Chronotropic Intolerance In Patients With Chronic Lyme Disease Identified By Serial Cardiopulmonary Exercise Testing

In the U.S., annual incidence of Lyme disease is approximately 300,000. In an estimated 5-30% of cases, post-treatment Lyme disease syndrome (PTLDS) develops; symptoms include post-exertional malaise characteristic of myalgic encephalomyelitis. The contribution of autonomic regulation has not been elucidated. PURPOSE: To evaluate cardiovascular responses to serial cardiopulmonary testing in patients with PTLDS. METHODS: 14 patients with PTLDS and 8 sedentary controls underwent 2 maximal exercise tests separated by 24 hours. Heart rate (HR) was measured continuously via electrocardiogram. Expired air was collected for determination of anaerobic threshold (AT) using V-slope methodology and maximal exertion was defined as a respiratory exchange ratio >1.09. Independent-samples t-tests compared baseline characteristics of PTLDS patients and controls. Linear regression determined the effect of PTLDS diagnosis on HR at AT and peak holding workload constant. RESULTS: Patients were 44.0±10.1 years old, weighed 69.8±16.2 kg, and achieved a peak VO2 of 23.8±6.2 mL/kg/min during test 1. HR was 116.2±21.8 bpm at AT and 162.6±25.1 at peak. PTLDS and controls did not differ in peak VO2 during test 1 (p=0.161), test 2 (p=0.134), or the difference between test 1 and test 2 (p=0.498). HR at AT was comparable in test 1 (p=0.127) but different in test 2 (p<0.001). HR at peak was different in test 1 (p=0.001) and test 2 (p<0.001). During test 1, holding workload constant, PTLDS patients had lower peak HR by 19.5 bpm (p=0.033; 95% CI: -37.3 to -1.8). During test 2, holding workload constant, PTLDS predicted a lower HR by 26.8 bpm at AT (p=0.004; 95% CI: -43.9 to -9.8) and 24.3 bpm at peak (p=0.007; 95% CI: -40.9±-7.7). CONCLUSIONS: Patients with PTLDS demonstrated abnormal cardiovascular responses to exercise. Despite accomplishing the same VO2, and holding workload constant, the HR response was diminished in the post-exertional state, potentially indicating dysautonomia in PTLDS.