Allison, T G

Abstract Background Inability to reach age-predicted peak heart rate (APPHR) of >85%, or submaximal heart rates, on treadmill exercise stress testing (TMET) is associated with increased mortality risk [1]. Evidence is limited on mortality outcomes with heart rates greater than APPHR, or ‘supramaximal’ heart rates, especially when using heart rate metrics alone. Purpose Use of a comprehensive, compositive assessment of heart rate, termed ‘vigor’, to determine mortality outcomes has yet to be explored, especially for those with supramaximal heart rates. We sought to investigate this relationship. Methods We queried our stress database from 1993-2010 for patients >30 years old without cardiovascular disease and not on antichronotropic therapy. Clinical and mortality outcomes were retrieved from patient records. Patients were stratified into groups based on APPHR as achieved on TMET: <75%, 75-84%, 85-94%, 95-104%, ≥105% of APPHR. For our study, heart rate ‘vigor’ served as a composite assessment of cardiovascular fitness based solely on heart rate. This was derived from resting heart rate, heart rate recovery, and achieved percentage of APPHR. A higher Heart Rate Vigor Score (HRViS) for this study was, by definition, indicative of better cardiac responsiveness and recovery following exertion. Patients were stratified based on their achieved HRViS. Scores were determined as follows: All patients were initially assigned 3 points. 1 point was subtracted for each of the following parameters met: resting heart rate >90 beats per minute (BPM), heart rate recovery <13 BPM, or submaximal heart rates of APPHR <85%. Patients that remained at HRViS 3 and achieved supramaximal heart rates (≥105% APPHR) were assigned an additional point, amounting to HRViS 4. HRViS stratifications are detailed in Table 1. Mortality rates were calculated for all HRViS stratifications, with adjustment for FAC and known confounders. HRViS 3 was used as the referent. Results 18,961 total patients were included. 88 patients were classified with HRViS of 0; 1,763 as HRViS 1; 5,409 as HRViS 2; 9,902 as HRViS 3; and 1,799 as HRViS 4. Those with lower HRViS scores had more comorbid conditions (Table 1). 2,144 patients achieved submaximal APPHR (<85%) on TMET, and 2,917 achieved supramaximal APPHR (≥105%). HRViS 0, 1, and 2 had higher mortality risks compared to referent HRViS 3: 0 [3.76 (2.34-6.04), p<0.0001]; 1 [1.80 (1.53-2.12), p<0.0001]; 2 [1.29 (1.12-1.48), p=0.0004]. HRViS 4 had a non-statistically significant trends towards lower mortality risk compared to 3: 0.85 (0.66-1.08), p=0.1768. Conclusions HRViS 4 had a non-statistical trend towards lower mortality risk. Our findings do not support concern for adverse outcomes with excessive heart rates during exercise, and rather, may indicate a trend towards mortality benefit.HRViS Table 1