Pre-syncope with exertion suggests arrhythmia risk
Systemic symptoms
Viral prodrome 1 to 2 weeks prior
Fever or myalgias
Time course
Abrupt onset within days
Fulminant phenotype consideration
Subacute progression over weeks
Inflammatory cardiomyopathy overlap
Recurrent episodes
Autoimmune or sarcoid consideration
Risk factors and exposures
Infectious exposures
Recent upper respiratory infection
Household contacts
Recent gastroenteritis
Dehydration and tachycardia confounders
Tick exposure
Lyme carditis with AV block differential
Travel or zoonotic exposure
Chagas consideration with appropriate geography
Medication and toxin exposures
Immune checkpoint inhibitors
Time since initiation within first 3 months common risk window
New antibiotics or anticonvulsants
Hypersensitivity myocarditis signal
Cocaine or stimulants
Demand ischemia and coronary vasospasm confounders
Autoimmune and inflammatory history
Known autoimmune disease
SLE
IBD
Sarcoidosis history
Prior pulmonary or skin involvement
Cardiac history
Prior myocarditis
Prior MRI findings and EF recovery
Cardiomyopathy or heart failure
Baseline EF and meds
Family history sudden cardiac death
Inherited arrhythmia overlap possibility
Red flags
High-risk symptoms
Syncope
Exertional syncope concern
Resting dyspnea
Rapid progression within 24 to 48 hours
Persistent chest pain with rising troponin
Coronary disease exclusion priority
Neurologic symptoms
Embolic stroke concern with LV thrombus
Immunocompromised state
Transplant recipient
Opportunistic infections
Active malignancy on therapy
ICI myocarditis and overlap syndromes
Physical Exam
General and hemodynamics
Vitals and perfusion
Tachycardia
Disproportionate to fever or pain raises concern
Hypotension
Narrow pulse pressure supports low output
Fever
Sepsis overlap and infectious myocarditis consideration
Cool extremities
Delayed capillary refill
Respiratory status
Work of breathing
Accessory muscle use
Hypoxemia
Pulmonary edema vs pneumonia differentiation
Volume assessment
Elevated JVP
RV involvement possibility
Peripheral edema
New onset suggests decompensated HF
Cardiovascular and systemic findings
Cardiac exam
S3 gallop
LV dysfunction marker
New murmur
Functional MR with LV dilation
Pericardial friction rub
Myopericarditis support
Pulmonary exam
Crackles
Congestion support
Wheeze
Cardiac asthma possibility
Signs of systemic inflammation
Rash
Hypersensitivity or autoimmune clue
Urticaria or facial swelling
Drug reaction overlap
Neurologic and embolic signs
Focal neurologic deficit
Embolic event concern
Painful cool limb
Peripheral embolus concern
PITFALLS
Common exam traps
Normal exam despite significant myocardial inflammation
Early disease with preserved EF
Attribution of tachycardia to anxiety alone
Persistent sinus tachycardia as myocarditis clue
Over-reliance on absence of chest pain
Heart failure or arrhythmia-first presentations common
Differential Diagnosis
Life-threatening causes of chest pain or shock
Ischemic and vascular
Acute coronary syndrome ICD-10 I21 to I22
Troponin elevation overlap
Aortic dissection ICD-10 I71.0
Pulse deficit or neurologic deficits
Pulmonary embolism ICD-10 I26
RV strain and troponin overlap
Cardiopulmonary emergencies
Cardiac tamponade ICD-10 I31.4
Effusion and pulsus paradoxus
Sepsis with myocardial dysfunction ICD-10 A41
Lactate elevation with distributive pattern
Massive GI bleed with demand ischemia
Anemia and tachycardia driver
Mimics and related cardiac conditions
Pericarditis ICD-10 I30
PR depression and diffuse ST elevation pattern
Troponin mild elevation in myopericarditis
Stress cardiomyopathy ICD-10 I51.81
Triggering stressor and typical echo pattern
Acute decompensated heart failure ICD-10 I50.9
Chronic HF features and known low EF
Arrhythmogenic disorders
SVT related demand ischemia
Brugada or inherited channelopathy
Cardiac sarcoidosis SNOMED CT sarcoidosis of heart
Conduction disease and ventricular arrhythmia pattern
Lyme carditis ICD-10 A69.23
Fluctuating AV block and exposure history
Laboratory Tests
Core ED labs
Acute myocardial injury and heart failure markers
High-sensitivity troponin I or T serial testing
Rise and fall pattern supports acute injury
Normal value does not exclude myocarditis
BNP or NT-proBNP
Elevation supports myocardial stress and HF
Baseline safety labs for therapy
Electrolytes with magnesium
Potassium goal at least 4.0 mmol/L for arrhythmia reduction
Magnesium goal at least 1.0 mmol/L for arrhythmia reduction
Creatinine and eGFR
Contrast and medication dosing implications
AST and ALT
Congestive hepatopathy vs systemic illness
Inflammation and infection screen
CBC with differential
Eosinophilia suggests eosinophilic myocarditis
CRP
Trend supports inflammatory activity
ESR
Supportive but non-specific
Shock and perfusion labs
Lactate
Serial downtrend target
VBG or ABG if respiratory failure or shock
pH and PaCO2 in mmHg for ventilatory status
Targeted etiologic labs
Infectious testing guided by presentation
Blood cultures for fever or sepsis physiology
Prior to antibiotics if possible
Respiratory viral PCR when viral syndrome present
Management impact limited for most viruses
HIV testing when risk factors present
Opportunistic infection and cardiomyopathy overlap
Lyme serology when exposure and AV block pattern present
Two-tier approach per local guidance
Autoimmune and inflammatory testing when suspected
ANA and ENA when systemic autoimmune features
Supports rheumatologic evaluation
ACE level and chest imaging correlation for sarcoid context
Low specificity and supportive only
PITFALLS and interpretation limits
Troponin limitations
Degree of elevation poorly correlates with severity
Fulminant cases can have variable values
Troponin elevation non-specific
ACS exclusion still required when presentation fits
Viral serologies pitfalls
Routine viral antibody panels low utility
False positives and delayed results
PCR positivity does not confirm myocarditis etiology
Association rather than proof
Diagnostic Tests
Scoring Systems
Shock and heart failure staging tools
SCAI shock staging
Stage A at risk
Stage B beginning shock
Stage C classic shock
Stage D deteriorating
Stage E extremis
NYHA functional class
Class I no limitation
Class II mild limitation
Class III marked limitation
Class IV symptoms at rest
ACC AHA heart failure stages
Stage A risk only
Stage B structural disease without symptoms
Stage C symptomatic structural disease
Stage D advanced refractory
Myocarditis risk features in ACC ECDP framework
High-risk clinical features
Hemodynamic instability
Syncope
Sustained ventricular arrhythmia
High-risk test features
Reduced LVEF on echo
High-grade AV block on ECG
MRI
Cardiac MRI role
Tissue characterization for myocardial inflammation
Edema assessment with T2-based techniques
Non-ischemic injury assessment with T1-based techniques
Revised Lake Louise criteria 2018 summary
At least one T2-based marker
At least one T1-based marker
MRI findings supporting myocarditis
T2-based markers
Regional myocardial edema on T2-weighted imaging
Elevated T2 mapping values
T1-based markers
LGE in non-ischemic distribution
Elevated native T1 mapping values
Elevated extracellular volume fraction
MRI limitations and contraindications
Early disease with negative MRI possible
Repeat imaging if high suspicion and evolving course
Hemodynamic instability limits feasibility
Stabilize first and consider alternative diagnostics
Gadolinium contraindication in severe renal failure context
Use non-contrast protocols when needed
CT
Coronary evaluation when ACS cannot be excluded
Coronary CT angiography in low to intermediate risk with stable vitals
Alternative to invasive angiography in selected patients
Invasive coronary angiography in high-risk ACS presentation
ST elevation or refractory chest pain
Alternative CT pathways by presentation
CT pulmonary angiography for PE concern
RV strain and hypoxemia pattern
CT aorta for dissection concern
Tearing pain or pulse deficit
Ultrasound (or US)
Point-of-care echocardiography
LV systolic function
Global hypokinesis supports myocarditis pattern
RV assessment
RV dilation suggests PE or RV myocarditis involvement
Pericardial effusion
Tamponade physiology evaluation
IVC size and collapsibility
Volume status support for resuscitation choices
Formal transthoracic echocardiography
LVEF quantification
Baseline for prognosis and therapy
Regional wall motion assessment
Focal abnormalities overlap with ACS
Valvular function
Functional MR with LV dilation
Intracardiac thrombus evaluation
Anticoagulation implications
Disposition
Admission and transfer criteria
ICU admission criteria
Cardiogenic shock or vasoactive support requirement
Consider VA-ECMO capable center if escalating
Sustained VT or VF
Antiarrhythmic infusion or repeated cardioversion
High-grade AV block
Temporary pacing requirement
Rapidly rising troponin with hemodynamic change
Ongoing ischemia exclusion and myocarditis monitoring
Stepdown or monitored bed criteria
Suspected myocarditis with stable vitals
Continuous telemetry for 24 to 48 hours
Mild LV dysfunction without shock
Guideline-directed HF therapy initiation
Transfer criteria
Need for mechanical circulatory support
Impella or VA-ECMO capability
Suspected giant cell myocarditis or ICI myocarditis
Advanced HF and immunosuppression expertise
Discharge criteria for selected low-risk patients
Low-risk outpatient pathway
Normal vitals and no arrhythmia on monitoring period
No syncope history in event
Preserved LV function on echo
No pericardial effusion with tamponade physiology
Troponin stable or downtrending
No dynamic ECG ischemic changes
Reliable follow-up within 72 hours
Cardiology or rapid access clinic
Treatment
Supportive and heart failure management
General principles
Activity restriction during acute phase
Avoid competitive sports and intense exercise
Volume management
Loop diuretic for congestion with stable perfusion
Loop diuretics
Furosemide IV 20 to 40 mg
If diuretic naive and mild congestion
Re-dose based on urine output response
If on chronic loop diuretic
Initial IV dose at least equivalent to home total daily dose
Electrolyte monitoring every 6 to 12 hours
Potassium and magnesium replacement targets
Guideline-directed medical therapy when stable
ACE inhibitor or ARB
Initiate when euvolemic and SBP adequate
Beta blocker
Avoid initiation during acute decompensated HF or shock
Initiate after stabilization with improving congestion
Mineralocorticoid receptor antagonist
Consider when LVEF reduced and potassium under 5.0 mmol/L
SGLT2 inhibitor
Consider in stable HFrEF without severe hypotension
Cardiogenic shock and fulminant myocarditis
Vasoactive strategy
Norepinephrine infusion initiation for hypotension
Start 0.05 to 0.1 mcg/kg/min
Titrate every 2 to 5 minutes to MAP target
Typical range 0.05 to 1 mcg/kg/min
Escalate with perfusion markers and lactate trend
Inotrope for low output with adequate BP
Dobutamine infusion initiation
Start 2.5 to 5 mcg/kg/min
Titrate to cardiac output and perfusion
Max commonly 20 mcg/kg/min
Monitor for tachyarrhythmia
Milrinone infusion alternative
Start 0.125 to 0.25 mcg/kg/min
Avoid bolus in hypotension
Renal dose adjustment needed
Hypotension risk monitoring
Mechanical circulatory support concepts
Indications
Refractory shock despite vasoactive escalation
Persistent lactate elevation with end-organ injury
Options
VA-ECMO for profound biventricular failure
Consider LV unloading strategy per center protocol
Impella for predominant LV failure
Hemolysis monitoring
IABP selected scenarios
Limited support compared with VA-ECMO
Respiratory support
Noninvasive ventilation for pulmonary edema
CPAP or BiPAP if mentation intact
Intubation strategy in shock
Hemodynamic optimization prior to induction
Post-intubation hypotension anticipation
Arrhythmias and conduction disease
Ventricular tachyarrhythmias
Amiodarone IV bolus and infusion
Bolus 150 mg over 10 minutes
Repeat bolus for recurrent VT as needed
Infusion 1 mg/min for 6 hours
Then 0.5 mg/min maintenance
Lidocaine IV alternative
Bolus 1 to 1.5 mg/kg
Repeat 0.5 to 0.75 mg/kg every 5 to 10 minutes
Max total 3 mg/kg
Infusion 1 to 4 mg/min after bolus
Bradyarrhythmia and AV block
Atropine IV for symptomatic bradycardia
1 mg IV
Repeat every 3 to 5 minutes
Max 3 mg
Prepare pacing if ineffective
Transcutaneous pacing
Bridge to transvenous pacing when persistent
Transvenous pacing
High-grade AV block with instability
Atrial fibrillation or flutter
Rate control strategy when stable
Beta blocker deferral in acute decompensated HF
Amiodarone for rate control when LV dysfunction and hypotension
Anticoagulation decision
CHA2DS2-VASc framework
Bleeding risk and hemodynamic stability
Etiology-directed immunotherapy
Endomyocardial biopsy driven therapy concepts
Giant cell myocarditis
High-dose corticosteroid plus additional immunosuppression per specialist
Eosinophilic myocarditis
Corticosteroid therapy consideration after infection exclusion
Cardiac sarcoidosis
Corticosteroid therapy with steroid-sparing agents per specialist
Immune checkpoint inhibitor myocarditis
Immediate ICI hold coordination with oncology
High-dose corticosteroid early per specialty pathways
Steroid-refractory escalation
Additional immunosuppressants per expert consultation
Myopericarditis pain control
Analgesia strategy
Acetaminophen
650 to 1000 mg PO or IV every 6 to 8 hours
NSAID caution
Avoid routine NSAIDs in isolated myocarditis due to theoretical harm
Use in pericarditis-dominant syndrome per cardiology guidance
Special Populations
Pregnancy
Diagnostic considerations
Pregnancy physiologic dyspnea confounder
Lower threshold for echo if symptoms progressive
PE overlap risk in pregnancy
Imaging choice balance with maternal risk
Medication considerations
ACE inhibitor and ARB contraindicated in pregnancy
Use pregnancy-safe HF regimen per obstetric medicine and cardiology
Anticoagulation approach
LMWH preferred when anticoagulation indicated
Disposition considerations
Maternal fetal medicine involvement for moderate to severe disease
Delivery planning if late gestation and unstable
Geriatric
Atypical presentations
Heart failure symptoms without viral prodrome
Higher coronary disease probability
Delirium as low perfusion marker
Early lactate and perfusion assessment
Medication safety
Higher hypotension risk with GDMT initiation
Slower titration and close monitoring
Renal function fluctuation
Dose adjustment for diuretics and milrinone
Pediatrics
Presentation patterns
Poor feeding and lethargy in infants
Tachycardia out of proportion clue
Abdominal pain and vomiting in older children
Misdiagnosis risk as gastroenteritis
Diagnostic considerations
Echocardiography early in suspected cases
Coronary anomaly consideration in chest pain differential
MRI feasibility challenges
Sedation risk and availability limitations
Treatment considerations
Weight-based vasoactive dosing per pediatric critical care
Early PICU involvement for fulminant cases
IVIG consideration in selected pediatric myocarditis pathways
Specialist-directed due to mixed evidence
Background
Epidemiology
Disease frequency and burden
Myocarditis as an important cause of sudden cardiac death in younger populations
Risk highest with active inflammation and ventricular arrhythmia
Viral etiologies common in high-income settings
Exact pathogen often unconfirmed without biopsy
Coding and terminology
ICD-10 acute myocarditis I40
I40.0 infectious myocarditis
I40.1 isolated myocarditis
I40.8 other acute myocarditis
I40.9 acute myocarditis unspecified
ICD-10 myocarditis unspecified I51.4
Chronic or unspecified clinical context
SNOMED CT myocarditis disorder concept
Use for clinical terminology mapping
Pathophysiology
Core mechanisms
Myocardial inflammation with myocyte injury
Direct pathogen injury in some cases
Immune-mediated injury in many cases
Electrical instability pathways
Inflammatory scar and edema as arrhythmogenic substrate
Hemodynamic failure pathways
Reduced contractility leading to low output and congestion
Phenotypes
Acute myocarditis
Chest pain and biomarker elevation
Fulminant myocarditis
Rapid onset severe HF and shock
Inflammatory cardiomyopathy
Persistent inflammation with chronic LV dysfunction
Therapeutic Considerations
Evidence and guideline themes
Supportive care as foundation
HF therapy and shock management principles
Etiology-directed immunosuppression in selected biopsy-proven subtypes
Giant cell and eosinophilic forms as key examples
Exercise restriction after acute myocarditis
Return-to-play decisions guided by symptom resolution and testing
ACC ECDP myocarditis guidance
Structured diagnostic pathway and risk stratification approach
Patient Discharge Instructions
Copy discharge instructions
Diagnosis explanation
Suspected myocarditis
Heart muscle inflammation that can affect rhythm and pumping
Activity
No strenuous exercise or competitive sports until cleared
Light daily activity only if symptoms allow
Medications
Take prescribed heart medications exactly as directed
Do not stop beta blockers or ACE inhibitors without clinician guidance
Follow-up
Cardiology follow-up within 72 hours to 1 week
Repeat testing plan for echo and labs as arranged
Return to ED immediately for red flags
Worsening chest pain
Pain at rest or lasting more than 10 minutes
Trouble breathing
New shortness of breath at rest or waking at night
Fainting or near-fainting
Especially with palpitations
Rapid or irregular heartbeat
Persistent palpitations or heart rate over 120 at rest
New leg swelling or sudden weight gain
Weight gain over 2 kg in 2 days
Fever with feeling very unwell
Possible infection or worsening inflammation
References
Guidelines and consensus
ACC Expert Consensus Decision Pathway on Diagnosis and Management of Myocarditis 2024
ACC Ten Points to Remember summary 2024
JACC Scientific Expert Panel updated Lake Louise Criteria 2018
Revised CMR criteria requiring at least one T1-based and one T2-based marker
ESC Working Group position statement on myocarditis 2013
Criteria for clinically suspected myocarditis and biopsy guidance
Review literature on myocarditis management updates 2024
Synthesis of ESC 2021 to 2022 guideline era changes
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