What EKG changes are associated with syncope and how are they managed?

ECG Changes in Syncope and Their Management

ECG monitoring is diagnostic when a correlation between syncope and an electrocardiographic abnormality (brady- or tachyarrhythmia) is detected, and should be employed strategically based on the suspected cause of syncope. 1

Key ECG Abnormalities Associated with Syncope

Diagnostic ECG Findings

• Bradyarrhythmias:

  • Sinus bradycardia <40 beats/min
  • Repetitive sinoatrial blocks or sinus pauses >3 seconds
  • Mobitz II 2nd or 3rd-degree atrioventricular block
  • Alternating left and right bundle branch block 1

• Tachyarrhythmias:

  • Rapid paroxysmal supraventricular tachycardia
  • Ventricular tachycardia
  • Atrial fibrillation with rapid ventricular response 1

• Other Diagnostic Findings:

  • Pacemaker malfunction with cardiac pauses 1

Suggestive ECG Abnormalities

• Conduction Abnormalities:

  • Bifascicular block (LBBB or RBBB with left anterior/posterior fascicular block)
  • Intraventricular conduction abnormalities (QRS duration >0.12s)
  • Mobitz I second-degree AV block
  • First-degree AV block 1, 2

• Rhythm Abnormalities:

  • Nonsinus rhythm
  • Multiple premature ventricular contractions 2

• Repolarization/Depolarization Abnormalities:

  • Pre-excited QRS complexes
  • Prolonged QT interval
  • Q wave/T wave/ST-segment abnormalities consistent with ischemia 1, 2

• Specific Syndrome Patterns:

  • Brugada syndrome (RBBB pattern with ST elevation in V1-V3)
  • Arrhythmogenic right ventricular dysplasia (negative T waves in right precordial leads, epsilon waves) 1, 3

Management Algorithm Based on ECG Findings

Step 1: Initial Evaluation

• Obtain a 12-lead ECG for all patients with syncope (Class I recommendation) 1
• Assess for high-risk features:
  • Abnormal ECG
  • History of structural heart disease
  • Syncope during exertion or in supine position
  • Absence of prodromal symptoms
  • Family history of sudden cardiac death 1

Step 2: Risk Stratification

• High Risk (requires immediate intervention):

  • Ventricular pauses >3 seconds when awake
  • Mobitz II or 3rd-degree AV block when awake
  • Rapid paroxysmal ventricular tachycardia 1

• Intermediate Risk (requires further monitoring):

  • Bifascicular block
  • Other intraventricular conduction abnormalities
  • Evidence of previous myocardial infarction
  • Non-sustained ventricular tachycardia 1

Step 3: Select Appropriate Monitoring Strategy

• For frequent symptoms (≥2 per week):

  • Holter monitoring (24-72 hours) 4

• For moderately frequent symptoms (every 1-4 weeks):

  • External loop recorder (2-6 weeks)
  • Patch recorder (2-14 days)
  • Mobile cardiac outpatient telemetry (up to 30 days) 4

• For infrequent symptoms (<1 per month):

  • Implantable loop recorder (up to 3 years) 4

• For high-risk patients with structural heart disease:

  • Consider in-hospital telemetry or electrophysiological study before long-term monitoring 1

Step 4: Specific Management Based on Findings

• Bradyarrhythmias:

  • Pacemaker implantation for symptomatic bradycardia or high-degree AV block 1

• Tachyarrhythmias:

  • Antiarrhythmic medications, catheter ablation, or ICD based on specific arrhythmia 1

• Structural heart disease:

  • Treat underlying condition (e.g., revascularization for ischemia) 1

• Channelopathies (Brugada, Long QT):

  • Consider ICD implantation, genetic testing, and family screening 3

Important Clinical Considerations

• The diagnostic yield of ECG monitoring increases with longer monitoring duration - implantable loop recorders have a higher diagnostic yield (55%) compared to conventional tests (19%) for syncope of unknown origin 4

• ECG monitoring excludes an arrhythmic cause when there is a correlation between syncope and normal sinus rhythm 1

• A normal baseline ECG is associated with a low risk of cardiac syncope, with few exceptions (e.g., paroxysmal atrial tachyarrhythmias) 1

• Presyncope may not be an accurate surrogate for syncope in establishing a diagnosis; therapy should be guided by findings during actual syncopal episodes 1

• In patients with unexplained syncope after comprehensive evaluation, an implantable loop recorder is indicated when there are clinical or ECG features suggesting arrhythmic syncope or a history of recurrent syncope with injury 1

• ECG monitoring is unlikely to be useful in patients who do not have clinical or ECG features suggesting arrhythmic syncope and should not be performed in these cases 1

• The gold standard for diagnosis is correlation between symptoms and documented arrhythmia during a spontaneous episode 4