Biomedical subjects

G Tomassoni

Publications and source records attributed to G Tomassoni.

23 records · Page 2Linked to original sources

PubMed1997

Defibrillation efficacy of commercially available biphasic impulses in humans. Importance of negative-phase peak voltage.

BACKGROUND: Recent studies have shown that specifically shaped biphasic waveforms can lower energy requirements for ventricular defibrillation. We prospectively compared the defibrillation efficacy of three different biphasic wave shapes incorporated in three commercially available implantable defibrillators. The results led to the development of a second protocol in which the importance of negative-phase peak voltage and duration was investigated. METHODS AND RESULTS: Defibrillation threshold (DFT) testing using different biphasic waveforms was performed randomly on 42 patients undergoing implantation of a cardioverter-defibrillator for ventricular arrhythmias. In 23 patients (group 1), 3 waveforms were tested: a CPI waveform with 60% positive-phase (P1) tilt and 50% negative-phase (P2) tilt, a Medtronic waveform with 65% fixed tilt in both P1 and P2, and a Ventritex waveform with 60% P1 tilt and a P2 leading edge voltage equal to half of the P1 trailing edge voltage. In 19 patients (group 2), 3 biphasic waveforms with equal P1 tilt at 65% but shorter P2 duration or smaller P2 peak voltage were tested. The Endotak C 60 series lead system (CPI) was used in 11 patients in group 1 and 10 patients in group 2. A Transvene lead system (Medtronics) was used in the remaining patients. Stored energy required for defibrillation was significantly lower with the CPI waveform compared with the Ventritex waveform. In group 2, energy requirements were significantly increased for the waveform with a smaller P2 peak voltage, whereas a short P2 duration did not influence defibrillation success. CONCLUSIONS: Our results suggest that specifically shaped biphasic waveforms delivered from commercially available devices can affect energy requirements for defibrillation. More importantly, the amplitude of the P2 peak voltage may be a more critical determinant than the P2 duration for defibrillation success of biphasic waveforms in humans.

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PubMed1997

Importance of electrode conductive surface area and edge effects on ventricular defibrillation efficacy.

INTRODUCTION: The role of edge effects and electrode surface area of the right ventricular (RV) transvenous lead (TVL) on defibrillation efficacy is unknown. METHODS AND RESULTS: Defibrillation threshold (DFT) testing was conducted randomly in 12 dogs using ring electrode leads in an RV/SVC (superior vena cava) or RV/SVC/patch system. The leads (RV-4, RV-8t, RV-8, RV-15) had electrode surface areas of 20%, 20%, 40%, and 70%, respectively. A computer model predicted the magnitude of electrode surface current (RV-8t > RV-4 > RV-8 > RV-15) and the potential distribution (PD) at four sites: electrode surface (site a) and at 2 mm (b), 4 mm (c), and 8 mm (d) away from the surface. Despite different near-field PDs (sites a, b, c), PDs were nearly identical at site d. Resistance decreased as the surface area increased. DFT energy for the RV-15 lead was lower than the RV-4 and RV-8t. There was no difference between energy requirements for the RV-15 and RV-8 leads. No difference was found in DFT current for each lead. Comparison of the RV-8t and RV-4 leads showed no difference in DFT energy despite a lower resistance and a greater number of edges. CONCLUSIONS: Increasing the RV TVL surface area lowered the resistance. However, surface area coverages > or = 40% did not lower DFT energy. No significant change in DFT current occurred despite different predicted near-field current densities. PDs were nearly identical 8 mm from the electrode surface. Thus, the far-field current density appears to play a more important role in determining defibrillation success.

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PubMed1996

Impact on ventricular function and quality of life of transcatheter ablation of the atrioventricular junction in chronic atrial fibrillation with a normal ventricular response.

We assessed left ventricular function and quality of life after atrioventricular junction ablation and pacemaker implant in 14 patients with chronic atrial fibrillation and normal ventricular response. A significant improvement in left ventricular ejection fraction, fractional shortening, and functional capacity were observed at follow-up, suggesting that in patients with chronic atrial fibrillation a regular heart beat may be preferable over rate control.

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PubMed1996

Testing different biphasic waveforms and capacitances: effect on atrial defibrillation threshold and pain perception.

OBJECTIVES: The goal of this study was to compare the effect of different tilts and capacitances for biphasic shocks on atrial defibrillation efficacy and pain threshold. BACKGROUND: Although biphasic shocks have been shown to be superior to monophasic shocks, the effect of tilt and capacitance on atrial defibrillation success and pain perception has not been studied in patients. METHODS: Atrial defibrillation threshold (DFT) testing was performed using a right atrial appendage/coronary sinus lead configuration in 38 patients with a history of paroxysmal atrial fibrillation undergoing an invasive electrophysiologic study. Biphasic waveforms with 40%, 50%, 65%, 80%, 30%/50% and 40%/50% were tested randomly in 22 patients (Group 1). In 16 patients (Group 2), a 65% tilt waveform with 50- and 120-microF capacitance was tested. Before sedation, pain sensation was graded by 15 patients in Group 1 after delivery of a 0.5-J shock and by 10 patients in Group 2 after two 1.5-J shocks with 50- and 120-microF capacitance were delivered. RESULTS: The DFT energy for the 50% tilt waveform was significantly lower than the 65%, 80% and 30%/50% tilt waveforms. The 40%/50% tilt waveform provided slightly lower energy requirements than the 50% tilt waveform. Nine patients (60%) described the 0.5-J shock as very painful, and four (26.6%) complained of slight pain. The 50-microF capacitor lowered energy requirements compared with the 120-microF capacitor. Six patients (60%) perceived the 1.5-J 50-microF capacitor shock as more painful, whereas three (30%) perceived both shocks as equally painful. CONCLUSIONS: Biphasic waveforms with 50% tilt in both phases and a smaller tilt in the positive phase than that in the negative phase (40%/50%) provided a decrease in energy requirements at atrial DFT. In addition, stored energy was reduced by biphasic shocks with 50-microF capacitance compared with 120-microF capacitance. Despite the reduction in energy requirements, shocks < 1 J continued to be perceived as painful in the majority of patients.

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PubMedDate not supplied

Surface coverage effects on defibrillation impedance for transvenous electrodes.

Transvenous defibrillation electrodes are constructed by wrapping conductive elements around an insulating base. However, these conductive elements do not cover the entire area of the base. The effects of varying the surface area coverage on the defibrillation impedance (DZ) are unknown. To understand the effects, four transvenous right ventricular test leads were specially fabricated. A ring design was used with 3 mm diameter cylinders equally spaced along a 5 cm length, ending 11 mm from the pacing tip. Three leads consisted of 4, 8, and 15 rings each of length approximately 2.4 mm so that the coverages were 20%, 40%, and 70%, respectively. The fourth lead used 8 rings of length approximately 1.2 mm each and had a coverage of 20%. DZ for each lead was obtained using three methods: (i) computer simulation; (ii) in vitro measurement in a tank; and (iii) in vivo measurement in nine dogs during defibrillation testing. The DZs from either of the first two methods correlated very well (r = 0.98) with the mean DZs from the third method, indicating that in vivo DZs can be predicted from computer and in vitro models. The study shows that: (i) at the same ring length, DZ decreases as coverage (number of rings) increases; (ii) at the same coverage, DZ decreases as ring length decreases; and (iii) in vivo, a statistically significant difference was observed in DZ between the leads with 20% coverage and the leads with higher coverages. No statistically significant difference was observed between leads with coverages > 40%.

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