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