Perfusion Cardiovascular Magnetic Resonance in a Child With Ischemic Heart Disease
Potential Advantages Over Nuclear Medicine
A 19-month-old boy presented with acute cardiac failure and was found to have an anomalous origin and course of the left coronary artery (LCA). It arose from the anterior aortic sinus and was compressed between the aorta and the pulmonary artery. He underwent placement of a left internal mammary artery graft to the left anterior descending coronary artery and made a good recovery. At 2 years of age, he had mild limitation of physical exertion. Cardiac catheterization showed the left internal mammary artery graft to be occluded and the proximal course of the LCA origin to be significantly narrowed (Figure 1). Serial technetium-99m single-photon emission computed tomography (SPECT) myocardial perfusion scans showed ongoing inducible ischemia in the anterior and anterolateral walls (Figure 2). He consequently underwent surgical enlargement of the LCA origin with a good final result.
By 7 years of age, he had developed significantly reduced exercise tolerance, chest pain on exercise, and shortness of breath. His treatment was optimized with β-blocker, calcium-antagonist, glyceryl trinitrate patch, aspirin, and angiotensin receptor blocker. On examination, there were no abnormal cardiovascular findings. The baseline ECG showed ST depression and equiphasic T waves laterally (V4 through V6), both of which are abnormal (Figure 3). An exercise test showed an at least 2-mm horizontal ST depression in V5 and V6 associated with chest pain.
The management options considered were ongoing medical therapy alone, insertion of a coronary stent, or repeat operation to unroof the coronary ostium. There were concerns about the long-term consequences of stent implantation. A further radionuclide scan was considered to assess the ongoing ischemia. In view of the cumulative radiation load to a young child, perfusion cardiovascular magnetic resonance (CMR) was considered a preferable diagnostic option that would avoid further radiation exposure. The child was referred for adenosine perfusion CMR to ascertain the degree and extent of his perfusion defect.
The 7-year-old boy was given time to get accustomed to the magnet, receiver coils, ear protectors, and breath-hold instructions with the assistance of a play therapist. He was given a compressible rubber hand grip in the left hand and asked to squeeze it repeatedly for ≈3 minutes to minimize the side effects of adenosine. Baseline blood pressure and heart rate were 90/45 mm Hg and 77 bpm, respectively. During adenosine infusion, he experienced chest pain, and his heart rate and blood pressure increased to 105 bpm and 102/50 mm Hg. The CMR perfusion scan showed extensive inducible ischemia in the septum, anterior, and lateral walls (Figure 4A and 4B). Left ventricular ejection fraction was 63%, with localized apical scar on the late gadolinium enhancement images (Figure 4C). Compared with the last SPECT scan (Figure 2), the perfusion defect identified by CMR was not limited to the anterior and anterolateral walls but extended to the anteroseptal wall from base to apex. CMR also identified a localized apical infarction that was missed by SPECT. After this perfusion CMR scan, repeat coronary angiography confirmed ostial LCA stenosis but demonstrated a good-sized right coronary artery, proving collateral circulation to the LCA (Figure 5). In consideration of the progressive increase in right coronary artery caliber and the development of collaterals, it was decided to manage the patient medically and to monitor the ischemic burden with perfusion CMR in the future.
Children with congenital or acquired coronary artery disease may require functional evaluation of myocardial perfusion to guide decision making. The intrinsic advantages of CMR over nuclear imaging are its higher spatial resolution and absence of radiation exposure, which is particularly important in children.
The estimated radiation dose from stress/rest SPECT in this young patient was 11 mSv (2.6 mSv for 3 mCi [stress] and 8.4 mSv for 8 mCi [rest] of Tc-99m sestamibi). For a child of this age undergoing a single SPECT study, the risk of inducing a fatal cancer is 11.1×10−2 per 1 Sv or a risk of 1 in 820. In addition, in infants, the resolution of the SPECT scan may be less than optimal because of their small heart size.
In the last 5 years, CMR has been validated and established in clinical practice in adults with known or suspected coronary artery disease.1,2,3,4,5 In particular, in adults, CMR demonstrated a diagnostic performance similar to, if not superior to, SPECT.6 CMR is widely used in the congenital heart disease population, but there is very limited evidence of the role of CMR perfusion imaging in the pediatric population. This case demonstrates that even in young children, perfusion CMR can be performed without sedation or anesthesia. This exciting new clinical application of CMR may obviate the need for nuclear perfusion scans in the pediatric population.
We are grateful to Dr Sima Gregg, principal clinical scientist at the Royal Brompton Hospital, for her assistance in estimating SPECT radiation exposure.
Sources of Funding
This work was supported by the National Institutes of Health Research Biomedical Research Unit at Royal Brompton Hospital and Imperial College London, London, UK.
Schwitter J, Nanz D, Kneifel S, Bertschinger K, Büchi M, Knüsel PR, Marincek B, Lüscher TF, von Schulthess GK. Assessment of myocardial perfusion in coronary artery disease by magnetic resonance: a comparison with positron emission tomography and coronary angiography. Circulation. 2001; 103: 2230–2235.
Rieber J, Huber A, Erhard I, Mueller S, Schweyer M, Koenig A, Schiele TM, Theisen K, Siebert U, Schoenberg SO, Reiser M, Klauss V. Cardiac magnetic resonance perfusion imaging for the functional assessment of coronary artery disease: a comparison with coronary angiography and fractional flow reserve. Eur Heart J. 2006; 27: 1465–1471.
Jahnke C, Nagel E, Gebker R, Kokocinski T, Kelle S, Manka R, Fleck E, Paetsch I. Prognostic value of cardiac magnetic resonance stress tests: adenosine stress perfusion and dobutamine stress wall motion imaging. Circulation. 2007; 115: 1769–1776.
Costa MA, Shoemaker S, Futamatsu H, Klassen C, Angiolillo DJ, Nguyen M, Siuciak A, Gilmore P, Zenni MM, Guzman L, Bass TA, Wilke N. Quantitative magnetic resonance perfusion imaging detects anatomic and physiologic coronary artery disease as measured by coronary angiography and fractional flow reserve. J Am Coll Cardiol. 2007; 50: 514–522.
Futamatsu H, Wilke N, Klassen C, Shoemaker S, Angiolillo DJ, Siuciak A, Morikawa-Futamatsu K, Suzuki N, von Ziegler F, Bass TA, Costa MA. Evaluation of cardiac magnetic resonance imaging parameters to detect anatomically and hemodynamically significant coronary artery disease. Am Heart J. 2007; 154: 298–305.
Schwitter J, Wacker CM, van Rossum AC, Lombardi M, Al-Saadi N, Ahlstrom H, Dill T, Larsson HB, Flamm SD, Marquardt M, Johansson L. MR-IMPACT: comparison of perfusion-cardiac magnetic resonance with single-photon emission computed tomography for the detection of coronary artery disease in a multicentre, multivendor, randomized trial. Eur Heart J. 2008; 29: 480–489.