Clinical challenges in the diagnosis and management of postural tachycardia syndrome.

Postural tachycardia syndrome (POTS) is a multifactorial clinical syndrome defined by an increase in heart rate of ≥30 bpm on standing from supine position (or ≥40 bpm in children). It is associated with symptoms of cerebral hypoperfusion that are worse when upright and improve when in supine position. Patients often have additional symptoms including severe fatigue and difficulty concentrating. There are several possible pathophysiologic mechanisms including hypovolaemia, small-fibre peripheral neuropathy and hyperadrenergic states. POTS can also be associated with several disorders including mastocytosis, Ehlers-Danlos syndrome (hypermobility type) and autoimmune disorders. The treatment is focused on symptom relief and not solely on reducing tachycardia. Given its varying presentations, it is important to employ a practical, mechanism-focused approach to the diagnosis and management of POTS.

Orthostatic hypotension: managing a difficult problem.

Orthostatic hypotension (OH) leads to a significant number of hospitalizations each year, and is associated with significant morbidity and mortality among affected individuals. Given the increased risk for cardiovascular events and falls, it is important to identify the underlying etiology of OH and to choose appropriate therapeutic agents. OH can be non-neurogenic or neurogenic (arising from a central or peripheral lesion). The initial evaluation includes orthostatic vital signs, complete history and a physical examination. Patients should also be evaluated for concomitant symptoms of post-prandial hypotension and supine hypertension. Non-pharmacologic interventions are the first step for treatment of OH. The appropriate selection of medications can also help with symptomatic relief. This review highlights the pathophysiology, clinical features, diagnostic work-up and treatment of patients with neurogenic OH.

Autonomic function testing: an important diagnostic test for patients with syncope.

Syncope is a common problem with a large differential diagnosis. The initial history and physical examination often provide initial clues; however, some cases warrant further testing to determine the underlying cause. Autonomic function testing is a safe way to evaluate patients with syncope further, and to assess their parasympathetic and sympathetic nervous systems. Autonomic testing can help to diagnose several conditions, including orthostatic hypotension, delayed orthostatic hypotension, postural tachycardia syndrome and neutrally mediated syncope. Thus, when the cause of syncope is unclear, autonomic testing can help to assess the autonomic nervous system, stratify the risk of future episodes and to guide treatment decisions.

The role of autonomic testing in syncope.

Syncope is a common presenting complaint in both the inpatient and outpatient settings. The main goals in the clinical evaluation of syncope are to identify an underlying etiology, to stratify risk and to guide plans for therapeutic intervention. Testing begins with an initial electrocardiogram to screen for any cardiac rhythm abnormalities. Heart rate variability to paced breathing provides a standard measure of cardiac parasympathetic function and offers clues towards an autonomic cause of syncope. A Valsalva maneuver is used to evaluate for parasympathetic dysfunction through the Valsalva ratio. In addition, sympathetic adrenergic function is assessed through evaluation of blood pressure response during the Valsalva maneuver. Abnormalities to the Valsalva maneuver can suggest clues towards an autonomic cause of syncope. Head-up tilt table testing is an important part of the autonomic evaluation of patients with syncope, and can be diagnostic for many disorders that result in syncope including orthostatic hypotension, neurally mediated syncope, postural tachycardia syndrome or delayed orthostatic hypotension. Autonomic function testing provides a safe and controlled environment for evaluation of patients, and plays a pivotal role in the diagnosis of syncope, particularly in challenging cases. While the initial clinical evaluation of syncope involves a detailed history and physical examination; in situations where the diagnosis is unknown, the addition of autonomic testing is complementary and can lead to identification of autonomic causes of syncope.