Surgical Head-Scratcher: What to Do When LVOTO Presents with Minimal Hypertrophy?

By Nicholas Smedira, MD

Classically, left ventricular outflow tract obstruction (LVOTO) was identified when symptomatic patients were found on echocardiography to have a septum measuring approximately 20 mm and had LVOTO at rest or when provoked by a Valsalva maneuver or administration of amyl nitrate.

When LVOTO due to this severity of septal hypertrophy is identified, treatment is straightforward: A myectomy or an alcohol septal ablation is performed, which eliminates the obstruction. The patient’s symptoms improve or completely disappear.

Increasingly not so simple

At Cleveland Clinic we are identifying increasing numbers of patients who have LVOTO with minimal to mild left ventricular (LV) hypertrophy (septum of 13 to 17 mm) (Figure). It is not known which of the following these cases of mild or no hypertrophy represent:

• A unique form of hypertrophic obstructive cardiomyopathy (HOCM)
• A very early presentation of what we have labeled adult HOCM defined by the magnitude of the hypertrophy
• Intrinsic mitral valve abnormalities that cause obstruction and then secondary hypertrophy

While these cases can be much more difficult to diagnose, our imaging experience has grown and our surgical arsenal has expanded, yielding more tools than ever to diagnose and treat these clinically challenging symptomatic patients who present with relatively normal resting echocardiographic images.

Limited options breed new techniques

Patients in this subgroup with LVOTO and mild or no hypertrophy often present a diagnostic dilemma. The lack of hypertrophy and absence of a resting gradient mean a more aggressive diagnostic approach (such as with amyl nitrate or exercise stress testing) is needed. Moreover, if such tests are performed and the LVOTO is identified, options are limited because there is insufficient hypertrophy for alcohol ablation or substantial myectomy to open the outflow tract.

These constraints have prompted us to develop new diagnostic approaches and surgical techniques to identify and treat LVOTO with minimal hypertrophy. In such cases, often seen in young and healthy patients, we typically perform a stress echocardiogram during vigorous exercise on an upright bicycle. This avoids the rapid heart rate recovery seen with standard treadmill testing and increases the chance we will provoke obstruction. We also employ MRI to look at the septal and subvalvular anatomy.

Surgical resourcefulness can avoid valve replacement

Once LVOTO is documented and the anatomy defined, we consider which surgical options can be used to eliminate the obstruction. While valve replacement can effectively address all cases of LVOTO caused by systolic anterior motion of the mitral valve, we favor repair techniques that avoid prosthetic valve replacement — especially in young, healthy patients.

The surgical options we use include:

• Limited myectomy based on detailed measurements of septal thickness
• Resection of anomalous structures, including muscle bands, fibrous bands, abnormal chordae and abnormally inserting papillary muscles
• Shortening the anterior leaflet of the mitral valve, resecting tethering secondary chordae, and reorienting and then reanchoring mobile papillary muscle heads to prevent systolic anterior motion (as shown in the illustration at the top of this post)

In our experience, about 75 percent of patients who have severe LVOTO with minimal or no LV hypertrophy are candidates for corrective repair that avoids valve replacement.

The following composite case vignette illustrates some of the approaches used by surgeons in Cleveland Clinic’s Department of Thoracic and Cardiovascular Surgery when a patient presents with symptoms of LVOTO and minimal septal hypertrophy.

Case vignette: Avoiding valve replacement in a young athlete

• History and presentation. The patient is a previously healthy 25-year-old male and a former NCAA Division I athlete. Over the 18 months following his graduation from college, he noted a gradual progression of exertional dyspnea, to the point that he was unable to participate in recreational sports. Symptoms progressed to shortness of breath when walking up hills and then while walking on level ground.
• Diagnosis. Diagnostic evaluation included normal resting transthoracic and transesophageal echocardiogram, with measurements of the LV septum ranging from 9 to 13 mm. Treadmill stress echo suggested systolic anterior motion of the mitral valve without a detectable outflow tract gradient. Upright bicycle stress echocardiogram at peak exercise capacity revealed severe systolic anterior motion of the anterior mitral valve leaflet with a peak gradient of 120 mm Hg and development of severe (grade IV) posteriorly directed mitral regurgitation. MRI confirmed normal septal thickness and suggested elongation of the anterior mitral valve leaflet and a multiheaded papillary muscle complex.
• Surgical intervention. At the time of surgery we found that (1) the anterior leaflet was elongated, (2) there was an anomalous inserting head of the anterior lateral papillary muscle into the A1 segment of the mitral valve, and (3) there was excessive mobility of the two papillary muscle heads. We eliminated the inducible LVOTO by resecting the anomalous papillary muscle head, shortening the anterior leaflet of the mitral valve and fixating the two papillary muscle heads posteriorly.
• Outcome.After an uneventful recovery, the patient is now NYHA class I and has resumed prior athletic endeavors without difficulty.

Figure. MRI of a patient with severe obstruction with minimal septal hypertrophy.

Dr. Smedira is a surgeon in the Department of Thoracic and Cardiovascular Surgery. Contact him at smedirn@ccf.org.