What is cardiac syncope?

Cardiac Syncope: Definition and Characteristics

Cardiac syncope is a type of syncope caused by inadequate cerebral blood flow due to cardiac disorders, including arrhythmias and structural heart disease, which can lead to sudden reduction in cardiac output and cerebral hypoperfusion.

Definition and Pathophysiology

• Cardiac syncope occurs when a cardiac disorder causes a sudden decrease in cardiac output, leading to cerebral hypoperfusion and transient loss of consciousness 1, 2
• It is part of the broader classification of syncope causes, which includes neurally-mediated (reflex) syncope, orthostatic hypotension, and cardiac syncope 1
• The reduction in cerebral blood flow below critical levels results in temporary loss of consciousness with spontaneous recovery 3, 4

Types of Cardiac Syncope

Arrhythmic Syncope

• Arrhythmias are the most common cause of cardiac syncope 5, 4
• Bradyarrhythmias that can cause syncope include:
  • Sinus node dysfunction with persistent bradycardia <40 bpm or repetitive sinoatrial block/pauses 1
  • Atrioventricular conduction disorders (Mobitz II second or third-degree AV block) 1
  • Alternating left and right bundle branch block 1
• Tachyarrhythmias that can cause syncope include:
  • Ventricular tachycardia (VT) 1
  • Rapid paroxysmal supraventricular tachycardia (SVT) 1
  • Polymorphic VT associated with long or short QT intervals 1

Structural Cardiac Disease

• Syncope can occur due to obstruction to blood flow in conditions such as:
  • Obstructive cardiac valvular disease (especially aortic stenosis) 1
  • Hypertrophic obstructive cardiomyopathy 1
  • Cardiac tumors (e.g., atrial myxoma) 1
  • Pulmonary hypertension or pulmonary embolus 1
• Acute cardiac conditions that can cause syncope include:
  • Myocardial ischemia/infarction 1
  • Acute aortic dissection 1
  • Pericardial tamponade 1

Clinical Presentation and Diagnostic Features

• Cardiac syncope often occurs suddenly with minimal or no prodromal symptoms, unlike the extensive prodrome in neurally-mediated syncope 2, 6
• Features suggesting cardiac syncope include:
  • Syncope during exertion or in supine position 1
  • Sudden onset palpitations immediately followed by syncope 1
  • Family history of unexplained sudden death or channelopathies 1
  • Presence of definite structural heart disease 1
  • Witnessed cyanosis during the episode (LR 6.2) 6
• Age at first syncope of at least 35 years increases likelihood of cardiac syncope (LR 3.3) 6
• History of atrial fibrillation/flutter (LR 7.3) or known severe structural heart disease (LR 3.3-4.8) increases likelihood of cardiac syncope 6

Risk Stratification and Prognostic Significance

• Cardiac syncope is associated with increased morbidity and mortality compared to neurally-mediated syncope, which typically has a benign course 7, 4
• Cardiac syncope may be an indicator of increased risk for sudden cardiac death, particularly in patients with structural heart disease or channelopathies 4, 6
• The EGSYS score (based on 6 clinical variables) can help identify patients at risk for cardiac syncope - a score <3 is associated with lower likelihood of cardiac syncope (LR 0.12-0.17) 6

Diagnostic Approach

• Initial evaluation should include detailed history, physical examination, and 12-lead ECG 1, 7
• High-risk features warranting urgent evaluation include:
  • Syncope during exertion or when supine 1
  • Abnormal ECG findings 1
  • Family history of sudden cardiac death 1
  • Presence of structural heart disease or heart failure 1
• Further cardiac testing may include echocardiography, prolonged ECG monitoring, and provocative testing in cases of unexplained syncope 7, 4

Treatment Considerations

• Management of cardiac syncope focuses on treating the underlying cardiac condition 1, 7
• Arrhythmic causes may require antiarrhythmic medications, pacemaker implantation, implantable cardioverter-defibrillator (ICD), or catheter ablation 7, 4
• Structural cardiac disease causing syncope often requires specific interventions (e.g., valve replacement for severe aortic stenosis) 1