Use of Magnetic Navigation to Facilitate Transcatheter Alcohol Septal Ablation for Hypertrophic Obstructive Cardiomyopathy

Percutaneous transcatheter alcohol septal myocardial ablation (PTSMA) is an effective alternative to septal myectomy for symptomatic patients with hypertrophic obstructive cardiomyopathy (HOCM).^1–6 While alleviating symptoms for most patients, the procedure may not be technically feasible in 5–10% of cases,⁷ potentially due to septal artery anatomy. In some cases, success may be limited by operator difficulty in cannulating septal branches due to the typical 90° or greater angulation of their origin. The Stereotaxis Niobe® magnetic navigation system (Stereotaxis, Inc., St. Louis, Missouri) has recently been used to facilitate placement of modified electrophysiologic catheters for radiofrequency ablation procedures.^8–10 We describe a case of a severely symptomatic patient with HOCM and an unusually sharply angulated origin of a septal artery where, after conventional techniques failed, use of magnetic navigation permitted septal artery cannulation to facilitate PTSMA. Case Report. The patient is a 50-year-old white man with HOCM. Three years prior he experienced palpitation, dyspnea, and syncope and was diagnosed with paroxysmal atrial fibrillation and nonsustained ventricular tachycardia. A pacemaker-internal defibrillator (ICD) was implanted; metoprolol and disopyramide were started with improvement. More recently he noted markedly diminished exercise capacity due to dyspnea and chest pain with mild exertion. An echocardiogram showed asymmetric septal hypertrophy with a septal thickness of 2.6 cm and a posterior wall thickness of 1.4 cm, systolic anterior motion (SAM) of the mitral valve, and a systolic gradient across the left ventricular outflow tract (LVOT) of 80 mmHg. There was moderate eccentric mitral regurgitation. Cardiac catheterization using a 5 Fr Halo pigtail catheter (AngioDynamics, Inc., Queensbury, New York) in the LV showed a resting intraventricular systolic gradient of 80 mmHg; following ventricular extrasystoles the gradient was 145 mmHg. Angiography showed coronary arteries with no fixed obstructions. There was visible systolic compression (“milking”) of the first septal artery, which originated at an extreme ~130 degree angle from the long axis of the left anterior descending (LAD) artery (Figure 1). The patient’s medications were increased with no improvement. He expressed a desire to avoid surgery, and was referred for PTSMA. The procedure was performed in a catheterization suite with Stereotaxis Niobe magnetic guidance capabilities. This system consists of a pair of 0.08T-strength magnets on motorized platforms on both sides of the fluoroscopy table capable of generating a precise magnetic field vector (Figure 2). By virtue of a small magnet bonded to its tip, a guidewire or catheter can align with the magnetic vector within the body. An interactive Navigant™ workstation (Stereotaxis, Inc.) allows the operator to select the magnetic vector using a patient-specific 3-dimensional roadmap. Prior to arterial cannulation, the patient’s pacemaker/ICD was tested within the activated Niobe magnets, demonstrating no significant alteration of pacing parameters by the magnetic field. The defibrillator function was inactivated for the procedure. For PTSMA, the patient was administered heparin, an 8 Fr XBLAD 3.5 guiding catheter was inserted into the ostium of the left coronary artery, and a Halo pigtail was inserted into the LV for LVOT gradient monitoring. Multiple attempts were then made by an experienced (fifteen years) operator to cannulate the first septal perforator using conventional 0.014-inch angioplasty guidewires typically selected in our laboratory for septal access (Trooper, Boston Scientific Corp., Natick, Massachusetts; Whisper, Guidant Corp., Indianapolis, Indiana) and modified with a variety of tip bends usually successful for entering angulated septal branches. Although the tip of each wire could be introduced into the proximal septal branch, application of forward push repeatedly prolapsed the wire down the LAD, precluding stable septal branch entry over several minutes of fluoroscopy. The wire was exchanged for a Cronus® 0.014-inch guidewire (Stereotaxis, Inc.) that has a 3 mm magnet at the tip with no bend. The wire was advanced into the LAD just proximal to the origin of the first septal branch. The magnets were rotated into position (Figure 2) and a three-dimensional roadmap was generated. A magnetic vector was created to approximate the direction of the retroflexed septal branch (Figure 3). With multiple fine re-adjustments of the vector, within two minutes the magnetically-guided wire entered and was advanced approximately 3 cm into the first septal branch. The magnetic field was left activated to anchor the guidewire and a 2.0 X 9 mm Maverick® (Boston Scientific) balloon was gradually advanced into the proximal septal branch and inflated to 4 atm (Figure 4). Occlusive balloon position was confirmed by contrast injection. The target area was then visualized by contrast echocardiography (Philips SONOS 5500) after injection of diluted Optison™ (Amersham Health, Inc., Mississauga, Ontario, Canada) via the balloon catheter. The territory involved the basal septum adjacent to the site of septal-SAM contact. The target region was ablated by slow injection of 2.5 ml of absolute dehydrated ethanol over 10 minutes. There were no arrhythmias and no atrioventricular block. Following 10 additional minutes, the balloon was deflated and withdrawn. Angiography showed the typical proximal occlusion of the first septal artery with patency of all other vessels (Figure 4). Follow-up hemodynamics showed a reduction of the resting intraventricular systolic gradient to 5–10 mmHg and the peak provocable gradient after ventricular extrasystoles to 30 mmHg (Figure 5). Following the procedure, the patient had an uneventful recovery. Three days later, given his exposure to the magnetic field, provocative testing of the ICD was done demonstrating no change in programming by exposure to the magnet. He is currently symptomatically improved several months following the procedure. Discussion One of the limitations of PTSMA may be the inaccessibility of certain septal arteries to cannulation using conventional angioplasty techniques. In the described case, the retroflexed 130° angulation of the origin of the septal artery precluded cannulation using a conventional guidewire. Even after wire entry, sharp branch angulation may preclude tracking of an angioplasty balloon catheter. In the current report the use of the magnetic navigation allowed successful wire and balloon cannulation despite the extreme angulation at the origin of the target septal artery where conventional techniques had failed. Current experience with the use of magnetic navigation for coronary intervention is limited, and the effect of the magnetic field, albeit 1/20th the field strength of a standard MRI machine, on previously implanted permanent pacemaker or ICD devices is unknown. As part of this procedure, the patient underwent careful assessment of the pacing and defibrillator functions of his device before and after exposure to the magnetic field. Of note, there was no alteration of device function by exposure to the magnet. Others^11–13 have reported cases where septal anatomy precluded PTSMA in whom covered stents were implanted into the LAD to occlude the ostia of adjacent septal branches. While one of these cases reported initial hemodynamic success,¹¹ that patient later had severe in-stent restenosis (reported in a subsequent letter to the editor). The other case described¹² a return of symptoms and severe outflow tract obstruction at 10-month follow up when angiography showed interim development of collaterals to the occluded septal artery. The efficacy of covered stents or of other techniques for occluding septal arteries in patients with HOCM remains largely unknown. This case illustrates how magnetic navigation provided feasibility for percutaneous treatment of this patient’s HOCM by PTSMA where conventional guidewire manipulation failed, avoiding the need to resort to more unusual methods of septal artery occlusion or to septal myotomy/myectomy surgery. This technology may also allow percutaneous coronary intervention for lesions in other arteries deemed inaccessible by conventional angioplasty techniques, expanding the capability of the interventional cardiologist to intervene for the benefit of more patients that currently may be denied a percutaneous approach to their disease.

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