Discussion
The main findings of this study are: 1) granulomatous myocarditis may present as recurrent atrial arrhythmia including AF. 2) These patients have a higher risk of stroke (26.7%) and predisposition to thromboembolism in the absence of traditional risk factors. 3) Isolated atrial involvement was observed in over 80% of this patient population. The etiology of granulomatous myocarditis could either be cardiac sarcoidosis or tuberculosis. 4) They respond well to immunosuppression (Sarcoidosis) and anti-tuberculosis therapy (TB).
The entity of atrial myocarditis has been described in the past but has not received much attention. An important study by Frustaci et. al showed evidence of atria limited myocarditis in 66% of “lone” AF patients studied by endomyocardial biopsy of atria.13A study has also demonstrated antibodies against myosin in the sera of AF patients.14 A series of 13 patients with AM has also shown that atrial giant cell myocarditis (GCM) has a favorable prognosis when compared to the classic variety of GCM.4 Our data indicates that “isolated atrial myocarditis” could be a substrate for atrial arrhythmias, which could also be life threatening.15
The sensitivity of 18F FDG PET in detecting cardiac involvement in sarcoidosis has been around 87.5%.16Cardiac MRI also aids in the diagnosis but its value in detecting atrial pathology is not well established. The sensitivity and predictive value of 18F FDG PET scan for detecting AF was 54% and 96.1% in a recent study.17
The possible consequences of AM have been highlighted in the Figure 4. An autopsy study of young sudden death victims with ventricular pre-excitation showed evidence of AM in 50%.15 Since inflammation is a potent pro-thrombotic state, the risk of thromboembolic complications could be heightened in this population. In the present study, 26.7% of patients with AM presented with an ischemic stroke with LA thrombus detected in one patient. Inflammation my alter the electrical milieu, resulting in multiple atrial arrhythmias that could be refractory to conventional management. Our study had 33.3% of the patients presenting with more than one atrial arrhythmia. Involvement of the sinus node may lead to sinoatrial node disease and bradycardia. Other possible presentations could be idiopathic atrial enlargement, atrial tumor mimic, macro re-entrant arrhythmias and AF.6,18
Corticosteroids have been conventionally used to manage myocarditis. A customised approach to granulomatous myocarditis has been shown to improve outcomes in patients presenting with ventricular arrhythmias. Patients with evidence of myocardial inflammation have been shown to benefit from immunosuppression and based on 18F FDG PET uptake.19 All our patient’s received immunosuppression with corticosteroids and methotrexate. After establishing an etiological diagnosis of granulomatous or lymphocytic myocarditis we managed our patients with immunosuppression in addition to standard rate and rhythm control for AF. At follow up there was recurrence of AF in 26.7% of patients. This was managed by intensification of immunosuppression along with standard anti-arrhythmic medications and cardioversion.
Limitations:
This is a single center study with a limited number of patients. The prospective cohort of patients is from a region where tuberculosis and sarcoidosis are prevalent. The etiology of myocarditis may vary in different parts of the world. Nevertheless, the study provides a framework for the evaluation of AF patients when no cause is readily evident. Larger studies from multiple regions may be required to shed light on the etiology of AM in different geographies.
Serological testing for viruses and anti-myosin cardiac antibodies was not performed.
Though we could follow up our patients for a significant period, longer follow up may be needed to observe the consequences of this condition.