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

1
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 KG11Department of
  Cardiology, Golden Jubilee National Hospital2BHF
  Glasgow Cardiovascular Research Centre, Faculty
  of Medicine, University of Glasgow

2
No conflicts of interest
3
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
• Keeley EC, et al Lancet 2003

4
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
• Hombach et al Eur Heart J 2005
• Wu et al Circulation 1998

5
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
• Aarnoudse W et al Catheter Cardiovasc Interv 2004
• Fearon W et al Circulation 2004
• Ng MKC, Yeung AC, Fearon WF Circulation 2006

6
Thermodilution derived mean transit times at rest
and hyperaemia
7
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
• Task force of the ESC Eur Heart J. 1998

8
Anterior STEMI
9
Anterior MI Late gadolinium contrast
MVO absent
MVO present
10
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.

11
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

12
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.

13
Methods ceCMR

• 1.5 T Siemens Avanto
• ceCMR at 24-48h
• ceCMR at 3 months
• Contrast agent
• gadolinium-DTPA

14
(No Transcript)
15
Demographics
Mean age (range) 58 (32-83)
16
Results ceCMR

• Successful physiological measurements where
  achieved in all patients
• 53/57 had complete baseline ceCMR
• 47/57 had complete follow up scans

17
Results MVO
18
Results MVO
19
Predictors of LVEF at baseline
20
Predictors of LVEF at 3 months
21
Predictors of Infarct Volumes at Baseline
22
Predictors of Infarct Volumes at 3 months
23
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

24
Acknowledgements

• Chief Scientist Office Scotland
• Robertson Centre for Biostatistics, University of
  Glasgow

25
Correlation between both methods of IMR
calculation
26
IMR vs. LVEF at baseline
27
IMR vs. Peak troponin I
28
Results MVO
29
Predictors of LVEF at baseline
30
Predictors of LVEF at 3 months
31
Predictors of Infarct Volumes at Baseline
32
Predictors of Infarct Volumes at 3 months
33
Inclusion/exclusion criteria

• Standard contraindications to MRI.
• Contraindications to Gadolinium.
• Contraindications to adenosine.
• Cardiogenic shock.
• Previous myocardial infarction in the same
  territory as the index event
• Pregnant

• Patients aged gt 18
• ECG and symptomatic evidence of acute STEMI and
  who undergo emergency PCI.
• Informed written consent.