Some factors affecting bubble formation with catheter-mediated defibrillator pulses.

Abstract

Factors affecting bubble formation during delivery of defibrillator pulses to arrhythmogenic cardiac tissue via a catheter are unknown. We investigated the role of energy, electrode surface area, interelectrode distance, and electrode polarity on bubble formation and on current and voltage waveforms during delivery of damped sinusoidal discharges from a standard defibrillator to anticoagulated bovine blood. Gas composition was studied with mass spectrometry. Defibrillator energy settings were varied between 5 and 360 J. The principal catheter used for study was a Medtronic 6992A lead. Additional electrodes tested included 2, 5, and 10 mm long No. 6F, 7F, and 8F copper electrodes.Interelectrode distances used to assess the effect of anode-cathode spacing were 1, 5, 10, and 20 cm. Bubble volume increased linearly from 0.043 to 0.134 ml per cathodal pulse and from 0.030 to 3.50 ml per anodal pulse as energy settings were increased from 5 to 360 J (r = .99). Typical smooth waveforms for both current and voltage were seen only in the absence of bubbles. The voltage waveform was distorted for each cathodal pulse of 100 J or more and for each anodal pulse of 10 J or more only if bubbles were present. The effect of electrode surface area on bubble formation was tested at a 200 J energy setting and at a 10 cm interelectrode distance with the use of cathodal pulses. Bubble formation varied inversely with electrode surface area (r = .876). Bubble formation, however, varied minimally as interelectrode spacing was changed from 1 to 20 cm. The effect of polarity on bubble formation when the Medtronic 6992A distal electrode and an 8.5 cm disk electrode separated by 10 cm were used was highly significant. For a 200 J pulse, bubble formation with the catheter as anode was 3.30 + 0.10 ml and with the catheter as cathode it was 0.070 + 0.002 ml (p < .001). Mass spectrometry of both anodal and cathodal gas samples demonstrated the constituents of the gas bubble to include a variety of gases, which is inconsistent with simple electrolytic production of the bubbles observed. The predominance of nitrogen in either polarity sample suggested that the principal source of the bubble was dissolved air. In summary, bubble formation at an electrode receiving damped sinusoidal outputs from a standard defibrillator does not vary significantly with varying interelectrode distance. However, it is directly proportional to energy and inversely proportional to electrode surface area. Anodal catheter discharges produce considerably more bubbles than do cathodal discharges. Distortions in the voltage waveform correlate with physical factors leading to high-pressure shockwave generation and to subsequent extrusion of dissolved gases from solution. Circulation 73, No. 3, 525-538, 1986.

Safety and Feasibility of Closed Chest Epicardial Catheter Ablation Using Electroporation

“…A cathodal polarity was chosen because that has the highest threshold for arcing in a blood environment. 13 Coronary angiography (CAG) was repeated after the last application.…”

“…A cathodal polarity was chosen because that has the highest threshold for arcing in a blood environment. 13 Coronary angiography (CAG) was repeated after the last application.After 3-month survival, CAG of the LAD and RCx was repeated, the thorax was opened by sternotomy, and the animal was euthanized by exsanguination. After the heart was removed, the pericardium was peeled off and the areas with ablation lesions were excised and fixated in formalin.…”

Myocardial Lesion Depth With Circular Electroporation Ablation

“…A cathodal shock polarity was chosen because that has the highest threshold for arcing in a blood environment. 7 With device D, applications were performed at 50, 100, or 200 J, corresponding to 5, 10, and 20 J per electrode, respectively. With Device M, only a 100-J application was delivered.…”

“…During ablation, voltage and current waveforms were stored on a digital oscilloscope for measurement of maximal ablation current and detection of discontinuities in the voltage waveform that coincide with vapor globe development and arcing. 7 After each ablation, the blood was removed from the pericardial sac and the lesion area and electrodes were inspected for abnormalities. Then, the ablation device was detached from the heart while the 3 sutures remained in place to mark the ablation site.…”

Long-term results of catheter ablation of a posteroseptal accessory atrioventricular connection in 48 patients.

“…The mean peak creatine kinase MB fraction after the catheter ablation procedure was 23+± 11 whom the coronary sinus was visualized angiographically. Among the eight patients who underwent surgical ablation of an accessory AV connection either because catheter ablation of the posteroseptal accessory AV connection was ineffective or because the patient had a second accessory AV connection, a 0.5 -cm2 endocardial ecchymosis was observed at the ostium of the coronary sinus in two patients.…”