Quantitative Perfusion with Adenosine Stress Cardiovascular Magnetic Resonance in a Child with Congenital Coronary Artery Fistula

Pezad Doctor MD¹, Mohammad Mehdi MD², Tarique Hussain MD PhD²

¹ Children’s Mercy, University of Missouri Kansas City, Kansas City, MO, USA
² Children’s Health, University of Texas Southwestern Medical Center, Dallas, TX, USA

Clinical History

A 10-year-old female with a large coronary artery fistula and right coronary artery (RCA) ostial atresia presented with exertional chest pain. She was initially evaluated at 4 months of age after a murmur was detected. Cardiac catheterization at 4 months age demonstrated a single coronary artery originating from the left coronary sinus, with no identifiable RCA ostium. A large coronary fistula was noted from the left coronary artery (LCA) that drained into the right ventricle (RV) (Figure 1, Movie 1).

Figure 1. Selective LCA angiogram at 4 months of age showed a tortuous coronary fistula arising from the dilated left anterior descending coronary artery (LAD) that drained into the basal inferior aspect of the RV.

Movie 1: Selective LCA angiogram at 4 months of age showed a tortuous coronary fistula arising from the dilated LAD that drained into the basal inferior aspect of the RV.

Over the years, she underwent serial transthoracic echocardiograms (TTE) to assess ventricular size and function. Coronary computed tomography angiography (CorCTA) at 10 years of age after onset of symptoms showed a dilated LCA system and an additional large caliber interarterial collateral vessel that coursed anterior to the aorta and then along the right atrioventricular groove, terminating in a fistulous connection to the RV inflow suggesting a LCA to RV fistula (Figure 2). The interarterial segment showed flow acceleration by TTE and concerns of narrowing on the CorCTA (Figure 2).

Figure 2: CorCTA at 10 years of age showed narrowing in the inter-arterial segment of the collateral vessel with dilated proximal LCA and LAD.

Given the child’s symptoms and RCA ostial atresia, adenosine stress cardiovascular magnetic resonance (CMR) with quantitative perfusion was performed to assess for inducible hypoperfusion due to narrowing of interarterial segment supplying the RCA.

CMR Findings

CMR was performed on an Ingenia 1.5T (Philips Healthcare, Best, The Netherlands), which showed normal RV size [RV end-diastolic volume index 85ml/m²] and left ventricular size [left ventricular end-diastolic volume index 83ml/m²] with normal biventricular systolic function and no regional wall motion abnormalities (Movie 2). First-pass stress perfusion imaging was performed with continuous adenosine infusion at 140 mcg/kg/min. At four minutes, when her heart rate increased by 20 beats per minute (BPM), she noted symptoms of chest discomfort, intravenous gadolinium 0.075 mmol/kg (gadobutrol, Gadavist, Bayer Healthcare, Berlin, Germany) was injected at 4ml/s followed by 20ml saline flush. Since her heart rate increased to 110 BPM, perfusion image acquisition was possible in only two slices, basal and mid-ventricle. Splenic “switch-off” was present, suggesting an adequate adenosine response. “Splenic switch-off” occurs due to reduced signal intensity in the spleen with adenosine compared to rest perfusion imaging, as adenosine constricts the splenic vasculature and reduces the contrast reaching the spleen. Rest perfusion was performed 15 min after stress imaging. For perfusion imaging, a dual-sequence, single-bolus technique with balanced gradient echo readout was performed to create an arterial input function for quantitative perfusion. With adenosine, hyperemia was noted in the basal anterior regions with no perfusion defects by visual inspection (Figure 3, Movie 3).

Movie 2: Short axis cine balanced steady state free precession stack shows normal biventricular systolic function with no regional wall motion abnormalities

Figure 3: Arterial input function (AIF) along with basal and mid ventricular perfusion slices demonstrate no perfusion defect in the RCA territory and hyperemia in basal anterior segments at stress.

Movie 3: Perfusion imaging at rest and stress of AIF along with basal and mid ventricular slices show no perfusion defect in the RCA territory and subtle myocardial hyperemia in basal anterior segments at stress.

Quantitative perfusion analysis of CMR perfusion imaging was performed using cvi42 software (Circle Cardiovascular Imaging, Calgary, Alberta, Canada), allowing automated pixel-wise quantitative perfusion mapping. For the relation of pixel-wise myocardial blood flow (MBF) estimates to coronary artery territories, pixels were assigned to standard American Heart Association (AHA) segments using the automatically computed RV insertion points, and AHA segments were assigned to their respective perfusion territory (Figure 4).

Figure 4: Pixel signal intensity derived perfusion curves representing baseline, slope and peak values at rest and stress perfusion. MBF values and myocardial perfusion reserve (MPR) along with relative MBF and relative MPR values were illustrated on a 16 segment AHA model.

Manual adjustments were made to the endocardial and epicardial contours to avoid including the blood pool, as well as to the RV insertion points, to accurately delineate the coronary territories. On quantitative perfusion analysis, despite increased hyperemia noted in the anterior region where the coronary artery fistula coursed and connected to the dilated LAD, there was appropriate augmentation of MBF in the RCA territory with no regions of reduced MBF or “coronary steal” in the rest of the coronary territories (Figure 5). No evidence of late gadolinium enhancement was noted (Figure 5).

Figure 5: A. Quantitative perfusion 16 AHA segment map demonstrates the MBF values in ml/gm/min at rest. Normal MBF with no regional differences. B. With Adenosine, there is significant increased MBF in the AHA segment 2 corresponding to basal anteroseptal LAD fistula territory with normal values in the RCA territory. C. MPR (ratio of MBF at stress over resting condition) map shows increased MBF in the LAD fistula territory and normal reserve in the RCA region.

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Conclusion

Quantitative perfusion with adenosine stress test helps assess coronary blood flow redistribution and myocardial perfusion in children with congenital coronary artery anomalies. In this case, assessing MPR in the RCA territory was valuable in the evaluation of a symptomatic child with RCA ostial atresia and a coronary artery fistula. At one-year follow-up, she occasionally complained of chest pain with no dizziness or syncopal episodes and no concerning findings of myocardial ischemia on exercise stress test.

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Perspective

Most infants and children with small fistulae are asymptomatic, whereas those with larger fistulae may present with congestive heart failure, arrhythmias, and, in rare cases, myocardial ischemia. Asymptomatic patients with small fistulae are typically managed conservatively, while surgical ligation or transcatheter coil embolization is reserved for infants and children with large or hemodynamically significant fistulae [1]. Although transcatheter interventions are increasingly performed in older children, they carry risks such as thrombus propagation and distal coronary occlusion, which may lead to myocardial ischemia. Therefore, a careful and individualized approach for serial evaluation and management is essential.

Assessment of myocardial ischemia in the presence of coronary artery anomalies is challenging in children, especially in the presence of non-specific exertional symptoms. Given complete RCA ostial atresia with a narrowed interarterial segment of the coronary fistula, the RCA territory has an increased risk of myocardial ischemia and coronary insufficiency if adequate collateralization is not formed. As the coronary fistula originates from the LCA, there is increased MBF in the LAD territory with stress, with potential for “coronary steal” in the RCA territory. Hence, adenosine stress imaging with quantitative perfusion was performed to assess MPR across different myocardial regions at rest and stress. Adenosine is a coronary vasodilator and has been used traditionally as a stress agent for assessing myocardial perfusion imaging in adults with coronary artery disease.

Quantitative perfusion analysis offers superior diagnostic accuracy and reduced operator dependence in assessing MBF, particularly in the setting of multivessel disease [2]. Unlike relative perfusion imaging, which relies on visual comparison between myocardial segments and may underestimate balanced ischemia, quantitative perfusion provides absolute MBF values, enabling the detection of global as well as regional perfusion abnormalities [3,4]. Although normative pediatric data on quantifying MBF are not available, a study by Brown et al. involving 151 healthy volunteers reported a mean MBF of 0.62 ± 0.13 mL/g/min at rest and 2.24 ± 0.53 mL/g/min during stress [5]. As myocardial ischemia is rare in children, there are limited studies evaluating the feasibility and clinical utility of quantitative perfusion in the pediatric population [6]. Further studies are warranted to evaluate the clinical application of quantitative perfusion in children. In this case, quantitative perfusion affirms adequate MBF augmentation in the RCA and LCA territories despite interarterial segment narrowing, suggesting adequate collateralization and allowing observation without intervention.

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References

1. Wu S, Fares M, Zellers TM, Jyothinagaram M, Reddy SRV. Diagnosis and Management of Congenital Coronary Artery Fistulas in Infants and Children. Curr Cardiol Rep. 2023;25(12):1921-1932.
2. Zhao SH, Guo WF, Yao ZF, et al. Fully automated pixel-wise quantitative CMR-myocardial perfusion with CMR-coronary angiography to detect hemodynamically significant coronary artery disease. Eur Radiol. 2023;33(10):7238-7249.
3. Knott KD, Camaioni C, Ramasamy A, et al. Quantitative myocardial perfusion in coronary artery disease: A perfusion mapping study. J Magn Reson Imaging. 2019;50(3):756-762.
4. Nazir MS, Milidonis X, McElroy S, et al. Quantitative Myocardial Perfusion With Simultaneous-Multislice Stress CMR for Detection of Significant Coronary Artery Disease. JACC Cardiovasc Imaging. 2022;15(9):1672-1674.
5. Brown LAE, Gulsin GS, Onciul SC, et al. Sex- and age-specific normal values for automated quantitative pixel-wise myocardial perfusion cardiovascular magnetic resonance. Eur Heart J Cardiovasc Imaging. 2023;24(4):426-434.
6. Scannell CM, Hasaneen H, Greil G, et al. Automated Quantitative Stress Perfusion Cardiac Magnetic Resonance in Pediatric Patients. Front Pediatr. 2021;9:699497.

Case prepared by:
Madhusudan Ganigara, MD
Editorial Board Member, Cases of SCMR
Division of Cardiology, Department of Pediatrics
The University of Chicago, Chicago, IL