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Temperature monitoring during radiofrequency catheter ablation is useful but requires specialized equipment that is not generally available. Previous studies have shown that impedance characteristically decreases as the result of heating at the electrode-tissue interface. The purpose of the current study was to determine if impedance changes during radiofrequency current application could be used to estimate endocardial temperature in patients undergoing catheter ablation. Data from 43 patients treated with a thermistor ablation catheter were retrospectively analyzed. The slope of the initial 2 seconds of the impedance curve and subsequent changes in impedance were incorporated into an equation for estimation of temperature in real-time. The accuracy of this equation was assessed by prospectively comparing the calculated and measured temperatures in 19 patients. Of the 88% of energy applications that were suitable for analysis, the average difference between calculated and measured temperatures was 5.2 +/- 5.6 degrees C. The average error was < 10 degrees C in 89% of applications. The results of this study suggest that impedance measurements can be used to quantify tissue temperature in real-time during radiofrequency catheter ablation. This method is sufficiently accurate to allow titration of power output to produce temperatures in the useful range (50-80 degrees C) while avoiding excessive heating (> 90 degrees C).

We are grateful for J.L. Sullivan's interest in and comments regarding our article. 1 Clearly, the use of polyethylene gloves is an important constraint to our experiments (We mention this in the article more than once). However, such gloves are a part of standard precautions during resuscitation. Moreover, we clearly demonstrate the safety of hands-on defibrillation in humans despite a direct bare-skin-to-bare-skin return current pathway between the patient and rescuer.Should our findings be interpreted as the "go-ahead" to ignore guidelines and perform compressions while shocks are delivered? Obviously, they should not. As pointed out in the Discussion, we do not advocate that this maneuver be used clinically until proven safe by further testing. We must, however, address and clarify several points made by Mr Sullivan.Mr Sullivan points out that the dielectric integrity of the gloves may break down when exposed to electric fields in the kilovolt range. For gloves to be exposed to this type of voltage, the defibrillator pads would essentially have to be applied directly to either side of the glove. Defibrillating the gloves instead of the patient is beyond the range of foreseeable medical error. In reality, we have found that the measured voltage on the skin surface of patients 15 cm from the pads is less than 1/20th the voltages proposed by Mr Sullivan (unpublished experiments). This is likely the reason that none of our experiments have shown evidence of dielectric breakdown.There is no recommendation in resuscitation guidelines for the use of biphasic shock energies of Ͼ200 J. In 8 of our experiments, we included 360-J biphasic shocks to further test the safety margin of this maneuver. These measurements used energies beyond what would be used in cardiac arrest scenarios. Therefore, these measurements bolster, not hinder as Mr Sullivan would suggest, our conclusions.In our continuing research regarding hands-on defibrillation, we recognize that the safety of rescuers is an absolute requisite. We remain confident that future resuscitation protocols will include streamlined, efficient maneuvers such as ours. Until that time, in the care of our patients, we and the remainder of clinicians should stick to the guidelines. DisclosuresNone. Michael

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It is well established that convulsive movements often accompany syncopal events yet many patients with these clinical features are misdiagnosed with seizures and often referred to epilepsy centers because they are refractory to treatment with anticonvulsant medications. Tilt table testing is the gold standard for diagnosing vasodepressor syncope, but it can fail to provide clinical details that help distinguish convulsive syncope from epileptic seizures and psychogenic events. This study evaluates the diagnostic utility of the addition of video and EEG monitoring during tilt table testing for patients with refractory episodes of unexplained loss of consciousness. Retrospective analysis was performed of 40 consecutive patients who were referred to the Emory Epilepsy Center and underwent tilt table testing with concomitant video-EEG between March 1, 2007 and December 1, 2008. EEG was recorded throughout the study in addition to video recording and single channel EKG. Events were classified as vasodepressor syncope, presyncope, or psychogenic. Tilt combined with video EEG was diagnostic in 26/40 (65%) of patients. Vasodepressor syncope was seen in 17/40 (42.5%), 9 of which had associated involuntary movements. Three patients experienced psychogenic non-epileptic events. Antiepileptic drugs (AEDs) were being prescribed for 17 patients, 7 of which were discontinued as a result of the testing. The majority of patients (38/40) had undergone prior neurological and cardiac evaluation with routine EEG, neuroimaging and/or Holter monitoring. Patients with convulsive syncope are often misdiagnosed and treated with AEDs despite prior neurodiagnostic and cardiac evaluation. Tilt table testing with video-EEG is useful in patients with refractory episodes of unexplained loss of consciousness and can avoid expensive non-diagnostic evaluations as well as ongoing treatment with unnecessary AEDs.

Patients with the Wolff-Parkinson-White (WPW) syndrome have preexcited tachycardia as the result of atrial arrhythmias or antidromic reentry. This article describes a patient with persistent wide complex tachycardia due to abnormal automaticity in the accessory pathway. Radiofrequency catheter ablation resulted in simultaneous elimination of accessory pathway conduction and automaticity. Accessory pathway automaticity may be an infrequent cause of preexcited tachycardia in patients with the WPW syndrome.

The use of computer simulation in the development of hospital systems, which has a major effect on the cost and quality of operation, is presented. Discussion of results achieved in specific areas include: inpatient admissions scheduling and control systems, surgical scheduling systems, maximum average occupancy prediction models, and patient classification systems for predicting the size of nursing staffs. The paper concludes with a discussion of the general problems encountered with computer simulation.