Use of cardiac magnetic resonance imaging for alcohol septal ablation in hypertrophic obstructive cardiomyopathy

Abstract

This is a report of a 58-year-old man with severe hypertrophic obstructive cardiomyopathy who underwent alcohol septal ablation to relieve symptoms due to severe left ventricular outflow obstruction. Cardiac magnetic resonance was performed before and after the procedure. This case highlights the potential use of cardiac magnetic resonance imaging in the surgical planning of alcohol septal ablation as well as following the procedure to assess for complications and morphological changes.

Keywords::

• Hypertrophic cardiomyopathy
• alcohol septal ablation
• cardiovascular magnetic resonance imaging

A 58-year-old man with hypertrophic obstructive cardiomyopathy (HOCM) presents with severe, progressive dyspnea and frequent epistaxis. His examination was notable for a grade III/VI harsh, mid-systolic murmur which became louder with Valsalva maneuver and squat-to-stand as well as a grade III/VI systolic apical blowing murmur. Echocardiography revealed left ventricular outflow tract (LVOT) obstruction (maximal systolic Doppler gradient, 101 mmHg), marked systolic anterior motion of the mitral valve (SAM), severe, posteriorly-directed mitral regurgitation, and severe left atrial enlargement (Figure 1). Brain natriuretic peptide was 1,419 mg/ml and there was evidence of acquired von Willebrand syndrome as reflected by a ratio of von Willebrand factor (VWF) latex activity to VWF antigen of 0.67 (normal ≥ 0.80), non-clotting platelet function analyzer 100 (PFA-100) results, and by loss of highest molecular weight VWF multimers based on gel electrophoresis. To help characterize sudden cardiac arrest risk factors, a cardiovascular magnetic resonance (CMR) was performed (1). This study revealed asymmetric septal hypertrophy (sigmoid configuration) with a maximal thickness of 23 mm and severe SAM (Figure 2). Minimal, focal fibrosis was visualized in the inferoseptum at the right ventricular insertion site, which is commonly observed in the setting of left ventricular hypertrophy and increased wall tension (2).

Figure 1. Echocardiographic images before and during alcohol septal ablation. Long-axis apical view depicting typical features of hypertrophic obstructive cardiomyopathy including asymmetric septal hypertrophy and severe systolic anterior motion of the mitral valve (A). Left ventricular outflow tract obstruction was demonstrated by Color flow Doppler (B) and continuous wave Doppler (C) with a maximal instantaneous gradient of 101 mmHg at rest. Long-axis apical view during contrast administration shows potential area of necrosis in the basal anteroseptum (arrow) immediately prior to alcohol septal ablation (D).

Figure 2. Cardiovascular magnetic resonance images before and after alcohol septal ablation. Steady-state free procession (SSFP) diastolic (A) and systolic (B) still-frame, long-axis images demonstrating hypertrophic obstructive cardiomyopathy with left ventricular outflow tract obstruction and secondary, severe eccentric mitral regurgitation (cine images provided in supplement). Delayed enhancement image post-gadolinium reveals no evidence of myocardial fibrosis (C). Prior to hospital discharge, repeat CMR was performed. A large, transmural, non-enhancing area of necrosis (arrow) was visualized in the basal anteroseptum on perfusion (D) and still-frame SSFP (E) images. Post-alcohol septal ablation cine images are provided in the supplement. Short-axis delayed enhancement image (F) reveals large area of microvascular obstruction, or ‘no reflow,’ as demonstrated by the large, non-enhancing inner core.

Despite maximal medical therapy, the patient remained severely symptomatic, and thus, alcohol septal ablation (ASA) was performed. Immediately following the procedure, maximal resting LVOT gradient decreased substantially from 60 to 11 mmHg. Prior to discharge, CMR was performed to evaluate procedural success and exclude complications. In addition to a perfusion abnormality and akinetic basal anteroseptum, it revealed diffuse microvascular obstruction (‘no reflow’), suggestive of acute, focal necrosis (Figure 2). Three months following the procedure, the patient was asymptomatic and epistaxis spontaneously resolved. Maximal LVOT obstruction was 23 mmHg and the severity of mitral regurgitation appeared mild based on echocardiography. Although frequent epistaxis abated, his von Willebrand function testing improved, but not normalized, with PFA-100 adenosine closure time 229 s (normal < 121 s), and VWF latex activity to VWF antigen ratio of 0.69. Pre- and post-procedure gel electrophoresis is shown (Figure 3).

Figure 3. Von Willebrand Factor gel electrophoresis before and after alcohol septal ablation. Gel electrophoresis of VWF before (left), after (middle) with pooled plasma control (right). Loss of highest molecular weight multimers (HMWM) due to high intravascular shear is present in both patient specimens. The fraction of HMWM (normal > 10%) improved from 3–6% post-procedure. In the low molecular weight region, more dense bands indicate increased proteolysis, and this also is less post- versus pre-procedure.

Since its introduction in 1994, ASA has become a viable, albeit less invasive alternative to surgical septal myectomy (SM) in patients with symptomatic HOCM. Alcohol is injected into the appropriate septal perforator supplying the basal septum, thereby causing myocardial necrosis, thinning, LVOT enlargement, and subsequent reduction in outflow obstruction. Based on a recent meta-analysis, improvement of LVOT obstruction as well as short- and long-term outcomes (e.g. mortality and functional status) were similar to SM (3). Procedural complications such as right bundle branch block, high-grade block and ventricular septal defect can occur due to anatomic variation of the septal perforator and large area supplied by this particular vessel. Intra- procedural echocardiography with echo contrast mapping of septal perforators is crucial for identification of appropriate target vessels prior to alcohol administration. Immediately post-procedure, the LVOT obstruction often diminishes due to myocardial ‘stunning’ of the injured septum. While this improvement may be transient, permanent delayed reduction in LVOT obstruction commonly occurs due to thinning and scarring of the basal septum which may take weeks to months.

A strong correlation of maximal LVOT obstruction and VWF abnormalities has been documented in HOCM, as well as an association with bleeding. The bleeding tendency typically improves or normalizes with successful medical therapy or SM (4). Our patient demonstrated significant reduction in LVOT obstruction and improvement in measures of VWF activity, as well as diminished bleeding, but not normalization of VWF multimers. This is likely due to the persistence of mild residual turbulence and LVOT obstruction.

Cardiovascular magnetic resonance has emerged as a potentially valuable tool before and after septal reduction therapy. Preoperatively, CMR can accurately confirm the diagnosis of HOCM as well as determine phenotype, location and extent of hypertrophy, and characterize areas of fibrosis (5). Prior to SM, CMR can aid surgical planning by further characterizing the hypertrophy and by excluding abnormalities of the mitral apparatus and papillary muscles. There has also been interest in the use of CMR to help predict sudden cardiac death based on the presence and extent of delayed enhancement. Indeed, various patterns of delayed enhancement have been observed including focal and diffuse scar within the septum and involvement of the right ventricular insertion sites into the septum. The value of CMR following ASA is controversial, but may further characterize location, quantity of tissue necrosis, and regression of myocardial tissue as well as exclude mechanical procedural complications (5). In a report by Valeti et al, tissue necrosis was highly variable following ASA based on CMR, with the majority of cases demonstrating transmural necrosis and microvascular obstruction in the basal septum, extending to the mid-ventricular inferoseptum and often involving a portion of the right ventricle (6). By comparison, patients with SM had focal excision confined to the basal anteroseptum without delayed enhancement or evidence of necrosis. While the indications for CMR in HOCM continue to evolve, this case highlights several key imaging characteristic before and after ASA.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.