A SENSOR-BASED EVALUATION OF HEART CONTRACTILITY IN PATIENTS WITH HEAD-UP TILT-INDUCED SYNCOPE

Studies using the head-up tilt test (HUT) suggest that a reflex increa se in sympathetic activity resulting in vigorous myocardial contractio ns precedes neurally-mediated syncope (NMS). The aim of this study was to evaluate heart contractility changes during positive HUT. Ten pati ents with recurrent NMS and positive HUT were investigated Before HUT we temporarily placed a standard right ventricular pacing electrode in corporating ill its tip a recently developed microaccelerometer (Sorin Biomedica, Italy) that measures the peak endocardial acceleration (PE A) during the isovolumetric phase as an index of heart contractility. PEA potential amplitude, heart rate and mean blood pressure were conti nuously studied during HUT. Syncope occurred 16.7 +/- 10.3 min after 6 0 degrees tilt, either at baseline (8 patients) or after sublingual ni trate administration (2 patients). PEA,, value was stable at 0.62 +/- 0.34 (lG = 9.8 m/sec(2)) during the supine phase. It slightly increase d to 0.72 +/- 0.44 G (p = NS) during the first minutes of 60 degrees t ill and then remained unchanged until a further increase of 71 +/- 79 % (range 10 to 266 %) as compared to tilt value (p = 0.004) at 2.8 +/- 2.4 min (range 0.25 to 6.5 min) before the syncope in 9 patients. The latter increase was not observed in the patient with dilated cardiomy opathy. In conclusion, a significant increase in heart contractility w as observed in 9 patients in the minutes preceding HUT-induced NMS. Th ese changes might be used for driving a rate adaptive, pacemaker when cardiac pacing is indicated to prevent NMS.