The index of microvascular resistance measured acutely predicts infarct severity and left ventricular function at 3 months in patients with ST segment elevation myocardial infarction
McGeoch RJ12, Watkins S1, Berry C1,2, Davie A1, Byrne J1, Hillis WS1, Lindsay MM1, Robb SD1, Dargie HJ1, Oldroyd
KG1
1Department of Cardiology, Golden Jubilee National Hospital2BHF Glasgow Cardiovascular Research Centre, Faculty of Medicine,
University of Glasgow
No conflicts of interest
Background
Immediate aim of reperfusion therapy in STEMI is to achieve patency of infarct related artery
TIMI grade 3 flow achieved 90% of patients1
Despite this a significant proportion of patients do not achieve complete myocardial perfusion
1. Keeley EC, et al Lancet 2003
Microvascular obstruction in STEMI
Can effect up to 50 % of patients who undergo successful reperfusion
Studies have shown MVO is associated with higher adverse clinical events including heart failure and death.1,2
No currently agreed gold standard for assessment of MVO in the cath lab
1. Hombach et al Eur Heart J 20052. Wu et al Circulation 1998
Index of microcirculatory resistance (IMR) using the RADITM
pressure and temperature wire Performed at the time of PCI.
Numerical value for myocardial resistance.
In vivo and in vitro validation1,2
Independent of variations in haemodynamic states.3
IMR = Pd x Tmn1
1. Aarnoudse W et al Catheter Cardiovasc Interv 20042. Fearon W et al Circulation 20043. Ng MKC, Yeung AC, Fearon WF Circulation 2006
Thermodilution derived mean transit times at rest and hyperaemia
Assessment of MVO and LV function by cardiac MRI
CMR allows accurate assessment of LV volumes, ejection fraction and visualisation of MVO and infarct size1
Cannot be performed at the time of emergency PCI when potential interventions would be of maximal benefit
1. Task force of the ESC Eur Heart J. 1998
Anterior STEMI
Anterior MI – Late gadolinium contrast
MVO absent MVO present
Hypothesis Microvascular function measured invasively
at the time of reperfusion will predict the severity of myocardial injury subsequently revealed by MRI.
Specifically, we aimed to determine whether IMR calculated immediately after successful epicardial reperfusion in patients presenting with STEMI could be used as a predictor of MVO and myocardial damage using ceCMR as the gold standard comparison.
Flow Diagram of the Study
57 patients with STEMI treated by emergency PCI
Initial consent
PCI with pressure wire assessment
Re-consent
ceCMR at 24-48 hours
ceCMR at 3 months
Methods: physiological assessment PCI performed in line with current
international guidelines.
Pressure wire (Radi Medical Systems, Uppsala, Sweden) was used as the primary guide-wire.
IMR calculated post procedure during maximal hyperaemia (adenosine 140 mcg/kg/min)
Mean aortic and distal coronary pressures were recorded during maximal hyperemia.
Methods: ceCMR
1.5 T Siemens Avanto
ceCMR at 24-48h
ceCMR at 3 months
Contrast agent: gadolinium-DTPA
Demographics
0
10
20
30
40
50
60
70
80
90
100 MaleSmokerDiabetesHypertensionLipidsAspirinClopidogrelThrombectomyGP2b3aACE IBeta BlockerStatin
Mean age (range) : 58 (32-83)
Results: ceCMR
Successful physiological measurements where achieved in all patients
53/57 had complete baseline ceCMR
47/57 had complete follow up scans
Results: MVO
0102030405060708090
MVO present(n=27)
MVO absent(n=26)
MaleSmokerDiabeticHypertensionLipidsGP2b3aThromectomy
Results: MVO
MVO present (n=27)
MVO absent (n=26)
P value
Mean age (SD)
57 (10.1) 58 (11.6)
Median IMR (IQR)
38.1
(29 – 55)
26.9
(18 – 36)
0.003
Predictors of LVEF at baseline
Univariate R2 value
P value Multivariate analysis
Smoking 5.4 0.08 P = 0.29
Diabetes 12.1 0.008 p = 0.03
IMR 29.1 <0.001 p = <0.001
Predictors of LVEF at 3 months
Univariate R2 value
P value Multivariate analysis
Lipidaemia 12 0.01 P = 0.017
GP2b3a inhibitor
10.8 0.02 P = 0.014
IMR 14.5 0.007 P = 0.004
Predictors of Infarct Volumes at Baseline
Univariate R2 value
P value Multivariate analysis
Lipidaemia 3.6 0.18 P = 0.16
GP2b3a inhibitor
5.3 0.09 P = 0.12
IMR 18.6 0.001 P = 0.002
Predictors of Infarct Volumes at 3 months
Univariate R2 value
P value Multivariate analysis
Lipidaemia 9.1 0.04 P = 0.07
GP2b3a inhibitor
5.5 0.11 P = 0.09
IMR 15.6 0.006 P = 0.008
Conclusions
IMR is significantly higher in those with MVO as assessed by ceCMR
IMR measured acutely at the end of emergency PCI independently predicts infarct size and LV function in the longer term
Potentially this relatively simple wire based technique could be used at the time of PCI as a marker of MVO and myocardial damage
Acknowledgements
Chief Scientist Office Scotland
Robertson Centre for Biostatistics, University of Glasgow
Correlation between both methods of IMR calculation
IMR vs. LVEF at baseline
IMR
LVEF
5.55.04.54.03.53.02.52.0
80
70
60
50
40
30
Scatterplot of LVEF vs IMR
IMR vs. Peak troponin I
Results: MVOIM
R
MVO absentMVO present
80
70
60
50
40
30
20
10
0
P = 0.003
Predictors of LVEF at baseline
Univariate R 2 value
P value Multivariate analysis
Age 2.6 0.23Male 2.6 0.23
Smoking 5.4 0.08 P = 0.29Hypercholestorelae
mia0.1 0.94
Hypertension 0.4 0.63Diabetes 12.1 0.008 p = 0.03
GP2b3a inhibitor 3.7 0.15Thrombectomy
catheter1.9 0.31
IMR 29.1 <0.001 p = <0.001CFIp 0.7 0.54
Wedge pressure 0.1 0.93
Predictors of LVEF at 3 months
Univariate R 2 value
P value Multivariate analysis
Age 0 0.97Male 2.0 0.34
Smoking 1.7 0.37Hypercholestorelae
mia12 0.01 P = 0.017
Hypertension 0.7 0.56Diabetes 2.0 0.34
GP2b3a inhibitor 10.8 0.02 P = 0.014Thrombectomy
catheter3.2 0.22
IMR 14.5 0.007 P = 0.004CFIp 0.1 0.81
Wedge pressure 0 0.95
Predictors of Infarct Volumes at Baseline
Univariate R 2 value
P value Multivariate analysis
Age 0 0.87Male 0.5 0.62
Smoking 1.9 0.33Hypercholestorelae
mia3.6 0.18 P = 0.16
Hypertension 2.6 0.25Diabetes 0.2 0.77
GP2b3a inhibitor 5.3 0.09 P = 0.12Thrombectomy
catheter1.2 0.43
IMR 18.6 0.001 P = 0.002CFIp 0.8 0.53
Wedge pressure 0.1 0.81
Predictors of Infarct Volumes at 3 months
Univariate R 2 value
P value Multivariate
analysisAge 0.1 0.84Male 1.1 0.49
Smoking 0.9 0.52Hypercholestorelaemi
a9.1 0.04 P = 0.07
Hypertension 0.8 0.55Diabetes 0.9 0.52
GP2b3a inhibitor 5.5 0.11 P = 0.09Thrombectomy catheter 2.8 0.26
IMR 15.6 0.006 P = 0.008CFIp 0.4 0.67
Wedge pressure 0.3 0.72
Inclusion/exclusion criteria
Patients aged > 18
ECG and symptomatic evidence of acute STEMI and who undergo emergency PCI.
Informed written consent.
Standard contraindications to MRI.
Contraindications to Gadolinium.
Contraindications to adenosine.
Cardiogenic shock. Previous myocardial
infarction in the same territory as the index event
Pregnant