Septal Ablation for Obstructive Hypertrophic Cardiomyopathy

19 Septal Ablation for Obstructive Hypertrophic Cardiomyopathy



Paul Sorajja


Hypertrophic cardiomyopathy (HCM) is a common, inheritable cardiac disorder with a prevalence of 1 in 500 persons. Dynamic left ventricular outflow tract (LVOT) obstruction frequently is present, affecting up to two thirds of these patients. Although the clinical significance of LVOT obstruction in HCM has been debated, recent studies have linked the presence of obstruction to heightened risk for heart failure and, in some reports, an increased risk of death. Negative inotropic agents, such as beta-receptor antagonists, disopyramide, or calcium-channel blockers (i.e., verapamil, diltiazem), are the cornerstone of drug therapy for symptomatic LVOT obstruction. When severe symptoms persist despite drug therapy, definitive septal reduction therapy should be considered.


The time-honored standard for septal reduction therapy has been surgical myectomy, in which a surgeon uses a transaortic approach to resect ventricular septal hypertrophy. In 1995, percutaneous alcohol septal ablation was introduced as an alternative to surgical myectomy for the relief of LVOT obstruction in patients with HCM. The aim of alcohol septal ablation is to induce a localized myocardial infarction and thinning of the basal ventricular septum, thereby leading to a reduction in septal thickening and systolic excursion into the LVOT.



Patient Selection


Proper patient selection is critical to the success of septal ablation. A comprehensive clinical evaluation and echocardiogram should be performed in all candidates, ideally in a center with expertise in the care of HCM patients. Criteria for septal ablation include:



1. Severe, drug-refractory cardiac symptoms (New York Heart Association functional class III/IV dyspnea or Canadian Cardiac Society angina class III/IV) due to obstructive HCM;


2. Dynamic LVOT obstruction (gradient ≥ 30 mmHg at rest or ≥ 50 mmHg with provocation) that is due to septal hypertrophy and systolic anterior motion of the mitral valve;


3. Ventricular septal thickness ≥15 mm;


4. Absence of significant intrinsic mitral valve disease;


5. Absence of the need for concomitant cardiac surgical procedure (e.g., bypass grafting, valve replacement); and


6. Informed patient consent. Informed consent requires a full understanding of the limited data on long-term survival after the procedure, the risk of pacemaker dependency, the relatively lower success rate due to its dependence on coronary anatomy, and potential complications related to cardiac catheterization and instrumentation of the coronary arteries. Although younger age has not been an absolute contraindication to the procedure, septal ablation generally has been reserved for older adult patients due to the limited data on long-term survival of the procedure. A comprehensive two-dimensional and Doppler echocardiogram is elementary to proper patient selection. This evaluation should document the dynamic nature of the LVOT obstruction and exclude anatomical findings that would impede the clinical efficacy of the procedure (Fig. 19-1).


image

Figure 19-1 Patient selection for septal ablation. A and B, Appropriate patient for septal ablation. There is septal hypertrophy, systolic anterior motion of the mitral valve, and posteriorly directed mitral regurgitation that is secondary to the outflow obstruction. C and D, This patient has obstructive hypertrophic cardiomyopathy, but the mitral regurgitation is secondary to a flail mitral leaflet. Note the anterior course of the mitral regurgitant jet, which is not typical for that due to outflow obstruction. LA, left atrium; LV, left ventricle.



Technique



Hemodynamic Evaluation


Proper performance of septal ablation requires a complete and accurate evaluation of the severity of LVOT obstruction due to HCM. Characteristically, LVOT obstruction in HCM is dynamic and exquisitely sensitive to ventricular loading conditions and contractility. The operator should be cognizant of this sensitivity when examining hemodynamic data from both the echocardiogram and invasive catheterization. Careful attention must be given not only to the initial LVOT gradient observed at rest, but all dynamic and provocable gradients (e.g., variation with respiration, post-premature ventricular contraction accentuation) observed during the procedure.



Transseptal Hemodynamic Assessment


The most accurate method for the invasive evaluation of LVOT obstruction in HCM entails a transseptal approach with positioning of a balloon-tipped catheter (e.g., a 7F Berman catheter, Arrow International Inc., Reading, PA) at the left ventricular inflow region and a pigtail catheter placed retrograde in the ascending aorta for simultaneous measurement of the LVOT gradient. The transseptal approach helps to avoid catheter entrapment, which can be difficult to distinguish from changes in left ventricular pressure that occur due to the dynamic nature of LVOT obstruction. Use of an 8F Mullins sheath for transseptal access also enables recording of left atrial pressure via the side arm for assessment for concomitant diastolic dysfunction.



Retrograde Hemodynamic Assessment


Alternatively, left ventricular pressure can be assessed with a 5F or 6F catheter placed retrograde across the aortic valve. In this technique, a catheter with shaft side holes should not be used because some or all of the holes will be positioned above the level of subaortic obstruction, leading to erroneous measurements of left ventricular pressure and the LVOT gradient. Catheters that may be used for this purpose are a multipurpose or a Halo pigtail catheter. Absence of catheter entrapment should be confirmed with hand contrast injections or demonstration of pulsatile flow from the catheter with disconnection from the extenders used for pressure transduction.



Temporary Pacemaker Placement


The risk of pacemaker dependency from septal ablation varies according to the baseline electrocardiographic abnormalities. Septal ablation frequently results in right bundle branch block (approximately 50% of cases). Thus, for those patients with left bundle branch block, severe left axis deviation, or a very wide QRS interval, the rate of pacemaker dependency approaches 50%. However, permanent pacemaker dependency from complete atrioventricular block still occurs in 10% to 15% of patients with a normal electrocardiogram. Thus, for patients without a permanent pacemaker, a temporary device is placed at the right ventricular septum via the right internal jugular vein prior to septal ablation. Conventional 5F or 6F temporary pacemakers or balloon-tipped catheters can be utilized. Of note, however, some pacemaker catheters have been associated with cardiac perforation, at least partly due to their long dwelling time while patients are observed in the intensive care unit after the procedure. In our practice, we have observed no cardiac perforations with the use of a low-profile, less traumatic temporary pacemaker. The temporary pacemaker should be placed distal or away from the target site of ablation to ensure continuous capture during induction of the septal infarction.



Coronary Angiography

Related posts:

  1. Antithrombotic and Antiplatelet Therapy for Percutaneous Coronary Interventions
  2. Angiography for Percutaneous Coronary Interventions
  3. Carotid Artery Stenting
  4. Peripheral Vascular Intervention

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Jun 4, 2016 | Posted by in CARDIAC SURGERY | Comments Off on Septal Ablation for Obstructive Hypertrophic Cardiomyopathy

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