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7.1.4 Inflammatory cardiac diseases

Cardiac inflammation has been associated with altered myocardial electrical properties and arrhythmias, and has been reported in various cardiomyopathies such as, obviously, myocarditis, but also inherited cardiomyopathies or after MI.773,774 Inflammatory cardiomyopathies are characterized by myocardial inflammation (i.e. myocarditis) as the primary cause of cardiac damage, whereas secondary myocardial inflammations are caused by an initial myocardial pathology.775,776 Myocarditis, sarcoidosis, and Chagas’ disease are among the major entities within inflammatory cardiomyopathies.

7.1.4.1 Myocarditis

The diagnosis of myocarditis can be challenging. There is no pathognomonic clinical presentation of this disease,777 with cardiac manifestations ranging from subtle symptoms to severe heart failure, complete AV block, and SCD.778 In young people, it is estimated that 2–12% of SCD are related to myocarditis.779–781 Myocarditis is diagnosed on endomyocardial biopsy by established histological, immunological, and immunohistochemical criteria, as well as polymerase chain reaction (PCR) to detect viral genomes.782,783 This implies that endomyocardial biopsy, although not widely used, is the diagnostic gold standard for myocarditis.778,784 In current practice, the diagnosis of myocarditis relies on clinical presentation, elevated troponin level, ECG changes, evidence of LV dysfunction, absence of significant CAD or valvular heart disease, and suggestive findings on CMR or PET-CT. In the context of suspected or confirmed acute myocarditis, patients with a life-threatening presentation (fulminant myocarditis, sustained VAs, or complete AV block) are to be referred to a specialized centre.785,786 A specialized centre must have the capacity to perform cardiac catheterization, endomyocardial biopsies, use mechanical circulatory support devices, and manage complex VAs. Sustained VAs may occur in acute myocarditis. In a large series of patients,786 in-hospital VF or CA was reported in 2.5% of cases. In another series of acute myocarditis in children,787 sustained tachyarrhythmias were reported in 11.5% of patients, with VAs accounting for most cases (79.5%). Tachyarrhythmias were associated with a 2.3-fold increased risk of death.787 Giant cell myocarditis, although rare, has a higher risk of life-threatening VAs, which are seen in 14% of giant cell myocarditis patients on initial presentation, and then develop as refractory arrhythmias in more than half of the patients during the course of the disease.788,789 The management of acute myocarditis depends on clinical presentation, viral PCR from myocardial biopsies, and histological findings. In patients with suspected myocarditis who present with mild heart failure, it is recommended to avoid exercise and use beta-blockers and ACE inhibitors.790 Patients with VAs or AV block must be admitted to the hospital and continuously monitored. Treatment of arrhythmias in patients with inflammatory heart disease does not differ from generally accepted clinical principles. Symptomatic VAs may require AADs such as amiodarone and/or beta-blockers.791–793 Of note, in a retrospective observational study, patients with sustained VAs during the acute phase of myocarditis (LVEF 53 + 10%) had a high risk (45% at 3 years) of VT/VF recurrences during follow-up.794 Myocarditis may resolve without sequelae, recur, or become chronic. Thus, myocarditis is often considered a precursor of DCM.795 Development of DCM has been observed in 21% of patients with acute myocarditis over a mean follow-up period of 3 years.796 The exact proportion of chronic DCM consecutive to the progression of acute myocarditis remains unknown, but myocarditis has been identified as the cause of DCM in up to 12% of cases in a large retrospective study.797 In patients with SMVT of unclear aetiology, myocarditis should be suspected especially when CMR reveals subepicardial and/or intramural abnormal fibrotic myocardial tissue. The presence of LGE at CMR has also been associated with the late occurrence of VAs in patients with endomyocardial biopsy-proven viral myocarditis.798–800

The management of documented VAs in chronic myocarditis is similar to that of patients with DCM, including ICD implantation and the use of AADs. Catheter ablation can be effective to treat SMVT, the arrhythmogenic substrate of which is often found on the epicardium of the lateral/basal left ventricle.752,801–803 In one publication,802 non-inducibility of VT after catheter ablation led to avoidance of ICD implantation in one-third of patients, with subsequently no VT recurrence during follow-up.

Recommendation Table 34 — Recommendations for sudden cardiac death prevention and treatment of ventricular arrhythmias in myocarditis

Recommendations Classa Levelb

General recommendations In confirmed or clinically suspected acute myocarditis, it is recommended that patients who present with life-threatening VAs are referred to a specialized centre.786,804 I C Secondary prevention of SCD and treatment of VA In patients with haemodynamically not-tolerated SMVT occurring in the chronic phase of myocarditis, an ICD implantation is recommended.794,805 I C In patients with haemodynamically not-tolerated sustained VT or VF during the acute phase of myocarditis, ICD implantation before hospital discharge should be considered.788,794,806 IIa C AADs should be considered (preferably amiodarone and beta-blockers) in patients with symptomatic non-sustained or sustained VAs during the acute phase of myocarditis. IIa C In post-myocarditis patients with recurrent, symptomatic VT, AAD treatment should be considered. IIa C Catheter ablation, performed in specialized centres, should be considered in post-myocarditis patients with recurrent, symptomatic SMVT or ICD shocks for SMVT in whom AADs are ineffective, not tolerated, or not desired.752,801,802 IIa C In patients with haemodynamically tolerated SMVT occurring in the chronic phase of myocarditis, ICD implantation should be considered. IIa C

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