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Anomalous coronary arteries are rare and, owing to their unfamiliar course, can significantly increase risk of coronary injury when ablating around the ventricular outflow tracts.
Computerized tomography coronary angiography can be merged with 3D electroanatomical mapping via the CARTO-Segmentation module (Biosense Webster), and this provides important insight into the proximity of coronary arteries to the ablation target. This can be further augmented with intracardiac echocardiography.
This case report shows how CARTO-Segmentation was effective in locating the path of an anomalous coronary artery with excellent spatial resolution during outflow tract ablation, and without the need for invasive coronary angiography.
Catheter ablation is a commonly undertaken and highly effective treatment for symptomatic right ventricular outflow tract (RVOT) ventricular ectopy / ventricular tachycardia (VT).
and may have an unfamiliar path involving the outflow tracts, posing a significantly increased risk with ablation. The approach to outflow tract ablation in a patient with an anomalous coronary artery has not been previously reported. Imaging is crucial. We present a case of successful RVOT VT ablation guided by a merged cardiac computerized tomography (CT) and intracardiac echocardiography (ICE), where an anomalous right coronary artery (RCA) resided 1 mm from the posterior RVOT.
A 46-year-old lorry driver, with no prior cardiac symptoms or history, presented to a local general hospital with repetitive bursting monomorphic outflow tract–type VT, associated with chest pressure and presyncope. Intravenous amiodarone in their emergency department settled the VT with persisting ventricular ectopics. The ectopic electrocardiography (ECG) morphology and VT were identical (Figure 1) and suggested an RVOT origin (left bundle branch block type, inferior axis, R-wave transition V4). Cardiac magnetic resonance imaging demonstrated a structurally normal heart with no scar.
An ECG-gated contrast enhanced CT coronary angiogram was also performed at the local hospital, as the presentation was associated with a small troponin rise, revealing an unobstructed anomalous RCA. This was seen to arise from the left coronary cusp, taking a low interarterial course, below the pulmonary valve, hugging the posterior aspect of the RVOT with 1 mm distance (Figure 2 and Supplementary Video 1). An invasive coronary angiogram was undertaken owing to some mid–left anterior descending artery (LAD) disease seen on CT, which was found to be nonobstructive. The cardiac interventionalists were unable to engage the RCA with multiple catheters. The case was reviewed by electrophysiologists in our center; as radiofrequency ablation was felt to pose an additional unknown risk of iatrogenic coronary injury, conservative treatment with beta-blockade was favored, especially as we would be unlikely to engage the RCA with a coronary catheter in the event of an iatrogenic occlusion. The patient was unfortunately prohibited from driving (his livelihood) pending further evaluation.
The patient presented again a few weeks later with the same VT and presyncope. Following discussion in a multidisciplinary team heart rhythm meeting, potentially curative ablation was considered reasonable if cardiac imaging allowed sufficient visualization of the vessel, with >5 mm distance between the vessel and ablation target.
This was discussed in detail with the patient, who preferred a potentially curative approach to stand a better chance of driving again. He understood there was an element of added risk that we could not quantify.
The contrast-enhanced cardiac CT was imported as a DICOM file into the 3D electroanatomical CARTO mapping system (Biosense Webster, Irvine, CA), and a semiautomatic 3D reconstruction of the cardiac geometry and coronary anatomy was created (CARTO-CT Segmentation module [CARTOSEGTM]), and was available for display during the case using the CARTOMERGE module (Figure 2 and Supplementary Video 1). This was achieved by registering landmark tomographic points around the ascending aorta on CARTO, along with corresponding points on the mesh reconstruction.
The patient presented in sinus rhythm with frequent RVOT ectopy (Figure 3A). An ultrasound-guided reconstruction of the contours of the cardiac chambers was created using ICE via the CARTOSOUND module, with particular attention paid to the RVOT, pulmonary artery, coronary cusps, and aortic root. The origin of the anomalous vessel was carefully imaged. This was merged with the reconstructed cardiac geometry depicted using CARTOSEG (Figure 3B and 3C) against these defined landmarks (particularly the ascending aorta). Importantly, the live display of the origin of the anomalous coronary artery seen with ICE entirely collocated with the path of the vessel on CARTOSEG. This gave us the assurance that the vessel depicted on our mapping system was accurate in location. No further attempts to visualize the RCA with invasive angiography were thus made.
Earliest activation was seen on the septal aspect of the RVOT (30 ms pre-QRS with a QS morphology on unipolar electrogram) (Figure 3A and 3B). This was just underneath the pulmonary valve and fortunately away from the anomalous coronary artery. This site is recognized to be close to the proximal LAD, readily apparent in the image; hence only 25–30 W of irrigated ablation was delivered (ThermoCool SmartTouch D-F; Biosense Webster), with <10 g contact force, and for no more than 30 seconds. This eliminated the ectopic focus (Figure 3E), with no ST change on 12-lead ECG. Subsequent VT stimulation protocols with isoprenaline, including 2 drive trains and double extrastimuli, resulted in no inducible ectopy or ventricular arrhythmia. Postoperative recovery was uneventful and no further sustained VT has recurred in 6-month follow-up. An exercise test revealed no signs of inducible myocardial ischemia or sustained VT recurrence, allowing the patient to return to professional driving.
Catheter ablation carries a class I indication for patients with symptomatic RVOT VT in the European Society of Cardiology (ESC) guidelines and is considered first line ahead of drug therapy.
The high course is associated with a risk of sudden cardiac death, usually during exercise, and may relate to compression of the anomalous orifice by aortic dilatation, or compression of the RCA between the great vessels.
which our patient did not have. Our patient had a low interarterial course, which, while a lower-risk scenario, can significantly increase the risk of iatrogenic myocardial infarction if radiofrequency catheter ablation is considered within its vicinity.
Ablating near to the coronary arteries carries a risk of inducing acute coronary spasm and iatrogenic myocardial infarction. The distance from a coronary artery at which it is safe to ablate is not well understood. Expert consensus, based upon the available evidence, suggests >5 mm, though this is in the setting of epicardial ablation.
In our case, the anomalous vessel hugged the posterior aspect of the RVOT with 1 mm distance. The risk was further increased as the interventionalists had been unable to engage the RCA at invasive angiography, meaning any intervention in the case of iatrogenic coronary occlusion may have required emergency bypass grafting. Integrated imaging using a combination of cardiac CT (CARTOSEG) and ICE allowed precise delineation of the anomalous coronary artery during the procedure and assured us that our ablation site in the RVOT was much greater than 5 mm from the RCA.
The efficacy of ICE and CARTOSOUND is well known and used routinely in clinical practice in many labs. While it allows direct visualization of the left main coronary ostium, the right coronary ostium is more difficult to image, and no visualization of the complete epicardial course of the coronaries is possible. In the setting of an anomalous RCA, operator confidence identifying the vessel in real time may be reduced owing to unfamiliarity of the vessel course. Merging of CT imaging into 3D electroanatomical mapping systems has been previously described and used to avoid injury to extracardiac structures, such as the phrenic nerve and—as in our case—the epicardial coronary arteries.
Prior commercial software for image integration had lower resolution, limiting precise anatomical depiction. CARTOSEG offers 1 mm spatial resolution of all heart chambers and coronary arteries based on contrast-enhanced cardiac CT. The system uses a semi-automatic “single-button” algorithm to reconstruct endocardial cardiac surface anatomy (including trabeculations and papillary muscles) from a contrast-enhanced CT scan within CARTO, and without additional manual input. In the only published study using this module, average segmentation time was <5 minutes and ablation was performed safely near the coronary arteries without the need for invasive coronary angiography.
Reassuringly, while RVOT radiofrequency ablation is commonly performed, iatrogenic thermal LAD injury is rare, perhaps owing to convective cooling of nearby coronary blood flow and catheter instability in the outflow tract.
In our case, CARTOSEG elegantly highlighted the relationship of the LAD to the site of earliest activation in the septal RVOT and encouraged us to use lower power, contact force, and duration of energy delivery.
Preprocedural coronary imaging is not routinely performed before outflow tract ventricular ectopy ablation in our center. The plan to undertake a cardiac CT was made by our local general hospital given the accompanying troponin leak. This report highlights how advanced cardiac imaging techniques (CARTOSEG and ICE) can help operators overcome the challenge of proximity to an anomalous coronary vessel when such an unusual circumstance is encountered. Given the rarity of such anomalies, routine preprocedural imaging of the coronary arteries is unlikely to be beneficial.
We describe the first reported case of successful RVOT VT ablation in a patient with an anomalous RCA in close proximity to the RVOT. Integrated imaging was crucial, with direct visualization of the vessel achievable using intracardiac echo and the recently implemented CARTOSEG module to rapidly delineate the vessel with high accuracy.
3D reconstruction of the great vessels from CT images showing the origin of the anomalous RCA; Mid-left: Merged images within the CARTOtm platform incorporating an electroanatomical map of the RV with CT-merged images of the LV, aorta and coronary vessels; Centre: Video rotating around the CARTO view, demonstrating the anomalous RCA as it tracks around the RV; an ICE probe shows the RCA location on ultrasound; Top-right: 12 lead ECG of the ectopic (LBBB type, inferior axis, R wave transition V4); with mapping catheter EGMs (blue/white) below; earliest bipolar (blue) and corresponding unipolar (white) EGM, 30ms pre-QRS with a QS Unipole; Mid-right: ICE view of the aorta and origin of the anomalous RCA; Bottom: Surface 12 lead ECG - note how two RVOT ectopics are seen initially and cessation is seen immediate after RF ablation begins. 3D - Three dimensional; CT - Computed Tomography; EGM - Electrogram; ICE - Intracardiac ultrasound; LV - Left Ventricle; RCA - Right Coronary Artery; RF - Radiofrequency; RV - Right Ventricle
Ablation of idiopathic right ventricular outflow tract tachycardia: current perspectives.
Funding Sources: No funding was received for this work.
Disclosures: D.G. and V.L. report institutional research grants from Biosense Webster. The other authors report no conflicts of interest. Written patient consent was received toward publishing this article.