Ten Tips and Tricks for Performing Alcohol Septal Ablation in Patients with Hypertrophic Obstructive Cardiomyopathy

Abstract

Alcohol septal ablation (ASA) is an effective interventional therapeutic strategy to reduce or eliminate left ventricular outflow tract obstruction in patients with hypertrophic obstructive cardiomyopathy (HOCM). Although ASA was introduced 25 years ago, there are still no available guidelines to follow. Therefore, most interventional cardiologists rely on their own experience, which is often limited by a relatively low number of performed procedures. This paper presents ten tips and tricks to safe and effective ASA for HOCM.

Alcohol septal ablation (ASA) is an effective interventional therapeutic strategy to reduce or eliminate left ventricular outflow tract (LVOT) obstruction in patients with hypertrophic obstructive cardiomyopathy (HOCM). ^{1 2 3 4 5} Although ASA was introduced 25 years ago, there are still no available guidelines to follow. Therefore, most interventional cardiologists rely on their own experience, which is often limited by relatively low number of performed procedures.

Below, ten “tips and tricks” are presented based on practical and empirical approaches to safe and effective ASA for HOCM.

Patient Selection

Appropriate patient selection is crucial to the performance of effective and safe ASA. It has been generally accepted that patients selected for ASA should be severely symptomatic and refractory to a medical therapy. ^{1 2 3} Some studies have suggested a positive prognostic outcome of septal reduction therapy (myectomy or ASA) when LVOT obstruction was eliminated. ⁶ Additionally, experienced centers have demonstrated a very low procedure-related mortality rate. ^{4 5} Therefore, even with the absence of randomized trials, based on recent observational outcomes only, we have become more liberal in selecting patients for ASA, bearing in mind patients' preferences and real physical limitations in their life ( Table 1 ).

Table 1. Ten ASA tips and tricks.

Patient selection	Symptomatic patients
Anatomical considerations	Septum thickness ≥15 mm, absence of redundant mitral apparatus, and/or papillary muscles abnormalities.
Pressure gradient	Pressure gradient ≥30 mm Hg, but in patients with a low-pressure gradient risk/benefit ratio should be considered.
Pre-ASA left bundle branch block	ASA is associated with a risk of right bundle branch block in half of the patients which might result in complete heart block in patients with left bundle branch block at baseline.
Have a plan	Myocardial contrast echocardiography of all proximal septal branches can be used to plan optimal ablation.
Alcohol injection	1 mL of desiccated alcohol per 1 cm of septum thickness injected slowly.
Do not repeat alcohol injection in the same septal branch	Open collaterals and/or back spill can drive alcohol to remote parts of septum or to the left anterior descending artery.
Hospital stay	Patients should stay for 1–2 d at a CCU and for 5–6 d in hospital.
Hemodynamic and clinical improvement	Reduction of LVOT pressure gradient is 75% and final NYHA class is approximately 1.5 less than the original.
Institutional experience	An institutional experience of >50 ASA procedures is associated with better outcomes.

Abbreviations: ASA, alcohol septal ablation; CCU, cardiac care unit; LVOT, left ventricular outflow tract; NYHA, New York Heart Association.

Anatomical Consideration

In the past, ASA was recommended only in patients with a septum thickness 17 to 30 mm. It has been recently demonstrated that in selected patients, with both the modest septum thickness (15–16 mm) and with severe septal hypertrophy, ASA was found effective and safe in the long-term follow-up. ^{1 7}

LVOT obstruction depends largely on the length of mitral leaflets and submitral chords, papillary muscle abnormalities including their number, hypertrophy, localization, and possible direct attachment to anterior mitral leaflet or short interposition of chords. Evidence suggests some patients encounter obstruction not only in LVOT but also in the midventricular part, therefore the precise evaluation of obstruction is necessary, and adding magnetic resonance imaging or computer tomography of a heart is very valuable. This assessment can identify patients who are more suitable for surgical myectomy than ASA. Thus, patients with only mild hypertrophy and long mitral leaflets and/or redundant chordae and/or significant papillary muscle abnormalities are considered good patients for surgical myectomy.

Pressure Gradient

Traditionally, an LVOT pressure gradient of 50 mm Hg at rest or with provocation has been considered a cut-off value for septal reduction therapy. ^{2 3} However, it is of note, that even lower levels of LVOT obstruction (30 mm Hg) have been shown to have prognostic significance. ⁶ In addition, there is a high variability of LVOT obstruction, and as a result, the cut-off value for LVOT obstruction should be evaluated in consideration with the entire scope of clinical assessment.

Preprocedural Left Bundle Branch Block

Given right bundle branch block occurs in approximately half of the patients undergoing ASA, we consider left bundle branch block a relative contraindication for ASA. Similarly, myectomy often leads to left bundle branch block which should be considered, especially in patients with a preprocedural right bundle branch block. As a result, both therapeutic options could lead to a complete heart block with a necessity of permanent pacing in approximately half of the patients with a specific preprocedural conduction disturbance.

Have a Plan

ASA is described as an interventional procedure guided by myocardial contrast echocardiography and the first septal branch is considered as the usual target of alcohol injection. ^{1 4 5 6 7 8} The morphological result of ASA should be similar to myectomy which is difficult to achieve in all patients because of anatomical variations of septal branches. A preprocedural computerized tomography coronary angiography could benefit in identifying the optimal septal (sub)branch. ⁹ Among the most important things to consider prior to ASA should be choosing the optimal size and localization of future ablation. This is accomplished by repeated injections of echo-contrast medium in all septal branches supplying the septum surrounding the contact point between the mitral apparatus and the septum. A proper elucidation of septal perfusion is critical for subsequent ablation, number of ablated septal (sub)branches, and volume of alcohol injected. In most patients it is possible/needed to ablate also very thin (<1 mm) septal branches.

Alcohol Injection

Recent observations have demonstrated a higher dose of alcohol has a greater effect on LVOT gradient but it is also associated with an increased risk of complete heart block. ⁸ Thus, in ASA we try to balance pros and cons of aforementioned. Currently, a slow injection (1 mL/min) of approximate dose of 1 mL of desiccated alcohol per 1 cm of septum thickness seems to be reasonable, leading to a risk of permanent pacing in approximately 10% of the patients.

Do Not Repeat Alcohol Injection in the Same Septal Branch

Thrombotic occlusion of microcirculation in the territory of an ablated septal branch can cause a significant resistance against a repeated alcohol injection. In these cases, open collaterals can drive alcohol to remote parts of the septum or to the left anterior descending (LAD) artery which might be dangerous. ¹⁰ Similarly, a back spill of alcohol to the LAD might be potentially fatal.

Hospital Stay

Patient should stay at a cardiac care unit (CCU) for 24 to 48 hours with temporary pacing kept in situ. If no complete heart block occurs during this time, temporary pacing can be removed. If a complete heart block persists for longer than 48 hours after ASA, permanent pacemaker should be implanted. ⁴ Approximately 96% of complete heart blocks occur within 5 days after ASA, therefore recommended hospital stay is usually 5 to 6 days. ⁴ It is also important to realize that during a long-term follow-up it has been shown, that only one-third of the patients with implanted pacemaker after ASA use its function. ¹¹ For this reason, a longer waiting period for a conduction recovery could lead to a decreased need for a permanent pacemaker implantation.

Other notable post-ASA complication is ventricular tachycardia requiring immediate electrical cardioversion. This occurs in the first two post-ASA days and occurs in approximately 1% of the cases.

Hemodynamic and Clinical Improvement

Improvement of patients' symptoms after ASA is expected in 90% of the patients, with a mean reduction of LVOT pressure gradient of 75% and final New York Heart Association (NYHA) class reduction of approximately 1.5. ^{1 4 5 6 7 8}

The immediate post-ASA reduction of LVOT obstruction, caused by necrosis and a subsequent stunning of the heart, is followed by a transient pressure gradient increase in the first post-ASA week, and is later followed by a gradual LVOT obstruction reduction/elimination in the following months. ^{12 13} This reduction is caused by shrinking of the ablated septum. With this in mind, we should avoid making a decision to repeat a procedure in the early post-ASA period.

Institutional Experience

An institutional experience of more than 50 ASA procedures was associated with a lower occurrence of ASA complications, better cardiovascular survival, better hemodynamic and clinical effect, and less need for repeated septal reduction therapy. ⁵ As such, only centers with multidisciplinary hypertrophic cardiomyopathy programs and sufficient experience in ASA should perform this procedure. ^{2 3 4 5}