Physiological phenomenology of neurally-mediated syncope with management implications.

Area of Science:

• Cardiology
• Neurology
• Clinical Medicine

Background:

• Neurally-mediated syncope treatment guidelines do not favor pacemakers due to low efficacy.
• Asystole during head-up tilt testing may lead to misdiagnosis of cardioinhibitory syncope and inappropriate pacemaker implantation.
• Physicians may be more inclined to implant pacemakers in older patients.

Purpose of the Study:

• To investigate the hypothesis that true cardioinhibitory syncope, where heart rate decrease precedes blood pressure fall, is rare.
• To explain the lack of pacemaker efficacy in neurally-mediated syncope.
• To analyze the temporal relationship between hypotension and bradycardia in syncope patients.

Main Methods:

• 173 patients with unexplained syncope underwent head-up tilt testing with lower body negative suction.
• Hemodynamic responses were classified using the modified Vasovagal Syncope International Study (VASIS) criteria.
• The precise timing of blood pressure and heart rate changes was analyzed to identify true cardioinhibitory syncope.

Main Results:

• The majority of syncopal events were classified as mixed (VASIS I, 63%) or vasodepressor (VASIS III, 29%).
• Cardioinhibitory responses (VASIS II) were less common in older patients.
• In 97% of cases, hypotension preceded bradycardia, including 10 out of 11 patients with asystole.

Conclusions:

• Hypotension precedes bradycardia in most head-up tilt-induced syncope events, even those appearing cardioinhibitory.
• True cardioinhibitory syncope is rare, characterized by bradycardia preceding hypotension.
• Cardioinhibitory syncope prevalence decreases with advancing age.