Alcohol ablation of the septum

Alcohol ablation of the septum is a non-surgical procedure to improve outflow tract obstruction. It is a percutaneous catheter-based method to decrease septal thickness by therapeutic myocardial infarction. It was first reported in 1995.

The technique grew out of the extensive experience with intracoronary interventions, such as balloon angioplasty and stents, that interventional cardiologists do for coronary artery disease. After local anesthesia and sedation, a thin tube is inserted in the central circulation from the leg. A small balloon catheter (similar to that used in balloon angioplasty in coronary disease) is placed into the left anterior descending coronary artery and then into a septal artery that supplies the interventricular septum.

ablation: Click for bigger picture.

It is inflated and a small amount of echocardiographic contrast is injected into the target septal perforator to assure that the septal site is correct and that the site of mitral-septal contact is supplied by the selected vessel. 7% of initially selected vessels are abandoned because echo contrast is seen in nonseptal structures, such as the papillary muscles, LV free wall or right ventricle. After occlusion of the selected septal perforator by a small balloon to prevent back leakage, 1 to 4 mL of absolute alcohol is then injected into the distal perforator. The balloon is left inflated for 5 to 10 minutes to prevent back leakage of alcohol. Patients experience chest pain and modest myocardial infarction with CK elevations.

Studies have reported sustained reduction in outflow gradients, and improvement in symptoms and exercise capacity. Myocardial contrast echocardiography has resulted in more effective gradient reduction and a lower permanent pacemaker rate.

The main benefit of alcohol ablation over surgery is that it avoids thoracotomy (opening the chest) and cardiopulmonary bypass (the heart-lung machine). The procedural risks of alcohol ablation are similar in frequency to surgery. There have been three nonrandomized comparisons of septal ablation and surgical myectomy. Follow-up pressure gradients were lower in the surgically treated patients, and need for permanent pacing was greater in the ablated group.

Mechanism of ablation benefit: Ablation appears to work in a biphasic manner. Immediately after the procedure, the pressure gradient is reduced, despite absence of alteration of the position of the mitral valve relative to the septum. This highlights the importance of the observed dynamic change in ejection acceleration. The immediate post-procedure reduction in gradient is caused by an immediate reduction in LV ejection acceleration, caused the direct negative inotropic effect of the septal infarct. Immediately after alcohol ablation peak LV ejection acceleration decreased 39%; reduced acceleration was still present 6 months later, 33%. This is very similar to the 36% reduction in acceleration seen after medication that abolishes gradient. The mechanism of early gradient reduction after ablation is similar to that of medication: reduced LV ejection acceleration.

Six weeks and 6 months later, decreased acceleration persists, but now in addition, septal thinning and increase in the LV outflow tract diameter is seen, very similar to surgical results; flow is directed anteriorly and medially away from the mitral valve. Anatomic and dynamic effects are synergistic in reducing SAM.

Complications of ablation include death in 0% to 4%, very uncommon left anterior descending (LAD) artery dissection <0.5%, rarely leakage of alcohol back into the LAD with LAD occlusion and large infarction <0.2%, and complete heart block requiring pacemaker in 5% to 38%. There is concern about the possible early and late development of an arrhythmogenic scar at the site of the infarction in patients already prone to arrhythmia though this has not been reported. In this regard there has been relatively short follow-up of ablated patients (~8 years) compared with surgically treated patients >30 years. Expertise not only with percutaneous catheter techniques but with the echocardiography, pathophysiology and medical management of patients with hypertrophic cardiomyopathy is required. An echocardiographer experienced with OHCM and use of echo contrast should monitor the procedure.

Though surgery is the preferred treatment for patients with medically resistant obstruction ablation has a role in the management of selected patients with refractory symptoms and refractory gradients. Alcohol ablation should only be undertaken after exhausting medical management options. It should never be done for patients who are not obstructed.

A patient experience with alcohol ablation. At present the choice of alcohol ablation or surgery is a judgement that depends on age, mitral valve anatomy, septal anatomy, presence or absence of coronary disease, presence or absence of other medical conditions, and patient preference.