A) THE 3 CLASSES OF SYNCOPE
Syncope can be divided into two main categories: 1) Cardiac syncope and 2) Non-cardiac syncope. Non-cardiac syncope is sub-divided into neurally mediated (reflex) and orthostatic hypotension syncope. This makes a total of 3 main classes of syncope.
1. NEURALLY MEDIATED (REFLEX) SYNCOPE
This includes the following 3 types of syncope. NB: Vasovagal is just one of them.
Vasovagal: Brought on by fear, heat exposure, noxious stimuli, pain, or stress
Situational: Triggered by coughing, sneezing, micturition (urination), defecation, GI stimulation, blood draw. It may also occur post-exercise and post-prandially.
Carotid hypersensitivity / Carotid sinus syndrome. Can be triggered by head rotation or pressure on the carotid sinus (e.g., from shaving or tight collar). Consider in patients with unexplained falls
Diagnostic test: Head-up tilt table test.
2. CARDIOVASCULAR
ARRHYTHMIAS
Bradyarrhythmias:
High-grade AV block,
sick sinus syndrome,
Permanent Pacemaker Failure (PPM Failure)
Meds (negative chronotropes)
Tachyarrhythmias:
VT
SVT (rarely causes syncope)
Long QT syndrome
Brugada syndrome
Diagnostic test: ECG, Holter, Event Monitor, Loop Recorder.
MECHANICAL
Obstructive / Mechanical
Hypertrophic cardiomyopathy (exertional syncope esp. in patients with a family Hx of SCD)
Structural Heart Disease
Myocardial infarction
Valvular heart disease (aortic stenosis)
Cardiac tamponade
Aortic dissection
Atrial myxoma
Subclavian Steal
Diagnostic test: Echocardiogram.
CARDIOPULMONARY
Pulmonary embolus (Saddle embolus)
Pulmonary hypertension
Hyperventilation / hypocapnia
Hypoxia
3. ORTHOSTATIC HYPOTENSION SYNCOPE
This includes the following types of syncope:
1. Volume depletion: Dehydration (diarrhea, inadequate fluid intake, vomiting), Acute blood loss (e.g., GI bleed, Ectopic pregnancy, Ruptured aortic aneurysm, Splenic Rupture, Ovarian Cyst)
2. Autonomic nervous system (ANS) problems.
-Drug-induced (Meds & Substance Use): Antihypertensives [Vasodilators, diuretics, negative chronotropes (e.g. CCB, BB),] proarrhythmic or QT-prolonging drugs (class IA, IC or III antiarrhythmics, etc.), and psychoactive drugs (e.g. antipsychotics, antidepressants, antiparkinsonian meds, barbiturates, benzos), antianginal agents, flibanserin, Illicit Drugs, alcohol. Anaphylaxis.
-Postural Orthostatic tachycardia syndrome (POTS): It is a form of dysautonomia that is characterized by severe orthostatic intolerance with marked tachycardia. It is usually seen in young adults (mostly female) and is associated with chronic fatigue syndrome and mitral valve prolapse.
-Primary autonomic failure (pure autonomic): Parkinson’s, Wernicke encephalopathy, Multiple sclerosis, multiple system atrophy (e.g., Shy-Drager syndrome),
-Secondary autonomic failure: Diabetes, amyloidosis, uremia, spinal cord injuries, chronic inflammatory demyelinating polyneuropathy, connective tissue diseases, Lewy body dementia, older age, spinal cord injury, uremia
Diagnostic test: Orthostatic vitals.
B) TWO THINGS THAT MIMIC SYNCOPE
There are two things that mimic syncope and should be considered in the differential.
METABOLIC
Hypoglycemia.
Electrolyte abnormalities.
Adrenal insufficiency, Addison’s disease
Anemia
Hypoxia
Diagnostic tests: Blood sugar, CBC, CMP
NEURO-PSYCHIATRIC
Neurologic
Seizure, pseudoseizure
Cerebrovascular (TIA, stroke)
Atypical Migraine
SAH
Cataplexy
Drop attacks
Falls
Vertebrobasilar insufficiency
Psychiatric
Psychiatric issue / Psychogenic
Faking it / Malingering
Panic attack
Diagnostic evaluation: A psychiatric evaluation.
References
Cardiol Clin. 2013 Feb; 31(1): 89–100. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3589989/
http://www.aafp.org/afp/2017/0301/p303.html
Pocket Medicine
Cecil Essential of Medicine, 9th Edition, Chapter 9