Left Ventricular Outflow Tract Obstruction (LVOTO)

OVERVIEW

Left ventricular outflow tract obstruction (LVOTO) is commonly associated with systolic anterior motion (SAM) of the mitral valve. Congenital heart disease is an important cause in the paediatric population.

• LVOTO is defined as “an instantaneous peak Doppler LVOT pressure gradient at least 30 mmHg at rest or during physiological provocation such as Valsalva manoeuvre (Slama et al, 2012)
• LVOTO occurs at the subvalvular level – technically the valvular (e.g. aortic stenosis) or supravalvular levels are not part of the LVOTO
• SAM can occur in the normal population, but is usually associated with hypertrophic cardiomyopathy (HCM)or acutely after mitral valve repair
• SAM occurs when “a permissive physiological state arises in an anatomically susceptible heart” (Ibrahim et al, 2012). 
• LVOTO and SAM are important to recognise as they can contribute to a low output state that paradoxically worsens with increased inotropic support

CAUSES

LVOTO usually results from SAM caused by:

• HCM
• Other causes of left ventricular hypertrophy (LVH)
• Mitral valve repair (of degenerative/ myxoedematous valves)

Rarer causes of LVOTO/SAM:

• After aortic valve replacement (AVR) for aortic stenosis
• Congenital heart disease (e.g. subaortic stenosis, transposition of the great arteries, LVOTO associated with atrio-ventricular septal defect) (Stephen’s et al, 2020; Aboulhosn & Child, 2006)
• Post-myocardial infarction (altered LV geometry due to opposition of hypokinetic and hyperkinetic regions)
• Takotsubo cardiomyopathy
• Sigmoid septum – interventricular septal bulge due to fibrosis and hypertrophy in the elderly
• Critically ill patients in hypovolaemic/ vasodilated states (e.g. septic shock)
• Cor pulmonale (enlarged RV with decreased LV size)
• Cardiac allograft rejection

PATHOPHYSIOLOGY

HCM

• HCM most commonly involves the interventricular septum (~60%), which is termed asymmetric septal hypertrophy
• HCM is the preferred term to HOCM because the presence of LVOT obstruction can be dynamic depending on loading conditions
• The mitral valve may appear normal in HCM during diastole
• Anteriorly displaced mitral papillary muscles may be seen in HCM resulting in anterior leaflet chordal laxity which predisposes to SAM
• In systole the MV apparatus moves anteriorly (SAM), and the bulge of the anterior mitral valve leaflet may touch the interventricular septum causing LVOTO
• SAM is most prominent in late systole as the LV empties and cavity size is decreased (SAM therefore is a dynamic obstruction i.e., gets worse throughout systole, as opposed to aortic stenosis which is a fixed obstruction)

Mitral valve repair

• SAM is rare in myxomatous mitral valve disease unless operated upon
• Hence SAM after mitral valve repair is considered an iatrogenic condition
• Defects of the mitral leaflets, the annulus, and subvalvular apparatus (e.g. chordae, papillary muscles) may all contribute to SAM after mitral valve repair

SAM is exacerbated by:

• factors that decrease the distance between the mitral valve
  • Decreased LV end-diastolic volume
    • Underfilled LV/ hypovolaemia
    • Tachycardia (decreased time for diastolic filling)
  • Hypertrophy (decreased cavity size)
• Factors that increase blood velocity through the LVOT, which pulls the mitral valve leaflet into the LVOT due to the Venturi effect (pressure falls with increased velocity) and drag forces
  • Hypercontractility (inotropes)
  • Decreased afterload
  • Exercise

ASSESSMENT

History

• Predisposing factors, especially:
  • HCM
  • Mitral valve repair if degenerative disease, with excessive redundancy of the anterior and/or posterior leaflets, and/or an undersized rigid ring
    • NOT ischaemic mitral valve repair (tethered leaflets) or mitral valve replacement (leaflet resected)
  • Other causes of LVOTO/SAM
• Exacerbating factors, such as:
  • Inotropes
  • Underfilled LV/ hypovolaemia
  • Tachycardia
  • Decreased afterload
• Symptoms consistent with low output state or predisposing factors (e.g. syncope, chest pain, dyspnoea, palpitations)

Examination

• late systolic murmur over the praecordium
• Low cardiac output state (without tamponade)

Investigations

• A TTE allows the best Doppler angle line up to assess the LVOT gradient. A TOE may be required if there the patient has poor transthoracic windows or if a sub-valvular membrane is suspected.
• Echocardiography findings  may include:
  • Reduced LV end-diastolic diameter (< 2.2 cm/m²)
  • Increased basal septal wall thickness (>1.2 cm)
  • Normal systolic function and no regional wall motion abnormalities (RWMA)
  • Flow acceleration noted in LVOT on colour Doppler
    • SAM is characterised by a “saber-shaped Doppler flow curve with late acceleration” (Slama et al, 2012)
  • Reduced LVOT area during systole on visual 2D assessment
  • Hypertrophy and anteriorly displaced papillary muscles
  • Systolic anterior motion (SAM) of mitral valve leaflets with or without septal-anterior leaflet contact
  • High peak gradient across LVOT (>30 mmHg) measured on CW
    • Generally >50 mmHg required for haemodynamic significance (Slama et al, 2016)

• Mitral regurgitation with posteriorly directed eccentric jet due to distortion of leaflet coaptation
• Concomitant mid-cavity LV obstruction in HCM
• ECG
  • ECG consistent with HCM: high voltages, nonspecific ST and T wave changes, and “dagger-like” Q waves (see LITFL ECG Library)
• For patients with complex anatomy, consider:
  • Cardiac MRI 
  • 3D echocardiography

MANAGEMENT

Specific therapy

• Medical therapies
  • Volume load to correct an underfilled LV and stop diuretics
  • Stop inotropes (e.g. adrenaline) to reduce hypercontractility
  • Consider beta-blockers to slow heart rate and reduce contractility
  • AV sequential pacing has a limited role and is considered only in HCM patients who are unable to undergo myomectomy or alcohol septal ablation (pacing may reduce the LVOT gradient and facilitate treatment with beta blockers/calcium channel blockers)
  • Increase afterload 
    • Stop vasodilators (e.g. GTN, nitroprusside)
    • Use vasoconstrictors with minimal inotropic effect (e.g. metaraminol, phenylephrine, low dose noradrenaline, vasopressin)
• Surgery if severe LVOTO or refractory to medical management, options depend on the underlying cause and include:
  • HCM options:
    • myomectomy
    • percutaneous alcohol septal ablation
    • Primary prevention implantable cardiac defibrillations (ICDs) may be indicated based on the patient’s clinical risk profile (i.e., degree of LV wall thickness, LA size, LVOT gradient and family history of SCD etc.).
    • Secondary prevention ICDs are generally indicated for survivors of cardiac arrest due to ventricular arrythmias (See ESC HCM guidelines for more details)
  • Post mitral valve repair options:
    • anterior valvuloplasty
    • sliding posterior leaflet plasty technique to move the coaptation point posteriorly

Supportive care and monitoring

• Serial echocardiography useful for assessing response to therapy (e. reduction in CW peak velocity across the LVOT)

References and Links

LITFL

• LITFL CCC — Hypertrophic cardiomyopathy
• LITFL ECG Library — Hypertrophic cardiomyopathy (HCM)

Journal articles

• Aboulhosn J, Child JS. Left ventricular outflow obstruction: subaortic stenosis, bicuspid aortic valve, supravalvar aortic stenosis, and coarctation of the aorta. Circulation. 2006;114(22):2412-2422. doi:10.1161/CIRCULATIONAHA.105.592089 [article]
• Authors/Task Force members, Elliott PM, Anastasakis A, et al. 2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy: the Task Force for the Diagnosis and Management of Hypertrophic Cardiomyopathy of the European Society of Cardiology (ESC). Eur Heart J. 2014;35(39):2733-2779. doi:10.1093/eurheartj/ehu284 [article]
• Daubert C, Gadler F, Mabo P, Linde C. Pacing for hypertrophic obstructive cardiomyopathy: an update and future directions. Europace. 2018;20(6):908-920. doi:10.1093/europace/eux131 [pubmed]
• Ibrahim M, Rao C, Ashrafian H, Chaudhry U, Darzi A, Athanasiou T. Modern management of systolic anterior motion of the mitral valve. Eur J Cardiothorac Surg. 2012 Jun;41(6):1260-70. doi: 10.1093/ejcts/ezr232. Epub 2012 Jan 18. PMID: 22290892. [article]
• Slama M, Tribouilloy C, Maizel J. Left ventricular outflow tract obstruction in ICU patients. Curr Opin Crit Care. 2016 Jun;22(3):260-6. doi: 10.1097/MCC.0000000000000304. PMID: 27054628. [pubmed]
• Stephens EH, Dearani JA, Johnson JN, Ackerman MJ, Ommen SR, Schaff HV. The Surgeon’s View of the Left Ventricular Outflow Tract in Congenital Heart Surgery. World J Pediatr Congenit Heart Surg. 2020 Sep;11(5):595-610. doi: 10.1177/2150135120936632. PMID: 32853058. [pubmed]
• Termini BA, Jackson PA, Williams CD. Systolic anterior motion of the mitral valve following annuloplasty. Vasc Surg. 1977 Mar-Apr;11(2):55-60. doi: 10.1177/153857447701100203. PMID: 616134. [pubmed]

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