Heart rate variability testing methods
British researchers studying the relationship between heart rate variability (HRV) and mortality in congestive heart failure patients needed data from ambulatory patients.
Information was gathered from 433 congestive heart failure patients of both sexes aged 18 to 80, with a mean age of 62.
Subjects wore miniature battery-operated tape recorder ECGs (Tracker model from Reynolds Medical Ltd.) similar to that employed in common clinical practice in the United States. They engaged in 24 hours of normal, unrestricted activity.
The recorder includes a crystal-generated time reference track that allows correction for recording and replay speed errors to within .5%, which researchers considered essential for an accurate measurement of HRV.
The 24-hour ambulatory ECGs were replayed through a Pathfinder arrhythmia analyzer (Reynolds Medical Ltd.) to document the presence of ventricular arrhythmias. U.S. experts say the key to charting HRV lies in the analysis of the left ventricular function.
Ambulatory ECGs less than 16 hours in duration or with less than 90% of recording suitable for analysis were excluded.
After initial analysis, the remaining normal-to-normal RR levels were measured and time-domain analysis of HRV was carried out.