Alcohol septal ablation is performed in the cardiac catheterization laboratory. A right and left heart catheterization are performed at which time pulmonary capillary wedge and pulmonary arterial pressures are measured. Left ventricular outflow gradients are measured, usually with an endhole pigtail or halo catheter so as to be able to record pressure at a precise location within the left ventricle with a catheter whose shape makes entrapment unlikely. Determination of the left ventricular outflow gradient is accomplished by comparing the left ventricular pressure to the central aortic pressure as recorded usually from the coronary guide catheter (Fig. 31.2). It is important to establish the gradient that will be followed to judge procedural efficacy and to establish, with the aid of echocardiography, that the location of obstruction to left ventricular outflow is subaortic. For those patients in whom the outflow gradient is either absent or small at rest, the magnitude of provocable obstruction is most appropriately determined with exercise. If exercise is not feasible, Valsalva maneuver or post-PVC beats are employed.

Prior to proceeding with alcohol infusion, all patients have a temporary pacemaker placed in the apex of the right ventricle as a precaution against the occurrence of complete heart block following alcohol injection. This is usually placed from the right internal jugular vein, as this is a stable route allowing for maintenance of proper positioning following the procedure.

Coronary angiography is performed to assess for the presence or absence of atherosclerotic epicardial coronary artery disease and to identify potential target septal perforator branches, which most often originate from the left anterior descending (LAD) coronary artery. Most practitioners employ myocardial contrast echocardiography, which involves two dimensional echocardiographic imaging during the infusion of 1–2 mL of echo or angiographic contrast through the lumen of an inflated balloon dilatation catheter. This technique enhances the efficacy and safety of the procedure by avoiding septal branches that supply areas of myocardium distant to the targeted region, limiting the number of vessels intervened on, thereby reducing the amount of alcohol used which aids in preventing the complication of complete atrioventricular block. The targeted myocardial region for ablation is that area of the basal septum where contact is made with the anterior leaflet of the mitral valve (Fig. 31.3) [2].

Once the target vessel or branch has been identified, angiographic contrast is injected through the coronary guide catheter and through the distal port of the inflated balloon catheter in the septal vessel. This is done to ensure that the inflated balloon completely occludes the septal vessel, so that upon injection, alcohol cannot leak back into the LAD, which is a potentially disastrous complication. Myocardial contrast echocardiography has taught us that contrary to what was originally thought, the entire septal branch need not be ablated in order to obtain a satisfactory hemodynamic result (Fig. 31.4).