What is the protocol for a stress cardiac MRI?

Stress Cardiac MRI Protocol

Stress cardiac MRI is performed using either vasodilator stress perfusion imaging (adenosine, dipyridamole, or regadenoson) or dobutamine-induced wall motion imaging, with vasodilator perfusion being the preferred and more commonly used approach due to higher sensitivity and easier performance. 1

Stress Agent Selection

Vasodilator Stress (Preferred Method)

• Adenosine (continuous infusion), dipyridamole (continuous infusion), or regadenoson (bolus injection) are used to induce hyperemia and detect perfusion defects 1
• Vasodilator stress perfusion demonstrates sensitivity of 91% and specificity of 81% for detecting obstructive CAD 1
• Easier to perform than dobutamine stress and has become the dominant clinical approach 1
• Contraindicated in patients with bronchospasm or severe chronic obstructive pulmonary disease 1

Dobutamine Stress (Alternative Method)

• High-dose dobutamine (up to 40 mcg/kg/min) combined with fractionated atropine (up to 1.0 mg maximum) to achieve target heart rate 2
• Detects wall motion abnormalities induced by ischemia 1
• Demonstrates sensitivity of 83% and specificity of 86% for detecting obstructive CAD 1
• Carries risk of ventricular arrhythmias; severe complications occur in 0.1-0.3% of patients 2
• Relatively contraindicated in patients with recent or active chest pain (acute coronary syndrome setting) 1

Complete Imaging Protocol Components

Standard Acquisition Sequence

• Baseline/rest imaging: Cine imaging for ventricular function and volumes 1, 3
• Stress perfusion or wall motion imaging: First-pass gadolinium perfusion during vasodilator stress OR cine imaging during dobutamine stress 1, 3
• Late gadolinium enhancement (LGE): Acquired 10-15 minutes post-contrast to assess for myocardial scar/infarction 1
• Rest perfusion imaging: May be included in comprehensive protocols 1

Physiologic Monitoring Requirements

• Baseline heart rate and blood pressure documentation required 1
• Maximum heart rate during stress must be recorded 1
• Maximum systolic and diastolic blood pressure during stress 1
• ECG monitoring throughout the procedure for ST-segment changes and arrhythmias 1
• Chest pain assessment during stress testing 1

Technical Specifications

Magnetic Field Strength

• 1.5 Tesla MRI is the standard clinical platform used almost exclusively in Ontario and most centers 4
• 3 Tesla MRI may be used but shows no significant difference in diagnostic performance compared to 1.5T (P=0.72) 4
• 3T is primarily used in research protocols 4

Imaging Duration

• Total examination time: 30-45 minutes 4
• Includes time for stress induction, image acquisition, and post-contrast delayed imaging 3

Contrast Administration

Gadolinium-Based Contrast

• Intravenous gadolinium contrast is required for perfusion imaging and LGE assessment 1, 3
• Contraindicated in severe renal dysfunction (eGFR <30 mL/min/1.73 m²) due to nephrogenic systemic fibrosis risk 1
• Dose adjustment required for mild to moderate renal dysfunction (eGFR 30-60 mL/min/1.73 m²) 1

Clinical Advantages

Key Benefits Over Other Modalities

• No ionizing radiation exposure, unlike SPECT or PET imaging 3, 4
• Higher diagnostic sensitivity than SPECT for detecting angiographically significant CAD 1, 3
• One-stop comprehensive assessment: ischemia, function, viability, and scar quantification in single session 1, 5
• Superior tissue characterization with ability to detect small infarcts (<2% of LV mass) 1

Specific Clinical Scenarios

• Particularly valuable for: women, patients with prior revascularization, left ventricular dysfunction, and moderate-to-high pretest probability of CAD 3
• Useful when echocardiography is nondiagnostic due to poor acoustic windows 1

Important Contraindications and Limitations

Absolute Contraindications

• Severe claustrophobia that cannot be managed 1
• Incompatible implanted devices (certain pacemakers, defibrillators) 1
• Severe renal dysfunction (eGFR <30) if contrast required 1

Relative Limitations

• Limited accessibility: most MRI scanners already in 24-hour use, making cardiac MRI scheduling difficult 4
• Technically challenging: requires specialized expertise and can be affected by arrhythmias and inability to breath-hold 1, 4
• Not suitable for critically ill patients who cannot lie flat or require intensive monitoring 1