coronary artery with correct identification in 94% of cases compared with 61% for dark blood (P<0.001). Conclusions— Bright-blood T2-weighted MRI has higher diagnostic accuracy than dark-blood T2-weighted MRI. Additionally, dark-blood T2-weighted MRI may underestimate area at risk and myocardial salvage.

Bright Blood T2 Weighted MRI Has Higher Diagnostic Accuracy Than Dark Blood STIR MRI for Detection of Acute Myocardial Infarction and for Assessment of the Ischemic Area-at-Risk and Myocardial Salvage

Background— T2-Weighted MRI reveals myocardial edema and enables estimation of the ischemic area at risk and myocardial salvage in patients with acute myocardial infarction (MI). We compared the diagnostic accuracy of a new bright-blood T2-weighted with a standard black blood T2-weighted MRI in patients with acute MI. Methods and Results— A breath-hold, bright-blood T2-weighted, Acquisition for Cardiac Unified T2 Edema pulse sequence with normalization for coil sensitivity and a breath-hold T2 dark-blood short tau inversion recovery sequence were used to depict the area at risk in 54 consecutive acute MI patients. Infarct size was measured on gadolinium late contrast enhancement images. Compared with dark-blood T2-weighted MRI, consensus agreements between independent observers for identification of myocardial edema were higher with bright-blood T2-weighted MRI when evaluated per patient (P<0.001) and per segment of left ventricle (P<0.001). Compared with bright-blood T2-weighted MRI, dark-blood T2-weighted MRI underestimated the area at risk compared with infarct size (P<0.001). The 95% limits of agreement for interobserver agreements for the ischemic area at risk and myocardial salvage were wider with dark-blood T2-weighted MRI than with bright-blood T2-weighted MRI. Bright blood enabled more accurate identification of the culprit coronary artery with correct identification in 94% of cases compared with 61% for dark blood (P<0.001). Conclusions— Bright-blood T2-weighted MRI has higher diagnostic accuracy than dark-blood T2-weighted MRI. Additionally, dark-blood T2-weighted MRI may underestimate area at risk and myocardial salvage.

Vasodilatory Capacity of the Coronary Microcirculation is Preserved in Selected Patients With Non–ST-Segment–Elevation Myocardial Infarction

Background—The use of fractional flow reserve in patients with non–ST-segment–elevation myocardial infarction (NSTEMI) is a controversial issue. We undertook a study to assess the vasodilatory capacity of the coronary microcirculation in patients with NSTEMI when compared with a model of preserved microcirculation (stable angina [SA] cohort: culprit and nonculprit vessel) and acute microcirculatory dysfunction (ST-segment–elevation myocardial infarction [STEMI] cohort). We hypothesized that the vasodilatory response of the microcirculation would be preserved in NSTEMI. Methods and Results—A total of 140 patients undergoing single vessel percutaneous coronary intervention were included: 50 stable angina, 50 NSTEMI, and 40 STEMI. The index of microvascular resistance (IMR), fractional flow reserve, and coronary flow reserve were measured before stenting in the culprit vessel and in an angiographically normal nonculprit vessel in patients with SA. The resistive reserve ratio, a measure of the vasodilatory capacity of the microcirculation and calculated using the equation: baseline resistance index (TmnBase×PaBase[PdBase–Pw/PaBase–Pw])–IMR/IMR, where TmnBase referred to nonhyperemic transit time; PaBase and PdBase, the nonhyperemic aortic and distal coronary pressures, respectively; and Pw referred to the coronary wedge pressure, was also measured. Troponin was also measured ⩽24 hours after percutaneous coronary intervention. The resistive reserve ratio was significantly lower in the STEMI patients compared with the stable angina patients both culprit and nonculprit vessel (STEMI, 1.7 versus SA culprit, 2.8; P⩽0.001 and SA nonculprit, 2.9; P<0.0001) and compared with NSTEMI patients (NSTEMI, 2.46; P⩽0.001). The resistive reserve ratio was similar in stable angina and NSTEMI patients (P=0.6). IMR was significantly higher pre-PCI in STEMI compared with SA and NSTEMI (IMR STEMI, 36.51 versus IMR NSTEMI, 22.73 [P=0.01] versus IMR SA, 18.26 [P<0.0001]). However, there was no significant difference in IMR pre-PCI between NSTEMI and SA (IMR NSTEMI, 22.73; IMR SA, 18.26 [P=0.1]). Conclusions—The vasodilatory capacity of the microcirculation is preserved in selected patients with NSTEMI. The clinical use of fractional flow reserve in the culprit vessel may be preserved in selected patents with NSTEMI.

Diagnostic utility of cardiac magnetic resonance imaging in STEMI survivors after emergency PCI

emergency PCI R.J. McGeoch ⁎, A.R. Payne , R. Woodward , A. Saul , T. Steedman , J. Foster , S. Hood , E. Peat , M.M. Lindsay , M.C. Petrie , A.P. Rae , M. McEntegart , H. Eteiba , N. Tzemos , K.G. Oldroyd , C. Berry a,b,c a Glasgow Heart and Lung Institute, Golden Jubilee National Hospital, Clydebank, United Kingdom b Department of Cardiology Western Infirmary, Glasgow, United Kingdom c BHF Glasgow Cardiovascular Research Centre, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom

Meta-Analysis of the Index of Microvascular Resistance in Acute STEMI Using Incomplete Data

The index of microvascular resistance (IMR) is a direct, invasive test of coronary microvascular resistance [(1)][1]. When measured in the culprit coronary artery after emergency percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI), IMR is well established

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 …

128 Bright blood t2 weighted MRI has higher diagnostic precision and accuracy than dark blood stir MRI for assessment of the ischaemic area-at-risk and myocardial salvage in acute myocardial infarction

Background T2-weighted MRI reveals myocardial oedema and enables estimation of the ischaemic area-at-risk and myocardial salvage in patients with acute myocardial infarction (MI). We compared the diagnostic accuracy of a new bright blood T2-weighted with a standard black blood T2-weighted MRI in patients with acute MI. Methods A breath hold bright blood T2-weighted ACUTE pulse sequence with normalisation for coil sensitivity and a breath hold T2 dark blood short τ inversion recovery (STIR) sequence were used to depict the area-at-risk in 54 consecutive acute MI patients. Infarct size was measured on gadolinium late contrast enhancement images. Results Compared with dark blood T2-weighted MRI, consensus agreements between independent observers for identification of myocardial oedema were higher with bright blood T2 -weighted MRI when evaluated per patient (p<0.001) and per segment of left ventricle (p<0.001). Compared to bright blood T2-weighted MRI, dark blood T2-weighted MRI under-estimated the area-at-risk compared to infarct size (p<0.001). The 95% limits of agreement for inter-observer agreements for the ischaemic area-at-risk and myocardial salvage were wider with dark blood T2-weighted MRI than with bright blood T2-weighted MRI. Bright blood enabled more accurate identification of the culprit coronary artery with correct identification in 94% of cases compared to 61% for dark blood (p<0.001). Conclusion Bright blood T2-weighted MRI has higher diagnostic accuracy than dark blood T2-weighted MRI. Additionally, dark blood T2-weighted MRI may underestimate area-at-risk and myocardial salvage.