Accelerometer-derived preejection period increased from 98.9 to 109.1 msec and left ventricular ejection time decreased from 295.5 to 247.2 msec (both P<0.0001) during head-upright tilt.
Observational (n=32)
Do accelerometer-derived systolic time intervals detect postural changes independent of autonomic tone in young patients with syncope?
Accelerometer-derived systolic time intervals can rapidly and stably detect postural changes independent of autonomic tone, suggesting that current PEP-sensing pacemakers may use an incorrect algorithm for physiological postural responses in syncope patients.
Absolute Event Rate: 109.1% vs 98.9%
p-value: p=<0.0001
BACKGROUND: Sensors of posture may improve rate-adaptive pacing in syndromes where syncope occurs in the upright posture, particularly in the young. No sensor of posture has been described to date. Previous studies suggest that two sensors currently under investigation (preejection period PEP and left ventricular ejection time LVET systolic time intervals STIs and accelerometers) may be affected by posture. A PEP-sensing pacemaker is available commercially in which heart rate (HR) decreases with an increase in PEP (delta(HR)/deltaPEP< 0). In patients with upright syncope, it is not known how such algorithms respond to posture. Also, it is not known whether STIs correlate with posture independent of autonomic tone. METHODS AND RESULTS: We studied accelerometer-derived STIs in head-upright tilt-testing with beta-blockade and catecholamine stimulation in patients with syncope or presyncope using an ultra-low-frequency accelerometer placed on the chest. Thirty-two patients age 6 to 22 years with unexplained recurrent syncope or presyncope underwent tilt-testing involving two to four tilts (60 degrees) at baseline, during esmolol infusion (500 micrograms/kg load, 50 to 140 micrograms/kg per minute), after esmolol withdrawal, and during isoproterenol infusion if not contraindicated. PEP, LVET, and other indexes were quantified, and their relations to posture and to autonomic state were determined. With tilt, PEP increased from 98.9 +/- 2.2 to 109.1 +/- 2.8 msec (P < .0001), and LVET decreased (supine-to-upright) from 295.5 +/- 4.5 to 247.2 +/- 4.7 msec (P < .0001). PEP/LVET changed from 0.337 +/- 0.01 to 0.45 +/- 0.02 (P < .0001). Similar postural changes were observed during tilt with beta-blockade and esmolol withdrawal, and during isoproterenol infusion. STI changes occurred immediately on postural change and were stable. Postural change of PEP was greater than the beta-adrenergic effect by 6:1. Postural change of STIs was independent of vagal tone. CONCLUSIONS: First, accelerometer-derived STIs detect postural changes. Because these changes are independent of autonomic tone and are rapid and stable, they may be useful as fast-response sensors of upright posture in rate-adaptive pacemakers. Second, with postural change, HR increases when PEP increases. However, PEP-sensing pacemakers presently under investigation assume the opposite (inverse) mathematical relationship. Therefore, current PEP-sensing pacemakers use an incorrect algorithm for physiological postural responses in syncope patients. These data predict a paradoxical tachycardic response to the supine posture in patients implanted with these devices.
Ovadia et al. (Sun,) conducted a observational in Unexplained recurrent syncope or presyncope (n=32). Head-upright tilt-testing vs. Supine posture was evaluated on Preejection period (PEP) in msec (p=<0.0001). Accelerometer-derived preejection period increased from 98.9 to 109.1 msec and left ventricular ejection time decreased from 295.5 to 247.2 msec (both P<0.0001) during head-upright tilt.