Defining Cardiac Dysautonomia - Different Types, Overlap Syndromes; Case-based Presentations

Abstract

The cardiovascular branch of autonomic nervous system (ANS) is responsible for the regulation of heart rate, blood pressure, and maintaining homeostasis during physiological stress such as exercise and standing upright. ANS constantly controls the rate and force of heart contractions and the vascular tone with the aim to maintain the sufficient tissue perfusion with oxygenated blood and secure venous return to the heart. Dysautonomias, result of ANS malfunction, are often found in patients with cardiovascular symptoms. Apart from the most prevalent one, arterial hypertension, the cardiovascular dysautonomic continuum encompasses other important although less known conditions: postural orthostatic tachycardia syndrome, inappropriate sinus tachycardia, orthostatic hypotension and reflex syncope. Moreover, heart diseases may evoke autonomic imbalance by themselves; cardiac pump failure is usually associated with sympathetic hyperactivity, neuroendocrine vasopressor activation, higher heart rate, reduced heart rate variability and baroreflex hyposensitivity, all of which are predictors of adverse outcomes. Cardiologists and electrophysiologist frequently see patients for the evaluation and management of unexplained syncope, orthostatic intolerance, heart rhythm abnormalities and symptoms of palpitations. Recognizing the presence of cardiac dysautonomia is an important skill which is necessary for the appropriate evaluation and treatment of these patients. Clinical presentations may overlap, and the importance of a thorough history cannot be over-emphasized. In this review we will present a cases of a patients with cardiac dysautonomia which is illustrative of a typical patient experience, followed by a review of the autonomic nervous system and discussion of prevalence, clinical presentation, and pathophysiology of common cardiac dysautonomias.

Keywords: Atrial fibrillation; Autonomic dysfunction; Autonomic nervous system; Obesity; Risk factors.

Figure 1.. Global blood pressure control and spectrum of cardiovascular dysautonomias. Two major types of cardiovascular autonomic dysfunction, cardiac i.e. “pump” dysfunction and vascular i.e. “pipeline” dysfunction may overlap, combine and convert to each other over the life span. For instance, patients with arterial hypertension may have orthostatic and postprandial hypotension, and reduced heart variability. Younger individuals may suffer from both POTS and VVS. Apart from global autonomic circulatory disorders, vascular bed may be affected in special areas, such as cerebral (e.g. migraine), coronary (e.g. spasm angina), and peripheral zones (e g. Raynaud’s disease) as well as in the venous capacitance vessels (abnormal venous pooling). The etiologies of cardiovascular dysautonomias are heterogenous and span over neurodegenerative diseases (e.g. Parkinson’s disease), chronic conditions such as diabetes and renal failure, chronic inflammatory states such autoimmune diseases (e.g. Sjögren’s disease), cardiovascular diseases (e.g. essential hypertension, a cardiovascular dysautonomia per se, and heart failure) and processes associated with aging. Genetic predisposing factors and rare genetic diseases may also contribute. (Figure adapted from Ricci et al 2015 (27)). Red colour – hyperadrenergic conditions/ sympathetic dominance. Blue colour – hypoadrenergic conditions/ parasympathetic dominance. POTS, postural orthostatic tachycardia syndrome; VVS, vasovagal syncope; CSS, carotid sinus syndrome.

Figure 2.. Pictures of a typical rash involving the axillae and lower extremities of a woman with Postural Orthostatic Tachycardia Syndrome.

Figure 3.. Symptomatic events from a Holter monitor in a patient with Postural Orthostatic Tachycardia Syndrome

Figure 4.. Results (in table format) of autonomic testing performed at a tertiary institution on a patient with Postural Orthostatic Tachycardia Syndrome

Figure 5.. Head-up tilt test performed on 15-year-old-girl with suspected POTS. Please, note a steep increase in heart rate after tilt-up (+60 bpm) associated with subjective symptoms of orthostatic intolerance, headache, dizziness and fatigue. Cerebral oximetry (normal values: 60-80%) measured through near-infrared spectroscopy demonstrates pronounced variation and fall tendency. Test is terminated after 15 min due to pronounced intolerance symptoms.

Figure 6.. Comparison of two typical 24-hour Holter monitoring circadian curves in postural orthostatic tachycardia syndrome (POTS) and inappropriate sinus tachycardia (IST). Please, note higher average heart frequency and lack of typical high heart rate spikes, especially after awakening in IST compared with POTS.

Figure 7.. Classical orthostatic hypotension. Head-up tilt test performed on 82-year-old-man. Please, note a steep decrease in blood pressure after tilt-up ( -70 mmHg) associated with subjective symptoms of orthostatic intolerance, dizziness and fatigue. Cerebral oximetry (normal values: 60-80%) measured through near-infrared spectroscopy demonstrates progressive fall. Test is terminated after 15 min due to pronounced intolerance symptoms and presyncope.

Figure 8.. Delayed orthostatic hypotension, carotid sinus hypersensitivity and vasovagal reflex. Head-up tilt test performed on 65-yearold- man with unexplained syncope. Please, note a progressive decrease in blood pressure after tilt-up (- 30 mmHg ), positive carotid sinus massage right side with symptom reproduction (dizziness) and finally positive nitroglycerine provocation with syncope. Cerebral oximetry (normal values: 60-80%) measured through near-infrared spectroscopy demonstrates only a slight progressive fall. CSM dx, carotid sinus massage right side; NTG, nitroglycerine 400 μg sublingually.