Approach to Syncope

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A table summarizing the Classification of Syncope:

Type of Syncope	Description	Examples
Reflex (Neurally-Mediated)	Caused by an exaggerated autonomic reflex, usually benign.	Vasovagal, situational (e.g., coughing, urination), carotid sinus syndrome
Cardiac Syncope	Due to arrhythmias or structural heart disease, with a higher risk of sudden death.	Bradyarrhythmias, tachyarrhythmias, aortic stenosis, hypertrophic cardiomyopathy
Orthostatic Hypotension (OH)	Caused by failure of the autonomic nervous system to regulate blood pressure upon standing.	Dehydration, autonomic dysfunction, medication-induced hypotension

Introduction

Syncope, or transient loss of consciousness (TLOC) due to temporary global cerebral hypoperfusion, is a common clinical condition that requires a thorough and systematic approach, particularly when suspected to be of cardiac origin. Syncope can arise from both benign and life-threatening causes, with cardiac causes being the most concerning due to the potential risk of sudden death. From an electrophysiological standpoint, identifying whether syncope is of cardiac origin is crucial for initiating appropriate therapy and preventing recurrent episodes or fatal outcomes.

1. Definition and Classification of Syncope

Syncope is defined as a sudden, brief loss of consciousness followed by spontaneous recovery. It should be differentiated from other causes of TLOC such as seizures, metabolic disturbances, or psychiatric causes. Syncope is broadly categorized into three main types:

• Reflex (Neurally-Mediated) Syncope: Includes vasovagal, situational, and carotid sinus syncope. This type is usually benign and is caused by an exaggerated autonomic reflex.

• Cardiac Syncope: Results from arrhythmias (e.g., bradyarrhythmias, tachyarrhythmias) or structural heart disease (e.g., aortic stenosis, hypertrophic cardiomyopathy).

• Orthostatic Hypotension (OH): Occurs when the autonomic nervous system fails to regulate blood pressure appropriately upon standing, leading to syncope.
  

2. Initial Clinical Assessment

2.1 History Taking

A detailed history is the cornerstone of syncope evaluation. Important aspects include:

• Onset and Triggers: Was the syncope sudden, or was it preceded by warning signs like palpitations or dizziness? Exertional syncope could suggest cardiac causes like aortic stenosis or hypertrophic cardiomyopathy, while situational syncope may point toward a reflex mechanism.

• Duration and Recovery: A quick recovery is typical of syncope, while a prolonged recovery or confusion points more towards seizures.

• Family History: A history of sudden cardiac death, especially before age 40, raises suspicion of inherited arrhythmia syndromes like long QT syndrome or Brugada syndrome.

2.2 Physical Examination

A focused physical exam helps identify structural heart disease or orthostatic hypotension. Key assessments include:

• Orthostatic Vital Signs: Blood pressure and heart rate should be measured in supine and standing positions. A decrease in systolic blood pressure of >20 mmHg or diastolic pressure of >10 mmHg within three minutes of standing suggests orthostatic hypotension.

• Cardiac Examination: Auscultation for murmurs (e.g., aortic stenosis) and assessment of heart rate and rhythm can uncover arrhythmias or valvular heart disease.
  

3. Diagnostic Workup

3.1 Electrocardiogram (ECG)

An ECG is mandatory in all patients with syncope to detect arrhythmias or structural heart disease. Key findings to evaluate include:

• Bradycardia (HR <50 bpm): May suggest sick sinus syndrome or complete heart block.

• Prolonged QT Interval: A corrected QT interval (QTc) >450 ms in males and >470 ms in females suggests long QT syndrome.

• Pre-excitation: Delta waves on the ECG can indicate Wolff-Parkinson-White syndrome, a cause of supraventricular tachycardia (SVT).

• Ischemic Changes: ST-segment elevation or depression may indicate myocardial infarction.

3.2 Holter Monitoring or Event Recorders

For intermittent arrhythmias not captured on ECG, a Holter monitor or event recorder is used for continuous monitoring over 24-48 hours or longer. These tests are particularly useful for detecting:

• Intermittent Bradycardia: Look for pauses >3 seconds, which may require pacemaker implantation.

• Supraventricular or Ventricular Tachycardia: SVT or ventricular tachycardia (VT) can cause syncope if the heart rate exceeds 180-200 bpm.

3.3 Echocardiography

An echocardiogram is essential when structural heart disease is suspected. Important findings include:

• Aortic Stenosis: Identified by a peak aortic jet velocity >4 m/s and a mean gradient >40 mmHg.

• Hypertrophic Cardiomyopathy (HCM): Defined by a septal thickness >15 mm with left ventricular outflow tract obstruction.

• Atrial Myxoma: A mobile mass that intermittently obstructs blood flow.

3.4 Electrophysiological Study (EPS)

EPS is indicated for patients with unexplained syncope and suspected arrhythmias. During this test, catheters are inserted into the heart to provoke arrhythmias. This is useful in patients at high risk for sudden cardiac death.

3.5 Tilt Table Test

The tilt table test is primarily used to diagnose neurally-mediated syncope and orthostatic hypotension. The patient is strapped to a table that tilts at various angles, mimicking the process of standing up. Blood pressure and heart rate are monitored continuously. A drop in blood pressure without a compensatory increase in heart rate suggests reflex syncope or orthostatic hypotension.

4. Management Based on Etiology

Once the cause of syncope is identified, management is tailored accordingly:

• Reflex Syncope: Treatment involves patient education, trigger avoidance, and, in some cases, medications such as beta-blockers or fludrocortisone. Pacemaker implantation may be considered for severe cardioinhibitory syncope.

• Cardiac Syncope:

  • Bradyarrhythmias: Pacemaker implantation is the definitive treatment.

  • Tachyarrhythmias: Anti-arrhythmic drugs, catheter ablation, or an ICD are appropriate for supraventricular or ventricular tachycardia.

  • Structural Heart Disease: Surgery, such as aortic valve replacement or myectomy, is often required for conditions like aortic stenosis or HCM.

• Orthostatic Hypotension: Treatment focuses on increasing salt and water intake, compression stockings, and adjusting medications. Pharmacologic agents like midodrine or fludrocortisone may be used.
  

5. Special Considerations

• Syncope in Athletes: Cardiac causes such as HCM or arrhythmogenic right ventricular cardiomyopathy must be ruled out.

• Syncope in the Elderly: Orthostatic hypotension is more common due to autonomic dysfunction and polypharmacy.
  

6. Prognosis

Cardiac syncope is associated with higher mortality due to the risk of sudden death, whereas reflex syncope and orthostatic hypotension generally have a benign prognosis. Proper risk stratification is key to determining the need for hospitalization or further testing.

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Tilt Table Test: Procedure and Interpretation

How to Do the Tilt Table Test:

1. Preparation: The patient lies flat on a motorized table for 15 minutes while baseline blood pressure, heart rate, and heart rhythm are recorded.

2. Tilt Phase: The table tilts at angles (30, 45, and 70 degrees) over the course of 2-45 minutes, depending on the patient’s response. Blood pressure and heart rate are monitored continuously.

3. Medication Phase (if needed): If no symptoms occur during the initial tilt, a medication (such as isoproterenol) may be administered to stimulate the heart, and the tilt phase is repeated.

Interpretation:

• Positive Test: A significant drop in systolic blood pressure (≥20 mmHg) or diastolic pressure (≥10 mmHg), or a large increase in heart rate (≥30 bpm), indicates conditions such as orthostatic hypotension or POTS.

• Negative Test: Stable blood pressure and heart rate without symptoms suggest that syncope is not due to a blood pressure or heart rate issue. Further diagnostic testing may be needed.
  

Conclusion

A comprehensive approach to syncope, integrating history-taking, physical examination, and appropriate diagnostic tests such as ECG, Holter monitoring, echocardiography, and tilt table testing, is essential in identifying high-risk patients. By understanding the underlying cause, particularly in cases of cardiac syncope, appropriate management strategies can be implemented to prevent recurrence and reduce the risk of sudden death.