Comprehensive scheme for detection of ventricular fibrillation for implantable cardioverter defibrillators

Implantable cardioverter defibrillators (ICDs) detect and defibrillate ventricular fibrillation (VF) and ventricular tachycardia (VT). Other therapies which use less energy are also available to terminate VT. Previous studies have shown that ICD rate schemes often misdiagnose VT as VF. In this study, an improved VF classification scheme was designed and tested, which employs the classic rate criteria plus paired signal concordance (PSC); PSC uniquely detects VF where VT and VF rates overlap (220-340 ms). Two signals from a bipolar pair (1 cm) recorded in a unipolar sense exhibit similar signal shape for concordant rhythms, such as sinus rhythm and VT, and disconcordance for VF. Once the rate criterion is met, PSC is measured by the peak normalized cross-correlation coefficient calculated over the depolarization. Variability, measured by a modified range, determined the contextual diagnosis over a passage. Sinus rhythm (20), VT (12), VF (22), atrial fibrillation (10), sinus rhythm with ventricular premature depolarizations (7), and polymorphic VT (4) passages were recorded from 38 patients. Rate-PSC was tested with unfiltered, digitized signals (1-500 Hz, 1,000 samples per second) and with filtered, downsampled signals (1-50 Hz, 100 samples per second). Sensitivity values, or percentage of correct VF detection, and specificity values, or detection of all other rhythms, were generated and compared with simulations of three commercial ICDs programmed to similar settings as rate-PSC and to nominal settings. The sensitivity values for rate-PSC with unfiltered and with filtered signals and for ICDs with 220 ms and with nominal settings were 100%, 100%, 48-80%, and 100%, respectively; the corresponding specificity values were 95%, 83%, 93%, and 7-13%, respectively. It was concluded that the rate-PSC scheme was able to reliably separate VF from other rhythms, even rhythms that have a variable morphology or variable rate. With the confidence of accurate VF detection, use of low-energy therapies for non-VF rhythms will increase device longevity and enhance patient comfort.

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 each depolarization of all other VTs induced subsequently in the same patient. The mean correlation coefficient (p mu) of cycle-by-cycle analysis was used as a discriminant function: p mu > or = 0.95 was considered matched; and p mu < 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 matching 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.

Augmented two-channel arrhythmia detection: an efficient diagnostic method for implantable devices

ICDs are highly effective in preventing sudden cardiac death. However, inappropriate device shocks caused by false-positive diagnoses are estimated to happen in 20% of all patients. The need for implantable electrical devices to detect with precision arrhythmias requiring therapy has spawned a variety of proposals for better means of tachycardia identification. To address this problem, the augmented two-channel arrhythmia detection (A2CAD) algorithm, a real-time scheme utilizing timing and morphology from both the atrial and ventricular channels, is introduced. The algorithm uses rate detection as a first stage and augments this with morphological signal analysis in rhythms that confound the rate only diagnoses. The software executes in real-time (online), and has been tested on 60 passages of two-channel intracardiac signals. The following arrhythmias constituted the test set: 10 AF and/or atrial flutter; 15 SVT; 16 VT; 10 ventricular flutter or VF; 5 sinus tachycardia; and 4 cases of AF concurrent with VF. Results from 60 patient cases indicate 57 (95%) of 60 success rate for A2CAD, validating its potential for implementation in future implantable devices.

A:V = 1:1 cardiac arrhythmia detection by VA interval analysis

Dual-chamber-sensing implantable-cardioverter defibrillators are soon expected to replace ventricular sensing devices. The addition of an atrial sensing lead will dramatically improve the specificity of arrhythmia detection. Even when using combined ventricular and atrial rate criteria, ambiguity in the case of atrial tachycardia with: anterograde conduction versus ventricular tachycardia with: retrograde conduction still remains. The introduction of dual-chamber sensing in antitachycardia devices allows for additional features, such as the measurement of atrioventricular (AV) and ventriculoatrial (VA) intervals. This study investigated relationships between AV and VA intervals to address problems arising in tachycardias with confounding 1:1 relationships. Thirty-one passages of 1:1 anterograde conduction from nine patients during atrial pacing at cycle lengths of 600-300 ms and 24 passages of 1:1 retrograde conduction from eight patients during ventricular pacing at cycle lengths of 600-300 ms were analyzed. Moving averages of three successive VA interval measurements were used to develop a criterion to be implemented into an algorithm to reduce ambiguity. Five randomly selected ventricular pacing passages were used as a training set. Upper and lower VA interval boundaries (234 ms and 132 ms) determined from the training set were used to classify 1:1 retrograde activation. To account for premature beats and outliers, the boundary criterion required 9 of 12 of the most recent moving averages to fall within the upper and lower limits. Of the 19 analyzed passages of ventricular pacing, 18 (95%) were correctly classified using the VA interval as an added feature. Of the 31 atrial pacing passages, 24 (77%) were correctly classified. Using only atrial or ventricular rates, all 1:1 tachycardias in this patient sample would be classified as ventricular tachycardia, resulting in false shocks. Specificity of diagnosis in ambiguous 1:1 tachycardias can be increased using VA interval measurements at the cost of minimum loss in sensitivity for ventricular tachycardia detection. This algorithm imposes little in additional computation for dual-chamber-sensing implantable-cardioverter defibrillators and greatly reduces the possibility of false shocks in 1:1 supraventricular tachycardias.

Discrimination of ventricular tachycardia from sinus tachycardia by antitachycardia devices: value of median filtering

Rate and rate variation algorithms used by implantable devices designed for management of life-threatening arrhythmias have major limitations in separating physiologic sinus tachycardia (ST) from pathologic ventricular tachycardia (VT) requiring therapy. These algorithms presently utilize criteria such as simple heart rate, stability of rate, or derivative of rate (sudden onset) which assumes a gradual onset for ST and an abrupt onset for VT. An alternative method employing median filtering was designed, tested, and compared to a previously published sudden onset rate algorithm using the same data set for analysis of performance. In 50 patients, the onset of ST during exercise and onset of VT were analysed. To accommodate occasional outlying intervals which might affect rate derived by averaging, a five-cycle median filter was used to smooth heart rate. Results from using a 'fixed-interval' or a 'percent' change in the median gave better discrimination of ST and VT than previously published 'fixed-interval' or 'percent' change algorithms. The superiority of median filtering performance was validated by statistical measures.

The value of rate regularity and multiplicity measures to detect ventricular tachycardia in the presence of atrial fibrillation or flutter

The predominant cause of inappropriate therapy by implantable antitachycardia devices with pacing and nonpacing cardioverter defibrillators, is mistaking a fast ventricular response during atrial fibrillation or flutter with true ventricular tachycardia (VT). The distinction between these arrhythmias is an important consideration in addressing the problem of reducing false-positives in detection mechanisms for implantable devices. Dual chamber analysis that examines atrial and ventricular event ratios has been proposed as a solution to this problem, but would still fail in distinguishing paroxysmal VT requiring treatment from a fast but otherwise benign ventricular response during atrial fibrillation or flutter. In this study, two methods for discriminating these tachyarrhythmias were evaluated. Method 1 examined ventricular rate and rate regularity as a method for VT detection. Method 2 combined rate and regularity as well as an additional multiplicity criterion for recognition of atrial flutter with a fast ventricular response. In 20 patients, Method 1 had 100% sensitivity of VT detection and 80% specificity for detection of atrial fibrillation or flutter. Method 2 had 90% sensitivity and 90% specificity. These results suggest that use of these algorithms in future implantable devices would result in a decrease in false-positive device therapies.

Digital signal processing chip implementation for detection and analysis of intracardiac electrograms

The adoption of digital signal processing (DSP) microchips for detection and analysis of electrocardiographic signals offers a means for increased computational speed and the opportunity for design of customized architecture to address real-time requirements. A system using the Motorola 56001 DSP chip has been designed to realize cycle-by-cycle detection (triggering) and waveform analysis using a time-domain template matching technique, correlation waveform analysis (CWA). The system digitally samples an electrocardiographic signal at 1000 Hz, incorporates an adaptive trigger for detection of cardiac events, and classifies each waveform as normal or abnormal. Ten paired sets of single-chamber bipolar intracardiac electrograms (1-500 Hz) were processed with each pair containing a sinus rhythm (SR) passage and a corresponding arrhythmia segment from the same patient. Four of ten paired sets contained intraatrial electrograms that exhibited retrograde atrial conduction during ventricular pacing; the remaining six paired sets of intraventricular electrograms consisted of either ventricular tachycardia (4) or paced ventricular rhythm (2). Of 2,978 depolarizations in the test set, the adaptive trigger failed to detect 6 (99.8% detection sensitivity) and had 11 false triggers (99.6% specificity). Using patient dependent thresholds for CWA to classify waveforms, the program correctly identified 1,175 of 1,197 (98.2% specificity) sinus rhythm depolarizations and 1,771 of 1,781 (99.4% sensitivity) abnormal depolarizations. From the results, the algorithm appears to hold potential for applications such as real-time monitoring of electrophysiology studies or detection and classification of tachycardias in implantable antitachycardia devices.

Automated analysis of spontaneously occurring arrhythmias by implantable devices. Limitations of using rate and timing features alone

Real-time automated systems for arrhythmia analysis by implantable antitachycardia devices have been designed to incorporate two-channel rate criteria with intracavitary atrial and ventricular electrogram morphology. Because the power requirements for morphologic analysis substantially limit antitachycardia device longevity, the authors sought to develop an alternative algorithm that relies solely on rate and three newly developed timing features: onset (median ventricular rate filtering to detect abrupt onset), loss of atrioventricular (AV) sequency (premature ventricular depolarizations), and regularity-multiplicity (minimal median cycle length variation concurrent with integral [n:1] AV periodicity). This system was assessed using spontaneously occurring arrhythmias in patients undergoing electrophysiology studies. Electrograms were captured on FM tape (1-500 Hz) using biopolar catheters in the high right atrium and the left ventricular apex. In 11 patients, 25 distinct arrhythmias were analyzed, which included sinus tachycardia (ST) (1 passage), supraventricular tachycardia (SVT) (6 passages), ventricular tachycardia (VT) with concurrent sinus rhythm (16 passages), VT with concurrent atrial flutter (VT/AFl) (2 passages), and ventricular fibrillation (VF) (1 passage). The algorithm correctly diagnosed 1 of 1 episode of ST, 4 of 6 episodes of SVT, 15 of 16 episodes of VT with concurrent sinus rhythm, 0 of 2 episodes of VT/AFl, and 1 of 1 episode of VF. Ventricular tachycardia episodes were misdiagnosed as SVT because of absence of loss of AV sequency in VT onset (1 episode), presence of multiplicity between VT and AFl (1 episode), and absence of VT regularity during AFl (1 episode).(ABSTRACT TRUNCATED AT 250 WORDS)

Real-time arrhythmia identification from automated analysis of intraatrial and intraventricular electrograms

Implantable cardioverter defibrillators have dramatically improved survival rates for patients at risk of sudden cardiac death, but the occurrence of inappropriate shocks remains an unresolved problem. Various means for better tachycardia detection, chiefly morphological analysis, have been proposed to address this problem. A new computerized scheme entitled Two-Channel Rate-Morphology (2CRM) was introduced. It is a real-time arrhythmia detection algorithm that combines timing and morphology information from intraatrial and intraventricular electrograms for arrhythmia diagnosis. The program 2CRM applies an initial cycle-by-cycle coding scheme followed by contextual diagnosis of underlying rhythm. The program was tested on 36 distinct passages of two-channel intracardiac signals from 30 patients. The distribution of the arrhythmias are as follows: 4 atrial fibrillation, 6 atrial flutter, 6 supraventricular tachycardia, 10 ventricular tachycardia, and 10 ventricular flutter-fibrillation. Of the analyzed 3,417 individual cardiac cycles 3,135 (91.7%) were correctly identified. Contextual diagnosis reversed 123 single-cycle errors to obtain a performance of 3,258 correct out of 3,417 (95.3%). Utilizing an uninterrupted continuous correct contextual diagnosis as indicator of successful arrhythmia detection, 2CRM obtained an accuracy of 34 out of 36 passages (94.4%).

Automated interpretation of cardiac arrhythmias. Design and evaluation of a computerized model

Historically, the development of computerized models that utilize the deductive methods used by clinicians for the interpretation of cardiac arrhythmias have been limited by the absence of a consistently reliable means of detecting atrial activation. In this study, a theoretical model was developed with a hierarchical organization of problem-solving strategies utilizing automated analysis of atrial activation from a commercially available esophageal pill electrode and ventricular activation from a simultaneously recorded surface electrocardiographic lead. The theoretical model was then tested in 21 patients with 1 or more of 28 distinct supraventricular and ventricular arrhythmias. Of the 641 individual cardiac cycles analyzed, 636 (99.2%) were correctly identified. The accuracy of a contextual, that is, more comprehensive, interpretation of consecutive cardiac cycles was 638/641 (99.5%). The following cardiac arrhythmias were identified: sinus rhythm, sinus bradycardia, atrial premature depolarizations, atrial flutter, and supraventricular tachycardias with normal and aberrant ventricular conduction, first-degree and second-degree heart block; junctional escape, junctional rhythm, idioventricular rhythm, ventricular premature depolarization, and ventricular tachycardia with and without retrograde activation; atrial bigeminy, atrial trigeminy, atrial couplets, ventricular bigeminy, ventricular trigeminy, and ventricular couplets. This study represents the first computerized model ever developed to incorporate the morphology and timing of atrial activation with the morphology and timing of ventricular activation for arrhythmia diagnosis. Such modeling appears to be capable of achieving accurate interpretation of spontaneous, complex clinical cardiac arrhythmias and atrioventricular relationships.

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 (SR1) and during induced monomorphic VT (VT1). 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 +/- 10) from its original site. The data were digitized at 1,000 Hz. Templates from SR1 and SR2, respectively, were compared subsequently with individual intraventricular electrograms from 15-25 sec passages of SR1 and VT1 and SR2 and VT2, respectively, using correlation waveform analysis. At site 1, the mean patient correlation coefficient ranged from 0.982-0.998 during SR1 and 0.062-0.975 during VT1. 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.

Separation of ventricular tachycardia from sinus rhythm using a practical, real-time template matching computer system

Template matching morphology analysis of the intraventricular 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/or 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, IVEGs, 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Driving restrictions advised by midwestern cardiologists implanting cardioverter defibrillators: present practices, criteria utilized, and compatibility with existing state laws

Although some patients remain at risk of losing physical control or collapsing after implantation of a cardioverter defibrillator for sustained ventricular arrhythmias, little is known about restrictions advised by arrhythmia specialists to patients with implanted devices concerning physical activities such as driving. In this study, all of the 58 cardiologists implanting cardioverter defibrillators in three contiguous midwestern states were surveyed to determine present practices and the compatibility of these practices with existing state law. Of the 51 respondents (88%), 27 cardiologists (53%) advised only those implanted patients who had had arrhythmia-induced presyncope or physical collapse to cease driving. Twenty two of the remaining cardiologists (43%) advised all implanted patients to cease driving, whereas two cardiologists (4%) never advised any implanted patient to restrict driving. Permanent driving abstinence was advised by seven of the responding cardiologists (14%), while temporary driving abstinence for periods of 2-12 months (mean 6 +/- 3 months) was recommended by the remaining 42 respondents (82%) who advised against driving. The criteria utilized, driving restrictions advised, and durations advised for driving restrictions were not uniform in any of the 13 surveyed university and nonaffiliated cardiology practices with greater than or equal to 2 implanting cardiologists. Overall, 38 cardiologists (74%) advised against driving and recommended durations that equaled or exceed their state's minimum legal requirements, although only 27 of the 51 cardiologists (53%) based their practice upon knowledge of their state's driving laws. The results of this survey suggest that the majority of cardiologists who implant cardioverter defibrillators advise their patients against driving postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of increased heart rate and sympathetic tone on intraventricular electrogram morphology

Electrogram pattern recognition by way of morphologic analysis has been proposed as a technique that may improve discrimination of ventricular tachycardia from sinus rhythm by antitachycardia devices. The potential impact that increases in heart rate and sympathetic tone could have on such techniques, however, has not been previously determined. A comparative study was undertaken to quantify possible changes in ventricular electrogram morphology using correlation waveform, area of difference, and amplitude analyses in 6 patients during atrial overdrive pacing at cycle lengths of 600 and 400 ms (group A), in 13 patients during infusions of physiologic doses of epinephrine (group B), and in 20 patients undergoing infusions of isoproterenol (group C). Four patients were in both groups A and B. A bipolar intraventricular template of cardiac depolarization during sinus rhythm at rest was compared with depolarization during subsequent passages of sinus rhythm at rest and subsequently increased heart rate. In 36 of 39 patients, waveform configuration as assessed by correlation waveform analysis remained relatively stable during atrial overdrive pacing, epinephrine infusion, and isoproterenol infusion when compared with sinus rhythm at rest. The correlation value did not fall below 0.950 in any patient. Area of difference values for the same 36 patients changed by an average of 6 and 37% during atrial overdrive pacing at cycle lengths of 600 and 400 ms intervals, respectively, by 3% during epinephrine infusion, and by 17% during isoproterenol infusion. In these same patients, there was an average change in electrogram amplitude of -1% during atrial overdrive pacing at 600 ms, 26% during pacing at 400 ms, -1% during epinephrine infusion, and 12% during isoproterenol infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

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 (VT) 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 demonstrated 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., greater than or equal to 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 pacemaker/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.

A comparison of four new time-domain techniques for discriminating monomorphic ventricular tachycardia from sinus rhythm using ventricular waveform morphology

Electrical management of intractable tachycardia via implantable antitachycardia devices has become a major form of therapy. Newly advanced methods of ventricular tachycardia detection propose examination of changes in intraventricular electrogram morphology in addition to or in combination with earlier rate-based detection algorithms. Unfortunately, most of the proposed morphology analysis techniques have computational demands beyond the capabilities of present devices or may be adversely affected by amplitude and baseline fluctuations of the intraventricular electrogram. We have designed four new computationally efficient time-domain algorithms for distinguishing ventricular electrograms during monomorphic ventricular tachycardia (VT) from those during sinus rhythm using direct analysis of the ventricular electrogram morphology. All four techniques are independent of amplitude fluctuations and three of the four are independent of baseline changes. These new techniques were compared to correlation waveform analysis, a previously proposed method for distinction of VT from sinus rhythm. Evaluation of these four new algorithms was performed on data from 19 consecutive patients with 31 distinct monomorphic ventricular tachycardia morphologies. Three of the algorithms performed as well or better than correlation waveform analysis but with one-tenth to one-half the computational demands.

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%). 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.

Computerized interpretation of the paced ECG

Analysis of the paced electrocardiogram (ECG) is important to the follow-up evaluation of patients with implanted pacemakers. Because of the complexity and variability of pacemaker algorithms, diagnosis of paced ECGs is often considerably more difficult than the interpretation of usual ECGs. Automated interpretation of the paced ECG can provide great clinical benefit because few clinicians are adequately trained in the diagnosis of such ECGs for the interpretation of pacemaker functionality. However, comparatively little work has been done in this area, mainly because the diversity and complexity of pacemaker logic makes interpretation, automated or manual, a difficult task. The following paper reviews research in computer interpretation of the pacemaker ECG and presents a new automated method which yields more detailed and accurate results than any previous technique.

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 less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of beta-blockade therapy for ventricular tachycardia induced with isoproterenol: a prospective analysis

Isoproterenol is sometimes required for ventricular tachycardia (VT) induction. However, the role of beta-blockade for treatment of such VT has not been critically assessed. The use of beta-blockade was evaluated prospectively in 14 consecutive patients who required isoproterenol 2.4 +/- 1.3 (+/- S.D.) micrograms/min to induce sustained monomorphic VT (greater than 30 seconds, or requiring termination due to hemodynamic collapse) after a negative baseline study. The VT mechanisms were enhanced automaticity (group A, six patients), triggered automaticity (group B, three patients), and reentry (group C, five patients). Groups A and B had serial intravenous electropharmacologic tests with propranolol alone (0.2 mg/kg), verapamil alone (0.15 mg/kg), and propranolol plus verapamil, and group C had serial tests with propranolol alone, procainamide or quinidine (class Ia drug) alone, and propranolol plus a class Ia drug until VT could no longer be induced. All six patients in group A responded to propranolol alone. In group B, one patient responded to verapamil alone, and two patients responded to propranolol plus verapamil. In group C, three patients responded to propranolol alone, one patient responded to a class Ia drug alone, and one patient responded to propranolol plus a class Ia drug. During a follow-up of 7 to 37 (17.9 +/- 10.7) (+/- S.D.) months, VT has not recurred in any patient. Three patients treated initially with propranolol alone have required substitution of amiodarone due to refractory congestive heart failure. In patients requiring isoproterenol for VT induction, beta-blockade alone appears to be effective in preventing reinduction of VT caused by enhanced automaticity. A heterogeneous response occurs when the VT mechanisms are triggered automaticity or reentry.

Detection of ventricular tachycardia using scanning correlation analysis

Cross correlation is an accurate method for distinguishing normal sinus rhythm (NSR) from ventricular arrhythmias. The computational demands of the method, however, have prohibited development of an implantable device using correlation. In this study, temporal data compression prior to correlation analysis was used to reduce the total number of computations. Unipolar and bipolar intracardiac electrograms of NSR and 23 episodes of ventricular tachycardia (VT) from 23 patients were obtained from a right ventricular apex electrode catheter during routine electrophysiology studies. The data were filtered (1-11 Hz), digitized (250 samples/sec) and temporally compressed to 50 samples/sec. Data compression removed four out of every five samples by only saving the sample with the maximum excursion from the last saved sample. The average squared correlation coefficient (r2) was computed for the NSR and VT episodes using each patient's NSR waveform as a template. In all 23 patients, the r2 values showed large separation between NSR versus VT in both unipolar (0.93 +/- 0.05 vs 0.20 +/- 0.16, P less than 0.005) and bipolar (0.91 +/- 0.07 vs 0.17 +/- 0.11, P less than 0.005) electrode configurations using template lengths of 80% the intrinsic interval (avg +/- SD). Narrow templates (40% intrinsic interval or less) often resulted in multiple r2 peaks during each heart cycle and degraded the r2 separation (n = 10, P less than 0.005). High pass filtering at 3 Hz also degraded the r2 separation (n = 10, P less than 0.05). Standard noncompressed correlations indicated that data compression had negligible effects on the results. Thus, a computationally efficient cross correlation method was found to be a reliable detector of VT.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Discrimination of retrograde from anterograde atrial activation using intracardiac electrogram waveform analysis

The prevention of pacemaker-mediated tachycardias requires a safe, reliable method for distinguishing retrograde from anterograde atrial activation by dual chamber pacemakers. In this study, a technique was developed to detect the morphological change that occurs in the waveform of the intra-atrial electrogram during retrograde atrial activation. The method employed for waveform analysis is based upon statistical correlation. In 19 patients undergoing electrophysiological studies, atrial electrograms were recorded from bipolar endocardial electrodes during sinus rhythm and 1:1 retrograde atrial depolarization while undergoing right ventricular pacing. Data were digitally sampled at 750, 1,000, and 1,500 Hz. Templates of anterograde atrial depolarization were constructed by signal averaging waveforms from an initial sinus rhythm passage. These were used for analysis of anterograde depolarizations from a subsequent passage of sinus rhythm and a passage of known retrograde atrial depolarization. In all 19 cases, a patient-specific threshold could be derived to separate anterograde from retrograde atrial depolarizations using 1,000 Hz and 1,500 Hz sampling rates. However, at a sampling rate of 750 Hz, separation of anterograde from retrograde atrial activation was possible in only 16/19 patients (84%). We conclude that correlation waveform analysis of a suitably sampled atrial electrogram is a reliable method of discriminating retrograde atrial depolarization from anterograde atrial depolarization in intracardiac electrograms.

A prospective comparison of programmed ventricular stimulation with triple extrastimuli versus single and double extrastimuli during infusion of isoproterenol

This prospective study compared the yield of programmed ventricular stimulation with single and double extrastimuli during an infusion of isoproterenol with that of programmed stimulation with triple extrastimuli. The subjects of this study were 58 patients who underwent programmed stimulation and did not have inducible ventricular tachycardia (VT) with single or double extrastimuli at two basic drive cycle lengths and at two right ventricular sites; 17 patients had a history of uniform VT unrelated to exercise, and 41 had no history of documented or suspected VT or ventricular fibrillation (VF). Programmed stimulation was performed with triple extrastimuli at both right ventricular sites. Isoproterenol was infused as a dose titrated to increase the sinus rate by 25% or to a rate of 100 beats/min, whichever was greater, and stimulation then was repeated with single and double extrastimuli. Among the 17 patients with a history of uniform VT, the clinical VT was induced by three extrastimuli in five patients (29%) and by two extrastimuli during isoproterenol infusion in six patients (35%, p greater than 0.05). Among the total study population of 58 patients, nonclinical multiform VT or VF was induced by three extrastimuli in 29 patients (50%), and by two extrastimuli during isoproterenol infusion in 15 patients (26%, p less than 0.05). Therefore stimulation with two extrastimuli during isoproterenol infusion has the same probability of inducing a clinical form of VT as does stimulation with extrastimuli, but the former has a significantly lower probability of inducing nonclinical multiform VT and VF.

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 identification 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 special 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.

Value of programmed ventricular stimulation in presumed carotid sinus syndrome

This study determines the results of programmed stimulation in patients with syncope or near-syncope presumed to have the carotid sinus syndrome based on the finding of carotid sinus hypersensitivity and the absence of any other apparent cause for syncope or near-syncope after clinical evaluation. Fourteen patients had coronary artery disease, 1 had dilated cardiomyopathy and 18 patients did not have structural heart disease. Programmed simulation was performed at 2 basic drive cycle lengths and 2 right ventricular sites with 1 to 3 extrastimuli. Sustained unimorphic ventricular tachycardia (VT) was induced in 5 of 15 patients who had structural heart disease, and in none of the 18 patients who did not (p less than 0.05). Polymorphic VT or ventricular fibrillation (VF) was induced in 5 of 15 patients (33%) who had structural heart disease, and in 5 of 18 patients (27%) who did not (p greater than 0.05). Patients who had inducible unimorphic VT were treated with antiarrhythmic drugs that suppressed the induction of VT, and 4 of 5 patients also received a pacemaker; no patient had a recurrence of syncope during follow-up. Patients who had inducible polymorphic VT and VF (n = 10) or no inducible VT (n = 18) received treatment directed at only carotid sinus syndrome. Two patients with inducible VT or VF and 1 patient without inducible VT had recurrent syncope during follow-up, but none had cardiac arrest or died suddenly.(ABSTRACT TRUNCATED AT 250 WORDS)

The hemodynamic effects of ventricular pacing with and without atrioventricular synchrony in patients with normal and diminished left ventricular function

The relative hemodynamic effects of heart rate, inotropic state, and atrioventricular (AV) synchrony during ventricular pacing were evaluated in 10 patients with normal left ventricular ejection fraction (LVEF) (0.66 +/- 0.07, mean S.D.) and in eight patients with a diminished LVEF (0.34 +/- 0.18). Hemodynamics were measured at AV intervals of 130, 0, and -130 msec during ventricular pacing at a baseline rate that was 10 pulses/min greater than the resting heart rate, at 130 pulses/min alone, and at 130 pulses/min during continuous intravenous infusion of dobutamine. During baseline ventricular pacing and during ventricular pacing at 130 pulses/min with and without dobutamine, both groups of patients had a significant decrease in cardiac index, stroke volume index, and stroke work index when the AV pacing interval was decreased from 130 to 0 msec. The observed decrease in these three hemodynamic variables was similar when patients with diminished LVEF were compared to patients with normal LVEF. No further significant decrease in cardiac index, stroke volume index, and stroke work index occurred in either group when the AV interval was changed from 0 to -130 msec during baseline ventricular pacing or during ventricular pacing at 130 with and without dobutamine. Beneficial hemodynamic effects occur during ventricular pacing when AV synchrony is maintained at resting heart rates and during increases in heart rate and inotropic state in patients with normal and diminished LVEF.

Electrophysiologic testing in patients with unexplained syncope: clinical and noninvasive predictors of outcome

To assess whether the level of risk of having significant electrophysiologic abnormalities can be determined, 29 clinical variables were analyzed in 104 patients with unexplained syncope who underwent electrophysiologic testing. A positive electrophysiologic study was defined as: a sinus node recovery time greater than or equal to 3 seconds; HV interval greater than or equal to 100 ms; infranodal block during atrial pacing; unimorphic ventricular tachycardia; and supraventricular tachycardia associated with hypotension. Thirty-one patients had a positive study, with inducible ventricular tachycardia being the most common finding (71% of positive studies). A left ventricular ejection fraction less than or equal to 0.40 was the most powerful predictor of a positive electrophysiologic study (p less than 0.00001), followed by the presence of bundle branch block (p less than 0.00003), coronary artery disease (p less than 0.0003), remote myocardial infarction (p less than 0.00006), use of type 1 antiarrhythmic drugs (p less than 0.00003), injury related to loss of consciousness (p less than 0.01) and male sex (p less than 0.01). A negative electrophysiologic study was associated with an ejection fraction greater than 0.40 (p less than 0.00001), the absence of structural heart disease (p less than 0.00001), a normal electrocardiogram (ECG) (p less than 0.0001) and normal ambulatory ECG monitoring (p less than 0.0001). The probability of a negative study increased as the number and duration of syncopal episodes increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of propranolol on ventricular rate during atrial fibrillation in the Wolff-Parkinson-White syndrome

Atrial fibrillation was induced during an electrophysiology study in 10 patients with the Wolff-Parkinson-White (WPW) syndrome, after determination of baseline properties of the accessory atrioventricular (AV) connection; intravenous propranolol (0.2 mg/kg) was then administered. Atrial fibrillation terminated during the drug infusion in three patients, allowing determination of propranolol's effects on conduction and refractoriness during sinus rhythm, before atrial fibrillation was reinduced. In these three patients propranolol had no effect on refractoriness or conduction properties of the accessory AV connection during sinus rhythm. The mean ventricular rate during atrial fibrillation was slowed by 15-56 beats/min in six patients, had no effect on the mean rate in three patients, and markedly increased the ventricular rate (203 to 267 beats/min) in one patient. In this patient, 54% of QRS complexes during atrial fibrillation were narrow, compared to 0-25% in the other patients. Propranolol reduced the percentage of QRS complexes that were narrow from 13 +/- 16% to 1 +/- 2% (mean +/- standard deviation, p less than 0.05). We conclude that propranolol may slow the ventricular rate during atrial fibrillation in some patients with the WPW syndrome, probably by blocking the effects of adrenergic activation. However, propranolol should not be used in patients with the WPW syndrome who have atrial fibrillation, if most QRS complexes during atrial fibrillation are preexcited. When a large percentage of QRS complexes are narrow, propranolol may increase the ventricular rate, probably by eliminating concealed retrograde conduction in the accessory AV connection.

Role of myocardial ischemia during programmed stimulation in survivors of cardiac arrest with coronary artery disease

The role of ischemia in the induction of ventricular tachycardia during programmed stimulation was studied in 19 patients who survived a cardiac arrest and were found to have a significant stenosis in at least one branch of the left coronary artery. The arterial-coronary sinus lactate difference was measured during electrophysiologic testing, before the induction of ventricular tachycardia. Ventricular tachycardia was induced in 15 patients; it was sustained and unimorphic in 6 patients and polymorphic in 9. Myocardial ischemia, as reflected by net myocardial lactate production, was present within 60 seconds before the induction of ventricular tachycardia in 8 of the 15 patients with inducible ventricular tachycardia. In 9 of the 15 patients, programmed stimulation was repeated after a 15 minute rest period, with the same coupling intervals that had induced ventricular tachycardia previously. Net myocardial lactate production was not present in any patient during this repeat attempt. In three patients without evidence of ischemia during the first induction of ventricular tachycardia, the arrhythmia was induced again by the specific coupling intervals that had induced it previously. However, in five of six patients with net myocardial lactate production during the first induction of ventricular tachycardia, the same coupling intervals that had induced the arrhythmia in the presence of ischemia no longer induced it in the absence of ischemia. The results of this study suggest that myocardial ischemia may be a requirement for the induction of ventricular tachycardia in some patients with coronary artery disease who survive a cardiac arrest.

Determinants of QRS alternans during narrow QRS tachycardia

This study was designed to prospectively determine the incidence of QRS alternans during various types of narrow QRS tachycardia and to clarify the determinants of QRS alternans. An electrophysiologic study was performed in 28 consecutive patients with a narrow QRS tachycardia. Persistent QRS alternans was observed in 6 (43%) of 14 patients during orthodromic reciprocating tachycardia, 5 (71%) of 7 patients during atrial tachycardia and 3 (43%) of 7 patients during atrioventricular (AV) node reentrant tachycardia. Incremental atrial pacing during sinus rhythm resulted in QRS alternans in patients who had QRS alternans during tachycardia, unless the shortest pacing cycle length associated with 1:1 AV conduction exceeded the tachycardia cycle length. In patients without QRS alternans during narrow QRS tachycardia, incremental atrial pacing during sinus rhythm resulted in persistent QRS alternans in five patients in whom the shortest pacing cycle length associated with 1:1 AV conduction was 60 to 180 ms less than the tachycardia cycle length. In an additional 20 patients without a narrow QRS tachycardia, persistent QRS alternans was observed during incremental atrial pacing in 11 (55%) of the patients. In six of six patients who had QRS alternans during abrupt rapid atrial pacing, QRS alternans was not observed when the same pacing rates were achieved gradually. Among the patients with narrow QRS tachycardia, the mean tachycardia cycle length in those who had QRS alternans (mean +/- SD 288 +/- 44 ms) was significantly shorter than in those who did not (369 +/- 52 ms, p less than 0.001). The presence of QRS alternans was not related to the tachycardia mechanism, relative or functional refractory period of the His-Purkinje system (at a drive cycle length of 500 ms), age, presence of structural heart disease, direction of input into the AV node or concealed retrograde conduction in the His-Purkinje system. In conclusion, QRS alternans during narrow QRS tachycardias is a rate-related phenomenon that depends on an abrupt increase to a critical rate and is independent of the tachycardia mechanism.

The interplay between endogenous catecholamines and induced ventricular tachycardia during electrophysiologic testing

Plasma epinephrine and norepinephrine concentrations were measured before, during, and shortly after induced ventricular tachycardia (VT) in 22 selected patients. Sustained, unimorphic VT was induced by programmed ventricular stimulation and terminated after 45 to 384 seconds by overdrive pacing in all patients. In no patient did VT result in loss of consciousness. The baseline plasma catecholamine concentrations did not correlate with the baseline right ventricular effective refractory period, the cycle length of induced VT, or the number of extrastimuli required to induce VT. Induced VT was not associated with a significant increase in the mean plasma epinephrine concentration. In contrast, the plasma norepinephrine concentration increased from a mean baseline level of 317 +/- 136 pg/ml (mean +/- standard deviation) to 418 +/- 220 pg/ml during VT (p less than 0.01) and increased further to 569 +/- 387 pg/ml shortly after VT (p less than 0.01). The plasma norepinephrine concentration shortly after VT correlated with the rate and duration of VT and with the magnitude of decrease in mean blood pressure during VT (p less than 0.05 for each). In eight patients the same configuration of VT was induced on two sequential attempts; in five patients the same number of extrastimuli were required for the second induction of VT as for the first, whereas in three patients fewer extrastimuli were required. Plasma catecholamine concentrations were not higher in patients requiring fewer extrastimuli to induce the second episode of VT, either shortly after the first episode of VT or shortly after the second episode of VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Differentiation of ventricular tachycardia from supraventricular tachycardia with aberration: value of the clinical history

The purpose of this study was to assess whether the clinical history is of any value in the differentiation in the emergency department of ventricular tachycardia (VT) from supraventricular tachycardia (SVT) with aberration. The records of 84 patients who presented with a wide-complex tachycardia and who were able to provide a history were reviewed. The wide-complex tachycardia was proven by a later electrophysiologic study to be VT in 62 patients and SVT with aberration in 22 patients. History of prior myocardial infarction, history of congestive heart failure, and history of recent angina pectoris all had positive predictive values for VT of greater than 95%, but had sensitivities of 66%, 24%, and 24%, respectively. Age greater than 35 years had a sensitivity of 92% and a positive predictive value of 85% for VT. None of the clinical characteristics was strongly predictive for SVT; the best was age less than or equal to 35 years, which had a positive predictive value of 70%. We conclude that clinical variables may be helpful in the emergency department diagnosis of wide-complex tachycardias. If a patient with a wide-complex tachycardia has a history of myocardial infarction, congestive heart failure, or recent angina pectoris, the tachycardia has a high likelihood of being ventricular in origin. However, there are no clinical variables that are highly predictive of SVT with aberration.

Effects of flecainide acetate on ventricular tachyarrhythmia and fibrillation in dogs with recent myocardial infarction

The antiarrhythmic and antifibrillatory actions of the class IC antiarrhythmic agent flecainide acetate were examined in urethane-anesthetized dogs with recent myocardial infarction. The intravenous administration of flecainide in a loading dose of 1.0 mg/kg (n = 7) or 2.0 mg/kg (n = 6), followed by a maintenance infusion of 1.0 mg/kg/h to achieve plasma drug concentrations considered clinically therapeutic, failed to significantly elevate the electrical threshold current required to provoke ventricular fibrillation at infarct zone, border zone and non-infarct zone stimulation sites in postinfarction dogs. In 8 dogs which responded to baseline programmed stimulation with inducible sustained ventricular tachycardia, flecainide administered as 1.0 or 2.0 mg/kg loading doses followed by a 1.0 mg/kg/h maintenance infusion failed to prevent ventricular tachycardia initiation in any animal tested, although the post-treatment ventricular tachycardia cycle lengths were prolonged compared to baseline values (pre: 178 +/- 11 ms vs post: 202 +/- 17 ms, p less than 0.05). Flecainide administration apparently facilitated the induction of newly sustained ventricular tachycardia in 3 previously noninducible postinfarction dogs. The development of acute posterolateral ischemia at a site remote from previous anterior myocardial infarction resulted in the development of ventricular fibrillation in 4 of 11 (36%) saline-treated postinfarction dogs vs a cumulative 10 of 12 (83%) flecainide-treated, baseline noninducible postinfarction dogs (p less than 0.05 vs saline-treated). The incidence of sudden ischemic ventricular fibrillation was 7 of 7 (100%) among flecainide-treated baseline inducible postinfarction dogs. These data suggest that flecainide acetate may have only limited efficacy in preventing ventricular tachycardia or ventricular fibrillation soon after myocardial infarction.

Effects of chronic amiodarone therapy on ventricular tachycardia induced by programmed ventricular stimulation

Several studies have reported upon the inducibility of ventricular tachycardia (VT) with programmed ventricular stimulation (PVS) during chronic amiodarone therapy; however, few studies have systematically described and compared the morphology, duration, and cycle length of VT induced by PVS before and after amiodarone. In this study, 26 patients with symptomatic VT or ventricular fibrillation were evaluated by PVS by means of one to three extrastimuli (ES) before treatment and after 2 months of amiodarone therapy. Before amiodarone, sustained unimorphic VT was induced in 21 patients (group A) and symptomatic, nonsustained VT was induced in five patients (group B). After 65 +/- 8 days of amiodarone (total dose 64.5 +/- 8.9 gm, mean +/- S.D.), 15 of 21 patients (71%) in group A had sustained VT, five patients (24%) had nonsustained VT, and one patient had no VT induced. Four of five patients (80%) in group B had sustained VT and one patient had no VT induced. VT was induced by the same or by fewer number of ES in 79% of cases. When the morphologies of the VT induced before and after amiodarone were compared, the morphology of VT induced after amiodarone was the same in only 8 of 24 patients (33%), unimorphic but different in 14 patients (58%), and polymorphic in the remaining two patients. No correlation was found between the serum concentrations of amiodarone, desethylamiodarone, tetraiodothyronine, triiodothyronine, or reverse triiodothyronine, and similarities or differences in VT morphology, VT cycle length, or the relative number of ES required to induce VT after treatment with amiodarone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of incremental doses of procainamide on ventricular refractoriness, intraventricular conduction, and induction of ventricular tachycardia

The short-term effects of incremental doses of procainamide (7.5, 15, 22.5, and 30 mg/kg) on right ventricular effective refractory period, intraventricular conduction, and induction of ventricular tachycardia were determined in 31 patients who had a history of sustained, unimorphic ventricular tachycardia. QRS duration during incremental ventricular pacing was used as an index of rate-dependent changes in intraventricular conduction. The mean plasma procainamide concentrations corresponding to the incremental doses were 5.5 +/- 1.2 (+/- SD), 9.0 +/- 1.6, 12.6 +/- 2.2, and 16.3 +/- 3.2 mg/liter. Each incremental dose of procainamide up to a dose of 30 mg/kg resulted in a significant increment in right ventricular effective refractory period and each dose up to 22.5 mg/kg potentiated a rate-dependent prolongation of QRS duration. After the 7.5 mg/kg dose of procainamide, induction of ventricular tachycardia was suppressed in eight of 31 patients. After higher doses of procainamide, induction of ventricular tachycardia was suppressed in two additional patients. In three of 10 patients in whom the induction of ventricular tachycardia was suppressed by 7.5, 15, or 22.5 mg/kg of procainamide, sustained unimorphic ventricular tachycardia was again inducible after a higher dose of procainamide. In three of 31 patients, only nonsustained ventricular tachycardia was inducible after a 7.5 to 22.5 mg/kg dose of procainamide; however, in two of these three patients, sustained ventricular tachycardia was again inducible after administration of a higher dose of procainamide. In conclusion, during electropharmacologic testing with procainamide, it is worthwhile to test a dose of 7.5 mg/kg, because this dose is often effective in patients who respond to this drug. However, the results of this study indicate that procainamide may be effective in suppressing the induction of sustained ventricular tachycardia at a relatively low plasma concentration, but not at a higher plasma concentration. Therefore, during long-term therapy with procainamide it may be important to avoid plasma procainamide concentrations not only lower, but also higher than the concentration that results in the suppression of induction of tachycardia.

Plasma levels of immunoreactive atrial natriuretic factor increase during supraventricular tachycardia

A significant diuretic and natriuretic response occurs during paroxysmal supraventricular tachycardia (SVT). Although the diuresis may be secondary to suppression of vasopressin secretion, the etiology of the natriuresis remains unexplained. To determine if atrial natriuretic factor (ANF) could contribute to the polyuric response during SVT, 10 patients were studied: five during spontaneous SVT and five during simulated SVT produced by rapid simultaneous atrial and ventricular pacing. Plasma immunoreactive ANF (IR-ANF) levels measured by radioimmunoassay were obtained at baseline (before and/or 24 to 48 hours after SVT) and after at least 15 minutes of SVT in all patients. During spontaneous and simulated SVT, IR-ANF was significantly elevated (mean +/- SE; 275 +/- 68 pmol/L) compared to baseline (28 +/- 7 pmol/L; p = 0.0036). Similar increases in IR-ANF were noted during both simulated and spontaneous SVT. To determine if this IR-ANF release was related to the increase in heart rate or the rise in right atrial pressure during SVT, IR-ANF levels were also measured in five patients with sinus tachycardia and in six patients with congestive heart failure. IR-ANF was significantly related to right atrial pressure (r = 0.93; p = 0.0009) but not to heart rate (r = 0.46). Thus, IR-ANF is elevated during SVT and may contribute to the natriuretic response. The stimulus to IR-ANF secretion during SVT appears to be related to the rise in right atrial pressure rather than to the increase in heart rate.

Electrophysiologic actions of pirmenol in dogs with recent myocardial infarction

The electrophysiologic actions of pirmenol, an investigational class I antiarrhythmic agent, were evaluated in eight anesthetized dogs, 5 to 10 days after anterior myocardial infarction. Before administration of the drug, programmed ventricular stimulation failed to initiate nonsustained or sustained ventricular tachyarrhythmias (VT) in any of the postinfarction dogs. After the cumulative administration of 2.5, 5.0, and 10.0 mg/kg pirmenol, programmed stimulation initiated sustained VT in six of the eight postinfarction dogs tested, with one additional dog responding with reproducible nonsustained VT (15 to 20 monomorphic complexes) after pirmenol administration. Only one of eight postinfarction dogs tested remained noninducible throughout the pirmenol dosing schedule. Administration of pirmenol tended to increase ventricular excitation thresholds, relative (p less than 0.05 after 10 mg/kg) and effective refractory periods in ischemically injured ventricular myocardium, and increased the difference or disparity in relative (p less than 0.05 after 5.0 and 10.0 mg/kg) and effective (p less than 0.01 after 2.5, 5, and 10, mg/kg) refractory periods between ischemically injured and normal noninjured ventricular myocardium. These findings suggest a potential for the provocation or aggravation of ventricular arrhythmias by pirmenol in the setting of recent myocardial infarction.

The plasma catecholamine response to ventricular tachycardia induction and external countershock during electrophysiologic testing

Adrenergic activation during electrophysiologic study could potentially alter the electrophysiologic properties of the arrhythmia substrate. However, the catecholamine response to ventricular tachycardia induction and termination during electrophysiologic testing has to date not been quantitated. Therefore, in 13 patients undergoing electrophysiologic study, arterial plasma norepinephrine and epinephrine were measured before, during and 1, 3, 5, 10 and 15 minutes after ventricular tachycardia induced by programmed stimulation and terminated by a single 100 J external countershock. Sinus rate and the effective refractory period at the right ventricular apex at a basic drive cycle length of 400 ms were measured after the countershock at the same time intervals used for the catecholamine measurements. The mean ventricular tachycardia cycle length (+/- SD) was 187 +/- 30 ms, and the mean duration of ventricular tachycardia was 18 +/- 4 seconds. Plasma norepinephrine and epinephrine increased, respectively, from a baseline of 286 +/- 141 and 119 +/- 40 pg/ml to 770 +/- 330 (169%) and 597 +/- 467 pg/ml (402%), (p less than 0.01) at 1 minute after the countershock. The mean plasma norepinephrine and epinephrine levels during ventricular tachycardia and at times greater than 1 minute after the shock did not differ significantly from baseline levels. Sinus rate increased from a baseline of 74 +/- 13 to 103 +/- 26/min (39%) at 1 minute after the shock (p less than 0.05) and then returned to baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic effects of bepridil in normal and infarcted canine myocardium

The electrophysiologic effects of bepridil, 10 mg/kg i.v., were determined in normal noninfarcted and in infarcted ventricular myocardium in 8 urethane-anesthetized dogs 4-6 days after anterior myocardial infarction. At drive cycle lengths of 400 and 333 ms, bepridil significantly increased relative (RRP) and effective (ERP) refractory periods in both normal ventricular tissue (mean increases, RRP 7-14%, ERP 5-6%, p less than 0.05-0.01) and in infarcted ventricular tissue (mean increases, RRP 12-15%, ERP 13-14%, p less than 0.01). Bepridil also selectively prolonged the local activation delay in infarcted ventricular myocardium (mean increases 37.5-45.1%, p less than 0.01), while ventricular excitation thresholds were not altered by bepridil in either normal or infarcted myocardium. Before bepridil administration, programmed ventricular stimulation initiated sustained ventricular tachycardias in 6 of the 8 postinfarction dogs tested. After bepridil, 2 of the 6 previously responsive animals were rendered noninducible, 3 animals responded to programmed stimulation with nonsustained tachyarrhythmias of relatively slower rates, and the one remaining dog responded with sustained ventricular tachycardia (VT). These data suggest that increases in refractoriness in both normal noninjured and in ischemically injured ventricular tissue, with a selective delay in conduction in ischemically injured tissue, contribute to the antiarrhythmic actions of bepridil in the setting of myocardial infarction.