Morbitz type I second degree AV block during recovery from dengue hemorrhagic fever

Two patients with serologically-proven dengue virus infection and Morbitz type I second degree atrioventricular (AV) block are described. A 7 years old boy (patient 1) with grade 2 and a 7 years old girl (patient 2) with grade 3 illness were admitted to the hospital on the 3rd and the 5th day of the illness, respectively. Both had typical resentation for dengue hemorrhagic fever including fever, hepatomegaly, thrombocytopenia and signs of extravascular leakage. The 7 year old girl also had epistaxis and anemia (Hct 24%). Morbitz type I second degree and 2:1 AV block developed on day 7 (patient 1) and day 8 (patient 2) of the illness, both during recovery periods. Patient 1 also had occasional monomorphic premature ventricular contraction (PVC). There was no other abnormality in the 12-lead EKGS and echocardiograms showed normal ventricular systolic function in both. Other than mild hypokalemia (3.3 and 3.4 mgq/l), serum electrolytes were normal. Neither patients had elevation of serum creatine phosphokinase (CPK). In patient 1, exercise (on day 10) normalized AV conduction and abolished the PVC. Follow up EKG and physical examination at 10 months after the illness was normal. The rhythm in patient 2 resolved to 1st degree AV block (with occasional morbitz type I second degree at night) on day 12. In this patient, exercise resulted in shortening of the PR interval and Valsalva maneuver resulted in further PR prolongation. The patient was well at 1-month follow up with a mormal EKG. Morbitz type I second degree AV block during recovery from dengue hemorrhagic fever may be a transient functional impairment of the AV node, in which altered autonomic tone may play a role.