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Biomedical subjects

S Swiryn

Publications and source records attributed to S Swiryn.

At least 19 recordsLinked to original sources
PubMed1992

Diagnosis of atrial fibrillation from surface electrocardiograms based on computer-detected atrial activity.

A computerized method to detect atrial fibrillatory activity on the surface electrocardiogram is presented. After ventricular activity was canceled by creating a remainder electrocardiogram, significant differences were found in the percent power of the remainder electrocardiograms for a group of rhythms with atrial fibrillation (mean +/- SD; lead V1, 47.4 +/- 29.7%; lead II, 39.4 +/- 26.8%) and a control group (irregular rhythms or rhythms without readily detectable P waves; lead V1, 17.6 +/- 14.6%; lead II, 19.2 +/- 13.9%) for both leads (p less than 0.0001). A discrimination algorithm that classified a rhythm as atrial fibrillation if the percent power was greater than 32% and if noncoupled P waves were not present had a specificity of 90.0% and a sensitivity of 69.7% for the training set and a specificity of 87.8% and a sensitivity of 68.3% for the test set. In addition, the algorithm correctly detected all 66 of the 66 sinus rhythms tested. The algorithm produced good results that may be incorporated into arrhythmia interpretation systems to improve their specificity.

Algorithms↗
PubMed1992

Atrial electrograms and the characterization of atrial fibrillation.

An improved method of calculating magnitude-squared coherence spectra on pairs of short-duration electrogram recordings is discussed. This method is based on adaptive signal processing techniques and yields spectra with higher resolution than those obtained using a straightforward direct method. The high-resolution spectra will make it possible to examine the time-varying relationship between activity at two sites during atrial fibrillation and may be useful for quick rhythm characterization by implanted devices or for constructing coherence maps in research studies. Example high-resolution spectra for sinus rhythm, atrial flutter, and atrial fibrillation are presented.

Atrial Fibrillation↗
PubMed1992

Evidence for transient linking of atrial excitation during atrial fibrillation in humans.

BACKGROUND: Atrial fibrillation is usually thought of as a "random" pattern of circulating wavelets. However, local atrial activation should be influenced by the constant anatomy and receding tail of refractoriness from the previous activation. The general tendency for wave fronts to follow paths of previous excitation has been termed "linking." We examined intra-atrial electrograms recorded during atrial fibrillation for evidence of linking. METHODS AND RESULTS: Two minutes of atrial fibrillation were recorded in 15 patients with an orthogonal catheter. We have previously demonstrated that this catheter can be used to detect changes in the direction of local atrial activation. A mean vector was calculated for each electrogram. The similarity of the direction of the vectors from two consecutive electrograms can be quantified on a scale of 1 to -1 by calculating the cosine (cos) of the smallest angle (theta) between them. Two vectors pointing in the same or opposite directions then have cos(theta) = 1 or -1, respectively. For the entire group of patients, mean cos(theta) was significantly greater than 0 (mean, 0.36; p less than 0.001). In nine of 15 patients, there were groups of six or more consecutive beats (total, 44 groups; range, six to 14 beats per group) in which the direction of activation of each beat was within 30 degrees of the previous beat. The likelihood of one group of six or 14 consecutive similar beats occurring by chance in any one patient in 1 minute is less than 0.05 and less than 0.0000001, respectively. There was a significant correlation (r = 0.90) between the amount of linking during the first and second minutes of atrial fibrillation in each patient. CONCLUSIONS: Transient similarities in the direction of wavelet propagation in the majority of patients with atrial fibrillation is consistent with the presence of transient linking. To our knowledge, this is the first direct evidence that atrial activation during atrial fibrillation in humans is not entirely random.

Aged↗
PubMed1991

Detection of changes in atrial endocardial activation with use of an orthogonal catheter.

The ability of a catheter with an orthogonal electrode configuration to sense differences in the direction of local atrial endocardial activation was tested in 18 consecutive patients with intact retrograde conduction. In all 18, discrimination of anterograde from retrograde conduction at a single atrial site was examined; in 5 of the 18, multiple sites were examined to determine if the discriminatory ability of the catheter was site dependent. The catheter was specially designed with bipoles in the x, y and z directions. A vector was computed for each electrogram during anterograde and retrograde conduction. Electrogram amplitude along the standard bipole was also compared for anterograde and retrograde conduction. Mean electrogram amplitude for the standard bipole was significantly different for anterograde than for retrograde conduction in 17 of 18 patients (mean +/- SD 4 +/- 1.9 vs. 2.7 +/- 1.3 mV; p less than 0.005), with complete separation of amplitude distributions in 4 patients. The electrogram vector during anterograde conduction was significantly different from that during retrograde conduction in all 18 patients (p less than 0.0001), with complete separation of vector distributions in 14. In some patients with multiple site recordings, the choice of site greatly affected separation based on electrogram amplitude or vector, or both. The orthogonal catheter can be used to sense directional differences in local endocardial activation. The catheter shows promise for discriminating anterograde from retrograde conduction and examining the direction of endocardial activation in the heart during an electrophysiologic examination.

Atrial Function↗
PubMed1990

Effect of bipole configuration on atrial electrograms during atrial fibrillation.

Despite an increasing body of work on the nature of fibrillatory rhythms, and the application of different bipole configurations in antifibrillatory devices, little published work has assessed the effect of bipole configuration on the endocardial recordings of fibrillatory rhythms. To address this issue, a specially designed 6 Fr decapolar catheter was used to record intra-atrial electrograms during sustained atrial fibrillation in 15 patients. Simultaneous filtered (30-500 Hz) and unfiltered (0.05-5,000 Hz) recordings of atrial fibrillation were performed of four different bipole configurations: (a) 1-mm interelectrode spacing adjacent to the atrial wall; (b) 10-mm interelectrode spacing adjacent to the atrial wall; (c) 10-mm inter-electrode spacing 24 mm from the distal catheter tip; (d) 1-mm interelectrode spacing 24 mm from the distal catheter tip. One minute of such data was recorded, and each 4.27-second segment (x 14 segments) was analyzed for atrial rate, electrogram amplitude, amplitude probability density function (apdf), median frequency in the 2-9 Hz band, and electrogram morphology. Changes in bipole configuration resulted in profound changes in calculated atrial rate, amplitude, and apdf (P less than 0.001 by two-way ANOVA in each instance). Specifically, closer interbipole spacing and closer proximity to the atrial wall resulted in lower calculated atrial rates, higher electrogram amplitudes, and higher apdf values. In contrast, median frequency proved to be a more robust measure despite multiple configurations (P greater than 0.10 by two-way ANOVA). These changes significantly affected the predictive value of previously published detection criteria for rate (P less than 0.01) and apdf (P less than 0.00001). Bipole location also affected morphology, with locations adjacent to the atrial wall and with closer interbipole spacing having more discrete electrograms and greater apparent organization (P less than 0.0001). Further, when data segments from all patients and bipole configurations were grouped, rate and apdf were found to be strongly inversely correlated (r = -0.808). (r = -0.808).(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1990

Differentiation of ventricular tachyarrhythmias.

Implantable devices capable of several modes of therapy will require differentiation of various ventricular tachyarrhythmias. Three methods of arrhythmia analysis, magnitude-squared coherence, ventricular rate, and irregularity of cycle length were performed for 45 episodes of induced ventricular tachyarrhythmia in 15 patients. Differentiation of monomorphic ventricular tachycardia from polymorphic ventricular tachycardia and ventricular fibrillation was possible by mean magnitude-squared coherence, less possible by rate, and not possible by beat-to-beat irregularity. Faster monomorphic ventricular tachycardia overlapped with rates of polymorphic ventricular tachycardia and ventricular fibrillation. Differentiation of polymorphic ventricular tachycardia and ventricular fibrillation was not possible by rate or irregularity. A progressive decrease in mean magnitude-squared coherence from monomorphic ventricular tachycardia to polymorphic ventricular tachycardia to ventricular fibrillation strengthens previous observations that coherence is a measure of rhythm "organization."

Adult↗
PubMed1989

Shortening of ventriculoatrial intervals with left bundle branch block during orthodromic reciprocating tachycardia in three patients with a right-sided accessory atrioventricular pathway.

Previous studies of the effects of bundle branch block on ventriculoatrial (VA) intervals during orthodromic reciprocating tachycardia have focused on the timing of the atrial electrograms. However, left bundle branch block importantly affects the timing of initial ventricular activation, and this effect would also be expected to affect VA intervals during orthodromic reciprocating tachycardia. Presented here are three patients with a single right-sided accessory atrioventricular pathway exhibiting left bundle branch block during orthodromic reciprocating tachycardia. Each had shortening of the VA interval by 10 to 30 ms during left bundle branch block beats. This shortening was accompanied by a nearly equal increase in the HV interval, with the His bundle to atrial interval remaining constant. It is concluded that the timing of ventricular as well as atrial electrograms impacts on the VA intervals with left bundle branch block beats during orthodromic reciprocating tachycardia. With left bundle branch block, delay in initial left septal activation results in later onset of the QRS complex and, with right ventricular activation occurring normally, shortening of the VA interval occurs in patients with a right-sided pathway.

Adolescent↗
PubMed1989

Lack of effectiveness of lidocaine for sustained, wide QRS complex tachycardia.

Records of 31 episodes of sustained, wide QRS complex tachycardia treated with IV boluses of lidocaine in 20 consecutive patients were reviewed. Most of the episodes were managed in the emergency department. Patient ages ranged from 18 to 91 years (mean +/- SD, 64 +/- 17), and 17 of 20 were men. All but three had coronary artery disease. Although 19 of 20 patients were admitted with a diagnosis of "rule out acute myocardial infarction," only two had this diagnosis confirmed. Seventeen patients had ventricular tachycardia, and three had wide QRS complex supraventricular tachycardia. Patients were given one to three boluses of lidocaine totaling 75 to 400 mg (127 +/- 64 mg). Termination of the tachycardia was temporally related to lidocaine administration in only six of 31 episodes (19%) occurring in five of 20 patients. In three of these five patients, lidocaine was given again for a recurrence of the tachycardia and was ineffective. A similarly low efficacy was seen in 20 episodes initially managed in the hospital compared with 11 episodes initially managed by paramedics. Thus, although lidocaine is widely considered the drug therapy of first choice for sustained wide QRS complex tachycardia, it was not usually effective in our study. Patients presenting to the ED with this rhythm disturbance rarely prove to have acute myocardial infarction. Although this small retrospective study should not be the basis for a change in standard medical practice, the recommendation of lidocaine as initial therapy for such patients should be reexamined.

Adolescent↗
PubMed1989

The coherence spectrum. A quantitative discriminator of fibrillatory and nonfibrillatory cardiac rhythms.

Previous work has suggested that a comparison of electrograms from two or more sites may best differentiate fibrillatory from nonfibrillatory rhythms. The coherence spectrum is a measure by which two signals may be compared quantitatively in the frequency domain. In the present study, the coherence spectrum was used to quantify the relation between spectral components of electrograms from two sites in either the atrium or ventricle during both fibrillatory and nonfibrillatory rhythms. Bipolar recordings of 35 rhythms from 20 patients were analyzed for coherence in the 1-59 Hz band. The 17 nonfibrillatory rhythms were sinus rhythm (six), paroxysmal supraventricular tachycardia (two), atrial flutter (four), and monomorphic ventricular tachycardia (five). The 18 fibrillatory rhythms were atrial fibrillation (12) and ventricular fibrillation (six). Nonfibrillatory rhythms exhibited moderate-to-high levels of coherence throughout the 1-59 Hz band, with peaks concentrated at the rhythm's fundamental frequency and its harmonics. Fibrillatory rhythms exhibited little coherence throughout the 1-59 Hz band, and harmonics were not evident. The mean magnitude-squared coherence (scale of 0 to 1) for the 1-59 Hz band ranged from 0.22 to 0.86 (mean +/- SD, 0.52 +/- 0.19) for nonfibrillatory rhythms and from 0.042 to 0.12 (0.067 +/- 0.021) for fibrillatory rhythms. Separation of fibrillatory and nonfibrillatory rhythms was possible whether signals were recorded by floating or fixed-electrode configurations. These findings indicate that comparison of two electrograms with magnitude-squared coherence measurements differentiates fibrillatory from nonfibrillatory rhythms. A recognition algorithm based on coherence spectra may provide a major variations in lead configuration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Worsening of ventricular tachycardia by amiodarone.

The details of worsening of ventricular tachycardia in 8 (4.1%) of 194 patients receiving treatment with amiodarone are reported. Two forms of amiodarone-induced tachycardia were recognized: first, the development of new tachycardias (three patients) and second, a change in the pattern of recurrence of clinical tachycardia (five patients). In retrospect, the time from the initiation of amiodarone to the initial documentation of worsening ranged from 1 to 23 days (mean +/- SD, 9.4 +/- 8.2 days) and the time from the initiation of therapy to the recognition of worsening ranged from 6 to 26 days (14.6 +/- 10.1 days). Seven patients survived the worsening of tachycardia and one died. The total dose of amiodarone received and the duration of administration did not correlate with time to manifestation or time to resolution of worsening. This report emphasizes that worsening of ventricular tachycardia as a result of amiodarone is often difficult to differentiate from inadequate drug loading or early recurrence of 2 patient's clinical tachycardia. Further, because of the pharmacokinetics of the drug, the manifestations of worsening may be prolonged. In the cases reported, it ranged from 2 to 26 days (7.9 +/- 8.3 days), which is longer than previously reported. Because of the potential for amiodarone to cause life-threatening worsening of ventricular tachycardia and in accordance with current results, a period of in-hospital monitoring of at least 10 days at the start of therapy with amiodarone is recommended.

Aged↗
PubMed1988

Ventricular response to atrial fibrillation: role of atrioventricular conduction pathways.

Irregularity of the ventricular rhythm is a hallmark of patients with atrial fibrillation, yet the genesis of the irregularity is not yet fully understood. The role of the atrioventricular (AV) node in determining the irregularity of the ventricular response to atrial fibrillation was investigated by comparing the frequency distributions of the atrial (AA) and the ventricular (RR) intervals. Atrial electrograms and surface electrocardiographic leads were recorded during sustained atrial fibrillation in 12 patients with conduction over the AV node. The scaling factor (mean RR interval/mean AA interval) quantified the ability of the conduction pathway to scale the atrial input to a slower ventricular response and ranged from 2.55 to 5.92 (mean +/- SD 3.77 +/- 0.92). The coefficient of variation (SD/mean) measured the relative variability of the AA and RR interval distributions. The atrial and ventricular coefficients of variation were not significantly different (0.20 +/- 0.04 versus 0.21 +/- 0.03, p greater than 0.27). Similar recordings were analyzed in six patients with conduction over a accessory AV pathway. The scaling factor ranged from 1.54 to 2.46 (2.02 +/- 0.39) and, as was the case for patients with conduction over the AV node, the atrial and ventricular coefficients of variation did not significantly differ (0.24 +/- 0.08 versus 0.27 +/- 0.10, p greater than 0.6). For both groups of patients, ventricular variability and the maximal RR intervals were predicted by the product of the scaling factor and either atrial variability or maximal AA intervals, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Computer discrimination of atrial fibrillation and regular atrial rhythms from intra-atrial electrograms.

Reliable detection of atrial fibrillation from intra-atrial data is an important requirement for automatic implantable anti-tachycardia devices. Simultaneous filtered and unfiltered intra-atrial electrograms were recorded from patients in regular rhythms (12 sinus rhythms and six regular atrial tachycardias) and atrial fibrillation (nine rhythms). Each rhythm was broken down into consecutive 4-second data segments for analysis by atrial rate calculation, power spectrum analysis and amplitude probability density function generation. Significant differences were found between regular rhythms and atrial fibrillation for atrial rate, for the percentage of the total power in the 4-9 hertz band and for amplitude probability density close to the isoelectric region. There was no overlap for any of these three parameters. For each method of analysis, algorithms were generated to discriminate individual data segments from regular rhythms and atrial fibrillation with high sensitivity and specificity. Comparable results were found when sinus rhythm was excluded from the analysis. Characteristics of intra-atrial recordings during atrial fibrillation were remarkably similar to previously published reports of intra-ventricular recordings during ventricular fibrillation. Each of the three methods of analysis may provide an algorithm for accurate detection of atrial fibrillation by anti-tachycardia devices.

Algorithms↗
PubMed1988

Effects of procainamide on intra-atrial [corrected] electrograms during atrial fibrillation: implications [corrected] for detection algorithms.

The effects of antiarrhythmic drugs on electrograms have implications for arrhythmia-detection algorithms in implantable antitachycardia devices. Filtered and unfiltered intra-atrial electrograms were analyzed in eight patients who received procainamide (50 mg/min iv, up to 1000 mg) during 11 episodes of atrial fibrillation. Continuous recordings were made before, during, and after the infusion. The recordings were digitized, divided into 4.27 sec segments, and analyzed for atrial rate, median frequency and amplitude probability density function. Significant differences were noted before and after infusion of procainamide for atrial rate (498 +/- 97 vs 356 +/- 146 beats/min; p less than .005), median frequency (5.50 +/- 1.22 vs 4.24 +/- 0.99 Hz; p less than .0005), and density (58.3 +/- 13.9% vs 69.1 +/- 15.0%; p less than .005). Pre- and postprocainamide values were compared with published criteria for detection of atrial fibrillation. Before procainamide, only 2.3%, 5.7%, and 3.4% of the data segments failed to meet criteria for atrial fibrillation by rate, frequency content, and density, respectively. In contrast, after procainamide, 50%, 36.4%, and 28.4% of the data segments failed to meet these same criteria, despite electrograms still meeting morphologic criteria for atrial fibrillation. Thus procainamide resulted in changes sufficient to cause failure of published criteria for detection of atrial fibrillation. These findings have broad implications for the function of antitachycardia devices in patients receiving antiarrhythmic drug therapy.

Adult↗