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Europace 2005 7(3):287; doi:10.1016/j.eupc.2005.02.004
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© 2005 The European Society of Cardiology. Published by Elsevier Ltd. All rights reserved.

CP01: USE OF INTRACARDIAC TRANSVALVULAR IMPEDANCE FOR HEMODYNAMIC ASSESSMENT. ANIMAL EXPERIENCE WITH IMPLANTED SOPHÒSTM PACEMAKER

R. Chirife1, F. Di Gregorio2, N. Galizio3, J.L. González3, J. Barra3 and S. Graf3

1Hospital Fernández Padova; 2Medico SpA Padova; 3Favaloro Foundation Buenos Aires

Intracardiac impedance (Z) has been shown to be a marker of right ventricular preload (end-diastolic volume, EDV) and contractility. Thus, Z-derived contractility could be used for pacemaker (PM) rate control, since increased metabolic demands cause neuro-hormonal changes affecting simultaneously chronotropism and contractility. The purpose of this study was to determine the efficacy of implanted Sophòs PMs (Medico SpA, Padova) to detect the intracardiac transvalvular Z (TVI) waveform. Efficacy criteria were: 1. PM TVI should compare favorably to external, high-resolution Z-device; 2. End-diastolic Z (EDZ) should be always smaller than end-systolic Z (ESZ). 3. TVI-derived rate prediction basedon contractility should match the animal's intrinsic sinus rate during inotropic challenge.

METHODS: Three adult, castrated male sheep with implanted DDDR Sophòs PMs were studied according to the Guide for the Care and Use of Laboratory Animals (US National Research Council,1996). Prior to PM implant, a high-resolution Z device was used to record TVI. At 4 weeks post-implant Isoproterenol (Iso) was infused until sinus rate approached 170 bpm. Before, during and after Iso, PM TVI waveforms were retrieved by telemetry at 15 sec-intervals. Z was converted to volume assuming an EDV of 140 ml and end-systolic volume of 70 ml. Contractility was calculated as preload-corrected stroke volume (SVc) and beat-by-beat rate was calculated as: TVI-Rate = SVcPrev / SVcR * RateR, where SVcPrev= prevailing SVc, SVcR= Resting SVc, and RateR= resting heart rate.

RESULTS: 1. TVI telemetry waveforms compared favorably to waveforms from external Z device; 2. EDZ was consistently smaller than ESZ. 3. TVI behavior during Iso was physiological, and TVI rate matched closely the animal's sinus rate, with R2 values of 0.92, 0.84 and 0.92 (all P-values < 0.001).

CONCLUSION: Implanted Sophòs PMs accurately detected changes in RV volumes and allowed calculation of contractility-derived rate during inotropic challenge.


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