Hypertrophic cardiomyopathy (HCM) with obstructive physiology not infrequently progresses to heart failure with varied degrees of debilitation, including lightheadedness, syncope, dyspnea, and chest pain, ultimately impacting survival. Indeed, alcohol septal ablation and surgical myectomy (together termed septal reduction therapies), performed successfully for 25 and 50 years, respectively, result in improvement of all symptoms and prognosis, increasing both heart failure-related and sudden cardiac arrhythmia-related survival. Patients followed for up to 8-10 years post-procedure show on average an 80% survival, matching the age- and gender-matched non-HCM population, indicating that these procedures can alter and normalize the natural history.¹ Accordingly, although the US guidelines in 2011 placed both procedures as Class 2 indications in appropriately selected patients when performed at high-volume experienced centers, the 2014 European guidelines advocated strongly for both procedures as Class 1 indications—they should be performed when at all possible.^2,3

Nonetheless, there are hazards and contraindications to both time-honored therapies. Namely, surgery requires sternotomy, mechanical ventilation, and substantial recovery, which together confer risk in older patients and those with comorbid conditions. Alcohol septal ablation is limited by coronary perforator anatomy relative to the hypertrophy of the basal septum in each patient. In addition, both result in conduction abnormalities ranging from left bundle branch block in myectomy patients to right bundle branch block in alcohol septal ablation patients. Both also confer a risk of permanent pacemaker requirement that increases with the age of the patient but is roughly 2-4% after surgery and 8-10% after alcohol septal ablation in experienced centers and up to 10-12% in both approaches in the real world.^4,5 Contraindications to both procedures include a relatively thin septum, with obstruction occurring instead due to marked abnormalities of the mitral valve or papillary apparatus, in which case surgical modification of the mitral valve or other obstructing anatomy may be undertaken. In addition, there is lower efficacy in those with mid-ventricular obstruction, and certainly in those with apical obstruction.^6,7

Alternatives to these procedures include mitral valve repair using the edge-to-edge trans-septal clip system, which in a preliminary series of patients has shown good results, and now a novel technique of percutaneous intramyocardial septal radiofrequency (RF) ablation (PIMSRA) with transthoracic echocardiographic guidance.^8,9 After an initial series of animal studies, 15 subjects with classic hemodynamic and anatomic indications for septal reduction therapy but contraindications to myectomy or alcohol septal ablation were included in a pilot series. The procedure involved an RF needle positioned transapically into the anterior septum via transthoracic echocardiographic guidance and positioned at the maximal thickness location in the basal septum, 8-10 mm away from the aortic annulus and in the middle of the thickened septum. RF ablations were visualized on echocardiography and were terminated when significant ectopy, conduction abnormality, or opacification within 3 mm of the endocardial surface occurred. The needle was then withdrawn for further ablations more distally in the septum and then completely withdrawn and reinserted to the posterior septum with both basal septum and more distal ablations again performed. Total ablation time averaged 1 hour. The results appear excellent, with reductions in maximal wall thickness, widening of the outflow tract, and marked improvement in gradients and New York Heart Association class over time and with no significant conduction disease or pacemaker requirement.

Several areas are worth discussing. First, the authors should be commended for introducing a novel technique that could be useful in minimizing complications, namely conduction injury, from the currently available and guideline-supported techniques. However, it is not clear from the manuscript how patients were determined to have contraindications to myectomy or alcohol septal ablation; in experienced centers, this is an unusual occurrence. Additionally, a significant learning curve is required to minimize complications and reproduce this efficacy, especially because transapical puncture is more invasive than alcohol septal ablation and resulted in tamponade in one patient in the study. The precise location in the anterior septum and posterior septum needs to be mapped properly, and burns need to be precise in terms of how extensive in each location. Procedure time is long; total case time was likely over 2-3 hours. It is unclear if patients require use of a hybrid laboratory in case open surgical drainage or repair is required. The authors do mention having surgical backup available. Fluoroscopic time and delivered radiation were not addressed in the article. Importantly, this procedure would not work for thin septa or very focal hypertrophy because risk of ventricular septal defect and conduction disease would likely increase. Indeed, the authors stayed at least 3 mm away from the left ventricular endocardium at the basal septum to avoid left bundle branch block and kept 8-10 mm of non-ablated septum in total in the basal septum. Therefore, it follows that the septum would have to be at least 20 mm thick in all directions to tolerate this procedure safely.

Other groups have reported on RF ablation for septal reduction as well; however, standard irrigated RF ablation catheters as used for arrhythmia ablation were utilized.¹⁰ The septum was approached endocardially from either the right or left ventricle. Early results have been promising, but, like the manuscript discussed here, long-term follow-up is lacking. With endocardial RF, there is a potential for conduction system damage, and indeed some patients required pacing afterwards. The PIMSRA technique appears to offer a similar result without this risk, although with a more invasive approach. It is of concern that the energies delivered with PIMSRA 17G needle (60-100 W) are much higher than those employed with a 7 Fr 4 mm tip RF catheter (30-60 W). It is well-known that tissue temperatures in excess of 100 degrees Celsius can lead to boiling and steam pops. The authors of the manuscript do not describe if temperature was monitored by the needle or if steam pops were experienced. The images presented do suggest some cavitation of the septum, and although not seen in this small study, perhaps ventricular septal defects might develop with wider usage.

Myectomy and alcohol septal ablation should remain the gold standard until at least 5- to 10-year data on this novel technique are documented. In addition, inclusion criteria need to be developed more comprehensively as an alternative in select patients. Until then, surgical myectomy should remain the gold standard for more severe thickness that extends to the mid-ventricle, especially if there are significant mitral valve or papillary muscle abnormalities that require correction. And alcohol septal ablation seems better suited for those with advanced age or comorbidities, especially when basal septal hypertrophy is more focal (a setting that would make the novel RF technique significantly more dangerous). Truth be told, alcohol septal ablation in centers that perform both myectomy and alcohol septal ablation is typically reserved for older patients with focal septal hypertrophy, with the ablation resulting in infarction of the anterior and posterior septum in one sitting. Such patients do quite well, albeit with a 6-8% pacemaker rate. It may be that this novel technique is more suited for younger patients with more severe hypertrophy who do not have any significant derangement of the mitral valve, which are the patients adequately represented in this initial series. In these younger patients, long-term pacing is not desirable, and this technique may evolve into an acceptable alternative to surgical myectomy. Until then, we anxiously await larger series with longer-term safety and efficacy outcomes and more comprehensive case-selection criteria.

References

1. Naidu SS, Panza JA, Spielvogel D, Malekan R, Goldberg J, Aronow WS. Does relief of outflow tract obstruction in patients with hypertrophic cardiomyopathy improve long-term survival? Implications for lowering the threshold for surgical myectomy and alcohol septal ablation. Ann Transl Med 2016;4:485.
2. Gersh BJ, Maron BJ, Bonow RO, et al. 2011 ACCF/AHA Guideline for the Diagnosis and Treatment of Hypertrophic Cardiomyopathy: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. J Am Coll Cardiol 2011;58:e212-60.
3. Elliott PM, Anastasakis A, Borger MA, et al. 2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy: the Task Force for the Diagnosis and Management of Hypertrophic Cardiomyopathy of the European Society of Cardiology (ESC). Eur Heart J 2014;35:2733-79.
4. Naidu SS, Jacobson J, Iwai S, et al. Interventional therapies for relief of obstruction in hypertrophic cardiomyopathy: discussion and proposed clinical algorithm. Hosp Prac (1995) 2018;46:58-63.
5. Kim LK, Swaminathan RV, Looser P, et al. Hospital Volume Outcomes After Septal Myectomy and Alcohol Septal Ablation for Treatment of Obstructive Hypertrophic Cardiomyopathy: US Nationwide Inpatient Database, 2003-2011. JAMA Cardiol 2016;1:324-32.
6. Kunkala MR, Schaff HV, Nishimura RA, et al. Transapical approach to myectomy for midventricular obstruction in hypertrophic cardiomyopathy. Ann Thorac Surg 2013;96:564-70.
7. Schaff HV, Brown ML, Dearani JA, et al. Apical myectomy: a new surgical technique for management of severely symptomatic patients with apical hypertrophic cardiomyopathy. J Thorac Cardiovasc Surg 2010;139:634-40.
8. Sorajja P, Pedersen WA, Bae R, et al. First Experience With Percutaneous Mitral Valve Plication as Primary Therapy for Symptomatic Obstructive Hypertrophic Cardiomyopathy. J Am Coll Cardiol 2016;67:2811-8.
9. Liu L, Li J, Zuo L, et al. Percutaneous Intramyocardial Septal Radiofrequency Ablation for Hypertrophic Obstructive Cardiomyopathy. J Am Coll Cardiol 2018;72:1898-1909.
10. Poon SS, Cooper RM, Gupta D. Endocardial radiofrequency septal ablation - A new option for non-surgical septal reduction in patients with hypertrophic obstructive cardiomyopathy (HOCM)?: A systematic review of clinical studies. Int J Cardiol 2016;222:772-4.

Keywords: Coronary Angiography, Angiography, Bundle-Branch Block, Heart Septal Defects, Ventricular, Papillary Muscles, Heart Ventricles, Mitral Valve, Endocardium, Sternotomy, Infarction, Respiration, Artificial, Cardiomyopathy, Hypertrophic, Heart Conduction System, Echocardiography, Syncope, Pacemaker, Artificial, Chest Pain, Heart Failure, Hemodynamics, Dyspnea, Hypertrophy, Comorbidity, Surgical Instruments

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