Getting to the Crux of the Matter

The posteroseptal epicardial space associated with the middle cardiac vein (MCV) and posterior descending artery (PDA), also known as the cardiac crux, is a relatively infrequent source of idiopathic ventricular arrhythmias (VA), constituting 1.8% of referrals at one tertiary referral center.¹ The 12-lead electrocardiographic (ECG) appearance of crux VA features a superior axis, QS patterns inferiorly, and tall R waves in lead V2. Lead V1 may harbor either a left or right bundle branch block (RBBB) type morphology. We describe a case of premature ventricular contractions (PVCs) arising from the cardiac crux.

Case Presentation

A 20-year-old female university student was evaluated for frequent symptomatic PVCs. At age 16, she began experiencing palpitations that worsened over time. Recent monitoring revealed non-sustained ventricular tachycardia and frequent PVCs of a single morphology, with a 49% ectopic burden. Electrocardiography demonstrated PVCs with a QRS duration 168 msec, RBBB-like morphology in lead V1, and superior axis with minimal R wave leads II, III and aVF, as well as apical origin from leads V3-V6 (Figure 1). Echocardiograms had demonstrated a mildly depressed ejection fraction of 45%, although a cardiac MRI revealed this to be 55%. A focal area of late gadolinium enhancement was noted in the inferolateral wall by the reading physicians at her referring institution, but this was not seen on review of the images by our imaging specialists. Metoprolol and verapamil were tried without relief, and led to untoward fatigue. The patient did not report alcohol intake and described her sleep pattern as normal. She also did not identify any associated environmental triggers for her symptoms. Sotalol had been suggested by her treating physicians as the next step in treatment, but due to her poor experiences with prior medication trials as well as a desire to avoid chronic use at her young age, she requested referral to our clinic for catheter ablation.

She was taken to our electrophysiology laboratory in the fasting state and general anesthesia was induced. Despite her exceptional burden at baseline, her ectopy was completely suppressed by anesthesia with sevoflurane, despite the addition of isoproterenol. Transition to an intravenous anesthetic strategy with propofol reinvigorated a slight but suitable burden for mapping. Bilateral femoral venous and right femoral arterial access were obtained. The procedure was performed with Carto 3 V7 (Biosense Webster, Inc., a Johnson & Johnson company) guidance. An intracardiac ultrasound catheter (8 French [Fr], SoundStar, Biosense Webster) was inserted into the right atrium and right ventricle, and utilized to create sound-based three-dimensional shells of the relevant anatomy and monitor the pericardial space. After systemic heparinization, transseptal access to the left ventricle (LV) was obtained and an open irrigation, force-sensing radiofrequency (RF) ablation catheter (SmartTouch Surround Flow, Biosense Webster) was advanced into the LV cavity. The earliest endocardial site, just basal to the posteromedial papillary muscle, was only on time with the QRS onset (Figures 2A and 2B). The MCV was subsequently mapped. The transseptal apparatus was withdrawn to the right heart and the coronary sinus (CS) was cannulated by the deflectable sheath. However, the ablation catheter was unable to be positioned into the MCV. The MCV ostium was subsequently engaged with a JR 4.0 diagnostic catheter, which was used in turn to advance a 2 Fr octopolar catheter (EPstar, Baylis Medical) as distally as possible, approximately midway through the vessel (Figures 2C and 2D). The earliest potentials were recorded from the distal bipole (Figure 2E) with a relatively far field component at the initial part of the electrogram being 11 msec pre-QRS. Some empiric RF was delivered with long lesions from the earliest endocardial sites in the LV, though without elimination of the patient’s PVCs.

The patient provided informed consent to return to the laboratory and was brought back several weeks later for subxiphoid epicardial access. The case was initiated with mild conscious sedation in order to minimize PVC suppression from anesthesia. The patient’s habitus (body mass index of 46) made traditional subxiphoid access challenging (Figure 3A). A decision was made to insufflate the pericardial space with CO₂ to increase the safety window for epicardial access. The CS was cannulated with an SL2 sheath (8.5 Fr, 63 cm, Abbott) over a deflectable decapolar catheter (7 Fr, CS Bi-Directional D-F curve, Biosense Webster). The catheter was exchanged for a Magic Torque guidewire (.035”, 260 cm, Boston Scientific), which was advanced into a lateral LV venous branch. A JR 4.0 catheter was advanced over the wire into the mid vessel and the Magic Torque guidewire was exchanged for a PT Graphix guidewire (.014”, Straight tip, 300 cm, Boston Scientific), over which a Caravel microcatheter (1.9 Fr, 135 cm, Asahi) was advanced as distally as possible. The wire was exchanged for a high-tip-weight wire (MIRACLEbros, 180 cm, tip load 12.0 gf, Asahi), which was advanced to perforate the branch. The microcatheter was advanced into the pericardial space and a subsequent contrast injection through the catheter demonstrated pericardial layering, confirming pericardial entry. Next, 150 cc of CO₂, previously equilibrated to 1 atm, was slowly insufflated, separating the pericardial layers to a sufficient degree to permit puncture in the left lateral fluoroscopic view with an anterior approach (Figure 3B). Care was taken to avoid diaphragmatic or visceral puncture, and the change of needle course was steep, just deep to the xiphoid process. While pericardial access was achieved, sheaths could not be advanced through the subcutaneous tissues, despite the attempted use of numerous dilators and wire exchanges. At this point, for the patient’s comfort, the case was converted from conscious sedation to general anesthesia, resulting in suppression but not elimination of ectopy. The pericardial space was re-inflated with CO₂ and two additional access attempts proved necessary, with the final skin entrance just above the umbilicus before the angle proved shallow enough to accommodate a deflectable sheath (Agilis Epi, 40 cm, 8.5 Fr, Abbott) into the pericardial space. A decapolar catheter (DecaNav, Biosense Webster) was used to create an activation map of the inferior wall of the LV. The earliest potentials were noted in the apical crux, slightly lateral and distal to the MCV recordings from the index procedure (Figures 3C and 3D). A signal 24 msec prior to QRS onset was bracketed with a near-perfect pace map from that location (Figures 3E and 3F). Coronary angiography revealed sufficient distance from the major coronary arteries, and therefore, RF energy was delivered at that location with immediate elimination of ambient ectopy (Figures 3G and 3H). A few insurance lesions were also placed. All access was removed at the end of a waiting period after administering intrapericardial methylprednisolone. A limited transthoracic echocardiogram the following day demonstrated a trivial posterior pericardial effusion and the patient was discharged in stable condition. A follow-up monitor revealed <1% ectopy and the patient reported complete resolution of symptoms.

Discussion

The collectively reported experience from electrophysiology circles of VA from the cardiac crux is sparse. In the largest series to date, crux origins constituted only 1.8% of cases referred for ablation of idiopathic VA.¹ These cases were roughly evenly split between basal and apical origins, defined by proximity (within 2 cm) from the MCV ostium. Similar to the case presented, all cases of apical crux VA featured a RBBB-like morphology in V1 and negative QRS complexes in lead V6. Also consistent with our case example, apical crux VA required subxiphoid epicardial access for successful ablation. Despite this, as the differential diagnosis for ectopy with such an electrocardiographic appearance may also include ectopy from the posteromedial papillary muscle, posteroseptal mitral or tricuspid annuli, left posterior superior process, and left posterior fascicle, we feel it is reasonable to begin with an endocardial approach to mapping. Nevertheless, should the case ultimately require it, several alterations have been developed to minimize the risk associated with epicardial puncture, including favoring an anterior approach, use of a micropuncture needle or “needle-in-needle,” or use of a pressure sensor needle.^2-4 Due to a desire to start the case without general anesthesia in order to avoid associated arrhythmia suppression noted during an index procedure, combined with the challenge posed by the patient’s body habitus, we chose insufflation of CO₂ due to our prior experience with the technique and excellent safety profile.^5,6 Such an approach proved fortuitous in our case example, eliminating the risk of right ventricular puncture, despite the multiple attempts ultimately required to achieve pericardial access through her subcutaneous tissues.

Conclusion

We have reported a case of ablation of PVCs from the apical crux, an infrequent source of idiopathic VA that often requires epicardial access. This case highlights the utility of modern CS-based techniques in catheter ablation, both venous branch mapping and coronary vein exit, to facilitate subxiphoid epicardial access. 

Acknowledgments

The authors would like to acknowledge Ashley Brooker, RT, and Jessica Dinan, BS, from Biosense Webster for their expertise in electroanatomical mapping for this case. We also would like to thank our partners and the remainder of the Maine Medical Center EP lab personnel for their assistance in this case.

Funding: This work was not supported by any granting agency.

Disclosures: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr. Leyton-Mange has received speaking fees from Sanofi US. The remainder of the authors have no conflicts of interest to report regarding the content herein.

References

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2. Kumar S, Bazaz R, Barbhaiya CR, et al. “Needle-in-needle” epicardial access: preliminary observations with a modified technique for facilitating epicardial interventional procedures. Heart Rhythm. 2015;12:1691-1697. doi: 10.1016/j.hrthm.2015.03.045

3. Gunda S, Reddy M, Pillarisetti J, et al. Differences in complication rates between large bore needle and a long micropuncture needle during epicardial access: time to change clinical practice? Circ Arrhythm Electrophysiol. 2015;8:890-895. doi: 10.1161/CIRCEP.115.002921

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6. Juliá J, Bokhari F, Uuetoa H, et al. A new era in epicardial access for the ablation of ventricular arrhythmias: the Epi-Co2 registry. JACC Clin Electrophysiol. 2021;7(1):85-96. doi: 10.1016/j.jacep.2020.07.027