Determination Of Defibrillation Threshold Research Articles

230 The usefulness of step-up search algorithm for determination of defibrillation threshold in ICD patients

@Background: modern ICDs use different detection algorithms for the discrimination between ventricular and supraventricular tachycardia. The Morphology Detection algorithm (MD, St. Jude Medical) uses the morphology match (MM) of each intracardiac heart beat with a stored reference ECG-signal of the patient. We compared the intraindividual MM during exercise with rapid atrial pacing (Apace) and developed a new method for the identification of MD responder (MR) and nonresponder (MnR). Methods: in 22 ICD patients (16 m, 614-14 y) standartized bicycle ergometry was performed up to maximum heart rate. MM was recorded for each 10 beat-interval between rest and peak exercise heart rate. Each measurement consisted of 8 consecutive beats and was compared with identical Apace rates. Patients with a MM 91% during Apace, the ROC analysis showed a sensitivity of 93.7% and a specificity of 83.3% for the identification of MR (figure).

230 The usefulness of step-up search algorithm for determination of defibrillation threshold in ICD patients

230 The usefulness of step-up search algorithm for determination of defibrillation threshold in ICD patients

Patent Foramen Ovale and Implantable Cardioverter Defibrillator

A case of patent foramen ovale opening was observed concomitantly to a defibrillation threshold determination in the setting of an internal cardioverter defibrillator implantation. The subsequent transient right-to-left shunt was confirmed by a peroperative transoesophageal echocontrast study. The underlying mechanism of this incident may be related to a transient reversal of the interatrial gradient, due to the pre-existence of pulmonary hypertension and tricuspid regurgitation, associated with ongoing mechanical ventilation and modifications of intracardiac pressures regimen secondary to the succeeding ventricular tachyarrhythmia and defibrillation. Paradoxical embolism can be an aetiology for neurologic injury during internal cardioverter defibrillator implantation.

Effects of repeated electrical defibrillations on cardiac troponin I levels

Multiple endocardial countershocks applied during intraoperative endocardial implantable cardioverter-defibrillator testing for the purpose of defibrillation threshold determination resulted in detectable myocardial injury in 5 of 12 patients, as indicated by elevations in cardiac troponin I levels. This injury was not associated with acute changes on the surface electrocardiogram.

Transoesophageal echocardiographic evaluation of ventricular function during transvenous defibrillator implantation.

Intraoperative testing and defibrillation threshold determination may jeopardise patients, scheduled for implantation of a cardioverter-defibrillator (ICD). The purpose of this study was the assessment of the influence of consecutive defibrillation attempts on left ventricular systolic and diastolic function by means of transoesophageal echocardiography (TEE). Eighteen patients with malignant ventricular arrhythmias that were resistant to antiarrhythmic drugs were monitored with TEE before, during and after implantation of a cardioverter-defibrillator. Left ventricular fractional area contraction as a measure of ejection fraction was assessed before and after each defibrillation attempt. Transmitral and right upper pulmonary venous flow parameters were evaluated before and after the whole implantation procedure. Adequate data were available in 14 patients during 4 consecutive attempts. No major alterations were observed in heart rate or fractional area contraction, measured at 30 s and 3 min after defibrillation. Overall, the ratio of early-to-late transmitral filling decreased significantly after the implantation procedure (from 0.91 +/- 0.12 to 0.82 +/- 0.14; P < 0.05). Systolic pulmonary venous flow velocity decreased from 0.49 +/- 0.11 to 0.41 +/- 0.10 m/s (P = 0.04); this decrease was observed in both groups. A significant increase of the atrial contraction wave (from 0.25 +/- 0.06 to 0.34 +/- 0.07 m/s; P < 0.03) was seen. Subdividing patients related to their precperative ejection fraction, a significant decrease of the early-to-late transmitral filling of the LV was revealed in patients with ejection fraction less than 35% (group 1). Also, a significantly lower systolic fraction of the pulmonary venous flow after ICD implantation in conjunction with a significantly longer diastolic flow time was shown in this patient group in comparison with patients with a preoperative ejection fraction of more than 35% (group 2). Defibrillation threshold testing of the ICD system changes LV inflow characteristics and impedes diastolic function of the left ventricle and may thus precipitate heart failure by this mechanism. No deleterious effects of threshold testing were observed with respect to fractional area contraction nor any deterioration of LV function was found in a clinically significant amount due to consecutive defibrillation attempts.

Defibrillation efficacy. Comparison of defibrillation threshold versus dose-response curve determination.

When an automatic defibrillator is implanted, it is essential to determine the efficacy of the defibrillating system accurately, while balancing the need to keep the number of fibrillation episodes to a minimum. Two methods have evolved to assess defibrillation efficacy: 1) the "defibrillation threshold," which requires few ventricular fibrillation episodes, and 2) the "dose-response curve," which requires many ventricular fibrillation episodes and relates percent success to energy. The purpose of this study was to compare these two methods directly. Twenty open-chest anesthetized pigs had triplicate defibrillation threshold determinations. To produce a dose-response curve, six shocks then were delivered at 0.5, 0.75, 1.0, 1.25, 1.5, and 2.0 times the mean defibrillation threshold, in a balanced randomized order, during separate episodes of ventricular fibrillation. The data were fitted by logistic regression, conversions of the logistic regression, and a saturable exponential and nonsaturable growth exponential. A comparison was made of the mean defibrillation threshold and the 50% point on the dose-response curve (ED50) for each model, for each animal. In addition, the reliability of each measure was assessed by comparing the coefficients of variation. There was no statistical difference between the group defibrillation threshold (6.6 +/- 0.5 J) and group ED50 values (ED50 range of the models, 5.7 +/- 1.9 to 7.0 +/- 0.9 J). However, the variability about the defibrillation threshold was less than that of the ED50 values for all mathematical models except the true logistic equation, which was virtually the same.(ABSTRACT TRUNCATED AT 250 WORDS)

Prospective comparison of sequential pulse and single pulse defibrillation with use of two different clinically available systems

Sixteen out-of-hospital survivors of ventricular fibrillation underwent a prospective, randomized, intraoperative comparison of sequential pulse and single pulse defibrillation with use of two distinct electrode systems and waveform shapes currently available for clinical use. Defibrillation was tested alternately with either the single pulse or the sequential pulse system 10 s into an episode of ventricular fibrillation. Sequential pulse defibrillation was performed with two 4 ms truncated exponential pulses of constant duration delivered to three equally spaced oval epicardial patch electrodes composed of concentric coils. The posterior left ventricular electrode served as the common cathode. The first anode was over the anterior right ventricle and the second anode was over the anterior left ventricle. Single pulse defibrillation was performed with the standard intracardiac defibrillation system with use of a single truncated exponential pulse with a fixed 65% tilt delivered across two rectangular, wire mesh epicardial patch electrodes positioned over the anterior right ventricle and posterolateral left ventricle. During defibrillation threshold determination, voltage and current waveforms were recorded and used to determine pulsing resistance and delivered and stored energy. Average defibrillation threshold leading edge voltage for the single pulse technique was 273 +/- 101 V compared with 246 +/- 67 V (11% less) for the sequential pulse technique (p = 0.136). Defibrillation threshold leading edge current for the single pulse technique was 6.7 +/- 2.5 A compared with 5.2 +/- 1.7 A (29% less) for the sequential pulse method (p = 0.005). The defibrillation threshold delivered energy was 5.6 +/- 4.0 J for the single pulse technique and 3.5 +/- 1.8 J (38% less) for the sequential pulse technique (p = 0.021).(ABSTRACT TRUNCATED AT 250 WORDS)

A Model to Evaluate Alternative Methods of Defibrillation Threshold Determination

The voltage (or, equivalently, energy) at which defibrillation occurs for a specific episode of fibrillation can be represented by specifying or estimating the probability of successful defibrillation for each voltage or energy. This relation of voltage to probability is the probability function. For a series of attempts, the probability function predicts the frequency with which defibrillation will occur at a given voltage. By defining the defibrillation threshold (DFT) as the voltage at which the probability function takes on a specific value, say 50%, a method of defibrillation threshold determination can be evaluated by how accurately and precisely it estimates the "true" defibrillation threshold. By utilizing estimated probability functions from animals and humans, the relative performance of different methods of defibrillation threshold determination can be evaluated. Three methods were evaluated using published animal data and human clinical data: (1) stepping down to the first voltage that fails; (2) stepping up to the first voltage that succeeds; and (3) doing both 1 and 2 and averaging. In all cases, Method 3 has lower total error. Definitions of defibrillation threshold other than the 50% level can also be evaluated in this fashion.

Intraoperative comparison of sequential-pulse and single-pulse defibrillation in candidates for automatic implantable defibrillators

Sixteen survivors of cardiac arrest underwent intraoperative comparison of the effectiveness of sequential-pulse and single-pulse defibrillation. Defibrillation was tested alternately with the single-pulse or sequential-pulse technique 10 seconds into an episode of ventricular fibrillation that was induced with alternating current. The sequential-pulse defibrillation technique using truncated exponential pulses was performed with a right ventricular endocardial catheter and a left ventricular epicardial patch electrode. The first pulse was delivered between the right ventricular apical and the superior vena caval electrode on the right ventricular endocardial catheter. The second pulse was delivered between the right ventricular apical electrode and the left ventricular patch electrode 0.2 ms after termination of the first pulse. Single-pulse defibrillation was performed with a standard intracardiac defibrillation system in which a single truncated exponential pulse was delivered across 2 epicardial patch electrodes positioned over the anterolateral right ventricle and the posterolateral left ventricle. During defibrillation threshold determination, voltage and current waveforms were recorded and integrated to determine delivered energy. Average defibrillation threshold leading-edge voltage for the sequential pulse technique was 496 +/- 140 V, compared with 365 +/- 157 V for the single-pulse technique (p less than 0.005). Defibrillation threshold leading-edge current for the sequential-pulse technique was 6.0 +/- 2.3 A, compared with 10.6 +/- 5.1 A for the single-pulse method (p less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)