Causes and Mechanisms of Pre-syncope

Definition and Presentation

Pre-syncope refers to a condition in which patients feel as though syncope is imminent, but without complete loss of consciousness, characterized by symptoms such as lightheadedness, dizziness, blurred or tunnel vision, nausea, sensation of warmth, weakness, and sweating, as described by the European Heart Journal 1
Common symptoms of pre-syncope include lightheadedness, dizziness, blurred or tunnel vision, nausea, sensation of warmth, weakness, and sweating, according to Circulation 2, 3
Signs of pre-syncope may include pallor, diaphoresis, diminished postural tone, and confusion, as reported in Circulation 2

Cerebral blood flow normally ranges from 50-60 ml/100g tissue/min, which is approximately 12-15% of resting cardiac output, as stated in the European Heart Journal 1
Pre-syncope occurs when cerebral perfusion decreases but not enough to cause complete loss of consciousness, as explained in the European Heart Journal 1
A decrease in systolic blood pressure to around 60 mmHg is associated with syncope, according to the European Heart Journal 4

Decreased venous filling is the most important physiological determinant of cardiac output reduction, which can lead to pre-syncope, as described in the European Heart Journal 1
Excessive blood pooling in dependent body parts, diminished blood volume or dehydration, bradyarrhythmias or tachyarrhythmias, valvular heart disease, and structural heart disease can all contribute to cardiac output reduction, as reported in the European Heart Journal 1 and the Journal of the American College of Cardiology 5
Widespread excessive vasodilatation, thermal stress-induced vasodilatation, impaired capacity to increase vascular resistance during standing, vasoactive medications, and autonomic neuropathies can all contribute to peripheral vascular resistance decrease, as explained in the European Heart Journal 1

Neurally mediated syncope is the most common type of syncope, accounting for 21.2% of cases, and involves a sudden decrease in blood pressure and heart rate, as reported in Circulation 3
Orthostatic hypotension accounts for 9.4% of syncopal episodes and can be classified into initial, classic, delayed, and neurogenic types, as described in the Journal of the American College of Cardiology 5
Cardiac causes of syncope, including arrhythmias, structural heart disease, coronary artery disease, cardiomyopathies, and aortic disease, are associated with increased morbidity and mortality, as reported in the European Heart Journal 1, the Journal of the American College of Cardiology 5, and the Journal of the American College of Radiology 6

Age greater than 60 years, male gender, known underlying cardiac disease, palpitations prior to episode, occurrence during exertion, occurrence in supine position, low number of prior episodes, and family history of sudden cardiac death are all high-risk features for serious outcomes, as reported in the Journal of the American College of Radiology 6

Understanding the underlying cause of pre-syncope is essential for appropriate management and prevention of progression to complete syncope, which can result in falls and injuries, as emphasized in Circulation 2, 3

The American College of Radiology recommends not ordering routine head CT for uncomplicated presentations of syncope or pre-syncope, as imaging has less than 1% yield for acute abnormalities without head trauma or focal neurologic deficits 7
The American College of Radiology suggests that both syncope and pre-syncope have similar short-term serious outcomes and mortality rates and should be evaluated identically, and therefore, pre-syncope should not be dismissed as less serious than syncope 7

A cardiac examination is necessary to assess for structural heart disease, murmurs, and arrhythmias in patients with suspected pre-syncope, according to the Journal of the American College of Radiology 7
A neurologic examination is required to rule out focal deficits that would suggest stroke or other neurologic process in patients with suspected pre-syncope, as recommended by the Journal of the American College of Radiology 7