Characterization of double potentials in human atrial flutter: studies during transient entrainment

Double potentials, defined as atrial electrograms with two discrete deflections per beat separated by an isoelectric interval or a low amplitude baseline, have been observed during right atrial endocardial mapping of human atrial flutter. In this study, bipolar atrial electrograms were recorded during atrial flutter (mean cycle length 235 +/- 27 ms [+/- SEM]) from the high right atrium, the His bundle region, the coronary sinus and at least 30 right atrial endocardial mapping sites in 10 patients. Double potentials were recorded from the right atrium in all patients during atrial flutter. Double potentials were evaluated during transient entrainment of atrial flutter by rapid high right atrial pacing in 5 of the 10 patients. In four of these five patients during such transient entrainment 1) one deflection of the double potential was captured with a relatively short activation time (mean interval 89 +/- 45 ms) and the other deflection was captured with a relatively long activation time (mean interval 233 +/- 24 ms), producing a paradoxical decrease in the short interdeflection interval from a mean of 75 +/- 20 ms to a mean of 59 +/- 24 ms; and 2) the configuration of the double potential remained similar to that observed during spontaneous atrial flutter. On pacing termination 1) the two double potential deflections were found to be associated with two different atrial flutter complexes in the electrocardiogram (ECG); 2) the previous double potential deflection relation resumed; and 3) when sinus rhythm was present, the double potentials were replaced by a broad, low amplitude electrogram recording at the same site.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of slow conduction in the common type of atrial flutter--using transient entrainment

To characterize slow conduction of the common type of atrial flutter (common AF), in which excitation wave propagated in a counterclockwise fashion, transient entrainment during the distal high lateral right atrium (HRAd) pacing and during the proximal coronary sinus (CSp) pacing was studied in 7 patients with common AF. In transient entrainment of common AF, conduction time from stimulus to CSp during HRAd pacing was always longer than that from stimulus to HRAd during CSp pacing. It was also longer than that from stimulus to CSp during HRAd pacing in 5 control patients without common AF in sinus rhythm. Return cycles at HRA and CS after cessation of rapid pacing during transient entrainment were studied. In HRAd pacing, return cycle at the proximal high lateral right atrium was almost equal to the pacing cycle length, or almost equal to or slightly shorter than the flutter cycle length (AFCL). Return cycle at CSp was almost equal to AFCL. In CSp pacing, return cycle at the distal coronary sinus was much longer than AFCL and increased at progressively shorter pacing cycle lengths. In conclusion, slow conduction was demonstrated in the lateral limb (from HRA laterally to CS) of the reentrant circuit in common AF, but it did not exhibit decremental conduction property. Return cycle at an endocardial recording site after transient entrainment in common AF does not always exhibit an uniform pattern, affected by the relative location of and the distance between the recording site, the pacing site, the reentrant circuit and the area of slow conduction.     

Boundary methods: A criterion for completeness

The application of methods which constitute an alternative to boundary integral equations to specific problems depends on development of complete systems of solutions, convergence of approximating procedures, and formulation of variational principles. This paper establishes a criterion for completeness. In this manner, greater flexibility of the theory is achieved; for example, systems of functions which are complete for different types of boundary conditions are developed.     

A simple modified technique for recording sinus node electrogram

We recommend a technique for recording a sinus node electrogram (SNE) that is quite simple and makes it easy to locate the electrode poles firmly in the place underlying the sinus node (SN); the success rate is 97%.     

Further observations on transient entrainment: importance of pacing site and properties of the components of the reentry circuit

Transient entrainment of circus-movement tachycardia utilizing an atrioventricular (AV) bypass pathway was studied in 13 patients (nine with the orthodromic form, two with the antidromic form, and two with both the orthodromic and antidromic forms). All patients had a left-sided AV bypass pathway. Pacing at selected rates faster than the spontaneous rate was performed during the tachycardia at a site proximal or distal to the AV node, an area of slow conduction within the reentry loop. Rapid pacing from a site proximal to the AV node (from the right atrium during the orthodromic form of the arrhythmia or the right ventricle during the antidromic form of the arrhythmia) always demonstrated at least one of the three entrainment criteria: constant fusion beats except for the last captured beat, which was entrained but not fused (first criterion); progressive fusion (second criterion); localized conduction block to a site(s) for 1 paced beat associated with interruption of the tachycardia followed by activation of that site(s) by the next paced beat from a different direction and with a shorter conduction time (third criterion). In contrast, rapid pacing from a site distal to the AV node (from the right ventricle during the orthodromic form of the arrhythmia, or the right atrium during the antidromic form of the arrhythmia) transiently entrained the tachycardia, but never demonstrated any entrainment criteria because the antidromic wave front from the pacing impulse always blocked in the AV node (concealed entrainment). We conclude that the location of the pacing site relative to the components of a reentry loop is critical to the demonstration of the criteria of transient entrainment; i.e., if it is proximal to an area of slow conduction and/or unidirectional block within a reentry loop, transient entrainment should be demonstrable, but if it is distal, it will not be demonstrable.     

Demonstration of transient entrainment in monomorphic sustained ventricular tachycardia associated with cardiac sarcoidosis

A 49-year-old man was referred for further treatment of sustained monomorphic ventricular tachycardia (VT) associated with cardiac sarcoidosis. During an electrophysiologic study (EP), dl-sotalol suppressed the spontaneous VT and prevented induction of VT. However, when predonisolone treatment was started, monomorphic VT recurred frequently. To terminate the VT, a temporal pacing lead was placed at the apex of the right ventricle, and programmed electrical stimulation was attempted from the lead. During the EP study, 2 different monomorphic VTs were repetitively induced and both types were able to be terminated by rapid ventricular pacing; in one of the VT morphologies, constant and progressive fusion was obvious during the ventricular pacing. Some monomorphic VTs associated with cardiac sarcoidosis are due to reentry with an excitable gap, but the clinical efficacy of EP-guided antiarrhythmic drug treatment seems to be less certain during steroid therapy. In the present case, a defibrillator device was implanted to prevent a possible arrhythmic event.     

Demonstration of the presence of slow conduction during sustained ventricular tachycardia in man: use of transient entrainment of the tachycardia

To test the hypothesis that an area of slow conduction is present during reentrant ventricular tachycardia in man, and that the earliest activation site during ventricular tachycardia is within or orthodromically just distal to the area of slow conduction in the reentry loop, we studied 12 episodes of ventricular tachycardia (mean rate 185 +/- 32 beats/min) that were induced in nine patients with ischemic heart disease. Rapid ventricular pacing was performed at selected sites during ventricular tachycardia while recording electrograms from an early activation site relative to the onset of the QRS complex (site A) and from a site close to the pacing site (site B). Rapid pacing from the right ventricular apex during ventricular tachycardia with a right bundle branch block pattern and from selected left ventricular sites during ventricular tachycardia with a left bundle branch block pattern (mean pacing rate 202 +/- 38 beats/min) resulted in constant ventricular fusion beats on the electrocardiogram except for the last captured beat (i.e., the ventricular tachycardia was entrained) in 11 of 12 episodes. During entrainment: sites A and B were activated at the pacing rate, conduction time from the last pacing impulse to the last captured ventricular electrogram at site A (St-A interval) was 359 +/- 69 msec and spanned the diastolic interval, while that at site B (St-B interval) was only 28 +/- 13 msec, site A had the same ventricular electrogram morphology as that during ventricular tachycardia, while site B had a different electrogram morphology, indicating that site A was activated in the same direction during entrainment as during ventricular tachycardia. Eight episodes of ventricular tachycardia were entrained at two or more different pacing rates. The St-A interval increased during pacing at the faster rate(s) in four of eight episodes, while the St-B interval remained unchanged. Rapid ventricular pacing performed from the same site during sinus rhythm (mean pacing rate 201 +/- 37 beats/min) resulted in an St-A interval of 103 +/- 37 msec (p less than .001 vs the value during entrainment) and an St-B interval of 31 +/- 15 msec (p = NS vs the value during entrainment). It is concluded that an area of slow conduction not demonstrable during sinus rhythm exists during ventricular tachycardia, and that the earliest activation site during ventricular tachycardia is at or orthodromically distal to this area of slow conduction.     

Incidence of reentry with an excitable gap in ventricular tachycardia: a prospective evaluation utilizing transient entrainment

The demonstration of transient entrainment has been proposed as evidence of reentry, with an excitable gap as the probable mechanism of tachycardia. A prospective series of 27 consecutive patients with sustained ventricular tachycardia induced by programmed electrical stimulation was studied to determine the frequency with which transient entrainment can be demonstrated and to define the optimal location of pacing and recording electrodes. In all patients, electrodes for pacing and recording were placed in both the left and right ventricles during electrophysiologic study. Among the 19 patients in whom the response to rapid pacing could be evaluated (25 episodes of ventricular tachycardia), transient entrainment was demonstrated in 79% (76% of episodes). Ten of 12 episodes of ventricular tachycardia with a left bundle branch block QRS configuration in lead V1 and 9 of 13 episodes with a right bundle branch block QRS configuration could be transiently entrained (p = NS). Transient entrainment was demonstrated for 8 of 11 episodes of ventricular tachycardia with a left bundle branch block configuration during pacing from the left ventricle, but for only 2 of 10 episodes during pacing from the right ventricular apex (p less than 0.05). Conversely, 9 of 13 episodes of ventricular tachycardia with a right bundle branch block configuration were transiently entrained during pacing from the right ventricular apex, but 0 of 10 episodes were transiently entrained by left ventricular pacing (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Conduction through the reentrant circuit in recurrent sustained ventricular tachycardia evaluated by use of transient entrainment

Using transient entrainment, the effect of the paced cycle length on the conduction through the reentrant circuit was assessed in recurrent sustained ventricular tachycardia (VT). Fourteen patients were included in the present study and their VTs were paced at multiple cycle lengths while the criteria of entrainment were confirmed at each paced cycle length. Then, the effect of the paced cycle length upon the conduction time, which was evaluated by the measurement of the time interval from stimulus to the entrained electrogram, was analyzed. In the overdrive pacings of VT, 3 response patterns in conduction time were observed: an increasing pattern (n = 8), a flat pattern (n = 5) and a decreasing pattern (n = 1) while the local conduction time outside the reentrant circuit remained unchanged at comparable paced cycle lengths. A decremental property is the likely mechanism responsible for the paced cycle length-dependent prolongation. As for the flat pattern, the existence of a fully excitable gap may be responsible. A paced cycle length related change in the reentrant circuit may account for the decreasing pattern. By using transient entrainment, the electrophysiological characteristics of the reentrant circuit can be evaluated and the information so gathered may be valuable in analyzing the action of antiarrhythmic drugs on the slow pathway.     

Avoiding inappropriate ventricular tachycardia detection due to T-wave oversensing in an implantable cardioverter defibrillator: a novel application of the electrogram width criterion.

Appropriate sensing is an essential function of an implantable cardioverter defibrillator (ICD). T-wave oversensing by an ICD can be a serious problem in some patients, causing overestimation of the heart rate, inappropriate tachyarrhythmia detection and therapy delivery. Decreasing the sensitivity or programming longer refractory periods can sometimes overcome T-wave oversensing, but these measures may interfere with the ability of the ICD to correctly detect tachyarrhythmias. This report proposes a novel application of the electrogram (EGM) width criterion using a recently introduced detection enhancement algorithm intended to improve the specificity of ventricular tachycardia detection, to avoid T-wave oversensing. Based on the course of a case with persistent T-wave oversensing and review of previously published reports, oversensing problems in ICDs and management strategies are discussed.     

72例短暂性脑缺血发作患者第四次长期随访龚涛

目的观察短暂性脑缺血发作（TIA）患者首次TIA后TIA的复发、完全性卒中与心肌梗死的发生以及生存情况,并探讨TIA患者行神经血管外科手术的临床价值。方法对72例TIA患者进行面对面的随访,以首次TIA发作为起点,到最后一次随访（1998年）止。结合前3次随访资料进行分析,并依据寿命表原理对随访资料进行生存分析。结果总的TIA复发率为27.9％,首次完全性卒中的发生率为65.7％,心肌梗死的发生率为8.4％,病死率为72.7％。主要死亡原因为完全性卒中,占所有死亡患者的59.6％,其中非老年患者的首位死亡原因为脑出血,老年患者的首位死亡原因为脑梗死。致死性心肌梗死患者2例,占死亡患者的3.8％。满20年的生存率为39.9％,其95％可信区间为(28.4%,51.4%)。有神经血管外科手术指征的患者19例,占所有患者的26.6％。结论首次TIA后约有近1/3TIA患者出现TIA复发,完全性卒中的发生率明显高于心肌梗死的发生率。主要死亡原因为完全性卒中而非心肌梗死。估计用神经血管外科手术来预防TIA患者发生完全性卒中的作用有限。     

72例短暂性脑缺血发作患者第四次长期随访

目的 观察短暂性脑缺血发作（TIA）患者首次TIA的复发、完全性卒中与心肌梗死的发生以及生存情况,并探讨TIA患者行神经血管外科手术的临床价值。方法 对72例TIA患者进行面对面的随访,以首次TIA发作为起点,到最后一次随访（1998年）止。结合前3次随访资料进行分析,并依据寿命表原理对随访资料进行生存分析。结果 总的TIA复发率为27．9％,首次安全性卒中的发生率为65．7％,心肌梗死的发生率为8．4％,病死率为72．7％。主要死亡原因因为完全性卒中,占所有死亡患者的59．6％,其中非老年患者的首位死亡原因为脑出血,老年患者的首位死亡原因为脑梗死。致死性心肌梗死患者2例,占死亡患者的3．8％。满20年的生存率为39．9％。其95％可信区间为（28．4％,51．4％）。有神经血管外科手术指征的患者19例,占所有患者的26．6％。结论 首次TIA后约有近1／3TIA患者出现TIA复发,完全性卒中的发生率明显高于心肌梗死的发生率。主要死亡原因为完全性卒中而非心肌梗死。估计用神经血管外科手术来预防TIA患者发生完全性卒中的作用有限。     

Implications of progressive aberrancy versus true fusion for diagnosis of wide complex tachycardia

At the onset of wide complex tachycardia, beats with intermediate morphologies sometimes occur between the normally conducted beats and the wide complex tachycardia QRS. Intermediate beats could be true fusion; however, progressive aberrancy has been reported to mimic true fusion. To evaluate the incidence of progressive aberrancy, wide complex tachycardia tracings were collected in which an intermediate beat was noted at the onset. When the associated electrocardiographic findings were diagnosed as supraventricular tachycardia, the beat was identified as progressive aberrancy. When diagnosed as ventricular tachycardia, the intermediate beat was identified as true fusion. Electrocardiographic criteria were then identified from this cohort to identify the distinguishing features between progressive aberrancy and true fusion. Of 24 episodes of wide complex tachycardia, 17 (71%) were identified as true fusion and 7 (29%) as progressive aberrancy. The QRS duration of the intermediate and wide complex tachycardia beats were shorter with progressive aberrancy than with true fusion (109 ± 23 ms vs 131 ± 20 ms, p <0.023; and 139 ± 21 ms vs 177 ± 24 ms, p <0.001, respectively). In progressive aberrancy (n = 3), the PR interval of the intermediate beat was always greater than the PR interval of the normally conducted beat. In contrast, in true fusion (n = 11), the PR interval of the intermediate beat was always less than the PR interval of the normally conducted beat. Multiple intermediate beats were present in 4 of 7 cases of progressive aberrancy and in 0 of 17 cases of true fusion. In conclusion, true fusion is the most common explanation for intermediate beats, but progressive aberrancy occurs a significant proportion of the time (29%). The identified criteria will be helpful in differentiating ventricular tachycardia from supraventricular tachycardia with aberrancy as a cause of wide complex tachycardia.