New definition of hypotension in patients with reflex syncope using 24-hour ambulatory blood pressure monitoring (SynABPM Study)

Abstract Background Diagnostic criteria for ambulatory blood pressure monitoring (ABPM) in patients with suspected reflex syncope are lacking. Purpose We hypothesized that patients with reflex syncope have a higher prevalence of systolic blood pressure (SBP) drops on ABPM than control subjects and we aimed to define the SBP cut-off values that allow identification of patients with hypotensive susceptibility. Methods We compared ABPM data from reflex syncope patients and controls, matched by average 24-hour SBP, age, sex and hypertension. Patients with constitutional hypotension, orthostatic hypotension, predominant cardioinhibition or competing causes of syncope were excluded. Daytime and night-time SBP drops (<110, 100, 90, 80 mmHg) were assessed. Findings were validated in an independent sample. Results In the Derivation cohort, daytime SBP drops were significantly more common in 158 syncope patients than 329 controls. One or more daytime drop <90 mmHg provided the best diagnostic yield (91% specificity, 32% sensitivity, Odds Ratio [OR]=4.6, p=0.001). Two or more-daytime drops <100 mmHg achieved 84% specificity and 40% sensitivity (OR=3.5, p=0.001). Results were confirmed in the Validation cohort: one or more daytime SBP drop <90 mmHg provided 94% specificity and 29% sensitivity (OR=6.2, p<0.001), while two or more daytime SBP drops <100 mmHg achieved 83% specificity and 35% sensitivity (OR=2.6, p<0.001) (Figure 1). Conclusion SBP drops during ABPM are more common in reflex syncope patients than in controls. Cut-off values that may be applied in clinical practice are defined. This study expands the current indications for ABPM to patients with reflex syncope. Funding Acknowledgement Type of funding sources: None.