MRI of Ischaemic Heart Disease

1. Danny Cho Wai Man, Rad I (DR), Queen Mary Hospital April 2011 MRI of Ischaemic Heart Disease

2. Outline • Introduction • Clinical investigations of IHD • MRI in the assessment of IHD • Safety in Cardiac MR examination • Imaging protocol for IHD in QMH

3. Introduction • In Hong Kong, heart disease is the second leading cause of death in 2009 (after cancer) • More than six thousand and four hundred people died from heart disease in 2009 • It accounts for 15% of all death

4. Introduction • Diagnosis of IHD requires careful history taking and physical examination, along with direct investigation • Diagnostic imaging plays an important role in the proper assessment and management of coronary artery disease

5. Clinical investigations of IHD • Electrocardiography (ECG) • Echocardiography • Nuclear medicine • Positron emission tomography (PET) • Computed tomography (CT) • Coronary angiography • Magnetic resonance imaging (MRI)

6. Electrocardiography(ECG) • One of the standard investigation performed in patients with chest pain • Exercise stress electrocardiography is the most widely applied test to obtain objective evidence of myocardial ischaemia and significant coronary artery disease

7. Echocardiography • Provides a good estimate of ventricular size as well as regional and generalized left ventricular wall motion • Stress echocardiography either by exercise or by pharmacological means is comparable in accuracy to radionuclide testing for diagnosis of coronary artery disease

8. Radionuclide Imaging • Provides higher sensitivity and specificity for the diagnosis of IHD than exercise ECG testing • It can provide functional or physiological and prognostic information, is quantifiable and reproducible

9. Positron Emission Tomography (PET) • Provides more accurate result for the detection of CAD • Provides an estimate of coronary blood flow and coronary flow reserve as well as myocardial viability • Popularity limited by the high cost

10. Computed Tomography (CT) • CT angiography provides high resolution imaging of the heart and give good visualization of the coronary arteries

11. Coronary Angiography • Gold standard in the diagnosis of ischaemic heart disease • It has a very good spatial resolution of 300m • Ascertains the anatomic extend and severity of the atherosclerotic involvement of the coronary arteries

12. Magnetic Resonance Imaging (MRI) • Global cardiac function and regional wall motion abnormalities • Regional perfusion • Myocardial infarction • Coronary MRA

13. Cardiac function & regional wall motion • For patients with heart failure or myocardial infarction due to IHD • Assessment of cardiac function is important prior to commencement and for monitoring of therapy

14. Cardiac function & regional wall motion • Good spatial and temporal resolution • Allowing imaging of systolic and diastolic phases of both right and left ventricles • Cine short-axis images from base to apex • Yields reproducible data for myocardial mass and ventricular size • Regional wall thickness of ventricle, valvular motion, and regional wall motion can be clearly defined • Good contrast between blood pool and myocardium

15. Cardiac function & regional wall motion • Commercially available software yields calculations of stroke volume, ejection fraction, end-systolic volume, end-diastolic volume, myocardial wall thickening within few minutes • Advantages of non-invasiveness, no irradiation, high reproducibility, and high repeatability of results make it an ideal tool for serial measurement and monitoring of cardiac function

16. First-pass Myocardial Perfusion • For the detection of regional ischaemia • Good temporal resolution to image first-pass of contrast medium through myocardium • Adequate contrast between normal and ischaemic myocardium • Adequate coverage from apex to base of the heart (multiple short axis slices in basal, mid-ventricular, and apical regions of left ventricle)

17. First-pass Myocardial Perfusion • In view of the auto-regulatory function of coronary arteriolar beds, stenosed coronary arteriolar beds will vasodilate to maintain adequate blood supply to myocardium • Stenosed coronary arteries usually have normal myocardial perfusion at rest • First-pass myocardial perfusion during stress condition is necessary for demonstration of perfusion defects

18. Stress Cardiac MRI Exam. Physical stress may not be feasible within the MRI environment Pharmacological stress will be more easily to implement using vasodilator e.g. adenosine Myocardial blood flow will increase fourfold to fivefold downstream of normal coronary arteries, but does not increase downstream of stenosed arteries because the related arteriolar beds have already vasodilated maximally

19. Stress Cardiac MRI Exam. • Myocardium receiving blood supply from an significantly stenosed coronary artery will show hypoperfusion compared with normal myocardium • Normally perfused myocardium shows greater enhancement at a faster rate than hypoperfused myocardium LV Normal myocardium Infarcted or Ischaemic myocardium

20. Adenosine Stress Cardiac MRI Exam. • Short half life (<10 secs) • Better patient tolerence • Side effects of Adenosine • Mild decrease in systemic blood pressure • Mild increase in heart rate • Increase respiratory rate • Headache • Dizziness • Shortness of breath • Nausea • flushing

21. Contraindications of Adenosine • Acute Myocardial infarction within few days • Asthma • Second- or third-degree atrio-ventricular block • Sick sinus syndrome • Symptomatic bradycardia

22. Patient Preparation for Adenosine Stress MRI Exam. • Refrain from caffeinated food and drink for 24 hours • Such as coffee, tea, coke and chocolate • Adenosine antagonist • Interfere with the ability of Adenosine to dilate arteries • False negative examination result

23. Adenosine Stress Cardiac MRI Exam. • Adenosine at 140g/kg/min intravenously for 4 mins • Gadolinium-DTPA (0.05 mmol/kg) is rapidly infused (4ml/sec) • First-pass imaging is performed using gradient echo pulse sequence on multiple short axis slices (basal, middle, and apex) of the left ventricle during a breath hold

24. Adenosine Stress Cardiac MRI Exam. • Normal myocardium shows a “blush” of bright signal throughout the cardiac cycle • Ischaemic or infarcted myocardium will show a persistent dark signal, either subendocardial or transmural in location • The perfusion defect shall follow the supply territory of the coronary arteries

25. Myocardial Viability • Differentiation between viable and non-viable myocardium is important • Transmural extent • Viable myocardium may benefit from revascularization and resume normal cardiac function • Function cannot be restored to nonviable tissue

26. Myocardial Infarction • Post-gadolinium myocardial delay enhancement technique • Areas of infarct or scar have increased volume of distribution of gadolinium as compared to normal myocardium • There is more efficient egress of gadolinium from normal myocardium compared to infarcted tissue • Hyperenhancement of infarcted myocardium 10-20mins after contrast administration

27. Ischaemia vs Infarction • Ischaemic and infarcted myocardium can be differentiated by first-pass myocardial perfusion and myocardial delay enhancement techniques

28. Safety of Stress Cardiac MRI Exam. • Staff of multiple disciplines (including Radiographers, Radiologists, Nurses & Cardiologists will be involved in stress cardiac MRI examination • Only properly screened personnel shall be allowed to enter the control access area of MRI Scanner Room

29. Safety of Stress Cardiac MRI Exam. • Patient screening for any contra-indications of MRI and Adenosine e.g. cardiac pacemaker or asthmatic history • ECG investigation will be performed before stress MRI examination to assess any second- or third –degree heart block or acute myocardial infarction, which are contraindications for Adenosine stress examination • Adequate patient preparation • ECG investigation will be performed after stress MRI examination to exclude Adenosine induced infarction

30. Safety of Stress Cardiac MRI Exam. • A total of 0.2mmol/kg Gd-based contrast medium will be administered for rest perfusion, stress perfusion and myocardial delay enhancement imaging • In view of the risk of Nephrogenic Systemtic Fibrosis (NSF) for patients with severe or end-stage renal disease, renal function test result should be checked for high-risk patients • Informed consent shall be obtained if necessary

31. Safety of Stress Cardiac MRI Exam. • Multiple MRI-safe ancillary equipment are necessary for stress MRI examination • Infusion pump • Power injector • Vital sign monitoring system • NIBP, Pulse rate, SaO2 • ECG electrode and leads

32. Safety of Stress Cardiac MRI Exam. • Examination checklist • Patient monitoring records

33. Safety of Stress Cardiac MRI Exam. • Aminophylline shall be ready for emergency situation • Belongs to a group of medicines known as xanthines • Treat breathing difficulties associated with reversible airway obstruction, as in bronchial spasm

34. Safety of Stress Cardiac MRI Exam. • Cardiologist will stay in the MRI scanner room during administration of Adenosine to monitor the patient’s condition • The infusion of Adenosine will be terminated in case of symptoms of flushing, SOB and chest pain • Continuous monitoring of vital signs during entire stress MRI examination

35. Protocols of Adenosine Stress MRI Exam. in DR, QMH Additional 0.1mmol/Kg MR Contrast Media injected immediately after rest perfusion study 0.05mmol/Kg MR Contrast Media 0.05mmol/Kg MR Contrast Media Myocardial Viability Study: Short axis, 2-, 3- & 4-chamber views Localizer Sequences Myocardial Perfusion (Stress*) Short axis view FIESTA Cine Short Axis View FIESTA Cine 2-chamber, 4-chamber or 3-chamber view Myocardial Perfusion (Rest) Short axis view Delay 10mins Delay 10mins Total Imaging Time: about 45mins

36. Localizers • 3-plane localizer, 2-chamber, 4-chamber localizer • The goal is to prescribe imaging planes along short- and long-axis of the heart • Short axis view • 2-chamber view • 3-chamber view • 4-chamber view

37. Localizers 3-plane localizer

38. Short Axis View • Cover from base to apex • Quantification of LV & RV volumes, ejection fraction and myocardial mass • Evaluation of regional wall motion

39. Long Axis Views 3-Chamber 2-Chamber Left Ventricular Segmentation 4-Chamber

40. First-pass Myocardial Perfusion Stress Rest

41. Myocardial Delay Enhancement

42. Conclusion • MRI has a definite role in the assessment and management of patients with IHD • It is an ideal imaging technique for serial follow-up and screening due to being non-invasive and involves no irradiation • An single examination can assess cardiac function, regional wall motion, regional perfusion, and the extent of infarction

43. Thank you