Head-up Tilt Test in Patients With Reflex Syncope and Asystolic Response Who Received a Dual-chamber Pacemaker With the Closed Loop Stimulation (CLS) and Participated in the BIOSync Trial

Study Overview
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Brief Summary
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The purpose of this study is to explore changes in patients' hemodynamic parameters during the Head-Up Tilt Test (HUTT) and their timing with respect to onset of the Closed Loop Stimulation (CLS) pacing. This study aims to add knowledge to better understand the mechanisms underlying recurrent syncopal events and optimal pacing programming.

Detailed Description
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The 2021 European Society of Cardiology guidelines recommend cardiac pacing in patients aged >40 years with tilt-induced asystolic reflex syncope (class I, level of evidence A). The recommendation relies on recent results from the multicentre, randomised, double-blinded, parallel-design BIOSync trial (NCT02324920). The BIOSync study provided evidence of benefit of dual chamber pacing in patients with tilt-induced reflex syncope and confirmed the role of Head-up Tilt Table (HUTT) test as a diagnostic method for cardiac pacing in reflex syncope. The Closed Loop Stimulation (CLS) is able to measure changes in intracardiac impedance during the systolic phase of each cardiac cycle which are strictly correlated to the increased heart rate and right ventricular contraction speed which are usually present during the pre-syncope phase of the reflex. It was hypothesized that an early onset of CLS pacing may be triggered by the compensatory increase in heart rate to counteract vasodilation and pressure drop during the pre-syncope phase of the reflex. The BIOSync study showed a 77% reduced risk of syncope in the DDD-CLS group as compared to pacing off. The design of the BIOSync study did not allow to assess the specific effect that CLS adds to dual-chamber pacing. Despite DDD-CLS pacing, 22% of patients had syncopal recurrence in 2 years. Further investigations are therefore needed in order to reduce this failure rate. Indeed, it is still unclear whether syncopal recurrences should be ascribed to dominant vasodilation or if the CLS programming/functioning needs optimization to more adequately sustain cardiac output during reflex in these specific cases.

Official Title
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BIO|Sync-HUTT: Head-up Tilt Test in Patients With Reflex Syncope and Asystolic Response Who Received a Dual-chamber Pacemaker With the Closed Loop Stimulation (CLS) and Participated in the BIOSync Trial

Conditions
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Syncope, Syncope, Vasovagal

Participation Criteria
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Eligibility Criteria
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Inclusion criteria Ability to understand the nature of the study. Willingness to provide written informed consent. Patients undergoing HUTT for monitoring of syncope, therapy adjustment, training or other medical reasons during ordinary follow-up, irrespective of study participation Patients who participated in the BIOSync study*. Patients with a dual-chamber pacing system equipped with the CLS algorithm. * If needed, inclusion of other patients who did not participate in the BIOSync study will be considered to complete study cohort, provided that they have already a CLS pacemaker system and fulfill the same inclusion/exclusion criteria of the BIOSync study. Exclusion criteria Pregnant or breast feeding women. Age less than 40 years. Patients who after the BIOSync study participation have developed the following: Any indication to pacemaker different from reflex syncope with positive HUTT response; or Any classified indication to implantable defibrillator, cardiac resynchronization therapy according to current guidelines; or Any cardiac dysfunctions likely leading to loss of consciousness (overt heart failure, ejection fraction <40%, myocardial infarction, diagnosis of hypertrophic or dilated cardiomyopathy, clinically significant valvular disease, sinus bradycardia <50 bpm or sinoatrial block, Mobitz I second degree atrioventricular block, Mobitz II second or third degree atrioventricular block, complete bundle-branch block).

Ages Eligible for Study
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Minimum Age: 40 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Heart rate [bpm] at time of maximum spontaneous heart rate, at time of pacing onset, at time of recovery of spontaneous rhythm after pacing, at time of syncope, at time of time of tilt-down | Instantaneous measurement of heart rate value at specific time-points during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Systolic and diastolic blood pressure [mmHg] at time of maximum spontaneous heart rate, at time of pacing onset, at time of recovery of spontaneous rhythm after pacing, at time of syncope, at time of time of tilt-down | Instantaneous measurement of blood pressure at specific time-points during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Stroke volume [ml] at time of maximum spontaneous heart rate, at time of pacing onset, at time of recovery of spontaneous rhythm after pacing, at time of syncope, at time of time of tilt-down | Instantaneous measurement of stroke volume at specific time-points during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Peripheral resistance [dyn·s/cm5] at time of maximum spontaneous heart rate, at time of pacing onset, at time of recovery of spontaneous rhythm after pacing, at time of syncope, at time of time of tilt-down | Instantaneous measurement of peripheral resistance at specific time-points during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Time of maximum spontaneous heart rate [s] | Recording of a specific time-point during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Time of pacing onset [s] | Recording of a specific time-point during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Time of recovery of spontaneous rhythm after pacing [s] | Recording of a specific time-point during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Time of syncope [s] | Recording of a specific time-point during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Time of tilt-down [s] | Recording of a specific time-point during HUTT examination | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Duration of the recovery phase [s] | Interval from maximum pacing rate to basic rate or spontaneous rhythm | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Slope in heart rate [bpm per sec] during the recovery phase | Calculation of the rate of change of heart rate from the time of maximum pacing rate to the time of basic rate or spontaneous rhythm recovery | From the start to the end of the HUTT examination, assessed up to 45 minutes | 
| Slope in systolic blood pressure (mmHg per sec) during the recovery phase | Calculation of the rate of change of systolic blood pressure from the time of maximum pacing rate to the time of basic rate or spontaneous rhythm recovery | From the start to the end of the HUTT examination, assessed up to 45 minutes | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Syncope, Head-up Tilt Test, Closed Loop Stimulation, CLS