13. Syncope

Definition

Complete loss of consciousness and postural tone that is sudden, transient, and typically brief. Hypothesized pathophysiology is cerebral hypoperfusion.

NOTE: syncope is one on many possible reasons for a loss of consciousness

Etiologies

Consider whether a non-syncopal etiology may explain the loss of consciousness:

  • Seizure.
  • Trauma.
  • Intoxication/medication-induced.
  • Metabolic derangement.
  • Sleep disorder.
  • Psychiatric (pseudosyncope).
  • Accidental fall.

True syncope is grouped into a few major categories:

Cardiac (5 - 21%):

  • Arrhythmia
    • Bradyarrhythmia – AV block or sinus pause.
    • Tacyharrhythmia – VT, SVT.
  • Structural: aortic stenosis, hypertrophic cardiomyopathy, atrial myxoma, pulmonic stenosis, pericardial tamponade.
  • Vascular: pulmonary embolus, pulmonary hypertension, acute coronary syndrome/ischemia, aortic dissection, subclavian steal, vertebrobasilar TIA.
  • Congenital: Long QT syndrome, Brugada syndrome, catecholaminergic polymorphic VT (CPVT), coronary anomaly.

Reflex (21 – 48%): inappropriate heart rate or blood pressure response.

  • Vasovagal syncope.
    • Situational (i.e micturition, defecation, coughing, choking) or triggered.
  • Carotid sinus hypersensitivity.

Orthostatic hypotension (4 - 24%): decrease in SBP >20mmHg or DBP >10mmHg upon movement from lying OR sitting to standing. May be immediate (within a few seconds) or delayed (one to several minutes).

  • Decreased intravascular volume.
  • Drug effect.
  • Primary/Secondary autonomic insufficiency.
  • Adrenal insufficiency.
  • Thyroid disorders.

Unexplained (17 – 37%).

Evaluation

All patients should get a thorough history and physical exam, and an electrocardiogram. Often the history is the most important part - try to get corroborating information from bystanders. The main question to address: is this cardiac syncope or high-risk?

HIGH-YIELD FINDINGS

1. HPI

  • Cardiac: preceding dyspnea or chest pain, cyanosis, preceding palpitations, history of afib/flutter, syncope during or just after exercise, sudden syncope without any clear prodrome.
  • Non-cardiac: pain/procedure immediately prior, mood change before or after, feeling warm/cold, headache, abdominal discomfort, having a prolonged prodrome beforehand, any vagal mediated event elicited.

2. Medical history

  • History of structural heart disease, neurologic conditions, diabetes.
  • Meds: diuretics, QT prolonging agents, antihypertensives, sedatives, psychiatric medications, marijuana.
  • Family history: sudden death especially <40 years old, cardiomyopathy, seizure disorder, predisposition to syncope.

3. Physical exam

  • Orthostatic blood pressure.
  • Bilateral blood pressure.
  • Cardiac murmurs.
  • Sinus tachycardia/tachypnea to suggest pulmonary embolism.
  • Neuro exam.
  • Carotid sinus massage (ventricular pause >3s or SBP drop >50mmHg).

4. ECG:

  • Ask for rhythm strip if EMS transported.
  • Rhythm: complete heart block, Mobitz II second degree AV block, VT, SVT, paced rhythm, sinus pauses (>3 seconds), conversion pause (from afib to sinus), persistent sinus bradycardia (<40 bpm).
  • QRS morphology: WPW, alternating LBBB and RBBB, Brugada syndrome, bifascicular block, intraventricular conduction abnormality (QRS >120ms).
  • Intervals: long or short QT.

Consider additional testing based on initial evaluation:

  • Labs: CBC, BMP, troponin, BNP, D-dimer.
  • Transthoracic echocardiography: structural heart disease (valves, significant pericardial effusion, HOCM, or LV dysfunction), also helpful in pulmonary hypertension.
  • Cardiac monitoring: if arrhythmia suspected. Choice of specific monitor is based on the frequency of events (consider constant vs triggered and time frame).
    • Options vary by institution but generally include: Holter (24-72h), patient-activated event monitor (2-6w), external loop recorder (2-6w), external patch recorder (2-14d), mobile cardiac telemetry (30d), implantable monitor (2-3y).
  • CT-PE: if pulmonary embolism is suspected.
  • Cardiac MR: if cardiac sarcoid or arrhythmogenic RV cardiomyopathy suspected.
  • Exercise stress testing: in select patients with syncope/presyncope during exertion, ensure advanced life support available.
  • Neurologic evaluation with head CT/MRI, carotid US, or EEG is only indicated if focal neurologic deficits are uncovered, or alternatives to syncope are being evaluated.
  • Electrophysiology study: rarely pursued. Only patients with known cardiac disease. Generally speaking, is not indicated if normal ECG and cardiac structure/function.
  • Tilt-table testing: recurrent suspected vasovagal syncope, delayed orthostatic hypotension, distinguishing between convulsive syncope and epilepsy, pseudosyncope.
  • Autonomic function tests: valsalva response, deep breathing, ambulatory BP monitoring can be considered but without strong evidence.

Management

NOTE: older adults ought to be carefully considered for cognitive assessment and physical performance in addition to syncope, with a broad differential diagnosis guided by quality of history.

Reflex syncope: avoid triggers, reassurance about benign prognosis, counter-pressure maneuvers (leg-crossing, squatting, fluid + salt intake), supine if prodromal.

  • Meds: midodrine, fludrocortisone, can consider b-blockers.
  • Consider de-escalation of antihypertensives.
  • PPM can be considered in discussion with EP if recurrent syncope due to pauses.

Carotid sinus syndrome: consider permanent cardiac pacing.

Orthostatic hypotension: IV or PO fluid challenge (at least 500mL is reasonable), counter-pressure maneuvers (leg-crossing, squatting), thigh-high compression garments. Increase water and salt in selected patients, education. Consider antihypertensive de-escalation.

  • Meds: midodrine, droxidopa (in Parkinson’s, autonomic failure, multisystem atrophy), fludrocortisone. Consider pyridostigmine if refractory, octreotide if postprandial.
  • If autonomic failure is suspected, consider neurology evaluation.

Cardiac arrhythmia, structural or congenital: treat underlying condition (e.g. valvular, cardiomyopathy, arrhythmia), consider ICD, and discuss with cardiology.
 

Albassam OT, Redelmeier RJ, Shadowitz S, Husain AM, Simel D, Etchells EE. Did This Patient Have Cardiac Syncope?: The Rational Clinical Examination Systematic Review. JAMA - J Am Med Assoc. 2019. doi:10.1001/jama.2019.8001

Brignole M, Moya A, De Lange FJ, et al. 2018 ESC Guidelines for the diagnosis and management of syncope. Eur Heart J. 2018. doi:10.1093/eurheartj/ehy037

Shen WK, Sheldon RS, Benditt DG, et al. 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope: A report of the American college of cardiology/American Heart Association task force on clinical practice guidelines and the Heart Rhythm Society. Circulation. 2017. doi:10.1161/CIR.0000000000000499