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H1N1 (Swine Flu): Myocarditis Associated With Pandemic H1N1 Virus in Children

February 17, 2010

A highly scientific and well-written and documented paper in the Journal of the American College of Cardiology reported an unusual complication of H1N1 in children. Acute myocarditis is a well-recognized, however rare, manifestation of numerous viral infections with a broad spectrum of symptoms and clinical features. Fulminant myocarditis may present with fatal arrhythmias and blocks, and/or varying degrees of cardiogenic shock.

  • The prevalence of myocardial involvement in influenza infection ranges from 0 to 11% depending on the diagnostic criteria used to define myocarditis. Fulminant myocarditis is an uncommon complication, typically diagnosed in association with circulatory collapse or at autopsy in patients with influenza-associated fatal outcomes.
  • A few case reports and series represent the incidental diagnoses of influenza-associated acute fulminant myocarditis, but the true prevalence remains unknown.

The article in the Journal reports on the first known cases of acute myocarditis in pediatric population associated with the present pandemic H1N1 influenza A virus infection. Four cases occurred within a 30-day period, and 3 of them were diagnosed as fulminant myocarditis with fatal or near-fatal outcomes.

Myocarditis is an inflammation of the myocardium (cardiac muscle).

A retrospective  review of medical records was conducted on all patients admitted to Rady Children’s Hospital–San Diego with the diagnosis of H1N1 influenza A infection during October 2009.

  • Within a 30-day period, 80 children were admitted with H1N1 influenza A infection to Rady Children’s Hospital–San Diego.
  • There were 4 H1N1 influenza–associated myocarditis cases based on elevated cardiac enzymes, significant acute decrease in cardiac function demonstrated by the echocardiogram, or histologic evidence of severe myocarditis.
  • Three children presented with fulminant myocarditis, 1 with a fatal outcome and 2 requiring extracorporeal membrane oxygenation support.
  • None of the children with fulminant myocarditis had evidence of sepsis or bacterial infections.
  • All 4 children had a positive rapid influenza test result from a nasopharyngeal swab sample that was subsequently confirmed as H1N1.

Fulminant myocarditis due to viral infection is an uncommon form of acute myocarditis. Influenza A virus–associated fulminant myocarditis is exceedingly rare, with only a few cases reported in the literature. The researchers report the first 4 cases of acute myocarditis in children associated with the pandemic H1N1 influenza A virus, all occurring within a 30-day period.

Rady Children's Hospital–San Diego, is a tertiary care hospital that serves a geographic region that includes approximately 800,000 children. During the past 3 years, there was an annual average of 2 cases of acute myocarditis due to suspected viral causes, none of which had evidence of influenza infection. Within a 30-day period in October 2009, there were 3 cases of acute fulminant myocarditis and 1 case of acute perimyocarditis at Rady Children's Hospital–San Diego, all associated with confirmed H1N1 influenza A infection.

The prevalence of influenza-associated fulminant myocarditis is not known because of the lack of comprehensive screening, with only a handful of clinical cases and autopsy findings reported in the literature. These documented 4 cases within a 30-day period, compared with the hospital’s previous experience, raise the possibility that the novel H1N1 influenza A virus is more commonly associated with a severe form of myocarditis than previously encountered influenza strains.

The authors of this study note that these observations warrant a high index of suspicion for myocarditis in children with H1N1 influenza A infection. Early detection and aggressive management are paramount. Timely intervention with circulatory support may decrease morbidity and mortality, with the potential for a favorable cardiac prognosis.

Journal of the American College of Cardiology

ProMED Digest V2010 #73

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