Sinus arrhythmia

My otherwise healthy 4 year old daughter had a well-child check-up today in which her pediatrician told me that she had a regularly irregular heartbeat and said it was probably a sinus arrhythmia in which there was no need to worry.  He ordered an EKG and the snoop of a mom I am read it over the tech's shoulder.  It said sinus arrhythmia at 94 bpm with an enlarged left ventrical.  She has seen the same pediatrician her whole life and I am concerned that this is arrythmia is new and not something she has already lived without treatment or obvious complication for 4 years.  I also am concerned about underlying cause, such as heart disease and if there may be another cause.  I realize without the EKG and an echo you may not be able to provide much information.  We won't receive results from the EKG until next week sometime and I am going to worry.  Please help.  

[Jeffrey R Boris, M.D.]

Dear Angela,

Without reviewing the study or seeing your daughter, I cannot say for sure what is happening with her.  However, I can say that sinus arrhythmia is an absolutely normal finding.  It correlates with the heart rate normally increasing with inspiration and decreasing with expiration; this is referred to as respiratory variation.  Unfortunately, we're stuck with the misnomer, sinus arrhythmia, which is scary sounding but quite benign.