Synchronizing Cardiac Cycle Phase With Foot Strike To Optimize Cardiac Performance In Heart Failure And Cardiac Resynchronization Therapy (CRT)

Despite advances in medical and Cardiac Resynchronization Therapy (CRT), individuals with chronic systolic heart failure (HF) have persistent symptoms including dyspnea on exertion and exercise intolerance. Optimizing cardio-locomotor coupling may increase stroke volume (SV) and skeletal muscle perfusion as previously shown in runners when foot strike occurred in diastole. PURPOSE: To compare the effects of diastolic versus systolic foot strike timing on exercise hemodynamics in patients with HF and CRT. METHODS: Ten participants (Age: 58 ± 17 years, 40% Female) with HF and previously implanted CRT pacemakers completed repeated 5-minute bouts of walking on a treadmill at a fixed but individualized speed (range: 1.5-3mph). Participants were randomized to walking to an auditory tone to synchronize their foot strike to either the systolic (ECG R-wave; 0 or 100% ± 15% of the R-R interval) or diastolic phase (45 ± 15% of the R-R interval) of their cardiac cycle. Participants were included if ≥50% of their steps were valid (i.e. in time) as assessed via either a worn chest strap with an attached ECG and accelerometer sensor (CounterpaceR) or post-hoc analysis of foot strike waveforms. We measured VO2 (indirect calorimetry) and cardiac output (acetylene rebreathing); SV was calculated as the quotient of cardiac output and heart rate (HR). Data were compared via paired samples t-tests. RESULTS: VO2 was similar between conditions (P = 0.298). When compared to systolic walking, SV (Diastolic: 80 ± 28 vs. Systolic: 74 ± 26 ml, P = 0.003) and cardiac output (8.3 ± 3.5 vs. 7.9 ± 3.4 L/min, P = 0.004) were higher during diastolic walking; HR (paced) was not different between conditions (101 ± 15 vs. 103 ± 14 bpm, P = 0.300). Mean arterial pressure was significantly lower during diastolic walking (85 ± 12 vs. 98 ± 20 mmHg, P = 0.007). CONCLUSION: In individuals with HF and previous CRT, synchronizing foot strike with diastole during walking increased SV and cardiac output and reduced arterial pressure. Our findings indicate that in such paced hearts, diastolic stepping increases oxygen delivery and decreases afterload. Therefore, if added to pacemakers, this cardio-locomotor coupling technology may maximize CRT efficiency and increase exercise participation and quality of life in patients with HF. This work was supported by Medtronic