Differential diagnosis

Vasovagal syncope

Type 1 Mixed   

• heart rate falls to  ≥ 40 beats/minute or  
• heart rate falls to < 40 beats/minute for less than 10 seconds  
• blood pressure falls before the heart rate falls

Type 2 A Cardioinhibition without asystole  

• heart rate falls to < 40 beats/minute for more than 10 seconds  

• asystole of > 3 seconds does not occur  

• blood pressure falls before the heart rate falls  

Type 2B Cardioinhibition with asystole

• asystole occurs for > 3 seconds
• blood pressure fall coincides with or occurs before the heart rate falls

Type 3 Vasodepressor

• heart rate does not fall more than 10% from its peak at the time of syncope Exception 1 Chronotropic Incompetence

Exception 1 Chronotropic Incompetence

• no heart rate rise during the tilt testing (i.e. less than 10% from the pre-tilt phase)   

Exception 2 Excessive heart rate rise

• An excessive heart rate rise both at the onset of the upright position and throughout its duration before syncope (i.e. greater than 130 beats/minute) 
  

Postural orthostatic tachycardia syndrome

Postural tachycardia in association with relatively mild hypotension is thought to represent a mild form of autonomic dysfunction rather than a variant of vasovagal syncope. Diagnosis is performed by means of tilt table testing, the syndrome is characterised as follows:

• heart rate increase of > 30 beats/minute (or a maximum heart rate of 120 beats/minute) during tilting
• no profound hypotension
• symptoms can include light-headed, fatigue, presyncope and dizziness

Carotid sinus hypersensitivity

The diagnosis of carotid sinus hypersensitivity is performed by means of carotid sinus massage:

• asystole of ≥3 seconds (cardioinhibitory subtype)
• fall in systolic blood pressure of ≥ 50 mmHg (vasodepressor subtype)
• asystole of ≥ 3 seconds + fall in systolic blood pressure of =50 mmHg (mixed subtype)