Background
Hypertrophic cardiomyopathy (HCM) is characterized by left ventricular hypertrophy not explained by secondary causes, with a predisposition for outflow tract obstruction in some patients. As the most commonly encountered genetic cardiac condition, HCM affects 1 out of 500 individuals in the general population with a myriad of morphologic variants and clinical presentations. HCM can manifest with symptoms of dyspnea, chest pain, and syncope from a variety of hemodynamic perturbations, including diastolic dysfunction, myocardial ischemia, outflow obstruction, and mitral regurgitation. Left ventricular outflow tract (LVOT) obstruction, defined as a resting or provoked gradient over 30 mmHg, is present in over two-thirds of patients with HCM. Obstructive HCM (HOCM) results from narrowing of the LVOT, anterior mitral leaflet abnormalities, and high ejection velocities of blood through the LVOT, which in turn can pull or push the anterior mitral valve leaflet toward the muscular septum ( Fig. 21.1 ). This systolic anterior motion (SAM) leads to contact between the anterior mitral valve leaflet and ventricular septum with consequent obstruction to blood flow and decrease in forward stroke volume. In addition, mitral regurgitation may occur as a result of SAM ( Fig. 21.2 ). The degree of LVOT obstruction is a predictor of symptoms and heart failure in patients with HOCM. Pharmacologic and invasive therapies are aimed at reducing symptomatic LVOT obstruction in HOCM.
Medical therapy remains the first-line management strategy in patients with symptomatic HOCM. This predominantly involves the initiation of beta-blockers or calcium channel blockers, which are effective at reducing LVOT obstruction through negative inotropic and chronotropic properties. Disopyramide is an additional agent with negative inotropic effects that can be used to improve symptoms. In select patients with refractory symptoms despite medical therapy or those unable to tolerate pharmacologic titration, septal reduction therapy may be required. Surgical septal myectomy, involving direct visualization and surgical resection of ventricular septal muscle, was previously the only available technique for invasive septal reduction. However in the mid-1990s, the technique of transcatheter chemical septal ablation was introduced as an alternative to surgery. Alcohol septal ablation (ASA) targets relief of LVOT obstruction by creating a localized myocardial infarction in the basal septum with resultant decreased contractility, and reduction in SAM. ASA has proven to be a safe and effective strategy in clinical practice to reduce LVOT obstruction and improve symptoms in appropriate patients.
AHA guidelines
| When surgery is contraindicated or the risk is considered unacceptable because of serious comorbidities or advanced age, ASA can be beneficial in eligible adult patients with HCM with LVOT obstruction and severe drug-refractory symptoms (usually New York Heart Association [NYHA] functional classes III or IV). | IIa | B |
| ASA, when performed in experienced centers, may be considered an alternative to surgical myectomy for eligible adult patients with HCM with severe drug-refractory symptoms and LVOT obstruction when, after a balanced and thorough discussion, the patient expresses a preference for septal ablation. | IIb | B |
ASA indications and patient selection
Septal reduction therapy is indicated in patients with HOCM who have severe (NYHA functional class III or IV) symptoms that limit quality of life despite optimization of medical therapy. Additionally, patients should have severe LVOT obstruction, defined as a gradient ≥50 mmHg at rest or with provocative maneuvers, in addition to SAM. ASA is generally preferred in older patients or in those with more extensive comorbidities for whom surgery is deemed high risk. Excessive septal hypertrophy can decrease the efficacy of ASA, and therefore the degree of septal thickness should be considered in patient selection. Generally in patients with a septum thickness over 30 mm, surgical myectomy should be considered. Myectomy may also be indicated in patients with coexisting valve disease or coronary atherosclerosis requiring surgery.
Careful interrogation of the mitral valve by echocardiography should be performed before ASA, as patients with primary abnormalities of the mitral valve, such as anomalous papillary muscle insertion or cleft, may be better served by surgical intervention. The typical jet of mitral regurgitation in HCM will direct posteriorly. Any other direction, central or anterior, should raise a concern that there is something unusual, such as a single papillary muscle or predominant midventricular obstruction.
In addition, the level of outflow tract obstruction is important. Patients with basal hypertrophy and obstruction with favorable septal artery anatomy are optimal candidates for ASA. Conversely, those with midcavity obstruction may require extended surgical myectomy for adequate hemodynamic improvement and symptom relief.
Finally, patient preference should be incorporated into the selection process after an informed discussion regarding risks, benefits, and current understanding of long-term outcomes between ASA and surgical myectomy. ASA interventions should be performed in high-volume cardiac catheterization laboratories by operators experienced with the procedure.
Coronary anatomy
The success and degree of symptom relief after ASA in patients with HOCM ultimately depend on the septal coronary anatomy and correct identification of the vessel(s) supplying the myocardial region of interest. Coronary angiography is used to identify the branch most likely to supply the septal distribution targeted for intervention. Angiography should include injections of both right and left systems, as septal branches can occasionally originate from the right coronary artery, ramus, or branch from the left main. In most cases the first or second septal branch will arise from the left anterior descending (LAD). Right anterior oblique (RAO) angiography images are useful to determine size, course, and suitability of the septal branch for wiring and alcohol ablation. Left anterior oblique views are crucial to ensure that the branch vessel indeed supplies the ventricular septum rather than coursing to the lateral wall ( Fig. 21.3 ). Septal branches that course deeper into the ventricular septum will result in a larger area of myocardium for ablation and likely enhance the hemodynamic improvement from ASA. In septal perforator vessels that have diameter >2 mm and multiple branches, a subbranch for ablation should be selected to avoid ablation outside of the target region.
