11/14/24, 10\:54 AM Myocarditis

Myocarditis

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A comprehensive topic overview

Introduction

Myocarditis refers to in
to 40. 1,2
The widespread availability and use of cardiac MRI in some countries have led to an increase in the reported
incidence of myocarditis.
Myocarditis accounted for 0.04% of all hospital admissions in England between 1998 and 2017. However, due to the broad
presentation and the overlap with other acute cardiac conditions, it is still believed to be under-recognised.
1,2
The all-cause mortality in the UK for patients presenting to hospital with acute myocarditis is around 4%.
2

Aetiology

Anatomy

The heart's wall is formed by three layers\: the endocardium, myocardium, and epicardium. The endocardium is the
innermost layer, which lines the cavities and valves.
The myocardium is the middle layer formed by cardiac myocytes, which depolarise autonomously under the in
the sinoatrial node, causing them to contract so that blood can be ejected from the heart.
The
myocardium.
Figure 1. Anatomical layers of the heart wall.

Causes of myocarditis

The causes of myocarditis are broadly classi
cause can be identi
The most common aetiology in patients with an identi
3
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Viral infections can in
myocarditis and dilated cardiomyopathy. While viral myocarditis or cardiomyopathy is a complication of systemic infection
of cardiotropic viruses, most individuals infected with these viruses do not develop signi
5
Some of the infectious and non-infectious causes are listed below\:
4
Infectious\: viral s t a p h y l o c o c c u s , l e i s h m a n i a )
(e.g. c o x s a c k i e v i r u s , p a r v o v i r u s B-1 9 , s t r e p t o c o c c u s and m y c o b a c t e r i u m ), h u m a n h e r p e s v i r u s 6 and fungal (e.g. a s p e r g i l l u s , E p s t e i n-B a r r v i r u s ), bacterial c a n d i d a and h i s t o p l a s m a ) and (e.g.
parasitic (e.g.
Immune-mediated\: allergens (e.g. vaccines and medications like penicillin), alloimmune (e.g. rejection after heart
transplant) and autoimmune (systemic lupus erythematosus, in, sarcoidosis and
thyrotoxicosis)
Toxins\: illicit drugs (e.g. amphetamines), alcohol, medications (e.g. lithium and clozapine) and radiation

Risk factors

Risk factors for myocarditis include\:
Age\: younger people, typically those aged under 50 years old, are at a greater risk of developing myocarditis
Sex\: myocarditis is more common in men
Immunocompromised patients\: individuals with certain comorbidities like diabetes or HIV/AIDS, or those receiving
cancer treatments or steroids, are more likely to develop myocarditis as they are immunocompromised
History of autoimmune disease\: if the patient has a history of an autoimmune disease associated with myocarditis, they
are more at risk
Alcohol and drugs\: alcohol consumption, medications and illicit drug consumption have been associated with increased
risk of developing myocarditis

Clinical features

The symptoms and signs of myocarditis can be varied as the presentation can be fulminant (cardiogenic shock), acute
(less than 1 month) or chronic (over 1 month).
2

History

Symptoms of myocarditis are a consequence of in
Typical symptoms of myocarditis include\:
4
Chest pain\: a very common symptom. The chest pain may be described as a squeezing or heavy discomfort, that may
radiate to the neck, jaw or down the arms, mimicking the presentation of an acute coronary syndrome. Other times the
pain may be described as central, worse on inspiration (pleuritic) and relieved by leaning forwards, which suggests an
associated pericarditis.
Shortness of breath\: the patient may describe new or worsening shortness of breath on exertion or at rest. They may
also report breathlessness when lying
sitting upright (paroxysmal nocturnal dyspnoea).
Palpitations
Dizziness
Syncope
Fatigue
Other areas of the history may help identify an underlying cause\:
2
Systems review\: an infective cause should be suspected if there were prodromal symptoms of fever, sore throat,
myalgia, cough, vomiting or diarrhoea. An underlying autoimmune condition should be considered if there are reports of
rash, hair loss, changes to bowel habits or uveitis.
Past medical and surgical history\: a known diagnosis of certain autoimmune conditions or a history of heart transplant
may raise suspicion of myocarditis.
Medications\: ask about any recent vaccinations or changes to medications.
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Family history\: to screen for an inherited cardiomyopathy or autoimmune disease.
Social history\: establish alcohol consumption, illicit drug use and recent travel.

Clinical examination

All patients with suspected myocarditis should undergo a full cardiovascular examination.
The cardiovascular examination may be normal, or there may be signs consistent with heart failure, arrhythmia or an
underlying cause\:
6
Tachypnoea
Gallop rhythm
Raised jugular venous pressure (JVP)
Peripheral pitting oedema
Inspiratory crackles
Arrhythmias\: palpation of a pulse may reveal a fast or slow heart rate
Rash
Ocular in
Lymphadenopathy
Pericardial rub and signs of cardiac tamponade (mu
is co-existing pericarditis and pericardial e
In severe cases, myocarditis may present as cardiogenic shock (systolic blood pressure \<90mmHg, pulmonary congestion
or elevated left ventricular pressure and signs of impaired organ perfusion) or sudden cardiac death.

Di

The di
musculoskeletal causes\:
6
Cardiovascular\: acute coronary syndrome (which includes STEMI, NSTEMI and unstable angina), pericarditis, valvular
heart disease (e.g. aortic valve stenosis), aortic dissection, primary cardiac arrhythmia and endocarditis
Respiratory\: pneumonia, pneumothorax and pulmonary embolism
Gastrointestinal\: gastro-oesophageal re
Musculoskeletal\: costochondritis and rib fracture
If the presentation is fulminant with haemodynamic instability, consider sepsis.

Investigations

Bedside investigations

A 12-lead electrocardiogram is essential when assessing a patient with chest pain.
In myocarditis, the ECG is usually abnormal and most commonly shows sinus tachycardia with or without ST segment or T
wave changes. The ST segment changes in myocarditis tend to be concave (convex in ischaemia) and present in most
leads without reciprocal changes.
Other ECG atrioventricular block, QTc interval prolongation and PR segment
depression.
4,6
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Figure 2. An ECG showing di

Laboratory investigations

Relevant laboratory investigations include\:
4,6
Full blood count (FBC)\: a full blood count is useful to help identify anaemia and sepsis.
CRP and ESR\: often raised in myocarditis.
Troponin\: very likely to be elevated due to in
Brain natriuretic peptide (BNP)\: increased in the presence of elevated intraventricular pressures, suggesting heart
failure.
Urea and electrolytes (U&Es)\: to assess for evidence of end-organ dysfunction, which is important in those presenting
with cardiogenic shock.
Liver function tests (LFTs)\: may be deranged in the presence of viral hepatitis or end-organ dysfunction.
It is recommended to do an autoimmune screen for those with ‘clinically suspected’ myocarditis. However, routine viral
serology is not recommended because a positive serology result does not imply myocardial infection. Therefore,
performing viral serology is only recommended if there is clinical suspicion of a viral cause (e.g. hepatitis C and HIV).
1

Imaging

Recommended imaging in suspected myocarditis includes\:
Chest X-Ray\: will often be normal in myocarditis, but it may show features consistent with heart failure (alveolar oedema,
bilateral pleural e
e
6
Transthoracic echocardiography (TTE) can rule out valvular disease, which can mimic symptoms and signs of
myocarditis.
Cardiac MRI\: can identify areas of myocardium a
in
structural, functional and prognostic information, too.
1,2
In myocarditis, TTE is particularly useful to look for a pericardial e
associated with myocarditis, like systolic or diastolic dysfunction, dilated cardiomyopathy, wall motion abnormalities or
ventricular thrombus.
4

Other investigations

Endomyocardial biopsy (EMB) is the gold-standard diagnostic test. It is an invasive procedure which involves placing a
catheter into the heart chambers via the radial or femoral arteries so that a biopsy can be made. The tissue sample is then
sent for histology, immunohistochemistry and viral polymerase chain reaction.
If the tissue sample reveals in
also has the advantage of identifying subtypes of myocarditis, which can help identify a cause, guide treatment and inform
prognosis.
This procedure comes with its risks hence, current guidelines suggest only performing EMB if the following high-risk
features are present\:
1,4
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Cardiogenic shock
Acute heart failure requiring inotropic or mechanical support
Ventricular arrhythmias
Mobitz type II atrioventricular block or higher
EMB can also be considered if there is strong clinical suspicion of identifying a treatable disorder (e.g. an autoimmune
condition). Otherwise, cardiac MRI is the investigation of choice in the absence of high-risk features.
1,4
Figure 3. This histological specimen shows
lymphocytic myocarditis. The white arrow is
pointing to lymphocytes and the black arrow is
pointing to a necrosed myocyte.

Diagnosis

A diagnosis of myocarditis is made after EMB if the biopsy specimen shows histological evidence of in
with myocyte degeneration and necrosis of non-ischaemic origin. This is known as the Dallas criteria.
1,4
However, as mentioned above, an EMB is invasive and poses risks, so it is not routinely performed. In most cases, a cardiac
MRI is diagnostic.
Without histology, patients are referred to as having ‘clinically suspected myocarditis’ if they have one or more clinical
presentation features and one or more diagnostic criteria from di
1,4
Table 1. Diagnostic criteria for clinically suspected myocarditis.
Clinical presentation Diagnostic criteria
Acute chest pain
ECG or Holter monitoring demonstrating
electrocardiographic changes seen in myocarditis
New or worsening shortness of breath on exertion/at rest Elevated troponin
Palpitations or syncope
Evidence of functional abnormalities on cardiac imaging,
and no other pathology that could account for the
presentation
Cardiac MRI showing evidence of myocarditis
Unexplained cardiogenic shock History of recent viral infection

Management

Initial management

In the acute setting of myocarditis, treatment is supportive and may involve the management of pain, acute
decompensated heart failure, cardiogenic shock and arrhythmia.
If there is pleuritic pain suggesting pericardial involvement, treatment with non-steroidal anti-in
colchicine can be considered.
Those presenting with features of acute decompensated heart failure should be treated with oxygen, non-invasive
ventilation (if appropriate) and intravenous diuretic therapy. Vasodilator therapy should be considered if there is an
inadequate response to diuresis.
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Alternatively, if a patient presents with cardiogenic shock, treatment options may include inotropes, vasopressors or
mechanical support (e.g. intra-aortic balloon pump, extracorporeal membrane oxygenation or left ventricular assist device).
Patients with myocarditis can also develop arrhythmias\:
Bradyarrhythmias (Mobitz II or complete heart block)\: temporary pacing is required
Tachyarrhythmias with an adverse feature\: synchronised direct current cardioversion should be used as per the
resuscitation council guidance
Narrow complex tachyarrhythmias\: antiarrhythmics or rate-limiting medications, the choice of which is guided by the
underlying rhythm. 1,4
For more information please see the articles on the acute management of atrial and
narrow complex tachcyardia.
If there is any evidence of cardiac tamponade, a pericardial drain is needed.

Long-term management

Once a patient is stable, if they have developed heart failure, then medications should be started to manage this\:
1,4
Diuretics
ACE-inhibitors/angiotensin receptor blockers
Beta-blockers
Sodium-glucose transport 2 inhibitors
Aldosterone receptor antagonists
It is also advised that patients avoid exercise for three to six months.
1,4
If an autoimmune cause is identi
appropriate specialist.

Complications

Complications of myocarditis include\:
5
Dilated cardiomyopathy
Heart failure
Arrhythmias
Pericardial e
Sudden cardiac death
Most patients with myocarditis will have a spontaneous resolution in a few weeks. Factors that predict a poor prognosis
include\:
6
Cardiogenic shock
Reduced ejection fraction on imaging
Ventricular arrhythmias
Heart block
Patients who have diagnosed or clinically suspected myocarditis should be followed up within a few months in clinic to
consider repeat ECG, troponin and echocardiography. If there is concern for ongoing myocyte damage, repeat cardiac
MRI and EMB can be considered.
4,6

Key points

Myocarditis is in
Although a cause is often not found, viral infections are the most commonly identi
developed countries
Typical symptoms include chest pain, which may be pleuritic or pseudo-ischaemic, new or worsening shortness of
breath or palpitations
Examination
Key investigations are troponin, ECG, echocardiography and cardiac MRI
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The gold standard diagnostic test is EMB, but if this is not indicated, then a cardiac MRI is the best non-invasive test.
Management in the acute setting is supportive and often involves treatment of heart failure and arrhythmias
Long term management focuses on the treatment of heart failure and arrhythmias with close follow-up

References

Basso C. Myocarditis. N Engl J Med. 2022;387(16)\:1488-500.
Lampejo T, Durkin SM, Bhatt N, Guttmann O. Acute myocarditis\: aetiology, diagnosis and management. Clin Med (Lond).
2021;21(5)\:e505-e10.
Tschöpe C, Ammirati E, Bozkurt B, Caforio ALP, Cooper LT, Felix SB, et al. Myocarditis and in
current evidence and future directions. Nat Rev Cardiol. 2021;18(3)\:169-93.
Caforio AL, Pankuweit S, Arbustini E, Basso C, Gimeno-Blanes J, Felix SB, et al. Current state of knowledge on aetiology,
diagnosis, management, and therapy of myocarditis\: a position statement of the European Society of Cardiology Working
Group on Myocardial and Pericardial Diseases. Eur Heart J. 2013;34(33)\:2636-48, 48a-48d.
Yajima T. Viral myocarditis\: potential defense mechanisms within the cardiomyocyte against virus infection. Future
Microbiol. 2011;6(5)\:551-66.
Bagshaw C. Causes and management of myocarditis. Kendall J, editor. [Internet]. 2023 [cited 2024 Jan 12]. Available from\:
[LINK]

Images

Figure 1. OpenStax College. Layers of the heart wall. License\: [CC BY 3.0]
Figure 2. James Heilman, MD. DiCC BY-SA 4.0]

Related notes

Figure 3. Mikael Häggström, M.D. Histopathology of lymphocytic myocarditis. License\: [CC0]
Acute Coronary Syndrome (ACS)

Reviewer

Acute Heart Failure
Atrial Fibrillation (AF)
Dr Shivasankar Sukumar
Atrioventricular Block
Cardiology Registrar (ST5)
Brugada Syndrome

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Contents

Introduction
Aetiology
Risk factors
Clinical features
Di
Investigations
Diagnosis
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