History
The concept of HRT was introduced to the medical community by Georg Schmidt and colleagues from the Munich University of Technology in 1999 in the British medical journal the Lancet. While studying PVC characteristics, Schmidt and his colleagues had noticed that heart rate seemed to speed up after a PVC. To get a clearer picture, they listed the time from one heartbeat's R-wave to the next R-wave (called RR intervals) and synchronized these lists to the time of the PVC beat and averaged the values in the list. A plot of this averaged RR interval list (called a PVC tachogram) not only confirmed their observation that heart rate sped up for a few beats after a PVC, but highlighted another less obvious feature, that heart rate then slows down beyond what it was before the PVC, before returning to the original heart rate.
If Schmidt et al. had stopped there, it would have been an interesting observation to be found in the footnotes of an electrocardiography textbook. Instead, they reasoned that just as loss of variability in heart rate indicated patients more likely to be at high risk of dying after a heart attack, this phenomenon might also be an indicator of a healthy control of heart rate in such patients. They proceeded to test this hypothesis using 24 hour electrocardiogram (Holter monitor) recordings from one hundred survivors of heart attacks with frequent PVCs. Greater turbulence seemed correlated with better prognosis. They then used this data to determine the optimal discriminating threshold between normal and abnormal HRT values, and came up with the values TS=2.5, TO=0%. Now came the test. Would HRT and these threshold values also work in the real world? These thresholds were applied to Holter records from a total of 1191 patients who had experienced a heart attack. There were 162 deaths (13.6%) during the follow-up period of about 2 years. Patients with abnormal HRT were approximately 3 times more likely to die than those with normal HRT, beating out some other commonly used predictors. Thus the field of HRT was born.
Read more about this topic: Heart Rate Turbulence
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