Exercise Intolerance and Excessive Chronotropic Response Due to Possible Autonomic Dysfunction Post COVID-19 Infection

Introduction and Objectives: In patients with Post-Acute Sequelae of Coronavirus 2 infection (PASC), a post infectious autonomic dysfunction may be one of the underlying mechanisms. Patients often present with exercise intolerance and exaggerated heart rate response to exercise. We report a single centre experience of patients with PACS and suspected autonomic dysfunction. Methods: Forty-two patients evaluated in the Outpatient Cardiology Department with suspected PASC were included in the study. Patients complained of compromised exercise performance persisting >3 months after recovery from COVID-19 infection, compared to the pre-COVID-19 period. The patients were evaluated with 12-lead electrocardiogram, echocardiography, 24-hour ECG ambulatory monitoring and either exercise stress test or a 6-minute walk test. Results: All 42 patients demonstrated an exaggerated chronotropic response, defined as the inappropriate increase in heart rate before the 6th minute of exercise >100% of the age-predicted maximal heart rate value with reproduction of clinical symptoms. In addition, 24-hour ambulatory electrocardiography revealed an increased mean heart rate of 92 beats/minute and decreased mean standard deviation of sequential 5-minute N-N interval (SDNN) of 74.4 ms. Pharmaceutical treatment with b-blockers, ivabradine or both was administrated in 29 (69%) resulting in symptomatic improvement in 82.8% of those under treatment. However, residual symptoms persisted in 69% of patients after 3 months. Conclusions: In patients with “Post-acute COVID-19” syndrome, we found an excessive chronotropic response to exercise suggesting autonomic dysfunction as the underlying mechanism of symptoms. Treatment with beta blockers or ivabradine resulted in clinical improvement but a substantial proportion of patients remained symptomatic.

Electrophysiologic testing guided risk stratification approach for sudden cardiac death beyond the left ventricular ejection fraction

Sudden cardiac death threats ischaemic and dilated cardiomyopathy patients. Anti- arrhythmic protection may be provided to these patients with implanted cardiac defibrillators(ICD), after an efficient risk stratification approach. The proposed risk stratifier of an impaired left ventricular ejection fraction has limited sensitivity meaning that a significant number of victims will remain undetectable by this risk stratification approach because they have a preserved left ventricular systolic function. Current risk stratification strategies focus on combinations of non invasive methods like T wave alternans, late potentials, heart rate turbulence, deceleration capacity and others, with invasive methods like the electrophysiologic study. In the presence of an electrically impaired substrate with formed post myocardial infarction fibrotic zones, programmed ventricular stimulation provides important prognostic information for the selection of the patients expected to benefit from an ICD implantation, while due to its high negative predictive value, patients at low risk level may also be detected. Clustering evidence from different research groups and electrophysiologic labs support an electrophysiologic testing guided risk stratification approach for sudden cardiac death.

Arrhythmic risk stratification in ischemic,non-ischemic and hypertrophic cardiomyopathy:A two-step multifactorial,electrophysiology study inclusive approach

Annual arrhythmic sudden cardiac death ranges from 0.6%to 4%in ischemic cardiomyopathy(ICM),1%to 2%in non-ischemic cardiomyopathy(NICM),and 1%in hypertrophic cardiomyopathy(HCM).Towards a more effective arrhythmic risk stratification(ARS)we hereby present a two-step ARS with the usage of seven non-invasive risk factors:Late potentials presence(≥2/3 positive criteria),premature ventricular contractions(≥30/h),non-sustained ventricular tachycardia(≥1episode/24 h),abnormal heart rate turbulence(onset≥0%and slope≤2.5 ms)and reduced deceleration capacity(≤4.5 ms),abnormal T wave alternans(≥65μV),decreased heart rate variability(SDNN<70ms),and prolonged QT_(c)interval(>440 ms in males and>450 ms in females)which reflect the arrhythmogenic mechanisms for the selection of the intermediate arrhythmic risk patients in the first step.In the second step,these intermediate-risk patients undergo a programmed ventricular stimulation(PVS)for the detection of inducible,truly high-risk ICM and NICM patients,who will benefit from an implantable cardioverter defibrillator.For HCM patients,we also suggest the incorporation of the PVS either for the low HCM Risk-score patients or for the patients with one traditional risk factor in order to improve the inadequate sensitivity of the former and the low specificity of the latter.