Understanding how closed-loop stimulation pacing suppresses cardioinhibition in vasovagal syncope

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  Figure 1. What if CI does not occur? This figure represents a thought experiment, using data of 149 patients with cardioinhibition (CI) and complete syncope.5 The time of onset of CI of individual patients was known. The logratio heart rate (HR) value was noted just before the onset of CI and copied to all points later than CI onset, creating a ‘virtual HR’ record. As the logratio value of mean arterial pressure (MAP) for each point in time is the sum of logratio values of HR, stroke volume (SV), and total peripheral resistance (TPR), a ‘virtual MAP’ was formed by adding the logratio values of virtual HR to the unaltered logratio values of SV and TPR. Further calculations reversed the logratio procedure, resulting in ratios and values in original measurement units, shown above. Red lines (bottom ones) show mean original data and blue lines (top ones) show mean virtual HR and MAP data, representing the situation in which CI did not occur. The main result is that without CI, MAP decreased much slower than originally. In reality, SV and TPR underwent large changes in the 20 s before syncope, indicating by a grey zone.5 To illustrate the effects of absent CI, values of MAP and HR are indicated…