Myocarditis

Tracing 1: This tracing shows a sinus rhythm, a narrow QRS, small amplitude Q-waves in the inferior leads; moderate amplitude elevation in the inferior leads; absence of reciprocity; This patient underwent a coronary angiography (which was normal) given the association of chest pain, an increase in troponin and a systematic elevation in the inferior territory. A subsequent MRI confirmed the diagnosis of myocarditis (probably of viral origin).

An electrocardiogram was performed 4 days later in the setting of chest pain with palpitations.

ECG 2: sinus tachycardia; compared to the previous tracing, the ST-segment has returned to the isoelectric line; presence of ventricular extrasystoles with a couplet and 2 different morphologies.

Comments: this patient presented an episode of viral myocarditis as a result of the association between clinical setting (young patient, gastrointestinal episode 15 days earlier), chest pain, increased troponin, changes in the ECG, and normal coronary angiography. The diagnosis was confirmed by MRI. There are certain electrocardiographic signs of myocarditis: ST-segment elevation, small Q-waves, sinus tachycardia and arrhythmogenic context (ventricular extrasystoles with 2 morphologies).

Myocarditis is an inflammatory myocardial disease caused by various infectious (enterovirus, coxsackievirus, cytomegalovirus, parvovirus, herpes virus, HIV, etc.), autoimmune (sarcoidosis, scleroderma, lupus, etc) or medicinal (anthracycline, etc) factors. The clinical presentation is highly variable with description of perfectly asymptomatic patients on the one hand, and patients with inaugural sudden death or fulminant heart failure on the other. Myocarditis is frequently revealed by the presence of chest pain accompanied by an increase in cardiac enzymes and electrocardiographic alterations of the ST-segment elevation-type, which renders differential diagnosis with myocardial infarction difficult. Retrospectively, it is common to find a flu-like syndrome with preferentially digestive or upper airway involvement followed, within a few days, by an aspecific cardiac symptomatology (fatigue, dyspnea, palpitations, syncope, chest pain). Myocarditis can be accompanied by substantial myocardial disease (reflected by increased troponin), which may favor the occurrence of fulminant acute heart failure or a progression to chronic phase dilated cardiomyopathy but also to the occurrence of conduction disorders, atrial or ventricular arrhythmias.

The definitive diagnosis of myocarditis can be made by performing a myocardial biopsy with histological, immunohistological and molecular analysis; its invasive nature, however, limits the clinical applicability and use to the most serious forms. Cardiac MRI is now the non-invasive reference method despite certain limitations in terms of accessibility. It is rarely possible to demonstrate the pathogen involved but it is recommended to look for the most common viruses and treatable bacterial agents. An emergency coronary angiography performed in doubtful situations allows precluding the diagnosis of myocardial infarction.

Treatment is mainly based on rest, a combination of angiotensin converting enzyme inhibitors and beta-blockers, the treatment of symptoms of heart failure, and specific treatment if a treatable pathogen has been identified. In the acute phase of fulminant forms, if an optimal drug treatment does not stabilize the situation, invasive extracorporeal or intracorporeal heart treatments (VAD, ECMO) may be proposed transiently or in awaiting a transplant.

As explained previously, acute myocarditis can be associated with a clinical and electrocardiographic picture similar to that observed during an acute coronary episode but also during a pericarditis. The electrocardiogram has a relatively low sensitivity, specificity and predictive value for the diagnosis of myocarditis. Indeed, different abnormalities can be found ranging from poorly-specific modifications of the T-wave to a ST-segment elevation evocative of a coronary syndrome, none of which are pathognomonic. There are also a number of patients with a subnormal electrocardiogram. This explains why an emergency coronary angiography is usually performed in the presence of a suspect clinical or electrocardiographic presentation. Myocarditis can be associated with pericardial damage, the electrocardiogram thus revealing a more or less typical pattern of pericarditis. Certain elements should evoke the diagnosis of myocarditis:

• the frequent presence of sinus tachycardia.
• modifications of the ST-segment are poorly-specific and usually transient. The main differential diagnosis of myocarditis is that of ST + infarction. An elevation is often found which makes the diagnosis difficult, especially since the patient may have chest pain or dyspnea accompanied by an increase in cardiac enzymes. Various more or less plausible theories have been proposed to explain the presence of an ischemic subepicardial lesion in myocarditis. Disorders in segmental kinetics could favor the occurrence of wall thrombi generating coronary emboli. The release of vasoactive kinins linked to inflammation may lead to the occurrence of a coronary spasm. Finally, inflammation may generate local hypercoagulability with formation of coronary thrombi.
• The ST-segment elevation is often of less amplitude in myocarditis than in a coronary syndrome but of more diffuse extension (not limited to a single coronary territory). The clinical (younger patient with notion of recent viral infection) or ultrasound setting (widespread alterations in segmental kinetics) can also point to a diagnosis of myocarditis.
• in rarer instances, a pattern of ST-segment depression can be observed.
• another relatively frequent electrocardiographic sign in myocarditis is the transient presence of symmetrical negative T-waves or of an aspecific flattening of the T-waves, mainly from V2 to V6.
• concomitant with the increase in troponin suggestive of myocardial necrosis, the presence of Q-waves (rarely deep but of poor prognosis) and low amplitude R waves can be observed.
• myocarditis can be complicated by the occurrence of conduction disturbances or rhythm disorders that can alter the prognosis. The appearance of a left bundle branch block, frequent and polymorphic ventricular extrasystoles and QT prolongation are all factors of poor prognosis.

Take-home message: it is not possible to define a typical electrocardiogram of myocarditis; it may be strictly normal, or display aspecific abnormalities similar to those observed in a coronary syndrome or pericarditis (diffuse or more localized ST-segment elevation, negative T-waves, more or less localized Q-waves).