Finite element analysis of defibrillation fields in a human torso model for ventricular defibrillation

In order to optimize defibrillation electrode systems for ventricular defibrillation thresholds (DFTs), a Finite Element Torso model was built from fast CT scans of a patient who had large cardiac dimensions (upper bound of normal) but no heart disease. Clinically used defibrillation electrode configurations, i.e. Superior Vena Cava (SVC) to Right Ventricle (RV) (SVC-RV), left pectoral Can to RV (Can-RV) and Can + SVC-RV, were analyzed. The DFTs were calculated based on 95% ventricular mass having voltage gradient > 5 V/cm and these results were also compared with clinical data. The low voltage gradient regions with voltage gradient < 5 V/cm were identified and the effect of electrode dimension and location on DFTs were also investigated for each system. A good correlation between the model results and the clinical data supports the use of Finite Element Analysis of a human torso model for optimization of defibrillation electrode systems. This correlation also indicates that the critical mass hypothesis is the primary mechanism of defibrillation. Both the FEA results and the clinical data show that Can + SVC-RV system offers the lowest voltage DFTs when compared with SVC-RV and Can-RV systems. Analysis of the effect of RV, SVC and Can electrode dimensions and locations can have an important impact on defibrillation lead designs.     

Effect of ventricular dilatation on defibrillation threshold in the isolated perfused rabbit heart

INTRODUCTION: Ventricular dilatation has important electrophysiologic effects, but its effect on ventricular defibrillation threshold (DFT) is unknown. METHODS AND RESULTS: A fluid-filled, latex balloon was placed in the left ventricular cavity of 19 isolated rabbit hearts. In each experiment, an undilated volume (equivalent to a left ventricular end-diastolic pressure of approximately 0 mmHg) was compared to a dilated volume achieved by adding 1.0 mL of saline (n = 10) or 5% dextrose (n = 9) to the intracavitary balloon. Left ventricular effective refractory period (ERP) and DFT were determined at each volume. Defibrillation was attempted with a monophasic shock delivered between a patch electrode positioned over the posterior left ventricle (cathode) and a metallic aortic cannula (anode). DFT was determined using a modified "down/up" protocol with 10 V steps. Ventricular dilatation increased the left ventricular end-diastolic pressure from 0 +/- 0.5 mmHg to 35 +/- 3 mmHg (P < 0.001), decreased the average left ventricular ERP 15% (from 116 +/- 3 msec to 99 +/- 3 msec; P < 0.001), and increased the average DFT 30% (from 96 +/- 4 V to 125 +/- 7 V; P < 0.001). In one third of experiments, the dilated DFT was > or = 150% of the DFT at zero volume. The mechanism of the observed increase in DFT is unknown but may be related to the decrease in refractoriness observed with ventricular dilatation. CONCLUSION: Acute ventricular dilatation in this model increased DFT an average of 30%, an effect not previously described. This observation may have implications for patients with implantable cardioverter defibrillators.     

Effect of the addition of an abdominal hot can cardioverter/defibrillator pulse generator on the defibrillation energy requirements in a single-lead endocardial defibrillation system

AIMS: The effects of a cardioverter/defibrillator system with an electrically active generator can, applied without recourse to thoracotomy, have not been investigated in the abdominal position in humans. The purpose of this acute clinical study was to evaluate the defibrillation efficacy of an abdominally positioned hot can electrode in connection with a single lead endocardial defibrillation system. PATIENTS AND METHODS: Thirty consecutive patients undergoing implantation of a cardioverter/defibrillator or pulse generator replacement were enrolled in this study Each patient received an integrated, tripolar single-lead system. This was tested using an asymmetrical biphasic defibrillation waveform with constant energy delivery. Defibrillation energy, peak voltage, peak current and impedance were compared between two electrode configurations: (A) in this configuration the distal right ventricular coil was negative and the proximal coil positive; (B) in this configuration the distal right ventricular coil was negative and the proximal coil and the abdominal hot can (65 ccm), as common anode, were positive. Defibrillation threshold testing started at 15 J with stepwise energy reduction (10 J, 8 J, 5 J and 3 J) until defibrillation was ineffective. RESULTS: Compared to the single-lead configuration, the abdominal hot can configuration revealed at 17.5% reduction in defibrillation energy requirements (8.6 J +/- 4.3 J vs 10.43 J +/- 3.9 J; P = 0.041), a 15.7% reduction in peak voltage (308.6 V +/- 63 V vs 365.3 V +/- 68 V; P = 0.003), and a 21.6% reduction in impedance (41.1 omega +/- 6.3 omega vs 52.4 omega +/- 6.6 omega; P < 0.001). Peak current showed a significant increase during hot can testing of 8.2% (7.2 A +/- 1.8 A vs 7.8 A +/- 2.2 A; P = 0.16). CONCLUSION: An abdominally placed hot can pulse generator lowered defibrillation energy requirements in patients with an endocardial defibrillation lead system.     

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.     

Stability of the defibrillation probability curve with the development of ventricular dysfunction in the canine rapid paced model

Most patients with implantable defibrillators have diminished cardiac function. Progressive heart failure might impair defibrillation efficacy, leading to interpreted device failure. This study sought to determine the effect of ventricular dysfunction on defibrillation energy using a biphasic endocardial system. Eleven dogs were ventricularly paced at 225 pulses/min for 2 weeks to induce ventricular dysfunction, and five control dogs remained unpaced. Dose response defibrillation probability curves were generated for each animal at baseline, after 2 weeks (at which time the pacemakers were turned off in the paced group), and then 1 week later. The defibrillation thresholds, ED20, ED50, and ED80 (the 20%, 50%, and 80% effective defibrillation energies, respectively) were determined for each dog at each study. In the paced dogs, the mean ejection fraction fell from 55% to 25% after pacing (P < 0.0001), and rose to 46% after its discontinuation (P = 0.0002). The defibrillation threshold, ED20, ED50, and ED80 remained unchanged in both the control and paced groups for all three studies, even after adjustment for dog weight or left ventricular mass. Rapid pacing produced no change in left ventricular mass. It induced ventricular cavity dilatation and wall thinning, which had opposing effects on defibrillation energy requirements, resulting in no net change of the ED50 in heart failure. In conclusion, the defibrillation efficacy of a biphasic transvenous system is not changed by the development of heart failure using the rapid paced canine model.     

发展性学校评价是现代教育的必然需求

学校是实施素质教育的基本场所,学校评价是整个教育评价工作的重要组成部分.随着教育事业的发展和教育体制改革的逐步深化,学校评价在教学管理体制中的地位不断提高,并在推动学校改革和发展、保障学校教育质量方面发挥着重要作用.然而传统的学校评价的局限性、内在缺陷和存在的诸多弊端,已越来越不适应经济、社会和教育水平的发展与提高,现代的、科学的、更趋完善的评价体系的产生迫在眉睫,而在现代教育改革的促动下,应时而生的发展性学校评价成为了现代教育发展的必然产物和必然需求.     

Echocardiography in the evaluation of ventricular function

The ultrasonic beam used for quantitative assessment of left ventricular (LV) function traverses the heart in a projection similar to the familiar angiographic left anterior oblique projection. It crosses the anterior wall of the right ventricle, the right ventricular cavity, the interventricular septum, the LV cavity and the posterior wall of the left ventricle. Whereas the cyclic changes of the right ventricular diameter are rarely clearly determined by echocardiography, the easily assessed cyclic changes of the LV endocardial transverse diameter are useful measure of LV FUNCTION. Of practical importance are the percentage of systolic shortening of the LV diameter (%Sh) and the mean velocity of circumferential fiber shortening (VCF). There are several factors, such as placing of the ultrasonic transducer, the shape and size of the LV cavity and rotational movements of the heart as a whole, that influence echocardiographic determination of the transverse LV diameter. In patients with asynergic contraction, %Sh and VCF cannot be used as measures of overall LV performance, but localized contraction disturbances of the septum and the posterior wall may be detected from the reduced extent of wall motion in a given LV segment during a full sweep from the base to the apex. The most important indications for echocardiographic assessment of LV function are valvar diseases with chronic LV pressure or volume overload, and congestive cardiomyopathy. Echocardiography has proved useful in serial evaluation of LV function in patients undergoing valvar heart surgery. Assessment of LV volume by standard echocardiography using the cubic formula is not satisfactory. More accurate determination of volumes is provided by formulas that include the actual ratio of the LV long axis to the minor axis.     

Low energy transcatheter atrial defibrillation in one patient with refractory atrial fibrillation]

Cholangiocarcinomas occasionally arise in the nonbiliary cirrhotic liver, but their pathobiologic features remain unsettled. To characterize such cholangiocarcinomas, we examined immunohistochemically the expression of MUC3, MUC5AC, MUC6, and MUC7 apomucins in hepatic tissue specimens from 4 patients with cholangiocarcinoma and viral cirrhosis, 24 patients with cholangiocarcinoma without cirrhosis, and 16 patients with combined hepatocellular-cholangiocellular carcinoma. The cholangiocarcinomas associated with cirrhosis and the cholangiocarcinoma elements of combined hepatocellular-cholangiocellular carcinoma rarely expressed MUC3 and MUC5AC, but the cholangiocarcinomas not associated with cirrhosis frequently expressed these apomucins. MUC6 apomucin was widely expressed in cholangiocarcinomas, irrespective of the association with cirrhosis and also in the cholangiocarcinoma elements of the combined hepatocellular-cholangiocellular carcinomas. MUC7 apomucin was expressed frequently in cholangiocarcinomas associated with cirrhosis and combined hepatocellular-cholangiocellular carcinomas and infrequently in cholangiocarcinomas without cirrhosis, particularly those arising at the hepatic hilus. The similarity of the apomucin profiles between cholangiocarcinomas associated with cirrhosis and the cholangiocarcinoma elements of combined hepatocellular-cholangiocellular carcinoma suggests a similar or common histogenesis and that cholangiocarcinoma associated with cirrhosis might be derived from the combined type.     

Left ventricular potential energy is represented in the ejecting left ventricular pressure curve

In this study, the authors describe a new "reactive syndrome," Reactive Intestinal Dysfunction Syndrome (RIDS), which has similarities to the previously described clinical syndromes Reactive Airway Dysfunction Syndrome (RADS) and Reactive Upper Airway Dysfunction Syndrome (RUDS). Given that at least 5 neuropeptides are common to both the respiratory tract and digestive tract, the authors propose that the abnormal secretion of these neuropeptides or the abnormal numbers of their receptors play a role in what is perceived clinically as RADS, RUDS, and RIDS. The relatively large surface areas of both the lungs and gut render them especially vulnerable to the environment to which they are exposed constantly.     

Long-term results of lower energy transurethral microwave thermotherapy

PURPOSE: We evaluate long-term results of lower energy transurethral microwave thermotherapy (Prostasoft 2.0*) and identify pretreatment characteristics that predict a favorable outcome. MATERIALS AND METHODS: Between December 1990 and December 1992, 231 patients with lower urinary tract symptoms were treated with lower energy transurethral microwave thermotherapy. Subjective and objective voiding parameters were collected from medical records and a self-administered questionnaire. Kaplan-Meier plots were constructed to assess the risk of re-treatment. RESULTS: Of the patients 41% underwent invasive re-treatment within 5 years of followup and 17% were re-treated with medication. The re-treatment-free period was somewhat longer in patients with a peak flow rate greater than 10 ml. per second, a Madsen score 15 or less, a post-void residual volume 100 ml. or less and age greater than 65 years at baseline. Prostate volume did not modify the outcome. No incontinence was caused by transurethral microwave thermotherapy, 8% had recurrent urinary tract infection and 8% had retrograde ejaculation. Only 1 patient had a urethral stricture after transurethral microwave thermotherapy. CONCLUSIONS: At 5 years after transurethral microwave thermotherapy 41% of the patients received instrumental treatment. Patients with a lower Madsen score and lower residual volume, and those with higher peak flow and age were somewhat better responders to lower energy transurethral microwave thermotherapy.     

Nonthoracotomy implantation of cardioverter defibrillators: preliminary experience with a defibrillation lead placed at the right ventricular outflow tract

Although morbidity and mortality associated with defibrillator implantation using a nonthoracotomy approach have decreased as compared with a thoracotomy approach, defibrillation thresholds have been higher and fewer patients satisfied implant criteria. It may be possible to improve on the success of nonthoracotomy defibrillator implantation by the placement of a right ventricular (RV) outflow defibrillation lead. Implantable cardioverter defibrillator implantation data of 30 consecutive patients with clinical VT or VF were reviewed. Three defibrillation leads were routinely used. When either pacing threshold at the RV apex was inadequate (n = 2) or 18-J shocks were not successful in terminating VF in 3 of 4 trials (n = 8), the RV apex lead was positioned to the RV outflow tract attaching to the septum. Defibrillation testing was first performed with the RV apex lead in combination with CS, SVC, and/or subcutaneous leads. Twenty patients satisfied implant criteria with a defibrillation threshold of 13.5 +/- 3.6 J. In 7 of the 10 patients, whose RV lead was repositioned to the RV outflow tract, this lead in combination with SVC, CS, or subcutaneous leads produced successful defibrillation at < or = 18 J or in 3 of 4 trials. This approach improved the overall success of nonthoracotomy implantation of defibrillators from 69% to 90%. After a follow-up of 27 +/- 6 months, there was no dislodgment of the RV outflow tract defibrillation leads. CONCLUSIONS: This article reports the preliminary observation that placement of defibrillation leads to the RV outflow tract in humans was possible and without dislodgment. RV outflow tract offers an alternative for placement of defibrillation leads, which may improve on the success of nonthoracotomy defibrillator implantation.     

Long-term evaluation of endodontic and periodontal treatment

One hundred and ninety-five teeth in 35 patients with periodontitis who had received both endodontic and periodontal treatment were evaluated 9 years after endodontic treatment and 8 years after periodontal treatment. Some 91.4% of cases were well maintained and 8.6% showed a deterioration in their periodontal condition. Twelve of the 195 teeth with endodontic treatment were lost, eight for periodontal reasons, three as a result of fracture and one because of caries, and the periodontal condition of 10 teeth had worsened. An apical lesion formed on one tooth. The results indicate that the risk of endodontic failure in this group of 195 teeth is very low, and that there is little risk of tooth loss for periodontal reasons, provided that the patients receive supportive periodontal treatment.     

Postshock sensing performance in transvenous defibrillation lead systems: analysis of detection and redetection of ventricular fibrillation

INTRODUCTION: The sensing performance of transvenous lead systems may be adversely affected by the delivery of high-energy shocks. This may be due to the proximity of the sensing and energy-delivery electrodes on transvenous leads. METHODS AND RESULTS: The time required for detection of ventricular fibrillation and redetection after a failed first shock was compared in 93 patients with five different lead system-pulse generator combinations: Cadence--Endotak 60 series, Ventak P--Endotak 60 series, Jewel--Transvene, Cadence--TVL, and Cadence--Transvene. A total of 418 successful and 204 failed first shocks were delivered during induced ventricular fibrillation. Redetection times (RED) were consistently shorter than detection times (DET) in the Jewel-Transvene (RED minus DET: -1.9 +/- 0.8 sec, P < 0.0001), the Cadence-TVL (-1.6 +/- 1.0 sec, P < 0.0001), and the Cadence-Transvene combinations (-2.0 +/- 0.9 sec, P < 0.0004). Redetection times were not significantly different than detection times in the Cadence-Endotak combination (0.9 +/- 3.1 sec; P = 0.09). Redetection times were significantly longer than detection times in the Ventak-Endotak combination (1.2 +/- 2.3 sec; P = 0.034). Prolonged individual redetection episodes (> 8.2 sec) were observed in the Cadence-Endotak (7 [10%] of 73 episodes) and the Ventak-Endotak (4 [10%] of 39 episodes), but not in the Jewel-Transvene, the Cadence-TVL, and the Cadence-Transvene combinations. CONCLUSIONS: Redetection of ventricular fibrillation may be delayed in some transvenous lead-pulse generator combinations. Successful redetection of ventricular fibrillation following a failed first shock should be demonstrated prior to hospital discharge of patients with implantable defibrillators.     

Long-term evaluation of the Gittes procedure for urinary stress incontinence

PURPOSE: We evaluate the long-term outcome of the Gittes procedure for urinary stress incontinence. MATERIALS AND METHODS: A total of 87 women with proved genuine stress incontinence were treated with the Gittes procedure. The same urologist performed 95 consecutive operations during an 8-year period. Patients were evaluated by a postal questionnaire. RESULTS: Of the patients 52 (60%) (55 operations) responded to the questionnaire. Mean and median followup were 53 and 46 months, respectively (range 24 to 103). Twelve patients (23.1%) reported complete absence of postoperative urinary incontinence and were considered cured, 14 (26.9%) were significantly improved and a total of 30 (57.7%) benefited from the operation. The short-term results were initially encouraging but by 2 years only 20 patients were completely continent (38.5% cured). Of the 40 patients who were not cured 32 (80.0%) experienced incontinence within 2 years postoperatively. There were 26 who had complained of frequency and/or urgency preoperatively. There was a statistically significant subjective failure rate in this group (p = 0.007). CONCLUSIONS: The Gittes procedure is simple and has minimal complications. Although it provides continence in the early weeks and months following surgery, the long-term cure rate is disappointing, with most failures occurring within 2 years of surgery. Preoperative irritative symptoms, even when multichannel cystometry did not reveal instability, were associated with a poor subjective outcome. Our results suggest that the Gittes procedure is not satisfactory for the management of genuine stress incontinence in women.     

Relative efficacy of monophasic and biphasic waveforms for transthoracic defibrillation after short and long durations of ventricular fibrillation

BACKGROUND: Recently, interest has arisen in using biphasic waveforms for external defibrillation. Little work has been done, however, in measuring transthoracic defibrillation efficacy after long periods of ventricular fibrillation. In protocol 1, we compared the efficacy of a quasi-sinusoidal biphasic waveform (QSBW), a truncated exponential biphasic waveform (TEBW), and a critically damped sinusoidal monophasic waveform (CDSMW) after 15 seconds of fibrillation. In protocol 2, we compared the efficacy of the more efficacious biphasic waveform from protocol 1, QSBW, with CDSMW after 15 seconds and 5 minutes of fibrillation. METHODS AND RESULTS: In protocol 1, 50% success levels, ED50, were measured after 15 seconds of fibrillation for the 3 waveforms in 6 dogs. In protocol 2, defibrillation thresholds were measured for QSBW and CDSMW after 15 seconds of fibrillation and after 3 minutes of unsupported fibrillation followed by 2 minutes of fibrillation with femoral-femoral cross-circulation. In protocol 1, QSBW had a lower ED50, 16.0+/-4.9 J, than TEBW, 20.3+/-4.4 J, or CDSMW, 27.4+/-6.0 J. In protocol 2, QSBW had a lower defibrillation threshold after 15 seconds, 38+/-10 J, and after 5 minutes, 41.5+/-5 J, than CDSMW after 15 seconds, 54+/-19 J, and 5 minutes, 80+/-30 J, of fibrillation. The defibrillation threshold remained statistically the same for QSBW for the 2 fibrillation durations but rose significantly for CDSMW. CONCLUSIONS: In this animal model of sudden death and resuscitation, these 2 biphasic waveforms are more efficacious than the CDSMW at short durations of fibrillation. Furthermore, the QSBW is even more efficacious than the CDSMW at longer durations of fibrillation.