< BACK

Hypertrophic Obstructive Cardiomyopathy (HOCM)

---

Pathophysiology:

• Genetically determined primary cardiac muscle disease.
• 60-70% caused by mutations in sarcomere genes.
• Characterized by LV Hypertrophy in the absence of other aetiologies.
• Asymmetric LV hypertrophy especially the interventricular septum is the Hallmark of HOCM
• There is diastolic dysfunction and varying degrees of dynamic LVOT obstruction.
• Myocardial ischaemia may also be present.
• Most commonly results from hypertrophy of the basal septum with mitral-septal contact secondary to SAM of the AML causing (posteriorly directed) MR caused by incomplete leaflet coaptation.
• Venturi or Drag Effect:
  • High LVOT blood velocities which pull the AML towards the septum (SAM)
    • Causing mechanical impedance to blood flow.
    • Create a pressure gradient between the LV and the aorta at mid-systole.
• Associated with a variety of anomalies of the mitral valve apparatus:
  • Elongated AML and PML
  • Anterolateral papillary muscle displacement. 
  • Anterolateral papillary muscle insertion into the middle of AML
  • Anomalous chords insertion into the middle of the AML.
• ​Subsets of HOCM:
  • ​Basal Septal Hypertrophy:
    • ​Associated SAM
    • LVOT Obstruction
  • Pure Mid-ventricular Obstruction:
    • ​Septal contact with papillary muscles causes obstruction to blood flow.
    • MV leaflets do not contribute to the obstruction
    • There is no SAM
    • Causes high intra-ventricular pressure in the apical area and in combination with subendocardial ischaemia, it predisposes to apical aneurysm.
    • Septal Myectomy is performed through an apical incision.
    • this can be combined with subaortic approach to adequately relieve obstruction. 
  • Apical non-obstructive HOCM:
    • ​Non-obstructive and most are asymptomatic.
    • Some may suffer from severe diastolic dysfunction.
    • Severe LV hypertrophy with very small ventricular cavity reducing LV diastolic filling.
    • ​​Apical Myectomy aiming to enlarge the LV volume:
      • Improves haemodynamics
      • Improves functional capacity
      • May delay or eliminate the need for Heart Transplant

Clinical Presentation:

• Asymptomatic:
  • ​Non-obstructive HOCM.
  • Good Prognosis
  • 10% progress to NYHA class III/IV symptoms.
  • Survival is comparable with age matched controls.
• Symptomatic Heart Failure caused by diastolic dysfunction, MR and LVOT obstruction.
• 70% have resting or provoked LVOT obstruction.
• 25% have resting LVOT gradient >30mmHg.
• Maximum subaortic pressure gradient >30mmHg
  • Resting or after provocation.
  • Diagnostic
  • Predicts HF and poor prognosis
• Syncope due to reduced CO from LVOT obstruction.
• Angina:
  • Coronary microvascular abnormalities.
  • Inadequate capillary densities for the degree of hypertrophy. 
• Arrhythmias:
  • Supraventricular and ventricular arrhythmias.
  • Sudden cardiac death 0.5 - 1.5% / year
  • more common in patient >30 years old.
  • Rare > 60 years of age.
  • Increased risk when associated with:
    • History of Cardiac arrest.
    • Family history of HOCM-related sudden death.
    • Sustained VT
    • Recurrent prolonged episodes of non-sustained VT. 
    • Massive LVH >30mm
    • Apical LV aneurysm.
    • LGE >15% of LV mass.
    • End-stage HOCM with EF <30% and an Apical LV aneurysm.
  • ​Atrial Fibrillation: 
    • in 20% due to left atrial dilatation.
    • Common in advanced HF and systolic dysfunction.
    • Poorly tolerated due to loss of atrial kick with severe LVH causing reduced CO.
    • A predictor of poor outcome.
    • Treated with:
      • amiodarone.
      • anticoagulation.
      • Catheter AF ablation.
      • Maze procedure at the time of surgical myectomy.
  • Advanced HF with systolic dysfunction that may require Heart Transplant.​​​

Preoperative Evaluation:

• TTE:
  • Most commonly used imaging to assess:
    • LV morphology including the subaortic area.
    • Haemodynamics by Doppler.
    • identify SAM and associated posteriorly directed MR jet.
    • Intrinsic mitral valve disease or anomalies of the mitral apparatus.
    • Intra-operative TOE to further assess the Mitral Valve.
• Provocative Tests:
  • For latent LVOT obstruction in patients with exertional symptoms patients with no or minimal LVOT gradients at rest.
  • Valsalva manoeuvres, amyl nitrate inhalation or simple exercise to elicit outflow tract obstruction murmur.
  • Confirmed using these manoeuvres with TTE.
  • Failure to confirm LVOT obstruction will necessitate further tests.
• Cardiac Catheterisation: 
  • Suspected labile LVOT obstruction not confirmed on TTE.
  • Provocative Tests:
    • Isoproterenol stimulation.
    • Nitrates infusion.
    • Eliciting PVC.
  • Documentation of LVOT gradient >50mmHg confirms the diagnosis.

Management:

• Consensus guidelines recommend initial medical therapy for Obstructive HOCM with:
  • Beta Blockers.
  • Calcium channel blockers
  • +/- Disopyramide (Class IA anti arrhythmic Na Channel Blocker)
• Invasive Relief of LVOT obstruction: 
  • those who continue to be symptomatic under optimal therapy:
    • with impaired functional capacity.
    • Subaortic pressure gradient >50mmHg (at rest or after provocation)
  • Do not tolerate side effects of medications.
• Transaortic septal myectomy is the standard treatment for septal reduction.
  • Survival after myectomy for obstructive HOCM is similar to non-obstructive HOCM
  • Survival after myectomy is superior to unoperated obstructive HOCM.
  • Evidence for beneficial effect on late survival:
    • Reduced incidence of ICD discharges.
    • Diminished MR
    • Improved PHT
    • Degree of reversed myocardial remodelling.
  • It is also possible to perform for other subsets of HOCM.
• Apical Myectomy:
  • Used for pure midventricular obstruction 
    • To enlarge LV volume and improve LV Filling.
    • Provides immediate relief of symptoms.
    • Has excellent long-term outcome.
    • Eliminate or delays the need for Transplant
  • Can be combined with Subaortic Myectomy to achieve adequate relief of obstruction.
• Contraindications to Surgical Myectomy:
  • General contraindications for Cardiac Surgery:
    • Advanced Age.
    • Frailty.
    • Multiple Comorbidities that limit expected survival.
  • Alcohol (Ethanol) Septal Ablation: ​​may be an alternative choice for High Risk Patients with contraindications to surgical myectomy.​

Septal myectomy performed through a low oblique aortotomy extending into the noncoronary sinus using ​no. 10 blade.
(Copyright ©2015, Mayo Foundation)

Long-segment septal hypertrophy may require both a transaortic approach and a transapical approach. 
(Copyright ©2017, Mayo Foundation)

Alcohol (Ethanol) Septal Ablation:​

• Also known as:
  • Percutaneous Transluminal Septal Myocardial Ablation
  • Trans-coronary ablation of Septal Hypertrophy.
  • Non-Surgical Septal Reduction Therapy.
• Relieves obstruction by creating a localized myocardial infarction in the basal septal muscle. 
• Following remodelling of this area, the LVOT is widened, relieving the obstruction.
• Improves symptoms and increases exercise capacity.
• Benefits are comparable in younger and older (age >60 year) patients
• Procedure:
  • During Cardiac Catherization the First and Second septal perforator branches of the LAD are injected with Ethanol to create a localized controlled MI in the basal septum 
  • Remodelling over time will widen the LVOT and relieves the obstruction.
  • A Large scar is created (10%) of total LV mass.
  • MCE (Myocardial Contrast Echocardiography):
    • Delineate the size of the septal vascular area
    • Predict the infarct size.​
    • May lower the risk of CHB requiring PPM. 
• Drawbacks:
  • Repeat Ablation may be required in 6%.
  • Conflicting data regarding efficacy in marked septal thickness:
    • Survival is significantly worse in septal thickness >25mm
    • Better long term survival in septal thickness <16mm but with increase early complication.
• Complications:
  • Coronary artery dissection (LAD 1.8%).
  • Pericardial effusion (0.6%)
  • Large MI secondary to escape of ethanol from the target vessel to another coronary artery (usually the LAD).
  • Complete Heart Block ( requiring PPM 10%) (More RBBB being supplied by the septal perforators)
  • Ventricular Tachyarrhythmia 
  • Arrhythmic Death (VF 2.2%) (there is no definitive evidence that septal ablation increased sudden cardiac death)
  • VSD ( should not be performed with septal thickness <15mm)

Depiction of alcohol (ethanol) septal ablation
© 2021 UpToDate, Inc. and/or its affiliates. (Graphic 78141 Version 6.0)

Comparison between Surgical Myectomy and Alcohol Ablation:

• Uncertain effectiveness in massive LV hypertrophy (>30mm), surgical myectomy should be considered instead.
• Surgical Myectomy results in significantly lower residual LVOT gradients.
• No significant difference in long-term survival.

Surgical Myectomy	Alcohol Septal Ablation
Higher success rate 90-95%	Success Rate 80-90%
Immediate sustained relief of LVOT obstruction and concomitant MR	Delay up to 3 months in improvement
Ability to obtain tissue biopsy	No Biopsy
Lower incidence of CHB 3%	Incidence of CHB 10%
Better Symptom resolution
Proven long-term efficacy (>20 years)
More chances of success in massive septal hypertrophy (>30mm)	Avoided in massive septal hypertrophy (>30mm)
No damage distal to target area	Risk of myocardial damage distal to the target area
Ability to perform concomitant procedures (AF ablation, CABG, MR repair/replacement)	Avoidance of Sternotomy and CPB especially in high risk patient,  shorter hospital stay, lower costs.
May reduce the risk of Sudden Cardiac Death and ICD discharges	Lower Risk of VSD

---

HOCM: Hypertrophic Obstructive Cardiomyopathy, ​LV: Left Ventricle, LVOT: Left Ventricular Outflow Tract, CO: Cardiac Output
AML: Anterior Mitral Leaflet, PML: Posterior Mitral Leaflet, MR: Mitral Regurgitation, LGE: Late Gadolinium Enhancement, PHT: Pulmonary hypertension, CHB: Complete Heart Block, ​PPM: Permanent Pacemaker