Testing for autonomic neuropathy: initial heart rate response to active and passive changes of posture

Sinus Tachycardia: a Multidisciplinary Expert Focused Review

Sinus tachycardia (ST) is ubiquitous, but its presence outside of normal physiological triggers in otherwise healthy individuals remains a commonly encountered phenomenon in medical practice. In many cases, ST can be readily explained by a current medical condition that precipitates an increase in the sinus rate, but ST at rest without physiological triggers may also represent a spectrum of normal. In other cases, ST may not have an easily explainable cause but may represent serious underlying pathology and can be associated with intolerable symptoms. The classification of ST, consideration of possible etiologies, as well as the decisions of when and how to intervene can be difficult. ST can be classified as secondary to a specific, usually treatable, medical condition (eg, pulmonary embolism, anemia, infection, or hyperthyroidism) or be related to several incompletely defined conditions (eg, inappropriate ST, postural tachycardia syndrome, mast cell disorder, or post-COVID syndrome). While cardiologists and cardiac electrophysiologists often evaluate patients with symptoms associated with persistent or paroxysmal ST, an optimal approach remains uncertain. Due to the many possible conditions associated with ST, and an overlap in medical specialists who see these patients, the inclusion of experts in different fields is essential for a more comprehensive understanding. This article is unique in that it was composed by international experts in Neurology, Psychology, Autonomic Medicine, Allergy and Immunology, Exercise Physiology, Pulmonology and Critical Care Medicine, Endocrinology, Cardiology, and Cardiac Electrophysiology in the hope that it will facilitate a more complete understanding and thereby result in the better care of patients with ST.

Autonomic testing, methods and techniques

The evaluation of autonomic function requires indirect assessment of neurophysiologic function using specialized equipment that is often available only at tertiary care centers, with few specialists available. However, the evaluation of autonomic function is rooted in basic physiology, and the results can be interpreted by careful consideration of the context of the problem. Many automated devices have become widely available to test autonomic function, but they tend to gather inadequate data leading to frequent misdiagnosis and clinical confusion. We review the details necessary for the neurophysiologist to properly perform, and interpret, autonomic function testing.

Dysautonomy in different death risk groups (Rassi score) in patients with Chagas heart disease

BACKGROUND

It has been difficult to prove that "catecholamine-induced cardiomyopathy" contributes to the mechanism of sudden cardiac death in Chagas heart disease. Also, it is almost impossible to rule out the possibility that it is not involved in the process. More importantly, the vagal-cholinergic pathway in the ventricle plays a direct role in the prevention of the initiation of complex ventricular arrhythmias, including nonsustained ventricular tachycardia, ventricular fibrillation responsible for sudden death.

OBJECTIVE

To determine frequency of parasympathetic autonomic indices among the different groups of risk of cardiovascular death when stratified by Rassi score.

METHODS

Patients with Chagas heart disease were selected and divided into three risk groups by Rassi score. A fourth group, non-Chagas group, was of similar age and gender. All were subjected to analysis of heart rate variability during controlled breathing (RSA) and tilt table passive test (tilt test). High frequency and low frequency/high frequency ratio were calculated and presented by box-plot. Also, t-test was used to compare the two groups.

RESULTS

It was observed that the parasympathetic and sympathetic component were affected, when the risk group increased the response was worsened to the stimulus (RSA or Tilt). Also, the low-risk group was jeopardized, when compared to the non-Chagas group.

CONCLUSION

The loss of parasympathetic modulation was present in all Rassi risk groups, including the low risk, indicating that a morphological change of the myocardium represents a detectable neurofunctional change.