Combined exercise test improves CV mortality prediction
MedWire News: Combined exercise assessment of heart rate recovery (HRR) and T-wave alternans (TWA) is a powerful predictor for all-cause and cardiovascular (CV) mortality in a low-risk population, study results show.
Indeed, high exercise TWA (≥60 μV) and low HRR (≤18 bpm difference) increased all-cause and CV mortality five- and 12-fold, respectively, relative to normal range measures.
“This novel approach could aid in screening of general populations during routine exercise protocols as well as improve insights into pathophysiology,” Mika Kähönen (Tampere University Hospital, Finland) and colleagues comment in the journal Heart Rhythm.
Reduction in heart rate during the first 30 to 60 seconds after exercise is caused mainly by reactivation of the parasympathetic nervous system and subsequent withdrawal of sympathetic tone. Meanwhile, TWA is an electrocardiogram phenomenon indicating an electrically unstable myocardial substrate.
Both measures individually have shown some power in predicting CV outcomes, and the aim of the study was to determine whether their combined analysis during routine exercise testing could enhance prediction further.
The researchers analyzed data from the Finnish Cardiovascular Study (FINCAVAS), which included 1972 participants (1254 men) aged an average of 57 years who underwent a clinical exercise test using a bicycle ergometer.
They determined HRR as the difference between maximum heart rate during exercise and heart rate during the first minute following cessation of exercise. They used 18 bpm as a cut-off point.
An exercise-based TWA cut-off point of 60 μV was used in line with previous studies, while a cut-off of 20 μV was used for recovery-based TWA values.
During a mean follow-up of 48 months, 116 participants died and 55 of these deaths were CV-related.
The researchers found that HRR was abnormal in 29.5% of the population. Exercise-based TWA ≥60 μV was found in 5.2%, and during recovery 51.3% had TWA ≥20 μV.
In multivariable Cox analysis, after adjustment for common coronary risk factors, high exercise-based TWA (≥60 μV) and low HRR (≤18 bpm) yielded relative risks for all-cause mortality of 5.0 and for CV mortality of 12.3.
High recovery-based TWA (≥60 μV) and low HRR (≤18 bpm) yielded relative risks for all-cause death of 6.1 and for cardiovascular mortality of 8.0.
“In addition to improving predictivity, the combined assessment of HRR and TWA may be helpful in gaining insight into the pathophysiologic mechanisms on an individual patient basis that could help to guide therapy,” Kähönen et al conclude.
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By Andrew Czyzewski