Syncope And Pre Syncope

Introduction to Syncope for MCCQE1

Syncope is a high-yield topic for the MCCQE1, falling under the internal medicine and cardiology domains. It is defined as a transient loss of consciousness (TLOC) due to global cerebral hypoperfusion, characterized by rapid onset, short duration, and spontaneous complete recovery.

Pre-syncope describes the sensation that one is about to faint (lightheadedness, vision tunneling) without actual loss of consciousness. The pathophysiology and diagnostic approach for pre-syncope are identical to syncope.

CanMEDS Framework Relevance

• Medical Expert: Differentiating benign causes (vasovagal) from life-threatening cardiac causes.
• Communicator: Explaining the diagnosis and safety measures to patients.
• Health Advocate: Addressing driving safety and occupational hazards (CMA Driver’s Guide).

Pathophysiology and Classification

Understanding the mechanism is crucial for determining the etiology. The three main categories are Reflex (Neurally Mediated), Orthostatic Hypotension, and Cardiac.

Clinical Evaluation

The goal of the evaluation is to separate the “benign” from the “deadly.”

Red Flags: The CHESS Mnemonic

While the San Francisco Syncope Rule is widely known, the CHESS mnemonic is a useful tool to remember high-risk features requiring admission or urgent workup.

Diagnostic Investigations

Investigations should be guided by the history and physical exam. Indiscriminate testing (e.g., CT head for everyone) is incorrect and often tested as a distractor on the MCCQE1.

Management

Management depends entirely on the etiology.

1. Reflex Syncope (Vasovagal)

• Education: Reassurance, avoid triggers.
• Physical Counter-pressure Maneuvers: Leg crossing, hand grip, arm tensing at onset of prodrome.
• Hydration: Increased salt and fluid intake (if no hypertension/HF).

2. Orthostatic Hypotension

• Medication Review: Deprescribe offending agents (diuretics, alpha-blockers).
• Lifestyle: Slow position changes, compression stockings.
• Pharmacotherapy: Fludrocortisone or Midodrine (refractory cases).

3. Cardiac Syncope

• Arrhythmias: Pacemaker (bradyarrhythmias), ICD (VT/VF), Ablation (SVT/WPW).
• Structural: Valve replacement (Aortic Stenosis), Septal myectomy (HOCM).

Canadian Guidelines

Driving Guidelines (CMA)

This is a frequent topic on the MCCQE1 (Ethical/Legal/Professionalism). Physicians must determine fitness to drive.

General Waiting Periods (Private Drivers):

• Vasovagal (single episode): No restriction if typical prodrome.
• Unexplained Syncope: No driving until investigated and treated (usually min. 1 week to 3 months depending on severity).
• Cardiac Syncope: No driving until treated (e.g., pacemaker implanted + 1 week).
• Commercial Drivers: Much stricter criteria apply.

Canadian Cardiovascular Society (CCS) Position

The CCS emphasizes the use of the Canadian Syncope Risk Score for ED risk stratification to reduce unnecessary admissions while identifying patients at risk of death or arrhythmia within 30 days.

Key Points to Remember for MCCQE1

• Syncope during exertion is ominous and suggests Aortic Stenosis or HOCM.
• Syncope while supine is strongly suggestive of a Cardiac Arrhythmia.
• CT Head is not part of the routine workup for syncope unless there are focal neurological signs or head trauma.
• Elderly patients often have multifactorial syncope (meds + age-related autonomic dysfunction).
• Differentiation from Seizure: Seizures typically have a post-ictal state (confusion), tongue biting (lateral), and urinary incontinence (though incontinence can occur in syncope too).
• ECG is the single most important initial diagnostic test.

Sample Question

# Sample Question

Scenario

A 72-year-old man presents to the emergency department after a distinct episode of loss of consciousness. He was sitting in his armchair watching television when he suddenly “blacked out” without any warning symptoms. His wife witnessed the event; she states he was unresponsive for about 30 seconds and then woke up spontaneously. He was not confused upon awakening. He has a history of previous myocardial infarction (5 years ago) and hypertension. His current medications include Ramipril, Metoprolol, and Aspirin. Physical examination reveals a blood pressure of 135/85 mmHg, heart rate of 64 bpm and regular, and an unremarkable cardiac exam with no murmurs. His 12-lead ECG shows sinus rhythm with a Q wave in lead III and aF but is otherwise unchanged from previous tracings.

Which one of the following investigations is most appropriate to establish the diagnosis?

Options

• A. 24-hour Holter monitoring
• B. Tilt table testing
• C. Electroencephalogram (EEG)
• D. CT scan of the head
• E. Reassurance and discharge

Explanation

The correct answer is:

• A. 24-hour Holter monitoring

Detailed Explanation

Why A is correct: This patient presents with “Cardiac Syncope” features. The key red flags in the stem are:

1. Patient Age: Elderly (>65).
2. Posture: Syncope occurred while sitting (supine or sitting syncope is highly suggestive of arrhythmia; reflex syncope usually occurs while standing).
3. Prodrome: Sudden onset without warning (“blacked out” without prodrome).
4. History: Structural heart disease (previous MI).

Even though the resting ECG is non-diagnostic for an acute arrhythmia, his risk profile strongly points towards a transient arrhythmia (e.g., Ventricular Tachycardia or intermittent AV block). Ambulatory ECG monitoring (Holter) is the most appropriate next step to capture the rhythm disturbance.

Why other options are incorrect:

• B. Tilt table testing: This is used for diagnosing neurally mediated (reflex) syncope, particularly when the diagnosis is unclear. It is not indicated for suspected cardiac syncope.
• C. EEG: The clinical picture (rapid recovery, no post-ictal confusion, no tonic-clonic movements) fits syncope, not seizure. EEG has a very low yield here.
• D. CT scan of the head: There are no focal neurological deficits or history of trauma. Syncope is a perfusion problem, not a structural brain problem.
• E. Reassurance: Given the high risk of cardiac arrhythmia and sudden death in a post-MI patient with syncope, discharging without investigation is unsafe.

References

1. Canadian Cardiovascular Society. (2020). Standardized Approaches to Syncope.
2. Medical Council of Canada. MCCQE Part I Clinical Decision Making and Objectives.
3. Thiruganasambandamoorthy, V., et al. (2016). Development of the Canadian Syncope Risk Score to predict serious adverse events after emergency department assessment of syncope. CMAJ.
4. Canadian Medical Association. CMA Driver’s Guide: Determining Medical Fitness to Operate Motor Vehicles (9th Edition).
5. Moya, A., et al. (2018). Guidelines for the diagnosis and management of syncope (The Task Force for the Diagnosis and Management of Syncope of the European Society of Cardiology). European Heart Journal.