Jeffrey M. Baerman

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 rhythms 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)

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)

Effectiveness of radiofrequency catheter ablation for treatment of atrial tachycardia

Catheter ablation has been used to treat atrioventricular node reentrant and atrioventricular reentrant tachycardias with extremely high success rates. The suitability of catheter ablation for treatment of atrial tachycardia, a much less common type of supraventricular tachycardia, has not been well addressed. Fifteen patients (8 females) ranging from 10 to 83 years (mean 38 +/- 22) were referred for catheter ablation of supraventricular tachycardia. The diagnosis of atrial tachycardia was established by standard electrophysiologic techniques. A combination of activation and pace mapping was used to identify a suitable site for radiofrequency current catheter ablation. Medical therapy was unsuccessful in all but 1 patient. Two patients had surgically corrected congenital heart disease, 2 had coronary artery disease and 1 had dilated cardiomyopathy. Seven patients had depressed left ventricular function. Six patients had incessant tachycardias. Presumed tachycardia mechanism was automatic in 11 patients and reentrant in 4. Mean tachycardia cycle length was 372 +/- 74 ms. Catheter ablation was acutely successful in 12 patients (80%) with application of 11.1 +/- 6.6 lesions at a mean voltage of 60 +/- 9 V. In the other 3 patients, 16 to 38 lesions were applied. At a mean follow-up of 18.5 +/- 6.5 months, 2 patients have had recurrences with different P-wave morphologies and underwent a second successful catheter ablation procedure. An additional 2 patients had recurrences with the same P-wave morphology and 1 underwent a second successful catheter ablation procedure. Thus, radiofrequency ablation can be used in a diverse population of patients with atrial tachycardia with an acute success rate of 80% and a long-term success rate of 73%.

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.

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)

Effects of procainamide on intra-arterial electrograms during atrial fibrillation: Implication 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.

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.

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.

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)

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 unfilfered (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 elecfrogram morphology. Changes in bipole configuration resulted in profound changes in calculated afrial rate, amplitude, and apdf (P < 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> 0.10 by two‐way ANOVA). These changes significantly affected the predictive value of previously published detection criteria for rate (P < 0.01) and apdf (P < 0.000001). 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 < 0.0001). Further, when data segments from all patients and bipole configurations were grouped, rate and apdf were found fo be strongly inversely correlated (r = ‐0.808). In conclusion: (1) Bipole configuration has important effects on calculated atrial rate, electrogram amplitude, and apdf during atrial fibrillation; (2) Median frequency and frequency domain analysis may be a more robust way of characterizing atrial fibrillation despite the use of different bipole configurations; (3) Changes in bipole configuration affect the efficacy of detection criteria, and considerations about the level of organization of a cardiac rhythm; (4) Rate and apdf may be largely redundant measures of fibrillatory rhythms; and (5) Traditional estimates of atrial rates up to 700/min during atrial fibrillation, based on the unipolar or widely spaced bipolar leads of the surface electrocardiogram, reflect the effects of their recording methods. and are an overesfimation of the true atrial rate.