Abstract

Introduction Post-COVID syndrome (PCS) is a well-recognised and frequently debilitating constellation of signs and symptoms that persist for at least 12 weeks after COVID-19 infection. Cardiovascular symptoms, particularly those associated with inappropriate sinus tachycardia (IST), are common and can include palpitations and breathlessness, which impede patients in their daily tasks and can be difficult to manage. Previous research has suggested that dysautonomia, a dysfunction in the autonomic nervous system, might underlie most PCS symptoms. However, its role in the development of IST within the context of PCS has not been fully investigated. This retrospective study aims to examine the prevalence of IST and cardiovascular symptoms in PCS patients who undergo 24-hour Holter monitoring. In addition, we aim to analyse the demographic characteristics of individuals affected by these symptoms and assess cardiovascular autonomic function by analysing heart rate variability (HRV), to investigate the role of dysautonomia in the development of IST in PCS. Methods We undertook a retrospective cohort analysis of symptomatic PCS patients referred to our multidisciplinary PCS Clinic at UCLH between March 2020 and February 2023. We identified 685 eligible patients who underwent diagnostic 24-hour ECG monitoring. Excluding patients on therapies or with conditions that could affect heart rate, we conducted a comparative sub-analysis on 524 patients, dividing them into two groups of IST (mean 24-hour HR≥90bpm, n=100) and non-IST (mean 24-hour HR<90bpm, n=424). The heart rate data extracted from the 24-hour ECG records of these patients were ported into the KUBIOS HRV standard software for HRV analysis and assessment of sympathetic and parasympathetic activity based on time and frequency domain analysis, which could indicate cardiovascular dysautonomia. Demographic data were analysed using basic descriptive statistics and a chi-square test between the two groups using GraphPad Prism software. Results The frequency domain component of the HRV analysis revealed that the LF/HF ratio was significantly higher in the IST group (2.78 ± 1.89) compared to the non-IST group (2.15 ± 1.93, p<0.001). The sympathetic nervous system (SNS) index was significantly higher in the IST group (1.50 ± 0.77 versus -0.13 ±0.70, p<0.001), whilst the parasympathetic nervous system (PNS) index was significantly lower in the IST group (-1.75 ± 0.65 versus -0.16 ± 1.61, p<0.001). Conclusions In PCS patients with IST, dysautonomia leads to an imbalance in the sympathovagal regulation of the heart, with decreased parasympathetic activity and increased sympathetic activity, with parasympathetic down-regulation being more pronounced. Addressing dysautonomia and promoting parasympathetic activity could thereby improve PCS management strategies to restore a balanced autonomic regulation of the cardiovascular system. Conflict of Interest None