As the COVID-19 pandemic continues to affect hundreds of millions of people worldwide, autonomic complications are being recognized with increasing frequency in both the acute and chronic form of the illness, the latter now designated as post-acute sequelae of SARS-CoV-2 (PASC), colloquially termed long-COVID. Tachycardia is a common symptom of PASC, and some patients may be diagnosed with postural tachycardia syndrome (POTS) or inappropriate sinus tachycardia (IST). While post-COVID POTS has garnered more attention from the scientific and popular press, IST may be equally or more common and has been reported in survivors of the prior SARS coronavirus pandemic [1]. The etiology of IST is unknown; however, the proposed mechanisms overlap with those of POTS, including increased sympathetic and/or reduced cardiovagal activity.
In their recent publication [2], “Inappropriate sinus tachycardia in post-COVID-19 syndrome” Aranyo and colleagues identified 200 consecutive patients with PASC. IST was defined according to consensus criteria as symptomatic sinus rhythm rate ≥ 100 bpm at rest with a mean 24-h heart rate above 90 beats/min in the absence of any acute physiological demand or conditions known to produce sinus tachycardia. All patients underwent a 10-min active stand test to help rule out disorders of orthostatic intolerance, such as POTS and orthostatic hypotension. In addition, patients underwent an echocardiogram, 24-h Holter monitoring, a 6-min walk test (6MWT), and measurements of blood markers of inflammation and myocardial damage, including ferritin and interleukin-6. Heart rate variability (HRV) analysis was performed from the 24-h Holter data, focusing on standard time-domain parameters such as the RR interval, standard deviation of the inter-beat interval (SDNN), and the percentage of adjacent NN intervals that differed from each other by more than 50 ms (PNN50), as well as standard frequency-domain parameters including very low-frequency (VLF; 0.003–0.04 Hz), low-frequency (LF; 0.04–0.15 Hz), and high-frequency (HF; 0.15–0.40 Hz) bands. The HF band and PNN50 are regarded as indicators of the parasympathetic influence on heart rate, whereas the LF and VLF bands have more complex physiology that integrates both the sympathetic and parasympathetic components. Comparison groups included age- and gender-matched PCR-confirmed COVID patients without IST (fully recovered group, N = 19) and age- and gender-matched controls who had no history of SARS-COV-2 disease, as confirmed by negative serology (uninfected group, N = 17).
The authors identified 40 patients with IST from the cohort of 200 patients with PASC yielding an estimated prevalence of 20%. Eighty-five percent of the subjects were women and 83% had a history of mild COVID defined as the presence of symptoms without evidence of viral pneumonia or hypoxia. Most patients reported cardiopulmonary symptoms at the onset of their infection, including palpitations (90%), dyspnea (83%), and chest pain (78%); 53% reported dizziness and 48% anosmia. Compared to fully recovered patients, patients with IST were more likely to report palpitations (90% vs. 5%; p < 0.001), dyspnea (82% vs. 16%; p < 0.001), chest pain (78% vs. 21%; p < 0.001), headache (73% vs. 37%; p = 0.007), dizziness (53% vs. 5%; p = 0.002), diarrhea (53% vs. 16%; p = 0.003), and dermatological alterations (35% vs. 5%; p = 0.009) during the acute phase of SARS-CoV-2 infection. Patients with IST were also more likely to report environmental allergies compared to the fully recovered and uninfected groups (25% vs. 0%; p = 0.01), hinting at a potential mast cell component.
The 6MWT showed that patients with PASC with IST had a significantly reduced exercise capacity, with a 60% reduction in their estimated normal distance. Frequency analysis of heart rate variability revealed that patients with IST had a reduction in VLF, LF, and HF domains compared to controls, with more severe impairment in the parasympathetic-influenced domains. There was no difference in blood inflammatory markers between groups.
Limitations of this work include the small sample sizes of the control groups, as well as the lack of systematic pulmonary evaluations, measurement of markers of physical deconditioning, and systematic autonomic testing. Nonetheless, this study provides the first glimpse of how common IST may be in PASC and adds to the growing body of literature on autonomic dysfunction as a potential mechanism in PASC-related disability. With the Omicron variant currently surging across the globe, PASC-related autonomic complications will, unfortunately, be with us for some time, and clinicians should be familiar with their manifestations and potential treatment options.
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Source: Miglis MG, Larsen N, Muppidi S. Inappropriate sinus tachycardia in long-COVID and other updates on recent autonomic research. Clin Auton Res. 2022 Feb 7. doi: 10.1007/s10286-022-00854-5. Epub ahead of print. PMID: 35129713. https://link.springer.com/article/10.1007/s10286-022-00854-5 (Full text)