“How we do” CMR in acute myocardial infarction

Derek J Hausenloy, Anna S Herrey, James C Moon UCLH Heart Hospital and

The Hatter Institute, University College London, UK.

This presentation posted for members of SCMR as an educational guide – it represents the views and

practicesof the author, and not necessarily those of SCMR.

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CMR in acute myocardial infarction

Established indications in AMI STEMI:• Assess global and regional LV function.• Detect LV thrombus.• Detect and quantify microvascular obstruction.• Detect and quantify acute myocardial infarct size• Detect and quantify preserved myocardium.

Potential future indications in STEMI:• Detect and quantify the area at risk of infarction- myocardial oedema. • Determine the myocardial salvage index

(infarct size-area at risk/area at risk)• Detect and quantify myocardial haemorrhage.• Detect and quantify the peri-infarct ‘grey’ zone.

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CMR and other Imaging Modalities in AMI

Function Infarct Thrombus MVO Radiation

Dose

Haem Area

at risk

Myocardial

salvage

Cardiac MRI +++ +++ +++ +++ 0 ++ ++ +++

Nuclear + ++ 0 0 ++ 0 ++ ++

Echo ++ + ++ + 0 0 + 0

Cardiac CT + + ++ + ++ 0 + 0

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Facilitating CMR in AMI

• Fine balance between time available and completeness of protocol.

• Need to optimize protocol to <45 min.• Non breath-hold approaches to CMR:

3D whole heart navigated sequences

Single-shot LGE

Motion corrected averaging

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CMR in AMI – general considerations

1. Aim to image on day 2-3 i.e. on day of discharge, although safe within 24 hours

Phrommintikul et al Eur J Radiol. 2009 Apr 16. [Epub]

2. Coronary stents are not a problemPatel et al Radiology. 2006;240(3):674-80.

3. Patient may still be unwell

4. Difficulty breath holding and tachycardia in patient

5. Ensure resuscitation facilities nearby

6. Check renal function. If eGFR<30, only rarely does the benefits of CMR outweigh risk of contrast (NSF)

7. Aim to complete scan within 45 minutes

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Summary of CMR protocol for AMI

1. Axial scouts. Time

2. Multi-slice SSFP cine MRI in long and short axes for volumes and function. (see ‘How I do a volume study’) 10 min

3. Early post-contrast T1-weighted 2D inversion-recovery GRE (or SSFP) with long TI. Multi-slice: a. MVO (presence and size)b. Acute thrombus 20 min

5. 5-15 min post-contrast T1-weighted 2D inversion-recovery GRE (or SSFP). Multislice for:a. Infarct (presence and size)b. MVO (presence and size) 30 min

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Optional imaging for AMI

Time2a Optional – before giving contrast: Multi-slice T2

weighted TIRM or STIR for: a. Area at risk (size)b. Myocardial haemorrhage (presence and size). +15 min

2b Optional resting perfusion – minimum 3 SA slices – basal, mid, apical for:a. no-reflow (microvascular obstruction) +5 min

Early gadolinium enhancement

RCA clip artefact

- 1-3 min post-gadolinium, IR GRE or SSFP sequence, 2D or 3D set inversion time to ~440ms-480ms (higher if ↓HR or trigger 1)

- To detect intra-cardiac thrombus (see arrow).

Late Gadolinium Enhancement (LGE) - 1

- Quantification of myocardial infarct size- T1 inversion recovery sequence (GRE or SSFP)- Usually image in diastole to reduce motion artefacts- Manually adjust TI (start depends on time, dose and trigger/HR)

Late gadolinium enhancement (2)

- Can also detect and quantify MVO (dark core –see arrow).- presence of MVO linked to worse clinical outcomes- preventing MVO is a viable target/mechanism for cardioprotection

Late gadolinium enhancement (3)

• Further LGE information: see• AMI ‘Resources’ section of SCMR website

• (includes protocols, cases, standardized datasets, talks)

• 2D Inversion recovery sequence (GRE) - Alternatives: IR–SSFP, 3D sequences, PS-IR

• Image in diastole to reduce motion artefacts. • Endocardial structures: systole (reduce segments) and later (blood pool down)

• Image technique• Go and learn it. artefact recognition and reduction

• Manually adjust TI (260ms-480ms)• Compulsory –even PS-IR sequences work better

• Gd dose: if not already given, use 0.1-0.2mmol/kg• Image positions: Copy from cines, phase swaps, cross cuts

Optional imaging -T2 oedema imaging (1)

- Myocardial oedema/inflammation appear as increased signal intensity on T2-weighted sequences (see AMI ‘Resources’ talks on T2W imaging)

- This can be used to detect an AMI, myocarditis, or delineate the ‘area at risk of infarction’.- Several T2 weighted sequence e.g. TSE (black blood), STIR, TIRM, T2P-SSFP, ACUT2E.

T2 TSE

Area at Risk

TIRM

Area at Risk

Problems with T2 oedema imaging

1. Low SNR-therefore difficult to delineate and quantify.

2. Surface coil sensitivity-T2 sequences are very prone to variations

3. Bright subendocardial rims

-due to stagnant blood.

4. Posterior wall signal loss -due to cardiac movement,

Optional imaging -T2 oedema imaging (2)

Early Gd• The presence of myocardial hemorrhage within the infarct is

associated with worse LV remodelling and clinical outcomes.• It can be detected using either STIR or dual-inversion black-

blood gradient multi-echo T2* imaging sequences.• Hypointense region on T2 weighted imaging.• Appears to correspond to area of MVO.

Ganame et al Eur Heart J 2009 Apr Epub

LGESTIR imaging

O’Regan et al Radiology 2009;250:916-22.

LGET2* imaging Perfusion

Optional imaging –Myocardial hemorrhage

Optional imaging – Rest perfusion

- Myocardial perfusion imaging (<1 min post-gadolinium).- To detect/quantify microvascular obstruction (see arrow). - See “How we do perfusion”

Optional imaging – Peri-infarct ‘grey’ zone

• Detecting and quantification of the peri-infarct ‘grey’ zone (intermediate contrast), which is associated with post-infarct sudden cardiac death, may be used for risk-stratification post-MI. Yan et al Circ 2006;114;32-39

Schmidt et al Circ 2007;115;2006-2014

• Detect using LGE and quantify using thresholds (SD±2-3) or full-width half max.

• See ‘On-Line talks:(copy and paste these into your browser)

http://www.scmr.org/Members/CMR-online-video-on-demand-lectures/scmr-2009/Sunday_Plenary/Sun_Plenary-2-Kwong.htmlhttp://www.scmr.org/Members/CMR-online-video-on-demand-lectures/scmr-2009/Sunday_Plenary/SunPlen-3-Lee.html

From Schmidt et al, above

LGE

Example- LAD infarct

TIRM LGEPerfusionCine

Acknowledgement:: Derek Hausenloy