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Computed tomography (CT) scanning is an essential diagnostic tool and has revolutionized care of patients in the acute care setting. However, there is widespread agreement that overutilization of CT, where benefits do not exceed possible costs or harms, is occurring. The goal was to seek consensus in identifying and prioritizing research questions and themes that involve the comparative effectiveness of "traditional" CT use versus alternative diagnostic strategies in the acute care setting. A modified Delphi technique was used that included input from emergency physicians, emergency radiologists, medical physicists, and an industry expert to achieve this.

Objectives: The effect of implantable cardioverter/defibrillator (ICD) lead placement in the right ventricle (RV) on defibrillation efficacy has not been thoroughly investigated. Therefore, the goal of this combined experimental and clinical study was to evaluate the effect of a septal and a non-septal position of the right ventricular endocardial spring lead on defibrillation energy. Methods: In 12 isofluraneanaesthetized swine and subsequently in 8 patients who underwent ICD implantation, two different positions of the distal spring lead in the RV were investigated in randomized order: non-septal position (free wall of the RV) and septal position (interventricular septum). For each position, separate 50% probability determinations of energy (E 50), peak voltage (V50) and peak current (A50) were calculated using the three reversal up/down defibrillation procedure. The E 50 ,V 50 ,A 50 and impedance (I) were averaged and compared using the two-sided t-test for paired samples. Results: Both the experimental study and the clinical study demonstrated that placing the distal defibrillation lead near to the septum rather than near to the ventricular free wall resulted both in the swine and in the patients in significantly lower E50 -31.6%/ - 37.1%, V50 -16.1%/-20.9% and A50 -10.0%/ - 24.2%, respectively. Defibrillation impedances were significantly reduced only in the experimental study. Conclusions: Defibrillation efficacy depends on the position of the distal spring electrode in the RV. A septal position significantly reduces the energy requirements compared to a non-septal position. The decrease in energy requirements might be explained by an increase in current flow through the septum and the posterolateral wall of the left ventricle. © 1998 Elsevier Science B.V. All rights reserved

The performance of an ICD system depends, in part, on the effectiveness with which the lead system functions. Engineering trade-offs are made during the design of a lead to optimize one or more performance characteristics: e.g., lead handling, fatigue life, size, and optimized therapy delivery. To assure low defibrillation thresholds, careful attention must be taken during the design process to prevent these trade-offs from hampering the lead's therapy effectiveness. Four basic design rules are described that capture many of the engineering concepts that will enhance a lead's efficacy: (1) minimize electrode pullback, (2) deliver current to the apex, (3) minimize energy loss in the lead, and (4) use large, efficient electrodes. These rules speak to optimizing delivery of current to the heart and efficiency of the lead and electrode interface. When the lead performs its function well, the complete ICD system of the heart, lead, and implantable pulse generator will provide optimal safety margins for device implant and an increased number of patients that can be implanted with a single-lead system.

OBJECTIVE To assess the impact of epicardial patch electrode position on internal defibrillation efficacy. METHODS Two mesh patch electrodes (13 cm2) were positioned on the epicardium of acute, isoflurane-anesthetized pigs (n = 7, 40-47 kg). Defibrillation efficacy was determined for three different patch positions: P1 = anterior-basal right ventricle (RV) and lateral-apical left ventricle (LV); P2 = lateral RV and lateral LV; and P3 = anterior-basal septal region and posterior-apical septal region. To quantify defibrillation efficacy, single capacitor discharge, fixed-tilt (68%) biphasic waveforms were delivered to the heart 10 seconds after initiation of ventricular fibrillation. Initial shock intensities were selected using an up/down protocol. Conversion data were used to construct sigmoidal curves relating probability of defibrillation to energy delivered, peak voltage, and peak current in each animal. RESULTS Mean peak voltage and current at 50% defibrillation probability were 40% higher for P2 than they were for either P1 or P3 (p < 0.05). Similarly, mean energy delivered was 75% higher for P2. In this pig model, position of epicardial patch electrodes affects defibrillation efficacy. CONCLUSION Apical-to-basal shock vectors (P1 and P3) yielded significantly lower defibrillation shock strength requirements than did a lateral-wall-to-lateral-wall vector (P2), which was perpendicular to the intraventricular septum. These data may help explain the disparity in defibrillation thresholds observed in the human population of patients undergoing implantable cardioverter defibrillator testing with epicardial patch electrodes.

The goal of this study was to determine whether delivering transvenous defibrillation shocks, coordinated with the up/down-slope VF waveform patterns in the shocking lead, would improve the probability of successful defibrillation. Anesthetized swine (32-38 kg, n = 8) were implanted with an RV-->SVC + SQArray transvenous system to measure VF waveform patterns and to deliver shocks. The shocks were generated by a Cardiac Pacemakers Inc. biphasic waveform generator. Energy required for 50% success probability (E50) was determined using the multishock up-down protocol. VF was repeatedly induced and defibrillation shocks at E50 were given after 10 seconds. The defibrillation outcome, delivered energy (Ed), peak voltage (V), peak current (I), system impedance (Z) and VF waveform pattern at the time of shock were recorded and measured. Out of a total of 685 shocks, 324 (47%) succeeded and 361 (53%) failed. The Ed, V, I, and Z were similar for the two defibrillation outcome groups (success or failure). VF patterns were classified as high or low amplitude at the time of the shock based on the peak-to-peak amplitude of signals recorded between the shocking electrodes. Shocks that coincided with high amplitude VF patterns were further divided into shocks that occurred on the up-slope or on the down-slope. The probability of success when the E50 shocks were coincident with high or low amplitude fibrillation did not differ significantly (Student's t-test: 46% vs 48%. P = NS). However, during high amplitude fibrillation, shocks delivered on the up-slope were significantly more successful than those delivered on the down-slope (Chi-square: 67% vs 39%; P < 0.001). These results suggest that delivering defibrillation shocks during the up-slope of the high amplitude signal in the shocking lead may improve the probability of successful defibrillation of ICDs.

This study tested the hypothesis that increasing capacitance would allow a reduction in ICD size without reducing the deliverable energy. For example, the volume of a single 450 μF capacitor (390 V peak) is 1/3 less than that of two 250 μF capacitors (780 V), but it can store equivalent amounts of energy.Methods: Endocardial defibrillation electrodes (3.4 cm) were positioned in the RV apex and at the RA/ SVC junction in six mixed-breed, isoflurane anesthetized pigs (41 ± 3 kg). Three 17-cm ribbon wires were positioned subcutaneously on the left lateral chest (SQArray). Two CPI VENTAK ECDs were equipped to deliver 60/40 biphasic waveforms using either 125 μF (STD) or 500 μF (LD) of capacitance. A 15 shock up/down protocol was used to determine the 50% probability of success levels for each waveform in each animal. Shocks were delivered from RV(-)SVC + SQArray(+) in random order. Results were compared using paired Student'sf-tests and are reported as mean ± SE. Results: The 500 μF long duration waveform reduced peak voltage 41% (374 ± 18 V [STD] vs 219 ± 14 V (LD], P < 0.001) and reduced peak current 38% (11.0 ± 1.1 A [STD] vs 6.8 ± 0.6 A [LD], P < 0.001) but did not significantly change the delivered energy(12.4 ± 1.3 J [STD] vs 13.4 ± 1.0 J [LD]). Durations increased from 10.0 ± 0.2 to 17.6 ± 0.5 msec (P < 0.001).Conclusions: Defibrillation with a 500 μF, long duration biphasic defibrillation waveform received similar amounts of energy but significantly reduced peak voltage and current compared to a waveform produced from 125 μF. A single large capacitor could be used to reduce the physical size of an ICD compared to the standard two capacitor system.

In light of recent technologic advances, we developed a canine renal allograft model utilizing implantable, programmable infusion pumps and biocompatible catheters to reexplore the concept of local immunosuppression. Thirteen mongrel dogs underwent bilateral nephrectomy and autotransplantation of 1 kidney via end-to-end renal-iliac artery and end-to-side renal-iliac vein anastomoses. The proximal end of an infusion catheter directed into the iliac artery was tunneled to a subcutaneously placed programmable pump. A second, sampling catheter was placed with its tip in the iliac vein just proximal to the venous anastomosis. During a period of i.a. infusion of heparinized saline ranging from 19 to 63 days, serum creatinine remained normal in all but 1 animal, which developed pyelonephritis and catheter-tip perforation of the iliac artery. No cases of arterial thrombosis or catheter migration were observed at necropsy. In 7 additional autotransplanted dogs, simultaneous iliac vein and systemic (jugular vein) concentrations of 6-mercaptopurine (6-MP), the major immunosuppressive metabolite of azathioprine, were determined during a continuous 24-hr i.a. infusion (10 mg/kg/24 hr). Following termination of the infusion, 10 mg/kg 6-MP was administered to the same 7 dogs as an i.v. bolus, and systemic drug concentrations were determined over a 4-hr period. Mean +/- SE total-body clearance and elimination half-life were 887 +/- 159 ml/min and 1.4 +/- 0.2 hr, respectively, in the i.v. bolus study, indicating that 6-MP is rapidly cleared from the systemic circulation. Unexpectedly, the kidney removed as much as 60-95% of locally infused 6-MP, reducing the amount of active drug entering the systemic circulation to 5-40% of that which would be present during an i.v. infusion of the same dose. According to the principles governing the advantages of i.a. infusions, these data demonstrate that 6-MP can be infused intrarenally to produce both a 4-fold increase in drug concentration within the kidney and an 80% decrease in systemic drug delivery when compared to same-dose i.v. administration. The overall result is the presence of a 30-fold gradient between local and systemic drug concentrations during intrarenal 6-MP infusion. We conclude that i.a. infusion of an immunosuppressive agent is technically feasible with preservation of renal function, and that 6-MP can be delivered locally in a canine model with great pharmacokinetic and potential therapeutic advantage.