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Bay Four

          Patterns, pearls and practical medicine

Myocarditis

  • A heterogenous set of conditions and definitions vary widely
  • Some cross over with pericarditis

Symptoms 

  • Chest pain (90%, often positional, often infarct-like, but in the absence of CAD)
  • Fever (65%)
  • SOB / HF
  • Palpitations / arrythmia
  • Syncope (5%)
  • Fatigue
  • Oedema
  • Prodrome / viral like illness (fever, flu-like illness, GI complaints) in 80%, usually 2-4 weeks prior
  • Giant cell myocarditis can cause an extremely rapid deterioration and often in young patients

Various classification systems

  • By clinical course
      • Fulminant, acute (<1/12), subacute (1-3 months) or chronic (>3 months)
  • By predominant infiltrate
      • Lymphocytic – microbes/viruses, radiation, drugs, autoimmune
      • Eosinophilic – parasitic, neoplastic, hypersensitivity/allergy, EGPA, HES
      • Giant cell – autoimmune, IBD
      • Granulomatous – sarcoid
  • By aetiology
      • Viral
      • Autoimmune
      • Hypersensitivity
      • Unknown
  • By presentation
      • Infarct like (75%, better prognosis)
      • Heart failure (15%)
      • Arrythmia (10%, various rhythms)

Definitions

    • Probable myocarditis – typical symptoms, no other identifiable cause (ie no significant coronary artery disease) plus one of (or no symptoms and two of)…
      • Elevated troponin
      • ECG consistent (can get diffuse ST elevations)
      • Abnormal cardiac function on echo or MRI
    • Confirmed myocarditis – typical symptoms + elevated troponin + changes on cardiac MRI

Aetiology

  • Infection is the most common
      • Especially viral
          • Parvovirus B19, also enteroviruses, adenovirus, HHV-6. Sometimes EBV and flu.
          • Covid myocarditis is v rare and much less common than previously assumed
      • Also bacterial, fungal, parasitic
          • Lyme disease, Chagas, diphtheria, rickettsia
  • Immune-mediated is the next most common
      • SLE, scleroderma, RA, EGPA, hyper-eosinophilic syndrome, sarcoid, tetanus, giant-cell myocarditis, DRESS
  • Drugs
      • Checkpoint inhibitors (1% of treated patients)
      • Clozapine (especially), amphetamines and cocaine, cyclophosphamide, lithium, heavy metals, arsenic
      • Can occur post-covid vaccine – highest with Moderna (20 per million), especially young males (risk might be 50 per million in this group)
  • Other – Pheochromocytoma, vitamin deficiencies, stings, carbon monoxide, inherited

Investigations

  • Take detailed family history for inherited cardiomyopathies (a differential)
  • ECG
      • Abnormal in 85%
      • Usually inferiolateral ST elevation (58%), sometimes other ST/T wave changes or conduction blocks
  • Bloods
      • Elevated trop, BNP, CK, CRP, WCC but all non-specific
      • Negative troponin and BNP does not rule it out
      • Viral serology – low yield so not recommended
      • TFTs and autoantibodies – ANA, RF, CCP, ENA, ANCA
      • FBC with eosinophils (although normal in 25% of eosinophilic myocarditis)
      • HIV, Hep C +/- Lyme serology
      • Consider: viral PCR, serum ACE, metanephrines, drug screen
  • Consider genetic tests if family history of perimyocarditis/cardiomyopathy, severe ventricular arrythmia, recurrent/refractory myocarditis
  • Echo
      • Global or regional wall motion abnormalities, especially inferiolateral
      • Increased wall thickness (oedema)
      • Diastolic dysfunction
      • RV dysfunction
      • Pericardial effusion in 25%
      • Abnormal myocardial echogenicity
      • Apical LV thrombus
      • Admission LVEF is a powerful prognostic marker
  • Coronary angiogram
      • Invasive angiogram required if acute chest pain and high likelihood of CAD (even if myocarditis suspected)
      • Consider CT angiogram if acute chest pain and moderate probability of CAD
  • Cardiac MRI
      • High specificity and sensitivity (especially for infarct like presentations)
      • Useful to look at T2 weighed imaging (myocardial oedema can lead to increased tissue water content that can be detected as increased signal intensities)
      • Myocyte necrosis and fibrosis can result in non-ischaemic (e.g. mid-wall, subepicardial, patchy) patterns of LGE, which do not typically follow a coronary artery distribution
      • Best done early (first 2 weeks)
      • Follow up CMR advised (3-6 months later, look for scarring – appears like ischaemia at this stage, LGE can show a pattern of myocardial fibrosis). This can help with management plans and exercise advice
      • Doesn’t tell you about aetiology/histotype, but can help distinguish myocarditis from mimics such as inherited cardiac conditions
  • Rarely needs biopsy
      • Reserved for the sickest patients or the ones where the mechanism is important
      • Useful in Giant Cell Myocarditis which usually presents as heart failure that does not respond to usual care. Immunosuppression helpful here
      • Can be negative as disease can be patchy (relatively low sensitivity)
      • Complication rate 1-2% in expert centres, 9% in low volume centres. Usually taken from RV septum.
      • Best done early
      • Sensitivity for GCM is around 88% if done 2-4 weeks from onset. Sensitivity for sarcoid is quite low as lesions can be focal.
      • Can help diagnose active/persistent/resolved lymphocytic myocarditis, eosinophilic myocarditis, giant cell myocarditis, sarcoid, infiltrative/storage diseases
      • Can do viral genome analysis

High risk features

  • Presentation with acute HF / severe SOB or shock
  • Ventricular arrythmias, syncope or high-level AV block
  • Newly reduced EF <40%
  • Extensive LGE on CMR
  • Giant cell myocarditis or eosinophilic myocarditis (although you won’t know this at the time of risk stratification)
  • Of note – elevated troponin not a negative prognostic marker if normal biventricular function

Treatment

  • Treat heart failure in the usual way – ACE-i, SGLT2 inhibitors, spiro, betablockers). Use for at least 6 months after complete LV recovery, but often patients stay on these treatments for life, even if EF recovers.
  • Even if EF preserved throughout illness, some evidence that heart failure treatments help as they might reduce risk of fibrosis in the long term
  • Betablockers used in most (both for HF and to prevent arrythmias)
  • Treat precipitants
  • Often avoid NSAIDs if LV dysfunction
  • Colchicine likely v helpful and currently recommended but not much evidence so far
  • Consider immunosuppressants / steroids if possible autoimmune disease, not useful in all comers
      • Often give if fulminant and likely non-infectious
      • 1st line in eosinophilic myocarditis
      • Consider if HF present and refractory to HF treatment
      • Usually avoid if preserved LV function
      • 1mg/kg/day of prednisolone then tapered for most, or methylprednisolone if more severe
  • For immunotherapy-induced myocarditis see separate guidelines, but again high dose steroids used
  • Interferon beta therapy if dilated cardiomyopathy and viral genome on biopsy
  • No evidence for IVIG

Special cases

  • If fulminant (6% of cases)
    • Consider IABP, inotropes, ECMO (bridging therapy) and liaise with a transplant centre early
    • High risk of ventricular arrythmias and SCD
    • Check if there is a myocarditis team to refer to locally
  • Giant Cell myocarditis
    • 85% risk of death or transplant at 3 years
    • Affects young people, rare
    • Associated autoimmune disorder in 20%
    • Requires biopsy to diagnose (and may need to be repeated if negative and high suspicion persists), but can treat on clinical suspicion
    • Use 2 or 3 immunosuppressive agents. Survival improved with cyclosporin and steroids (azathioprine also used), and withdrawing immunosuppression increases risk of recurrence
    • ATG, cyclophosphamide and rituximab have also been used
  • Checkpoint inhibitor-associated myocarditis
    • Especially arrhythmogenic and high mortality
    • Often associated with peripheral myositis
    • Stop checkpoint inhibitor and give high dose steroids
    • 50% refractory to steroids

Complications

  • Inflammatory cardiomyopathy – chronic myocarditis in association with cardiac dysfunction and ventricular remodelling
  • Evolution to dilated cardiomyopathy – myocarditis accounts for 12% of non-ischaemic DCM cases
  • Ventricular arrythmias – usually wait 3-6 months after acute myocarditis to decide on ICD
  • Sudden Cardiac Death – accounts of 20% of cases of SCD
  • Recurrence

Clinical course

  • If uncomplicated, 75% resolve spontaneously
  • If complicated, prognosis largely depends on the short-term response to therapy
  • > 50% resolve in 2-4 weeks
  • 25% develop persistent cardiac dysfunction due to fibrosis
  • 20% either die or progress to end stage dilated cardiomyopathy and require transplant
  • Risk of VF/arrest is 2.5% in hospitalised patients
  • Giant Cell Myocarditis – 50% die within 5 years without transplant
  • ACS-like phenotype has a much better prognosis than HF or arrythmia presentation

Follow up

  • Clinical assessment, trop and BNP, ECG, exercise test, Holter, echo, CMR within 6 months for all
  • Exercise – Advice as per pericarditis, but athletes should refrain from exercise for 6 months and until normal trop/ECG/CRP (but evidence is a bit patchy esp if relatively benign phenotype)

 

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