Hypotension During Ambulatory BP Monitoring and Reflex Syncope

Quick Takes

  • Systolic blood pressure drops on ambulatory blood pressure monitoring identify susceptibility to reflex syncope.
  • Ambulatory blood pressure monitoring is found to be helpful in the diagnosis of patients with reflex syncope.

Study Questions:

Do patients with reflex syncope have a higher prevalence of systolic blood pressure (SBP) drops on ambulatory blood pressure monitoring (ABPM), and if so, are there BP cut-off values which might be useful in predicting vulnerability to reflex syncope?


The authors compared ABPM data between reflex syncope patients and controls (matched by average 24-hour SBP, age, sex, and hypertension). Daytime and nighttime SBP drops (<110, 100, 90, 80 mm Hg) were assessed in two samples: a derivation sample and a validation sample. Patients with constitutional hypotension, orthostatic hypotension, and predominant cardioinhibition, or competing causes of syncope were excluded.


In the derivation sample, there were 158 syncope patients and 329 controls. Daytime SBP drops were significantly more common in syncope patients than in controls. One or more daytime drops <90 mm Hg had 91% specificity and 32% sensitivity for identifying patients with reflex syncope. Two or more daytime drops <100 mm Hg achieved 84% specificity and 40% sensitivity. These results were confirmed in a validation sample of 164 syncope patients and 164 controls: one or more daytime SBP drops <90 mm Hg had 94% specificity and 29% sensitivity, while two or more daytime SBP drops <100 mm Hg achieved 83% specificity and 35% sensitivity.


The authors concluded that SBP drops during ABPM are more common in reflex syncope patients than in controls and they propose cut-off values that may be useful in identifying patients with reflex syncope.


Reflex syncope, also known as vasovagal syncope, is understood to have two distinct components: cardioinhibition (bradycardia) and peripheral vasodilation (hypotension). Hypotensive susceptibility may be the predominant hypotensive mechanism of reflex syncope. The authors found that one or more daytime SBP drops <90 mm Hg on ABPM attained 94% specificity and 29% sensitivity for reflex syncope. This is the first study in the adult population suggesting that a 24-hour ABPM may be a useful instrument for the identification of hypotensive susceptibility. ABPM may help distinguish patients with a hypotensive from those with a dominant cardioinhibitory component. Nota bene, patients with a major cardioinhibitory component demonstrated on implantable loop recorder benefited from pacing as a means of preventing recurrent syncope, in contrast to prior studies of head up tilt positive patients. It is possible that ABPM may identify the other group of patients—those with the hypotensive phenotype of reflex syncope—and allow for the development of therapies tailored to abolish SBP drops to prevent syncopal recurrences.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Hypertension

Keywords: Arrhythmias, Cardiac, Blood Pressure Monitoring, Ambulatory, Blood Pressure, Bradycardia, Hypertension, Hypotension, Pacemaker, Artificial, Primary Prevention, Recurrence, Reflex, Secondary Prevention, Syncope, Syncope, Vasovagal, Vasodilation

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