FRCA Notes

Hypertophic (Obstructive) Cardiomyopathy

Resources

  • Hypertrophic cardiomyopathy is an inherited myocardial disorder characterised by unexplained, inappropriate LV hypertrophy in the absence of an hypertrophic stimulus

  • Several subtypes exist:
    • Associated diastolic dysfunction
    • Asssociated dynamic LVOT obstruction secondary to systolic anterior motion of the mitral valve apparatus (SAM), which may result in MR
    • As a phenotype of several conditions e.g. Friedrich's ataxia, Anderson-Fabry's disease, bicuspid aortic stenosis, WPW syndrome
  • Affects 1 in 500 i.e. the commonest genetic cardiovascular disease
  • Twice as common in men as in women
  • Autosomal dominant disease but with variable pentrance and expressivity
  • Mutations occur in genes encoding for sarcomere proteins e.g. myosin heavy chains, actin, tropomyosin

  • There is LVH with poor ventricular compliance, leading to impaired LV filling and raised LV filling pressures → diastolic dysfunction
  • Septal hypertrophy and SAM causes dynamic, sub-valvular LVOT obstruction
  • SAM causes MR and mitral valve prolapse
  • The myofibril disarray and fibrosis can be pro-arrhythmogenic
  • Myocardial ischaemia occurs due to myocardial oxygen demand-supply imbalance

Symptoms

  • May be asymptomatic and picked up incidentally
  • Conversely, may cause sudden death (see below)
  • If present, symptoms include:
    • Pre-syncope and syncope
    • Fatigue
    • Dyspnoea, particularly exertional
    • Chest pain
    • Palpitations

Signs

  • Low-volume pulse
  • LV heave
  • ESM or pan-systolic murmur
  • Hypotension

Sudden cardiac death

  • Particularly high risk of sudden cardiac death, especially if:
    • Family history of sudden death
    • LV hypertrophy >30mm
    • Abnormal BP/HR response to exercise
    • Sustained or multiple VT on Holter monitoring

ECG

  • LVH voltage criteria
  • Left axis deviation
  • LBBB
  • May be evidence of old infarct e.g. Q-waves
  • May be evidence of current myocardial ischaemia e.g. ST-depression, TWI

TTE

  • Asymmetrical septal and LV hypertrophy
  • Non-dilated LV cavity; often chamber size is small
  • LA dilatation

  • Mitral valve
    • Abnormal SAM of mitral valve
    • Mitral valve prolapse ± regurgitation

  • LVOT obstruction
  • Can classify degree of LVOT obstruction as:
    1. Non-obstruction (33%); peak gradient <30mmHg
    2. Labile obstruction e.g. on provocation (33%); peak gradient >30mmHg only with stress e.g. Valsalva, amyl nitrate vasodilation, exercise
    3. Obstruction at rest (33%); peak gradient >30mmHg

Cardiac MRI

  • Apical hypertrophy

Supportive

  • Genetic counselling
  • Screening of first-degree relatives

Pharmacological

Aim Drugs
Reduce LV contractility β-blockers (1st line)
Verapamil/diltiazem
Disopyramide
Mavacamten
Manage AF/arrhythmia Amiodarone
Anticoagulation
Treat HF if LVEF <50% ACE-I, ARA, MRA, SGLT2i etc.
  • Avoid digoxin and arterio- or veno-dilators in those with LVOT obstruction

Interventional

  • Relieve LVOT obstruction
    • Myotomy or myomectomy + MVR
    • Septal ablation with alcohol

  • ICD to mitigate sudden cardiac death risk

  • Cardiac transplant

Perioperative management of the patient withy hypertrophic cardiomyopathy


  • At risk of several perioperative complications:
    • LVOT obstruction
    • Arrhythmia
    • Ischaemic heart disease
    • Heart failure
    • Sudden death

  • Full history and examination
  • Involvement of cardiology to optimise patient reduce risk of aforementioned complication

  • First on list ± pre-hydration to maintain adequate preload
  • Consider anxiolytic pre-medication to reduce sympathetic tone

Monitoring and IV access

  • AAGBI
  • 5 - lead ECG
  • A-line pre-induction
  • ± TOE to assess fluid status, biventricular contractility, and LVEDV/LVESV
  • Consider application of defibrillator pads before induction

Anaesthetic technique

  • RA relatively contra-indicated

  • General anaesthesia
    • Considered safer in HoCM
    • Opioid-heavy, carefully titrated induction to minimise tachycardia, reductions in SVR and sympathetic surges
    • Use high RR/low VT/lower PEEP strategy to minimise reduction in venous return

Haemodynamic goals

  • Vasopressors (e.g. phenylephrine) and judicious fluids are first line for hypotension
  • Avoid positively ino-chronotropic agents which may tip myocardial oxygen demand/supply balance
  • Use β-blockade rather than nitrates for hypertension
Cardiovascular feature Goal of management
Heart rate Avoid tachycardia (HR <90bpm)
Heart rhythm Maintain sinus rhythm with rapid treatment of arrhythmia
Preload Maintain adequate preload
Contractility Reduce contractility
Avoid positive inotropes
Afterload Prevent large decreases in SVR (e.g. spinal anaesthesia)


  • Multimodal analgesia to avoid tachycardia from pain
  • Multimodal anti-emesis to avoid dehydration and tachycardia from PONV
  • Normothermia