Detection of Pathological Tachycardia by Analysis of Electrogram Morphology

Pacemaker recognition of pathological tachycardia relies on heart rate analysis. This can lead to misdiagnosis when sinus tachycardia exceeds the preset tachycardia response trigger rate. We have explored a method for automatic tachycardia diagnosis by analysis of bipolar endocardial electrogram morphology. Electrograms were recorded from 11 patients (pts) during sinus rhythm and during a total of 20 abnormal rhythms: retrograde atrial depolarization from ventricular pacing in six patients; atrioventricular reentry tachycardia in five patients with intermittent left bundle branch block in one of those; AV nodal reentry tachycardia in five patients and ventricular tachycardia in three patients. Posture and respiration were varied during all rhythms except ventricular tachycardia. The electrograms were then digitized and converted to a form in which the amplitudes were proportional to the rates of change of the original electrogram (equivalent to a first time derivative); the derived signal was then analyzed by a new gradient pattern detection (GPD) program. Analysis of the processed atrial signals by GPD resulted in automatic recognition of abnormal rhythms from sinus rhythm in all cases except for one patient's retrograde atrial depolarization. At the ventricular level, GPD successfully distinguished all abnormal rhythms from sinus rhythm including recognition of left bundle branch block and varying degrees of preexcitation. Respiratory and postural variation did not affect the recognition process. We conclude that electrogram GPD has successfully and automatically detected a variety of arrhythmias which can be treated by implantable pulse generators and may, therefore, be a useful adjunct to heart rate analysis in future generations of such antitachycardia pacemakers.     

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.     

A Prospective Study of Right Ventricular Pulse Pressure and dP/dt to Discriminant-Induced Ventricular Tachycardia from Supraventricular and Sinus Tachycardia in Man

In the future, automatic implantable cardioverter defibrillators (AICD) may incorporate sensors to differentiate hemodynamically stable from unstable ventricular tachycardias (VT). These sensors should also discriminate between ventricular and supraventricular tachycardias to avoid inappropriate responses from the device. Right ventricular pulse pressure (RVPP) and maximal systolic right ventricular dP/dt (dP/dt) were measured before, during and after 91 episodes of hemodynamically stable VT (VTs), hemodynamically unstable VT (VTus), supraventricular tachycardia (SVT) and sinus tachycardia (ST) induced in 49 male patients. The mean percent changes (mean +/- S.E.M.) in RVPP from baseline (% delta RVPP) during VTs and VTus were -35 +/- 3% and -72 +/- 3%, respectively (both P less than 0.001). The % delta RVPP during ST was +56 +/- 11% (P less than 0.01) and % delta RVPP was unchanged from baseline during SVT (+2 +/- 9%; P greater than 0.01). Mean % change in RV dP/dt from baseline was -20 +/- 3% during VTs (P less than 0.001), -36 +/- 5% during VTus (P less than 0.001), +15 +/- 13% during SVT (P less than 0.01), and +85 +/- 23% during ST (P greater than 0.01). The mean percent changes in RVPP were significantly different between each arrhythmia group (P less than 0.01). The mean % changes in RV dP/dt were significantly different only between ST and VTs or VTus and between SVT and VTus. The range of values for % delta RVPP during VTs overlapped considerably with the ranges of % delta RVPP during VTus and SVT. The ranges of % delta RVPP overlapped minimally between VTus and SVT. Percent change RVPP separated each episode of VTs and VTus from those of ST. The range of common values for % delta dP/dt between all four groups was extensive. It is concluded that % delta RVPP from baseline is significantly different between groups of patients during VTs, VTus, SVT, and ST, but that a large degree of overlap in the range of values for % delta RVPP and RV dP/dt between different arrhythmias groups may limit the specificity of these hemodynamic variables in separating different arrhythmias.     

Intraventricular Electrogram Analysis for Ventricular Tachycardia Detection: Statistical Validation

THRONE, R.D., ET AL.: Intraventricular Electrogram Analysis for Ventricular Tachycardia Detection: Statistical Validation. Time-domain analysis of intraventricular electrogram morphology during ventricular tachycardia (VT) and sinus rhythm or atrial fibrillation (SR/AF) has been proposed as a method for increasing the specificity of pathological tachycardia detection by antitachycardia devices. However, few studies have validated the use of such analysis with statistical methods. When statistical methods have been utilized, it has been assumed that the distribution of the values derived from analysis of the intracardiac electrograms have had a normal (gaussian) distribution. In this study, we sought to determine whether: (1) the distribution of values derived from analysis of intracardiac electrogram during SR/AF and VT is gaussian or nongaussian; and (2) the discrimination of monomorphic VT from SR/AF using SR/AF templates can be validated statistically. Two previously proposed time-domain methods—correlation waveform analysis (CWA) and area of difference (AD)—were selected for evaluation of 29 patients with 33 distinct, sustained monomorphic VTs. An initial SR/AF template was used to analyze subsequent SR/AF and VT passages with a minimum of 50 consecutive depolarizations using a “best-fit” alignment. The values derived from each analysis were examined subsequently for skewness (asymmetry) and kurtosis (shape) using two-tailed tests (p < 0.02). For passages of SR/AF, a normal (gaussian) distribution was present in only 24% (CWA), and 45% (AD); for passages of VT, normal distribution was present in only 58% for both CWA and AD. Using appropriate statistical testing with nonparametric tolerance intervals, CWA and AD discriminated VT from SR/AF in 29 out of 33 (88%), and 30 out of 33 (91%) instances, respectively, with 95% confidence. Thus, the assumption of a gaussian distribution for values derived from time-domain analysis of intraventricular electrograms for VT detection is not uniformly valid. Both CWA, which is independent of both baseline and amplitude fluctuations, and AD, which is not independent of these fluctuations, have similar performance when validated with appropriate statistical methods.     

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.     

Ventricular Tachycardia Detection Using Bipolar Electrogram Analysis is Site Specific

While algorithms for bipolar intraventricular electrogram analysis have potential use in complementing rate criteria for ventricular tachycardia (VT) detection by implantable antitachycardia devices, the sensitivity of such algorithms to the intracavitary site of electrogram detection has not been determined. In this study, unfiltered (1-500 Hz) electrograms were recorded from a bipolar electrode catheter initially positioned at the right ventricular (RV) apex (site 1) of 12 patients during sinus rhythm (SRI) and during induced monomorphic VT (VTI). Sinus rhythm (SR2) and the identical VT (VT2) were recorded a second time after repositioning the same electrode catheter within the RV apex (site 2) 7-44 mm (mean ± SD = 15 ± W) from its original site. The data were digitized at 1,000 Hz. Templates from SRI and SR2, respectively, were compared subsequently with individual intraventricular electrograms from 15-25 sec passages of SRI and VTI and SR2 and VT2, respectively, using correlation waveform analysis. At site 1, the mean patient correlation coefficient ranged from 0.982-0.998 during SRI and 0.062-0.975 during VTI. At site 2, the mean patient correlation coefficient ranged from 0.995-0.998 during SR2 and 0.113-0.983 during VT2. Using a correlation threshold of 0.9, VT was differentiated from SR in 11/12 patients (91%) overall: 8/12 patients (67%) at site 1, 9/12 patients (75%) at site 2, and 6/12 patients (50%) at both sites. Thus, while discrimination of VT from SR is feasible with morphological analysis of bipolar right ventricular intracavitary electrograms, the accuracy of bipolar intraventricular electrogram analysis may depend upon intracavitary electrode location in selected patients.     

Treatment of Out-of-hospital Supraventricular Tachycardia: Adenosine vs Verapamil

Objective: To compare the use of adenosine and the use of verapamil as out-of-hospital therapy for supraventricular tachycardia (SVT). Methods: A period of prospective adenosine use (March 1993 to February 1994) was compared with a historical control period of verapamil use (March 1990 to February 1991) for SVT. Data were obtained for SVT patients treated in a metropolitan, fire-department-based paramedic system serving a population of approximately 1 million persons. Standard drug protocols were used and patient outcomes (i.e., conversion rates, complications, and recurrences) were monitored. Results: During the adenosine treatment period, 105 patients had SVT; 87 (83%) received adenosine, of whom 60(69%) converted to a sinus rhythm (SR). Vagal maneuvers (VM) resulted in restoration of SR in 8 patients (7.6%). Some patients received adenosine for non-SVT rhythms: 7 sinus tachycardia, 18 atrial fibrillation, 7 wide-complex tachycardia (WCT), and 2 ventricular tachycardia; no non-SVT rhythm converted to SR and none of these patients experienced an adverse effect. Twenty-five patients were hemodynamically unstable (systolic blood pressure < 90 mm Hg), with 20 receiving drug and 13 converting to SR; 8 patients required electrical cardioversion. Four patients experienced adverse effects related to adenosine (chest pain, dyspnea, prolonged bradycardia, and ventricular tachycardia). In the verapamil period, 106 patients had SVT; 52 (49%) received verapamil (p < 0.001, compared with the adenosine period), of whom 43 (88%) converted to SR (p = 0.11). Two patients received verapamil for WCT; neither converted to SR and both experienced cardiovascular collapse. VM resulted in restoration of SR in 12 patients (11.0%) (p = 0.52). Sixteen patients were hemodynamically unstable, with 5 receiving drug (p = 0.005) and 5 converting to SR; 9 patients required electrical cardioversion (p = 0.48). Four patients experienced adverse effects related to verapamil (hypotension, ventricular tachycardia, ventricular fibrillation). Recurrence of SVT was noted in 2 adenosine patients and 2 verapamil patients in the out-of-hospital setting and in 23 adenosine patients and 15 verapamil patients after ED arrival, necessitating additional therapy (p = 0.48 and 0.88, for recurrence rates and types of additional merapies, respectively). Hospital diagnoses, outcomes, and ED dispositions were similar for the 2 groups. Conclusion: Adenosine and verapamil were equally successful in converting out-of-hospital SVT in patients with similar etiologies responsible for the SVT. Recurrence of SVT occurred at similar rates for the 2 medications. Rhythm misidentification remains a common issue in out-of-hospital cardiac care in this emergency medical services system.     

Electrophysiologic studies of patients with hypertrophic cardiomyopathy presenting with syncope of undetermined etiology

Patients with hypertrophic cardiomyopathy (HC) have a high risk of sudden death. The best clinical predictors of sudden death from HC are young age, strong family history of sudden death, ventricular tachycardia (VT), and progression of symptoms such as syncope. We performed 24-hour Holter monitoring and electrophysiologic studies (EPS) on 26 patients with HC, some with the obstructive form of the disease and some with syncope, in order to predict their vulnerability to syncope and to potentially malignant arrhythmias. Holter monitoring demonstrated supraventricular tachycardia (SVT) in 9/26 patients whereas atrial programmed electrical stimulation induced SVT in 17/26 patients. Of the 17 patients, nine had symptomatic hypotension with SVT while lying supine. Holter monitoring demonstrated nonsustained VT in 7/26 patients whereas ventricular programmed electrical stimulation induced VT or ventricular fibrillation (VF) in 6/26 patients. The patient who had the longest run of nonsustained VT on Holter had VF induced by ventricular programmed electrical stimulation. He was cardioverted to normal sinus rhythm with no untoward effects. We found that atrial programmed electrical stimulation induced SVT with hypotension best predicted a history of syncope in these patients. Although one patient required direct current cardioversion, EPS was conducted safely in all patients. Further long-term studies are needed to demonstrate the value of clinical decisions based upon EPS in patients with HC.     

A Time-Domain Analysis of Intracardiac Electrograms for Arrhythmia Detection

The analysis of intracardiac electrogram morphology has been proposed as a complementary method for accurate discrimination between sinus rhythm (SR), supraventricular dysrhythmias, and ventricular dysrhythmias by automatic antitachycardia and cardioverter defibrillator devices. In this study, the performance of a traditional time-domain method for surface electrocardiogram interpretation—Correlation Waveform Analysis (CWA) and a newly developed technique—Bin Area Method (BAM) were used to analyze unfiltered intraatrial and intraventricular electrograms obtained from 47 patients during routine cardiac electrophysiology studies. Nineteen patients had 31 distinct, sustained, monomorphic ventricular tachycardias (VTs) induced; 13 patients had paroxysmal bundle branch block of supraventricular origin (BBB) induced; 19 patients had retrograde atrial activation during ventricular overdrive pacing. Three patients were common to two or more groups. Using a best fit electrogram alignment, both CWA and BAM distinguished VT from SR in 28/31 cases (90%), BBB from SR in 15/15 patients (100%), and anterograde from retrograde atrial activation in 19/19 patients (100%J. We conclude that the use of time-domain techniques that are independent of amplitude and baseline fluctuations appear to be reliable for discrimination of retrograde atrial activation, paroxysmal BBB, and VT from SR using intracardiac electrograms. Reduction of computational time and power constraints, without sacrificing reliable dysrhythmia discrimination, is possible. These features may make real-time morphology analysis of intracardiac electrograms feasible for automatic antitachycardia and cardioverter-defibrillator devices.     

Impact of Filtering Upon Ventricular Tachycardia Identification by Correlation Waveform Analysis

Signal analysis of digitized waveforms has been postulated as a method for improving sensitivity and specificity of ventricular tachycardia (VTJ detection in implantable antitachycardia devices. Such improvement may alleviate the problem of unwarranted delivery of therapy by adding precision to the identification of the pathological VT. Morphological analysis could also allow distinct therapies to be initialized for multiple VTs in the same patient. Correlation waveform analysis (CWA) has been demon-struted to be effective in separating benign rhythms from VT in wideband recordings (1–500 Hz) but the effect of filtering has not been previously examined. Bipolar (1 cm) intraventricular recordings (1–500 Hz) of sinus rhythm (SR) and 25 distinct VTs in 18 patients were analyzed by CWA using a signal-averaged SR template. Passages contained 65.9 ± 19.8 VT depolarizations (range 45–108). Digital filtering was performed on all data passages with varying passbands. Results for passages with a bandwidth of 1–250 Hz were equivalent to wideband results, i.e., ≥92% paired sets of SR and VT were separable at a 95% confidence level. A bandwidth of 1–100 Hz decreased discrimination to 84%. At a bandwidth of 1–80 Hz, 80% of cases were successfully separated, but at 10–80 Hz these results improved to 88%. Bandwidths of 20–80 and 30–80 Hz reduced reliability of CWA performance to 72% and 60%, respectively. Filtering at typical pace-maker/defibrillator passbands produced morphological analysis results equivalent to those yielded at wideband settings. Differences in the range between SR versus VT decreased in filtered recordings but overall detection of VT was not degraded.     

The Bin Area Method: A Computationally Efficient Technique for Analysis of Ventricular and Atrial Intracardiac Electrograms

Recent studies have reported a significant false positive rate in delivery of therapy by implantable antitachycardia devices utilizing detection algorithms based on sustained high rate. More selective decision schemes for the recognition of life-threatening arrhythmias have been recently proposed that use analysis of the intrinsic electrogram rather than rate alone. Morphological discrimination of abnormal electrograms using correlation waveform analysis (CWA) has been proposed as an effective method of intracardiac electrogram analysis, but its computational demands limit its use in implantable devices. A new method for intracardiac electrogram analysis, the bin area method (BAM), was created to detect abnormal cardiac conduction with computational requirements of one-half to one-tenth those of CWA. Like CWA, BAM is a template matching method that is sensitive to conduction changes revealed in the electrogram morphology and is independent of amplitude and baseline fluctuations. Performance of BAM and CWA were compared using bipolar right ventricular and right atrial electrode recordings from 47 patients undergoing clinical cardiac electrophysiology studies. Nineteen patients had 31 distinct monomorphic ventricular tachycardias (VTs) induced (group I), thirteen patients had paroxysmal bundle branch block of supraventricular origin (BBB) induced (group II), and 19 patients had retrograde atrial activation during right ventricular overdrive pacing (group III). (One patient was common to all three groups, and two patients were common to groups II and III.) Using the ventricular electrogram, both BAM and CWA distinguished VT from sinus rhythm in 28/31 (90%) cases, and BBB from Normal Sinus Rhythm (NSR) in 13/13 (100%) patients. Using the atrial electrogram, both BAM and CWA distinguished anterograde from retrograde atrial activation in 19/19 (100%) patients. BAM achieves similar performance to CWA with significantly reduced computational demands, and may make real-time analysis of intracardiac electrograms feasible for implantable pacemakers and antitachycardia devices.     

Do Traditional VT Zones Improve Outcome in Primary Prevention ICD Patients?

Aims: We reviewed outcomes in our primary prevention implantable cardioverter defibrillator (ICD) population according to whether the device was programmed with a single ventricular fibrillation (VF) zone or with two zones including a ventricular tachycardia (VT) zone in addition to a VF zone. Methods: This retrospective study examined 137 patients with primary prevention ICDs implanted at our institution between 2004 and 2006. Device programming and events during follow‐up were reviewed. Outcomes included all‐cause mortality, time to first shock, and incidence of shocks. Results: Eighty‐seven ICDs were programmed with a single VF zone (mean >193 ± 1 beats per minute [bpm]) comprising shocks only. Fifty ICDs had two zones (mean VT zone >171 ± 2 bpm; VF zone >205 ± 2 bpm), comprising antitachycardia pacing (100%), shocks (96%), and supraventricular (SVT) discriminators (98%) . Discriminator “time out” functions were disabled. Mean follow‐up was 30 ± 0.5 months and similar in both groups. All‐cause mortality (12.6% and 12.0%) and time to first shock were similar. However, the two‐zone group received more shocks (32.0% vs 13.8% P = 0.01). Five of 16 shocks in these patients were inappropriate for SVT rhythms. The single‐zone group had no inappropriate shocks for SVTs. Eighteen of 21 appropriate shocks were for ventricular arrhythmias at rates >200 bpm (three VF, 15 VT). This suggests that primary prevention ICD patients infrequently suffer ventricular arrhythmias at rates <200 bpm and that ATP may play a role in terminating rapid VTs. Conclusions: Patients with two‐zone devices received more shocks without any mortality benefit. (PACE 2010; 1353–1358)     

Analysis during Sinus Rhythm and Ventricular Pacing of Reentry Circuit Isthmus Sites in Right Ventricular Cardiomyopathy

Background: The entrainment mapping algorithm is used for ablation of ventricular tachycardia (VT) in right ventricular (RV) cardiomyopathy, but ablation at endocardial isthmus sites has only a moderate success rate. This study was performed to identify additional local electrogram characteristics associated with successful ablation. Patients and Methods: Using entrainment mapping, 45 reentry circuit isthmus sites were detected in 11 patients with RV cardiomyopathy presenting with 13 monomorphic VTs. Local bipolar electrograms were retrospectively analyzed at reentry circuit isthmus sites during VT, sinus rhythm, and programmed stimulation from the right ventricular apex (RVA), and compared between successful and unsuccessful ablation sites. Results: Ablation was successful at 10 reentry circuit isthmus sites and unsuccessful at 35 isthmus sites. During VT, a longer endocardial activation time relative to QRS onset, an increased electrogram‐QRS interval as a percentage of VT cycle length, and a longer electrogram duration were found at successful in comparison to unsuccessful ablation sites. The presence of isolated diastolic potentials during sinus rhythm at reentry circuit isthmus sites, consistent with slow conduction or unidirectional conduction block, was associated with successful catheter ablation. Prolongation of the duration of the local multipotential electrogram by >100 ms during programmed RVA pacing at reentry circuit exit sites, indicating functional conduction disorder was also a marker of successful ablation. Conclusions: The demonstration of multipotential electrogram characteristics indicating fixed or functional conduction block may increase the likelihood of successful VT ablation at exit and central isthmus sites of reentry circuits in RV cardiomyopathy.     

Resuscitation in the hospital: relationship of year and rhythm to outcome

OBJECTIVE: determine the frequency of initial rhythms in in-hospital resuscitation and examine its relationship to survival. Assess changes in outcome over time. METHODS: retrospective cohort (registry) including all admissions to the Medical Center of Central Georgia in which a resuscitation was attempted between 1 January, 1987 and 31 December, 1996. RESULTS: the registry includes 3327 admissions in which 3926 resuscitations were attempted. Only the first event is reported. There were 961 hospital survivors. Survival increased from 24.2% in 1987 to 33.4% in 1996 (chi(2)=39.0, df=1, P<0.0001). Survival was affected strongly by initial rhythm (chi(2)=420.0, df=1, P<0.0001) and decreased from 63.2% for supraventricular tachycardia (SVT) to 55.3% for ventricular tachycardia (VT), 51.0% for perfusing rhythms (PER), 34.8% for ventricular fibrillation (VF), 14.3% for pulseless electrical activity (PEA) and 10.0% for asystole (ASYS). PEA was the most frequent rhythm (1180 cases) followed by perfusing (963), asystole (580), VF (459), VT (94) and SVT (38). DISCUSSION: the powerful effect of initial rhythm on survival has been reported in pre-hospital and in-hospital resuscitation. VF is considered the dominant rhythm and generally accounts for the most survivors. We report good outcome for each; however, VF represents only 13.8% of events and 16.7% of survivors. PEA accounts for more survivors (169) than does VF (160). Our improved outcome is partially explained by changes in rhythms, but other institutional variables need to be identified to fully explain the results. Further studies are needed to see if our findings can be sustained or replicated.     

Activation of the Right Ventricular Apical Electrogram during Ventricular Tachycardia: Suitahility for Synchronizing Intracavitary Cardioversion

An intravascular catheter positioned in the right ventricular apex has been used for intracavitary cardioversion in patients with recurrent ventricular tachycardia. We examined the timing of the right ventricular apical electrogram during sinus rhythm and ventricular tachycardia (VT) in order to determine if this signal could be used to synchronize the delivery of a countershock. Sixty-three distinct morphologies of VT were observed in 33 patients undergoing electrophysiologic testing with programmed stimulation. Regardless of VT morphology or site of origin, the bipolar right ventricular electrogram always occurred within the peripheral QRS complex during ventricular tachycardia. Relative timing occurred within the QRS ranging from the initial 13% of the QRS to the last 12%. When all episodes of VT were examined, the timing of the right ventricular electrogram did not correlate linearly with the peak of the ECG, but the right ventricular electrogram occurred within 60 ms of the peak ECG in 83% of episodes of ventricular tachycardia. In one case of arrhythmogenic right ventricular dysplasia, the right ventricular electrogram occurred 160 ms after the peak ECG in ventricular tachycardia, a time when delivery of a countershock may have precipitated ventricular fibrillation. Six of these patients underwent cardioversion utilizing an intracavitary catheter and external generator. Acceleration of VT, or conversion to ventricular fibrillation, occurred following two of 27 shocks (7.4%). The right ventricular electrogram occurred the latest within the QRS complex in the two patients who developed acceleration of the tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis of the Intraventricular Electrogram for Differentiation of Distinct Monomorphic Ventricular Arrhythmias

This study investigated the effectiveness of correlation waveform analysis for identifying different ventricular electrogram morphologies of multiple VTs in the same patient. Patients with implantable antitachycardia devices are commonly subject to the occurrence of more than one distinct monomorphic VT. Each of these VTs may have unique therapeutic alternatives for termination. VTs with identical and different monomorphic configurations were recorded (1–500 Hz) using distal bipolar (1 cm) and distal unipolar electrograms from the right ventricular apex. Thirty-six distinct monomorphic VTs induced in 15 patients were analyzed. Nine VTs with identical morphologies (12/12 surface ECGs) were induced twice and used as a control. A template was created for each VT induced. Correlation waveform analysis was used to compare eacb depolarization of all other VTs induced subsequently in tbe same patient. The mean correlation coefficient (pμ) of cycle-by-cycle analysis was used as a discriminant function: pμ≥ 0.95 was considered matched; and pμ < 0.95 was considered distinct. From the control population, VTs were successfully classified as identical in 9 of 9 cases (100%) using both bipolar and unipolar electrograms. VTs with different monomorphic configurations were successfully classified as being different in 31 of 33 cases (94%) using bipolar electrogram analysis and in 29 of 33 cases (88%) using the unipolar. Template matcbing is effective for detecting: (1) the recurrence of VTs, which are identical; and (2) the occurrence of a VT with a different configuration. This method appears effective using either unipolar or bipolar intracardiac waveforms.     

Dissociation of the site of origin from the site of cryo-termination of ventricular tachycardia

We performed conventional electrogram mapping and cryomapping in dogs with one-week-old experimentally-induced myocardial infarctions and programmed stimulation-induced sustained ventricular tachycardias to assess whether there is a correlation between the "site of origin" and site of cryo-termination of ventricular tachycardia (VT). Electrogram maps showed that 4 of 8 induced sustained VTs were due to macro- and 4 of 8 to microre-entry. Local cooling of the site of origin terminated 4 of 4 microre-entrant VTs, but only 1 of 4 macrore-entrant VTs. In the other 3 macrore-entrant VTs, the sites of cryo-termination were 2, 2.5, and 4 cm distant from the sites of origin. In contrast, cooling of the mid-to-late diastolic portions of the re-entry loops terminated all 8 VTs. These data demonstrate a dissociation of the site of origin from the site of cryo-termination of macrore-entrant VT.     

Rhythm Classification by Correlation-Waveform Morphology Analysis of Atrial and Ventricular Electrogram Signals

We tested the use of correlation-waveform analysis (CWA) of atrial and ventricular electrograms (EGMs) to distinguish ventricular tachycardia (VT) from supraventricular tachycardia (SVT). Patients undergoing electrophysiologic testing were enrolled. EGMs recorded during induced tachycardias were compared with EGMs recorded during sinus and paced rhythms, taken as templates, by assigning a CWA percent-match (CPM) score. Twenty-two patients were studied: 15 men and 7 women (mean age 48 years); 16 with SVT and 6 with VT. Using a sinus-rhythm template, the atrial CPM scores for SVT and VT were 66%± 20% and 93%± 5%, respectively (P = 0.0034). With a CPM-score cutoff of 85%, the sensitivity for correctly identifying VT was 100% and the specificity for rejection of SVT was 80%. The corresponding ventricular-CPM scores for SVT and VT were 81%± 12% and 72%± 24%, respectively (P = 0.13, cutoff = 65%, sensitivity = 50%, and specificity = 90%). Using a ventricular template with atrial pacing, the ventricular-CPM scores for SVT and VT were 87%± 9% and 76%± 14%, respectively (P = 0.028, cutoff = 70%, sensitivity = 50%, and specificity = 93%). Atrial CWA matching is superior to ventricular CWA matching in discriminating between SVT and VT. CWA matching in both chambers could potentially achieve better discrimination.     

Underdetection of Ventricular Tachycardia Using a 40 ms Stability Criterion: Effect of Antiarrhythmic Therapy

Inappropriate shocks can complicate cardioverter defibrillator therapy. Among solutions proposed to avoid oversensing are algorithms to reduce inappropriate detection of atrial fibrillation (AF) or sinus tachycardia. In patients not on antiarrythmic drugs, an interval stability criterion of 40 ms has been validated with the Medtronic PCD to discriminate ventricular tachycardia (VT) from AF. With this algorithm, VT is considered stable if no interval varies from one of the three preceding in tervals by more than 40 ms. If an interval does not fulfill this criterion, the VT event counter is reset to zero. The aim of this study was to investigate the incidence of underdetection when this criterion is ap plied in patients treated with antiarrhythmic drugs. We studied 132 sustained monomorphic VTs induced in 42 patients during 101 electrophysiological studies (EPS). EPS were performed without treatment (group I. 24 patients, 44 VTs); on Class Ia drug (group II, 17 patients, 24 VTs); Class Ic drug (group III, 22 patients, 39 VTs); or sotalol (group IV, 17 patients, 25 VTs). The endocardial electrogram of all VT episodes was digitized and the stability algorithm was applied. The reset arrhythmias were distributed among no delay, small, moderate (<10 s) and important (>15 s) delay in VT detection. The relation be tween drug use and reset was analyzed. Beset was found in 86 (65%) of induced VTs. No difference in heart rate or induction mode was shown between reset and nonreset VTs. There was a significative asso ciation between drag use and reset probability (Chi² significantly different, P < 0.05). In patients treated with Class Ic drugs, the probability of finding an important delay in VT detection was 12.5% versus 0% in nontreated patients or in patients treated with sotalol. We conclude that a stability criterion of 40 ms is probably safe in nontreated patients but should be used with caution in patients treated with antiarrhythmics, especially in the presence of Class Ic drags.     

A pilot study examining the performance of polynomial-modeled ventricular shock electrograms for rhythm discrimination in implantable devices

BACKGROUND: Inappropriate shocks continue to be a problem for patients with implantable defibrillators (ICD). We evaluated the performance of polynomial-modeled ventricular electrograms (EGM) to discriminate between supraventricular tachycardia (SVT) and ventricular tachycardia (VT). METHODS: Seven sets of EGM from patients having both SVT and VT documented during a single ICD interrogation were included. The cardiac cycle was analyzed off-line in two parts, QR and RQ segments, which were modeled separately using third-order and sixth-order polynomial equations, respectively. These segments were then analyzed to determine which polynomial coefficients were most significant for rhythm discrimination. RESULTS: When analyzing the QR segment during arrhythmia, there were statistically significant (P<0.05) correlations in 4 of 4 (100%) of the QR coefficients when comparing normal sinus rhythm (NSR) to SVT and 2 of 4 (50%) when comparing NSR to VT or SVT to VT. When analyzing the RQ segment during arrhythmia, there were statistically significant (P<0.05) correlations in 4 of 7 (57%) of the RQ coefficients when comparing NSR to SVT, 5 of 7 (71%) when comparing NSR to VT, and 3 of 7 (43%) when comparing SVT to VT. Using a cutoff value of 50% change from NSR, the ratio of first-order to zero-order QR coefficient was able to completely separate VT from SVT (P=0.03) in this series of patients. CONCLUSION: Our data demonstrate the feasibility of simple polynomial equations that reproduce the depolarization and repolarization phases of human ventricular shock EGM. The ratio of first-order to zero-order QR coefficient was able to reliably discriminate between SVT and VT while reducing the polynomial model to a first-order system. The results of this pilot trial may serve as the basis for a larger prospective trial implementing a discrimination algorithm for use in low computational power implantable devices.