Septal myectomy is open-heart surgery that removes a strip of thickened heart muscle from the interventricular septum to widen the outflow path of the left ventricle. It is the standard surgical treatment for obstructive hypertrophic cardiomyopathy (HCM) when medications fail to control symptoms like breathlessness, chest pain, and fainting. At experienced centers, the procedure drops the pressure gradient across the left ventricular outflow tract from dangerously high levels down to near-normal, and long-term survival after surgery matches that of the general population.
Why the Surgery Is Needed
In hypertrophic cardiomyopathy, the muscular wall of the heart grows abnormally thick. When the thickening is concentrated in the septum, the wall between the two ventricles, it can bulge into the outflow tract and partially block blood from leaving the left ventricle during each beat. That narrowing gets worse because the mitral valve’s front leaflet gets pulled forward into the flow (a phenomenon called systolic anterior motion, or SAM), creating a dynamic obstruction that worsens with exercise or dehydration. The resulting pressure buildup inside the ventricle causes symptoms and, over years, can lead to heart failure.
Several anatomical features make obstruction more likely. In imaging studies, the presence of a basal muscle bundle in the septum, a large mitral valve–aortic angle, and an elongated anterior mitral leaflet all independently predict worse obstruction.1European Heart Journal – Cardiovascular Imaging. Left ventricular basal muscle bundle in hypertrophic cardiomyopathy: insights into the mechanism of left ventricular outflow tract obstruction In practice, this means the obstruction is not just about how thick the septum is. It involves the geometry of the outflow tract, the size and position of the mitral valve, and even the attachment points of the papillary muscles that anchor the valve in place.
How the Procedure Works
The surgeon reaches the septum through an incision in the aorta, looking down past the aortic valve into the left ventricle. The goal is to carve a trough in the thickened septal muscle, widening the channel enough that blood flows freely and the mitral valve no longer gets pulled into the stream. One widely taught framework divides the septum into three zones of resection. Zone 1, in the center of the septal band, corresponds roughly to the area addressed by the original Morrow procedure developed in the 1960s. Zone 2 extends toward the left trigone (a fibrous landmark near the mitral valve). Zone 3 extends in the opposite direction toward the base of one of the papillary muscles.2The Annals of Thoracic Surgery. Septal Myectomy: How I Teach It
The resection must be aggressive enough to relieve the obstruction but carefully placed to avoid the heart’s electrical conduction system. The first guiding incision is made at the junction of the membranous septum and the right coronary annulus, using a standard scalpel blade. Cutting too far to the right risks damaging the bundle of His, which carries electrical signals from the atria to the ventricles. Zone 3 includes the left bundle branch, so if a patient already has a right bundle branch block before surgery, removing muscle in that area raises the chance of complete heart block.3The Annals of Thoracic Surgery. Septal Myectomy: How I Teach It
The original Morrow procedure used a relatively short incision of about two to three centimeters. Modern modifications extend the resection to five or six centimeters, reaching further toward the apex of the heart. A comparison of the two approaches found the extended version was better at reducing the outflow tract gradient and velocity, restoring normal chamber dimensions, and relieving symptoms.4PubMed Central. Comparison of Modified With Classic Morrow Septal Myectomy in Treating Hypertrophic Obstructive Cardiomyopathy
What Happens to the Obstruction After Surgery
The drop in outflow tract gradient is dramatic and immediate. In one series, the peak pressure gradient fell from about 83 mmHg before surgery to roughly 12 mmHg afterward, and mitral regurgitation (the backward leak of the valve caused by SAM) also improved significantly.5PubMed Central. Impact of septal myectomy on diastolic function in patients with obstructive hypertrophic cardiomyopathy A study with a mean follow-up of nearly five years showed similar results: the outflow gradient dropped from about 90 mmHg to 16 mmHg, septal thickness fell from roughly 19 mm to 14 mm, and mitral regurgitation grade dropped substantially. Functional class improved from an average that indicated marked limitation to one indicating mild or no limitation.6PubMed Central. Septal Thickness Does Not Impact Outcome After Hypertrophic Obstructive Cardiomyopathy Surgery (Septal Myectomy and Subvalvular Mitral Apparatus Remodeling): A 15-Years of Experience
This relief is durable. A study following patients for a mean of over six years found that long-term survivors had minimal or no symptoms at last follow-up.7The Annals of Thoracic Surgery. Long-lasting improvement after septal myectomy for hypertrophic obstructive cardiomyopathy A prospective cohort study also confirmed that myectomy significantly improved both overall quality of life and functional capacity, as reported by patients themselves.8JAMA Network Open. Association of Septal Myectomy With Quality of Life in Patients With Left Ventricular Outflow Tract Obstruction From Hypertrophic Cardiomyopathy
Long-Term Survival
The survival data after myectomy are reassuring. A landmark study of over 200 patients found that one-, five-, and ten-year survival after surgery was 98%, 96%, and 83%, respectively, with a procedural mortality rate under 1%. Those numbers did not differ from the age- and sex-matched general U.S. population.9PubMed. Long-term effects of surgical septal myectomy on survival in patients with obstructive hypertrophic cardiomyopathy A separate series from Tufts Medical Center reported five-year and ten-year survival of 94% and 91%, which likewise matched the general population.10PubMed Central. Results of surgical septal myectomy for obstructive hypertrophic cardiomyopathy: the Tufts experience
Put another way, a successful myectomy effectively normalizes life expectancy for most patients. That is remarkable for a condition that, untreated or undertreated, carries a real risk of progressive heart failure and sudden death.
Risks and Complications
No open-heart surgery is without risk, and myectomy has a specific complication profile shaped by the anatomy involved. The most tracked complication is damage to the electrical conduction system. In a large study of nearly 2,500 patients, about 39% of those with normal baseline conduction developed a new left bundle branch block after surgery, but this is typically well tolerated and rarely causes symptoms on its own. Complete heart block, which requires a permanent pacemaker, occurred in only about 2.3% of all patients. The risk was much higher, around 35%, in the small subgroup who already had a right bundle branch block before surgery.11PubMed. Conduction Abnormalities and Long-Term Mortality Following Septal Myectomy in Patients With Obstructive Hypertrophic Cardiomyopathy
A rare but serious complication is an iatrogenic ventricular septal defect, where the resection accidentally creates a hole between the two ventricles. This is uncommon enough that individual case reports describe novel repair techniques.12Annals of Thoracic Surgery. A Novel Surgical Technique to Address Post-Septal Myectomy Ventricular Septal Defect When it does occur, it can sometimes be closed with a catheter-based device rather than a second open surgery.13PubMed Central. Retrograde percutaneous closure of a ventricular septal defect after myectomy for hypertrophic obstructive cardiomyopathy
When the obstruction returns after a first myectomy, the usual cause is that too little muscle was removed the first time. In a study of patients needing reoperation, the most common mechanism was a limited initial resection, followed by obstruction at the mid-ventricular level. Other causes included unusual papillary muscle anatomy and accessory chords attaching the mitral valve to the septum or ventricular wall.14The Annals of Thoracic Surgery. Mechanisms for Recurrent Left Ventricular Outflow Tract Obstruction After Septal Myectomy for Obstructive Hypertrophic Cardiomyopathy
Why the Hospital You Choose Matters Enormously
Myectomy is one of the operations most sensitive to surgical volume. In a national analysis, hospitals performing fewer than one myectomy per year on average had dramatically worse outcomes: about five times the early mortality, over nine times the rate of ventricular septal defect, double the rate of complete heart block, and roughly nine times the likelihood that the mitral valve would need to be replaced rather than simply repaired.15PubMed. Impact of Hospital Volume on Outcomes of Septal Myectomy for Hypertrophic Cardiomyopathy A separate study confirmed that myectomy-specific volume, not the hospital’s overall cardiac surgery volume, was the factor that mattered. Higher myectomy volume was also associated with greater use of mitral valve repair over replacement.16PubMed. Volume-outcome relationship in septal myectomy for hypertrophic obstructive cardiomyopathy
Even at the operator level, the pattern holds. Low-volume operators had roughly double the odds of 30-day mortality and about 50% higher risk of 90-day hospital readmission compared to high-volume operators.17PubMed Central. Procedural Volume and Outcomes After Septal Reduction Therapies in Hypertrophic Obstructive Cardiomyopathy The practical takeaway is blunt: if you or someone you know needs this surgery, traveling to a center that does it regularly can be the single most important decision in the process.
Myectomy Versus Alcohol Septal Ablation
The main alternative to surgery is alcohol septal ablation, a catheter-based procedure that injects ethanol into a small artery feeding the thickened septum, deliberately causing a controlled heart attack to thin the muscle. It avoids open-heart surgery, which makes it appealing, but the two approaches are not equivalent in outcomes.
A systematic review and meta-analysis found that ablation produced less gradient reduction (about 48 mmHg versus 58 mmHg with myectomy) and less symptom improvement. Ablation had a lower rate of complications around the time of the procedure, but patients were far more likely to need a repeat procedure (about 10% versus well under 1% for myectomy) and more likely to end up pacemaker-dependent (roughly 12% versus 4%).18PubMed Central. Alcohol Septal Ablation versus Septal Myectomy Treatment of Obstructive Hypertrophic Cardiomyopathy: A Systematic Review and Meta-Analysis Another meta-analysis similarly found that ablation was associated with less gradient reduction and a substantially higher reoperation rate compared to myectomy.19PubMed. Alcohol septal ablation versus surgical septal myectomy of obstructive hypertrophic cardiomyopathy: systematic review and meta-analysis
The survival difference is stark. Over a median follow-up of about six years, the ten-year all-cause mortality rate was roughly 26% in the ablation group versus about 8% in the myectomy group.20PubMed. Survival Following Alcohol Septal Ablation or Septal Myectomy for Patients With Obstructive Hypertrophic Cardiomyopathy Some of that difference likely reflects patient selection: ablation is often offered to older or sicker patients who are not good surgical candidates. Still, the data strongly favor myectomy when a patient is a reasonable candidate for both. Ablation remains a useful option for patients who cannot safely undergo open surgery or who strongly prefer to avoid it.
When the Mitral Valve Needs Attention
Mitral regurgitation in obstructive HCM is usually caused by SAM, and it resolves once the outflow obstruction is relieved by myectomy. Sometimes, though, the mitral valve has its own structural problems, like a prolapsing leaflet, or SAM persists after resection. In those cases, the surgeon may add a mitral valve procedure during the same operation.
Current guidelines strongly prefer repair over replacement when the valve needs intervention. A national propensity-matched analysis covering 15 years of data found that mitral valve replacement, compared to repair, carried about three times the procedural mortality (roughly 8% versus 3%), a higher rate of complete heart block, and a greater need for permanent pacemakers.21PubMed. Surgical Outcomes of Septal Myectomy With and Without Mitral Valve Surgeries in Hypertrophic Cardiomyopathy: a National Propensity-Matched Analysis (2005 to 2020) One repair technique that has shown good long-term results is the edge-to-edge repair, which stitches the tips of the mitral leaflets together to prevent SAM. It is especially useful when the septum is too thin for a safe or effective myectomy on its own.22PubMed. Edge-to-Edge Mitral Repair Associated With Septal Myectomy in Hypertrophic Obstructive Cardiomyopathy
Transapical Myectomy for Mid-Ventricular Obstruction
Not all obstruction happens right below the aortic valve. Some patients have obstruction in the middle of the ventricle, where the standard transaortic approach simply cannot reach well. For these cases, surgeons can make a small incision at the apex of the heart and resect the offending muscle from below. This transapical approach provides direct visualization of the mid-cavity and can be combined with the standard transaortic myectomy when obstruction exists at both levels.23PubMed. Transapical Septal Myectomy for Hypertrophic Cardiomyopathy With Midventricular Obstruction Some centers consider it the preferred method for complex, long-segment obstruction because it offers better exposure than trying to work through the aorta or the mitral valve.24Operative Techniques in Thoracic and Cardiovascular Surgery. Role of Transapical Incision in the Surgical Management of Hypertrophic Cardiomyopathy
A recent comparison of the transapical beating-heart approach with the traditional transaortic on-pump method found similar rates of complete heart block requiring a pacemaker (about 4% in both groups). Patients in the transapical group had less post-operative atrial fibrillation, though the two cohorts differed in baseline characteristics, making direct comparisons imperfect.25PubMed Central. Septal myectomy for obstructive hypertrophic cardiomyopathy: Comparison of outcomes of the transapical beating-heart and transaortic on-pump approaches
Myectomy in Children and Adolescents
HCM can affect children, including infants, and the disease tends to be more aggressive in younger patients. Myectomy in the pediatric population has been shown to be safe and effective, with operative mortality of about 1% in one large series of 199 patients. Outflow tract gradients dropped from a median of 50 mmHg to 4 mmHg immediately after surgery and remained low (about 5 mmHg) at ten years. Overall ten-year survival was 90%, compared to roughly 47% in a previously reported group of pediatric HCM patients who did not undergo surgery.26PubMed Central. Septal Myectomy Outcomes in Children and Adolescents With Obstructive Hypertrophic Cardiomyopathy
The catch with younger patients is that the heart continues to grow, and hypertrophy can recur. The cumulative rate of redo myectomy was about 6% at five years and 8% at ten years, and the children who needed a second operation tended to be younger at their first surgery. Infants who undergo myectomy show favorable long-term outcomes overall, but they do trend toward a higher reoperation rate later in life.27European Journal of Cardio-Thoracic Surgery. Clinical long-term outcome of septal myectomy for obstructive hypertrophic cardiomyopathy in infants
Effect on Sudden Cardiac Death Risk
HCM is one of the most recognized causes of sudden cardiac death in young people, and many patients have implantable defibrillators (ICDs) as a safety net. There is evidence that myectomy itself reduces the risk of dangerous heart rhythms. In a study comparing HCM patients with ICDs who had undergone myectomy to those who had not, the rate of appropriate ICD discharges (meaning the device fired because a life-threatening rhythm actually occurred) was about 0.24% per year in the myectomy group versus 4.3% per year in the non-myectomy group. No patient in either group died suddenly during follow-up.28European Heart Journal. Surgical septal myectomy decreases the risk for appropriate implantable cardioverter defibrillator discharge in obstructive hypertrophic cardiomyopathy
That said, myectomy does not eliminate arrhythmia risk entirely. Case reports describe patients who developed dangerous ventricular rhythms or even sudden death after surgery, particularly when risk factors persisted.29PubMed Central. Risk stratification for sudden cardiac death after septal myectomy The decision about whether to keep or implant an ICD after myectomy remains individualized and is made based on ongoing risk assessment.
Exercise Capacity After Surgery
One of the main reasons patients seek myectomy is that they cannot exercise comfortably. Early research showed that about 89% of patients achieved higher exercise levels after surgery, with an accompanying increase in their oxygen consumption during exercise.30PubMed. Exercise performance after septal myotomy and myectomy in patients with obstructive hypertrophic cardiomyopathy However, the improvement is not universal. More recent work has shown that the change in peak oxygen uptake after myectomy is variable, and some patients actually see a decrease. Researchers have worked to identify clinical predictors of who will and will not improve, but the variability underscores that removing the obstruction addresses one bottleneck in a disease that can involve diastolic dysfunction, microvascular disease, and other issues beyond the outflow tract.31PubMed. Predictors of exercise capacity following septal myectomy in patients with hypertrophic cardiomyopathy
Does Genetic Subtype Affect Surgical Outcomes
HCM can be caused by mutations in a number of different genes, and genetic testing is increasingly part of routine care. A natural question is whether the specific mutation a patient carries changes how well they do after myectomy. A study that grouped patients into those with confirmed disease-causing mutations, those with variants of uncertain significance, and those with no identified variant found some interesting differences before surgery: mutation-positive patients were younger, had higher rates of ICD use, and showed more severe hypertrophy and fibrosis on tissue examination. But the results that matter most were reassuringly similar: the outflow gradient at hospital discharge and the long-term survival after surgery were comparable across all genetic groups. No individual gene mutation significantly affected survival.32PubMed. Does the genotype of hypertrophic cardiomyopathy impact the outcomes of septal myectomy?
This is encouraging news for patients undergoing genetic testing. While the mutation you carry influences the disease’s natural history and may affect screening recommendations for family members, it does not appear to change the surgical result when myectomy is performed. The operation works on the mechanical problem regardless of which gene created it.