Improved Nonthoracotomy Defibrillation Based on Ventricular Fibrillation Waveform Characteristics

The heart has been shown to be more susceptible to defibrillation at a higher absolute ventricular fibrillation voltage (AVFV) measured on the surface ECG. This study evaluated in a closed-chest canine model (n = 7) the clinical applicability of using a real-time VF waveform analysis system using an electrogram defined between the generator can and an RV endocardial electrode. Under fluoroscopic guidance, superior vena cava and RV spring coil catheter electrodes were inserted through the external jugular vein. A subcutaneous patch was placed on the left chest. A two-parameter tracking algorithm was used to dynamically identify the high AVFV area, and a biphasic shock was triggered synchronously at the next peak. The performance of this new peak shock method (PSM) was compared to the conventional method of shocking at a fixed time in 175 paired trials. Five shocks per voltage and five voltages per animal were randomized between the two methods to permit the generation of sigmoidal dose response curves for the estimation of 50% (E50), 75% (E75), and 100% (E100) success energies. Induction of VF and discharge voltage were kept constant while energy delivered, impedance (R), and AVFV at the point of shock were measured. Energy (8.63 ± 0.40 vs 8.64 ± 0.40 J), R (48.60 ± 0.30 vs 48.59 ± 0.30 Ω), and current (7.50 ± 0.18 vs 7.51 ± 0.16 A) were not significantly different between trials for either the conventional or the PSM. The time from the onset of VF until the defibrillation shock was 7.98 ± 1.44 seconds. Higher overall successes (46.3% vs 33.1%; P < 0.01) and lower E50, E75, and E100 were observed for the PSM. Finally, the significantly higher AVFV (9.12 ± 0.32 vs 4.73 ± 0.34 mV; P < 0.0001) with the peak method suggests that the high VF voltage could be detected as it occurred in real-time. The improved defibrillation success supports the use of this method for nonthoracotomy defibrillation.     

Genesis of Sigmoidal Dose-Response Curve During Defibrillation by Random Shock: A Theoretical Model Based on Experimental Evidence for a Vulnerable Window During Ventricular Fibrillation

The sigmoidal dose-response curve (percent success vs shock energy) suggests a probabilistic nature of defibrillation. The mechanism is still largely unknown, however, random variation in the excitable state during ventricular fibrillation (VF) is suspected. A canine defibrillation study was designed to determine whether random variation in absolute VF voltage (AVFV) (a crude marker of number of excitable cells) was related to success of defibrillation, using a DC shock successful at the 50% level. The results were: (a) transmyocardial resistance (73.4 +/- 1.4 vs 73.6 +/- 1.5 ohms) and delivered energy (6.1 +/- 1.2 vs 6.2 +/- 1.2 joules) were similar; however, (b) AVFV 2 msec prior to DC shock was greater for successful as compared to unsuccessful attempts (0.5 +/- 0.1 vs 0.3 +/- 0.0 mV, P less than 0.01). A mathematical model was subsequently developed based on fluctuation in the number of excitable cells. Variation in the state of excitability resulted in a cyclic window potentially vulnerable to defibrillation. The vulnerable window occurred at a point when the number of excitable cells was low, i.e., a higher state of total depolarization, which was in agreement with the experimental finding. For a given VF pattern, duration of the vulnerable window was regulated by the shock energy. A larger shock energy generated a wider vulnerable window and, in turn, a higher success rate. Finally, the sigmoidal dose-response curve of defibrillation was theoretically constructed by calculating the variable chances of a random DC shock occurring either in a vulnerable window or elsewhere during VF. It is concluded that a vulnerable window susceptible to defibrillation can be demonstrated in the early stages (10 sec) of VF. The mathematical model provides a theoretical basis for the vulnerable window and helps elucidate the probabilistic nature of defibrillation.     

Identification of Ventricular Tachycardia Using Intracardiac Electrograms: A Comparison of Unipolar Versus Bipolar Waveform Analysis

Implantable antitachycardia devices suffer a high false-positive rate of delivery of therapy because current detection schemes based upon ventricular rate and rate variations are excessively sensitive at the cost of specificity. Several methods have been proposed for providing complementary information derived from morphologic analysis of intraventricular electrograms in order to increase specificity. The majority of these techniques have utilized bipolar electrogram analysis to detect changes in ventricular activation indicative of ventricular tachycardia. Whether bipolar or unipolar intracardiac electrogram analysis might be preferred for discriminating ventricular tachycardia from sinus rhythm has not been determined. In this study, a previously demonstrated method for identification of ventricular tachycardia using intracardiac electrograms, correlation waveform analysis, was used to analyze both unipolar and bipolar signals during sinus rhythm and ventricular tachycardia recorded during electrophysiology studies of 15 patients with inducible sustained monomorphic ventricular tachycardia. Correlation waveform analysis consistently discriminated between all depolarizations during ventricular tachycardia in 14/15 patients (93%) using either electrogram configuration; 13 of the 14 patients were common to both groups. Of these patients, 8/15 (53%) had greater separation between sinus rhythm and ventricular waveforms with bipolar electrogram analysis while 7/15 (47%) had greater separation with unipolar electrogram analysis. We conclude that morphologic analysis of unipolar and bipolar electrograms may be equally effective in distinguishing ventricular tachycardia from sinus rhythm. For individual patients, either a unipolar or bipolar ventricular configuration may be preferable, and should be chosen on a patient-specific basis during electrophysiology study prior to antitachycardia device implantation.     

Transvenous Single Lead Atrial Defibrillation: Efficacy and Risk of Ventricular Fibrillation in an Ischemic Canine Model

Transvenous atrial defibrillation with multiple atrial lead systems has been shown to be effective in models without the potential for ventricular arrhythmias. The specific aim of this study was to evaluate the efficacy and safety of transvenous single lead atrial defibrillation in a canine model of ischemia cardiomyopathy. Ten dogs had ischemia cardiomyopathy induced by repeated intracoronary micmsphere injections. The mean LV ejection fraction decreased from 71%± 9% to 38%± 14% (P = 0.003). Spontaneous atrial fibrillation (AF) developed in four dogs, and in six AF was induced electrically. Atrial defibrillation thresholds (ADFTs) were determined with synchronous low energy shocks using a transvenous tripolar lead with two defibrillation coils (right ventricle, superior vena cava) and an integrated sensing lead (RV coil vs electrode tip). The ADFTs derived by logistic regression were compared at 50% and 90% probability of success (ED₅₀, ED₉₀): ED₅₀ was 2.4 ±1.7 J and 2.9 ±2.1 J, respectively, for 5- and 10-ms monophasic shocks, and 1.8 ± 0.9 J and 2.1 ± 1.3 J, respectively, for 5- and 10-ms biphasic shocks. Immediately after 3 of 2,179 (0.1%) synchronized shocks, ventricular fibrillation (VF) developed. VF was induced in 3 of 1,062 (0.3%) shocks with integrated sensing (RV coil vs electrode tip) compared to 0 of 1,117 shocks when a separate bipolar RV sensing electrode was used for synchronization. In our canine model of ischemic cardiomyopathy, low energy atrial defibrillation via a transvenous single lead system was highly effective. However, there was a small but definite risk of VF induction, which seemed to be greater when an integrated as opposed to a true bipolar RV sensing was used.     

Using the Surface ECG to Identify Right Ventricular Pacing Lead Position: A Cautionary Tale

Chronic right ventricular (RV) apical pacing may lead to the development of heart failure in some patients. Although pacing of the RV septum has been proposed as an alternative, positioning a lead in the true septum has proven challenging. In addition to fluoroscopy at implant, it has been suggested that 12‐lead surface electrocardiogram (ECG) can be used to determine septal lead position; however, studies show this may be inaccurate. We present a case where a change in the ECG QRS axis late after pacemaker insertion with an active fixation lead highlights the difficulties of ECG localization of pacing leads.     

Biphasic Defibrillation Using a Single Capacitor with Large Capacitance: Reduction of Peak Voltages and ICD Device Size

The volume of current implantable cardioverter defibrillators (ICD) is not convenient for pectoral implantation. One way to reduce the size of the pulse generator is to find a more effective defibrillation pulse waveform generated from smaller volume capacitors. In a prospective randomized crossover study we compared the step-down defibrillation threshold (DFT) of a standard biphasic waveform (STD), delivered by two 250-μF capacitors connected in series with an 80% tilt, to an experimental biphasic waveform delivered by a single 450μF capacitor with a 60% tilt. The experimental waveform delivered the same energy with a lower peak voltage and a longer duration (LVLDj. Intraopera-tively, in 25 patients receiving endocardial (n = 12) or endocardial-subcutaneous array (n = 13) defibrillation leads, the DFT was determined for both waveforms. Energy requirements did not differ at DFT for the STD and LVLD waveforms with the low impedance (32 ± 4Ω) endocardial-subcutaneous array defibrillation lead system (6.4 ± 4.4 J and 5.9 ± 4.2 J, respectively) or increased slightly (P - 0.06) with the higher impedance (42 ± 4 Ω) endocardial lead system (10.4 ± 4.6 J and 12.7 ± 5.7 /. respectively), However, the voltage needed at DFT was one-third lower with the LVLD waveform than with the STD waveform for both lead systems (256 ± 85 V vs 154 ± 53 V and 348 ± 76 V vs 232 ± 54 V, respectively). Thus, a single capacitor with a large capacitance can generate a defibrillation pulse with a substantial lower peak voltage requirement without significantly increasing the energy requirements. The volume reduction in using a single capacitor can decrease ICD device size.     

Identification of Ventricular Tachycardia Using Intracavitary Ventricular Electrograms: Analysis of Time and Frequency Domain Patterns

Tachycardia detection by implantable antitachycardia devices using rate alone has major limitations. Several alternative methods have been proposed to distinguish ventricular tachycardia or ventricular fibrillation from normal sinus rhythm using intracardiac electrograms. These methods have not been tested, however, for recognition of ventricular tachycardia in patients with abnormal surface QRS conduction during sinus rhythm or with antiarrhythmic drug therapy. In this study, three techniques for the indentification of ventricular tachycardia from intracavitary bipolar ventricular electrograms were examined and compared: correlation waveform analysis, amplitude distribution analysis, and spectral analysis using Fast Fourier transformation. Thirty episodes of induced monomorphic ventricular tachycardia were analyzed and compared sinus rhythm in four groups of patients with: I. Normal surface QRS conduction during sinus rhythm without antiarrhythmic drug therapy (five episodes); II. Intraventricular conduction delay or bundle branch block during sinus rhythm without antiarrhythmic drug therapy (nine episodes); III. Normal surface QRS conduction during sinus rhythm with antiarrhythmic therapy (six episodes); and IV. Intraventricular conduction delay or bundle branch block during sinus rhythm with antiarrhythmic drug therapy (ten episodes). Correlation waveform analysis had 100% sensitivity and specificity in distinguishing ventricular tachycardia from sinus rhythm, even in the presence of an intraventricular conduction delay, bundle branch block, and antiarrhythmic drug therapy. In contrast, amplitude distribution analysis differentiated 15/30 episodes (50.0%) of ventricular tachycardia from sinus rhythm, and a maximum of 18/30 episodes (60.0%) of ventricular tachycardia were identified by specal analysis using Fast Fourier transformation. Correlation waveform analysis appears to be a reliable technique to discriminate ventricular tachycardia from sinus rhythm using intracavitary ventricular electrograms. Its computational demands are modest, making it suitable for consideration in an implantable antitachycardia device.     

Detection of Atrial Activation By Intraventricular Electrogram Morphology Analysis: A Study to Determine the Feasibility of P Wave Synchronous Pacing From a Standard Ventricular Lead

The detection of atrial activation from a standard ventricular pacing lead with standard ventricular electrodes would provide patients with VVI and VVIR pacing systems atrial rate response and atrial synchrony. In addition to potentially increasing cardiac output appropriately in these patients at rest and during moderate exercise, P wave sensing with such a device could help reduce pacemaker syndrome. In this study, unipolar signals from distal and proximal intraventricular electrodes were recorded from the right ventricular apex in 20 patients. Unipolar eJectrograms from 16 patients were recorded using temporary electrophysiology catheters and in four patients using permanent pacemaker leads. Approximately 3 minutes of data per patient were acquired and analyzed. After selection of a P wave template, the difference in baseline normalized area between the template and signal was calculated on a point-by-point basis. The percent of atrial depolarizations correctly detected was determined for each patient and lead configuration at the optimal threshold. Far-field P wave accuracy was better at the proximal electrode (74 ± 25%) than at the distal electrode (57 ± 34%) (P < 0.025). At the proximal electrode, 15/20 (75%) patients had > 70% accuracy and 11/20 (55%) patients had > 80% accuracy. At the distal electrode, 10/21 (48%) patients had > 70% accuracy and 7/21 (33%) patients had > 80% accuracy. In conclusion, far-field detection of atrial activation at the ventricular proximal electrode appears possible with sufficient accuracy to provide periods of atrial rate response and synchrony in patients with a single standard lead.     

Separation of Ventricular Tachycardia From Sinus Rhythm Using a Practical, Real-Time Template Matching Computer System

Template matching morphology analysis of the infra-ventricular electrogram (IVEG) has been proposed for inclusion in implantable cardioverter defibrillators (ICDs) to reduce the number of false ventricular tachyarrhythmia detections caused by rate overlap between ventricular tachycardia (VT) and sinus tachycardia and for supraventricular tachycardia. Template matching techniques have been developed that reduce the computational complexity while preserving the perceived important aspects of electrogram amplitude and baseline independence found in such computationally unsolved methods as correlation waveform analysis (CWA). These methods have been shown to work as well as CWA for separation of VT, however, they have not been proven in real-time on a system that incorporates many of the constraints of present day ICDs. The present study was undertaken with two purposes: (1) to determine if real-time IVEG template matching analysis on an ICD sensing emulator was accurate in separating VT from sinus rhythm (SR) electrograms; and (2) to compare amplitude normalized area of difference (NAD) with signature analysis (SIG), a new, computationally less expensive technique that normalizes for amplitude variation within the expected physiological level of variability. In this study, JVEGs, obtained from 16 patients who underwent electrophysiological study (EPS) for evaluation of sustained ventricular arrhythmia, were digitized to 250 Hz with 6-bit quantization after filtering (16-44 Hz) and differentiation. After an SR template was selected and periodically updated, it was compared to subsequent IVEGs using NAD and SIG. In general, SIG calculates the fraction of samples occurring outside template window boundaries. Eleven-beat running medians from beat-by-beat NAD and SIG results were determined. The maximum median during VT was subtracted from the minimum median during SR with the result equal to the separation margin. With the minimum separation threshold set to 0 (i.e., no overlap), 0.1, and 0.2, NAD separated 16/16, 14/16, and 9/16 VTs, while SIG separated 15/16, 14/16, and 13/16 VTs, respectively. While NAD separated more VT episodes on the strict basis of no overlap, SIG separated more than NAD as the safety margin was further increased. Conclusions: (1) template matching morphology techniques can potentially be implemented in ICDs; (2) using a patient specific threshold, NAD and SIG appear capable of separating VTfrom SR in most patients; and (3) SIG and NAD appear to be similar in accuracy. Thus, SIG may be preferable since it significantly reduces the computational load.     

Sixteen Failures in a Single Model of Bipolar Polyurethane-insulated Ventricular Pacing Lead: A 44-Month Experience

During a 44-month period, 105 Medtronic model 6972-58 polyurethane-insulated, bipolar ventricular pacing leads were implanted, of which 16 failed clinically at a mean of 20.5 months post-implant. Pacing dysfunction presented as either intermittent or complete loss of sensing and/or capture and, rarely, oversensing. Thirteen of the 16 patients were asymptomatic, and problems were detected in 11 instances during routine telephonic surveillance. At the time of lead replacement, low or widely fluctuating lead resistance values and high current drain were uniformly observed. The single lead capable of total extraction revealed rupture of both internal and external insulation. A brief summary of the currently much-discussed "polyurethane controversy" is presented, and the issue of patient management is discussed.     

A Critical Appraisal of Quantitative Spectro-Temporal Analysis of the Signal-Averaged ECG: Predicting Arrhythmic Events After Myocardial Infarction

The objective of this study was to determine if spectra-temporal analysis of the signal-averaged ECG (SAECG) predicts spontaneous sustained ventricular tachyarrhythmias and sudden death in patients prospectively followed after myocardial infarction (MI). A SAECG was recorded in 177 patients 9 ± 5 days after MI. Spectro-temporal analysis of the SAECG involved incrementing a Hanning window every 3 ms beginning 20 ms before the end of the QRS complex and extending into the ST segment. Quantitative analysis was performed using a cross-correlation function to create a normality factor. A normality factor < 0.3 was deemed abnormal. The SAECG was abnormal in 41 % of patients using time-domain analysis and 44% of patients using spectra-temporal analysis. There was no correlation between an abnormal SAECG in the time domain and the frequency domain. Patients with inferior wall MI were more likely to have an abnormal spectra-temporal map (odds ratio 2.26, P < 0.05). Time-domain analysis of the SAECG (relative risk (RE) 2.6) was a statistically significant univariate predictor of arrhythmic events. Spectra-temporal analysis of the SAECG was only weakly (RR 1.8) and not significantly (P = 0.15) associated with the spontaneous occurrence of these arrhythmias. When both time-domain analysis and spectra-temporal analysis of the SAECG were abnormal, the relative risk for an arrhythmic event was increased by 3.3-fold. Quantitative spectra-temporal analysis of high frequency signals within the SAECG cannot by itself predict the occurrence of spontaneous ventricular arrhythmias in patients after MI.     

Paroxysmal Bundle Branch Block of Supraventricular Origin: A Possible Source of Misdiagnosis in Detecting Ventricular Tachycardia Using Time Domain Analyses of Intraventricular Electrograms

Current implantable antitachycardia devices use several methods for differentiating sinus rhythm (SR) from supraventricular tachycardia (SVT) or ventricular tachycardia (VT). These methods include sustained high rate, the rate of onset, changes in cycle length, and sudden onset. Additional methods for detecting VT include techniques based upon ventricular electrogram morphology. The morphological approach is based on the assumption that the direction of cardiac activation, as sensed by a bipolar electrode in the ventricle, is different when the patient is in SR as compared to VT. Whether paroxysmal bundle branch block of supraventricular origin (BBB) can be differentiated from VT has not been determined. In this study, we compared the morphology of the ventricular electrogram during sinus rhythm with a normal QRS (SRNIQRS) or SVT with a normal QRS (SVTNIQRS) with the morphologies of BBB and VT in 30 patients undergoing cardiac electrophysiology studies. Changes in ventricular electrogram morphology were determined using three previously proposed time domain methods for VT detection: Correlation Waveform Analysis (CWA), Area of Difference (AD), and Amplitude Distribution Analysis (ADA). CWA, AD, and ADA distinguished VT from SRNIQRS or SVTNIQRS in 16/17 (94%), 14/17 (82%), and 12/17 (71%) patients, and BBB from SRNIQRS or SVTNIQRS in 15/15 (100%), 13/15 (87%), and 6/15 (40%) patients, respectively. However, the ranges of values during BBB using these methods overlapped with ranges of values during VT in all cases for CWA, AD, and ADA. Hence, BBB may be a source of misdiagnosis in detecting VT when these time domain methods are used for ventricular electrogram analysis.     

Ventricular fibrillation waveform characteristics differ according to the presence of a previous myocardial infarction: A surface ECG study in ICD-patients

BackgroundCharacteristics of the ventricular fibrillation (VF) waveform reflect arrest duration and have been incorporated in studies on algorithms to guide resuscitative interventions. Findings in animals indicate that VF characteristics are also affected by the presence of a previous myocardial infarction (MI). As studies in humans are scarce, we assessed the impact of a previous MI on VF characteristics in ICD-patients.MethodsProspective cohort of ICD-patients (n = 190) with defibrillation testing at the Radboudumc (2010–2013). VF characteristics of the 12-lead surface ECG were compared between three groups: patients without a history of MI (n = 88), with a previous anterior (n = 47) and a previous inferior MI (n = 55).ResultsAs compared to each of the other groups, the mean amplitude and amplitude spectrum area were lower, for an anterior MI in lead V3 and for an inferior MI in leads II and aVF. Across the three groups, the bandwidth was broader in the leads corresponding with the infarct localisation. In contrast, the dominant and median frequencies only differed between previous anterior MI and no history of MI, being lower in the former.ConclusionsThe VF waveform is affected by the presence of a previous MI. Amplitude-related measures were lower and VF was less organised in the ECG-lead(s) adjacent to the area of infarction. Although VF characteristics of the surface ECG have so far primarily been considered a proxy for arrest duration and metabolic state, our findings question this paradigm and may provide additional insights into the future potential of VF-guided resuscitative interventions.     

Retromammary Implantation of an ICD Using a Single Lead System: An Alternative Approach to Pectoral Implantation in Women

Pectoral ICD implantation, although feasible with the release of smaller devices, can be cosmetically disturbing to some patients due to the device protruding under the skin. An ICD was implanted using the retromammary approach in a 25-year-old female patient. Retromammary implantation of an ICD is feasible and offers an alternative approach in women.     

Impact of Image Integration on Catheter Ablation for Atrial Fibrillation Using Three‐Dimensional Electroanatomic Mapping: A Meta‐Analysis

Background: Studies comparing the procedural and clinical outcomes of catheter ablation for atrial fibrillation (AF) guided by CartoMerge and that by Carto have achieved mixed results (Carto, Biosense Webster, Diamond Bar, CA, USA). We collected these studies and conducted a meta‐analysis to determine whether CartoMerge results in better procedural and clinical outcomes. Methods and Results: Three randomized controlled trials and two controlled observational studies were collected for analysis. The clinical and procedural outcomes of interest were AF recurrence after catheter ablation, major complications, procedure durations, and fluoroscopy time. Meta‐analysis was performed using RevMan 5.0.18 software (The Cochrane Collaboration, Copenhagen, Denmark) and pooled estimates of effect were reported as risk ratios with 95% confidence intervals (CI). The overall results of this meta‐analysis indicate that catheter ablation for AF guided by CartoMerge is insignificantly associated with a decreased risk of recurrences (RR = 0.76; 95% CI: 0.55–1.04; P = 0.09) and major complications (RR = 0.73; 95% CI: 0.37–1.45; P = 0.37) compared with that by Carto. Conclusion: The image integration using CartoMerge guiding catheter ablation for AF does not improve the main clinical outcomes significantly compared with that by Carto in centers with experienced operators. (PACE 2012; 35:1242–1247)     

Influence of Pulse Oximetry and Capnography on Time to Diagnosis of Critical Incidents in Anesthesia: A Pilot Study Using a Full-Scale Patient Simulator

Objective. Many studies (outcome, epidemiological) have tested the hypothesis that pulse oximetry and capnography affect the outcome of anesthetic care. Uncontrollable variables in clinical studies make it difficult to generate statistically conclusive data. In the present study, we eliminated the variability among patients and operative procedures by using a full-scale patient simulator. We tested the hypothesis that pulse oximetry and capnography shorten the time to diagnosis of critical incidents. Methods. A simulator was programmed to represent a patient undergoing medullary nailing of a fractured femur under general anesthesia and suffering either malignant hyperthermia, a pneumothorax, a pulmonary embolism or an anoxic oxygen supply. One hundred thirteen anesthesiologists were randomly assigned to one of two groups of equal size, one with access to pulse oximetry and capnography data and the other without. Each anesthesiologist was further randomized to one of the four critical incidents. Each anesthetic procedure was videotaped. The time to correct diagnosis was measured and analyzed. Results. Based on analysis of 91 of the subjects, time to diagnosis was significantly shorter (median of 432 s vs. >480 s) for the anoxic oxygen supply scenario (p = 0.019) with pulse oximetry and capnography than without. No statistical difference in time to diagnosis was obtained between groups for the other three critical incidents. Conclusions. Simulation may offer new approaches to the study of monitoring technology. However, the limitations of current simulators and the resources required to perform simulator-based research are impediments to wide-spread use of this tool.