Haemodynamic Sensor: Evaluation of Sensor Safety
N. GALIZIO1, J. GONZALEZ1, R. CHIRIFE2, H. FRAGUAS1, J. BARRA1, S. GRAF1, E. DEFORTEZA1, F. DIGREGORIO3
Introduction
The autonomic nervous system stimulation of the heart affects, simultane- ously, chronotropism, dromotropism, and inotropism. Intracardiac haemo- dynamic sensors detect changes in the performance of the heart, which depends on the inotropic regulation of myocardial fibres. Intracardiac haemodynamic sensors include:
- Intraventricular pressure - Peak endocardial acceleration - Ventricular impedance - Transvalvular impedance
Transvalvular impedance (TVI) is a measure of blood impedance derived between the right atrium and ventricle. With conventional electrodes, the low-amplitude, constant-current is driven from the source to the atrial ring and ventricular ring or tip. This configuration has the least wall motion arte- fact and the best correlation with intracardiac volumes (Fig. 1). Combining more than two poles offers better rendering of volume changes and gives a better signal-to-noise ratio than intraventricular impedance [1].
Figure 2 shows TVI and volume waveforms, ECG, and atrial electrograms.
TVI increases during ventricular systole and throughout the QT period, and decreases during passive and active ventricular filling.
TVI is the opposite of volume waveform: atrial contraction produces an increase in volume (atrial kick) followed by a rapid volume decrease (ven- tricular ejection). After ejection, the rapid-filling (RFW) and slow-filling waves (SFW) are seen. The minimum TVI is sensitive to all conditions known to modify the preload. The maximum TVI corresponds to end-sys-
1Electrophysiology Division, Institute of Cardiology and Cardiovascular Surgery, Favaloro Foundation and Rene G. Favaloro University, Buenos Aires;2J. A. Fernandez Hospital, Buenos Aires Argentina;3Medico Clinical Research, Rubano (Padua), Italy
Fig. 1.Transvalvular impedance (TVI). Current source, signal and the injection of the low-voltage pulsed carrier signal between the pacing electrodes
Fig. 2.TVI and volume waveforms, ECG, and atrial electrograms
tolic volume (ESV), which is sensitive to changes in cardiac contractility [2–5]. Relative variations in end-diastolic volume, end-systolic volume, stroke volume, and ejection fraction define a cardiac inotropic index, com- pletely independent of preload effects, which is a direct expression of the autonomic nervous system’s regulation of the heart [6–9].
Study Objective
Measurement of intracardiac impedance requires the injection of a low-volt- age pulsed carrier signal between the pacing electrodes. The aim of the study was to evaluate whether these pulses interfere with standard functions of the Sophòs (Medico-SpA) pacemaker.
Methods
The experimental protocol was approved by the Institutional Animal Care and Use Committee of Favaloro University, and the study was conducted in three castrated adult male sheep according to the Guide for the Care and Use of Laboratory Animals published by the United States National Research Council (1996). Five days before surgery, three pairs of subcutaneous elec- trodes were implanted for Holter monitoring. Cables were tunnelled subcu- taneously to emerge at the interscapular space.
Anaesthesia and Intraoperative Monitoring
After 24 h starvation and 12 h without drinking water, general anaesthesia was induced in the animals with sodium thiopental and maintained with 1.5–2% halothane carried in pure oxygen (2.5 l/min) under assisted ventila- tion. Ventilation was performed using positive pressure ventilation at a rate of 12 breaths per minute and a tidal volume of 600 ml adjusted to maintain an end-tidal CO2 of approximately 25–30 mmHg. Surface ECG and PCO2
were continuously displayed on a monitor. Heart rate and blood oxygen satu- ration were measured by pulse oximetry.
Data Acquisition
Blood pressure was measured using a pressure transducer (Gould 6600 SeriesTransducer). Aortic pressure and ECG signals were registered on a six- channel signal conditioner (Gould 5900) and simultaneously on a chart recorder which allowed the signals to be displayed on a PC monitor.
Instantaneous pressure and/or ECG signals were sampled and analysed off- line on a computer equipped with a multi-channel 12-bit analogue-to-digital
converter. Signals were digitised every 4 ms and stored as ASCII text files using specific sof tware developed in the Biomedical Eng ineer ing Department of Favaloro University.
Surgery
With the animals in right lateral decubitus, pacing leads (Oscor HT52 PSBV atrial screw-in and Medico 340 tined ventricular leads) were inserted via the jugular vein guided by fluoroscopy using a C-arm angiography apparatus.
Atrial and ventricular pacing and sensing thresholds were measured with TVI on and off. Then, the pacemaker was placed subcutaneously in the later- al surface of the neck. After implantation, recording of arterial pressure and ECG were performed under baseline conditions and during intravenous infusion of isoproterenol (2 µg/ml). Holter monitoring was performed 2 weeks and 4 weeks after implantation to look for pacemaker malfunctions (undersensing or oversensing).
Results
Figure 3 shows ventricular capture and sensing threshold at implantation and 2 and 4 weeks after implantation. Ventricular capture thresholds had increased a little after 2 weeks, as usual, but there was no difference between measurements with TVI on or TVI off. There was no difference in ventricu- lar sensing thresholds either. The same result was obtained for measure- ments of atrial capture and sensing thresholds with TVI on or off (Fig. 4).
Fig. 3.Ventricular capture and sensing threshold at implantation and 2 and 4 weeks after implantation
In Figure 5 we can see normal sinus rhy thm (a) before pacemaker implantation and normal pacemaker function after implantation (b).
Sporadic atrial undersensing was found after 2 weeks (c). This was corrected by reprogramming the atrial pacemaker sensitivity.
Fig. 4.Atrial capture and sensing thresholds at implantation and 2 and 4 weeks after implantation
Fig. 5.a Normal sinus rhythm. b Normal pacemaker function after implantation.
cSporadic atrial undersensing
a
c
b
Conclusions
In the present animal model study, TVI sensor operation did not interfere with conventional pacemaker functions of implanted Sophòs pacemakers.
These results look promising since this sensor could play an important part in haemodynamic monitoring: for physiological rate adaptation, for beat-to- beat capture confirmation, in patients with neurocardiogenic syncope, for the follow-up of patients with heart failure, to indicate the best interventric- ular delay in CRT, and to identify arrhythmias and their haemodynamic impact in implantable cardioverter–defibrillators [10–12].
References
1. Chirife R (2003) Haemodynamic assessment with implantable pacemakers. How feasible and reliable is it? In: Raviele A (ed) Cardiac arrhythmias 2003. Springer, Milan pp 705–712
2. Di Gregorio F, Morra A, Finesso M et al (1996) Transvalvular impedance (TVI) recording under electrical and pharmacological cardiac stimulation. Pacing Clin Electrocardiol 19(II):1689–1693
3. Bongiorni MG, Soldati E, Arena G et al (1997) Transvalvular impedance as a marker of cardiac activity. In: Vardas PE (ed) Europace ’97. Monduzzi, Bologna, pp 525–528
4. Morra A, Panarotto D, Santini P et al (1997) Transvalvular impedance (TVI) sensing: a new way toward the haemodynamic control of cardiac pacing. In:
Vardas PE (ed) Europace ’97. Monduzzi, Bologna, pp 529–533
5. Bongiorni MG, Soldati E, Arena G et al (2003) Transvalvular impedance: does it allow automatic capture detection? In: Raviele A (ed) Cardiac arrhythmias 2003.
Springer, Milan, pp 733–739
6. Chirife R, Ortega DF, Salazar A (1993) Feasibility of measuring relative right ventricular volumes and ejection fraction with implantable rhythm control devices. Pacing Clin Electrophysiol 16:1673–1683
7. Gasparini M, Curnis A, Mantica M et al (2002) Hemodynamic sensors: what clinical value do they have in heart failure? In: Raviele A (ed) Cardiac arrhyth- mias 2001. Springer, Milan, pp 576–585
8. Bongiorni MG, Soldati E, Arena G et al (2001) Hemodynamic sensors: what clin- ical value do they have in chronotropic incompetence? In: Raviele A (ed) Cardiac arrhythmias 2001. Springer, Milan, pp 595–601
9. Di Gregorio F, Curnis A, Pettini A et al (2002) Trans-valvular impedance (TVI) in the hemodynamic regulation of cardiac pacing. In: Mitro P, Pella Rybár R, Valo?ik G (eds) Cardiovascular diseases 2002. Monduzzi, Bologna, pp 53–57 10. Gasparini G, Curnis A, Mascioli G et al (2003) Clinical test of a pacing device
driven by trans-valvular impedance. XII World Congress on Cardiac Pacing and Electrophysiology. Hong Kong, 19–22 February 2003. Pacing Clin Electrophysiol 26(II):S204 (abstract)
11. Gasparini G, Curnis A, Gulizia M et al (2003) Can hemodynamic sensors ensure physiological rate control? In: Raviele A (ed) Cardiac arrhy thmias 2003.
Springer, Milan, pp 725–731
12. Gulizia M, Gasparini G, Curnis A et al (2003) Hemodynamic rate-responsive pacing by trans-valvular impedance detection. Europace Supplements 4:B96 (abstract)
