Catheter ablation of idiopathic left ventricular tachycardia with multiple breakthrough sites guided by an electroanatomical mapping system

Idiopathic ventricular tachycardia (VT) has been considered to be amenable to radiofrequency catheter ablation guided by Purkinje potentials. However, there appear to be various types of reentrant circuits associated with this VT deduced from the results of the successful radiofrequency catheter ablation cases. We describe in this report a patient with idiopathic left ventricular tachycardia which was electrically inducible and verapamil sensitive. Multiple earliest ventricular activation sites during tachycardia were detected with electroanatomical mapping using the CARTO system. Multiple applications at these sites failed to eliminate the VT. The earliest Purkinje potential was recorded at least 1.5 cm away from the earliest ventricular activation sites, and the radiofrequency current application at this site resulted in the complete abolition of this VT. The reentrant circuit of this tachycardia seemed to have multiple breakthrough sites to the ventricular myocardium, which were distant from the requisite part of the reentrant circuit of this VT involving the Purkinje fiber network conduction system.

Syncope in patients with atrial flutter during treatment with class Ic antiarrhythmic drugs

We describe 2 atrial flutter (AFL) patients with syncope during treatment with class Ic antiarrhythmic drugs. During the syncope, 1:1 atrioventricular (AV) conduction during AFL preceded a wide QRS tachycardia. The class Ic drugs, flecainide and pilsicainide, slowed the atrial rate, resulting in AFL with 1:1 AV conduction, and the width of the QRS complexes became wider during the tachycardia. Syncope was abolished after successful radiofrequency catheter ablation of the AFL. These potential proarrhythmic effects of the class Ic drugs should be taken into account in AFL patients, and concomitant use of beta-blocking agents would be critical to prevent proarrhythmias.

Diagnostic significance of the morphological change in the atrial electrogram during Para-Hisian pacing

Para-Hisian pacing (PHP), a pacing method to differentiate between conduction occurring over an accessory pathway (AP) from that over the atrioventricular node (AVN), is assessed essentially by comparing the timing in the atrial electrogams. Morphological change in the atrial electrograms is often observed during PHP, but its significance has not been investigated. Prior to the catheter ablation procedure, PHP was performed in 52 patients with an AP and in 36 patients with AV nodal reentrant tachycardia (AVNRT). The morphological change in the atrial electrograms, which was retrospectively assessed between the His bundle and proximal right bundle branch (HB-RB) captured and non-captured beats, was identified in 15 of 52 patients with an AP and in 26 of 36 patients with AVNRT. The atrial electrogram in the 6 of these 15 AP patients changed its morphology without overlapping the ventricular electrogram. All 6 AP patients exhibited a PHP pattern with the presence of 2 retrograde conduction routes, an AP and the AVN. In the patients demonstrating no morphological change in the atrial electrogram, 33 of 37 AP patients and all 10 AVNRT patients had only one retrograde conduction route. Morphological change in the atrial electrogram without overlapping the ventricular electrogram seems to have diagnostic significance indicating the presence of both AP and AVN conduction.

Experimental study of the effects of multi-site sequential ventricular pacing on the prophylaxis of ventricular fibrillation

Previous studies report a significant prophylactic effect on the occurrence of atrial fibrillation by simultaneous multi-site atrial pacing. We investigated the effects of multi-site sequential ventricular pacing (MSVP), which may be preferable to simultaneous multi-site pacing in terms of the prophylaxis of the occurrence of ventricular fibrillation (VF). Needle electrodes were inserted at ten different epicardial sites on both ventricles for MSVP in 12 adult beagle dogs. Four premature ventricular extrastimuli (PVE) were introduced to provoke VF reproducibly from a separate electrode in the left ventricle. The 4 PVE were applied to try to provoke VF during MSVP in a comparable fashion to the activation sequence during sinus rhythm. We compared the prophylactic effects of MSVP on the inducibility of VF by changing the number of stimulation sites to either 1, 3, 5, or 10 epicardial sites. We performed a total of 363 trials of induction and suppression of VF. The occurrence rates of VF by the 4 PVE for the various number of epicardial stimulation sites of MSVP, i.e., at 1, 3, 5, and 10 sites, were 0.8263, 0.4286, 0.4450, and 0.2857, respectively (p < 0.05). There was a significant prophylactic effect of MSVP on the inducibility of VF, and this effect became stronger as the number of MSVP sites was increased from 3 to 10. The hemodynamic state was relatively stable during MSVP. MSVP seems to be a promising method with which to reduce the occurrence of VF, and a larger number of stimulation sites would be more effective in terms of the prophylaxis of VF.

Demonstration of phase-3 and phase-4 retrograde block in a second concealed accessory pathway after an initial successful radiofrequency ablation of a 'normal' concealed accessory pathway

We report a patient with concealed Wolff-Parkinson-White syndrome who, following catheter ablation, demonstrated phase-3 and phase-4 retrograde block in a concealed accessory pathway. After an initial 'apparently successful' ablation, retrograde conduction was through the atrioventricular node during constant ventricular pacing. Ventricular extrastimulus testing was performed at a basic drive cycle length of 600 ms. Unexpectedly, ventricular extrastimuli at coupling intervals of 440-380 ms were conducted retrogradely over an accessory pathway, consistent with a phase-3 and phase-4 retrograde block in the accessory pathway. Residual accessory pathway conduction was eliminated in a single ablation session.

Augmentation of QRS wave amplitudes in the precordial leads during narrow QRS tachycardia

INTRODUCTION

QRS morphology during narrow QRS supraventricular tachycardia in patients without ventricular preexcitation generally is considered the same as that seen during sinus rhythm. This study presents a new ECG observation that the QRS amplitude increased significantly in leads V2 through V5 during tachycardia.

METHODS AND RESULTS

Using the same ECG machine and the same electrode patches applied to the same electrode positions, 12-lead ECGs during sinus rhythm and narrow QRS tachycardia were analyzed comparatively in 23 patients without ventricular preexcitation. Precordial QRS amplitudes were measured as the vertical distance from the peak of the R to the nadir of the S wave. The amplitudes also were measured during atrial rapid pacing and extrastimulation. Furthermore, ventricular excitation during sinus rhythm and tachycardia was studied using body surface mapping. Body surface distributions of QRS potentials and ventricular activation time (VAT) were displayed as maps. Gross area of QRS (AQRS, equivalent to the QRS amplitude) was compared during sinus rhythm versus tachycardia. During tachycardia, QRS amplitude significantly increased in leads V2 through V5, without any noticeable change in the transitional zone or QRS wave duration. Increase of QRS amplitude also was noted during atrial rapid pacing and extrastimulation. Gross AQRS values during tachycardia significantly increased in the left parasternal area, whereas QRS isopotential and VAT isochronal maps were similar during sinus rhythm and tachycardia, suggesting a minimal role of conduction delay in the increase of QRS amplitude.

CONCLUSION

QRS wave amplitude significantly increased in leads V2 through V5 during narrow QRS tachycardia compared with QRS waves in sinus rhythm. Increase of QRS amplitude seemed unlikely due to a conduction delay within the ventricular myocardium.

Marked anterograde decremental conduction over a rapidly conducting accessory pathway after radiofrequency ablation

We report on a patient with the Wolff-Parkinson-White syndrome who temporarily exhibited a marked anterograde decremental conduction over a rapidly conducting accessory atrioventricular pathway after successful radiofrequency ablation. By recording the intracardiac electrogram via the ablation catheter placed at the successful ablation site, we were able to exclude the possibility of the occurrence of anterograde decremental conduction in the atrial or ventricular myocardium between the accessory pathway and the recording electrodes.

Diastolic potentials observed in idiopathic left ventricular tachycardia

Radiofrequency catheter ablation (RF-CA) has demonstrated a high success rate in eliminating idiopathic left ventricular tachycardia (ILVT), and the target site is determined by the score of pace mapping or the Purkinje potential (PP) preceding the onset of the ventricular activation, which is considered to indicate the exit site of the reentrant circuit. However, only a few reports have described the potential obtained from the slow conduction zone. RF-CA was successfully performed in 8 patients with ILVT. Careful mapping of the left ventricle during tachycardia was carried out to find the diastolic potential (DP). A DP was obtained in 4 patients (group 1), but not in 4 others (group 2). The local electrogram was recorded from the distal tip of the ablation catheter during the RF current application in order to investigate the pattern of termination of ILVT. A DP was recorded at the point where the catheter was slightly pulled back to a site proximal to the exit site of the reentrant circuit at the left interventricular basal septum. In group 1, conduction block between the DP and PP eliminated ILVT in 3 out of 4 cases, and 1 case showed conduction block between the DP and ventricular potential. In 2 out of 4 patients in group 2, the local electrogram showed conduction block between PP and the ventricular potential when VT terminated. The ablation site in group 1 was located relatively more basal than that in group 2 in anatomy. A DP was obtained in a half of the cases with ILVT and RF-CA at this site could eliminate ILVT. A DP was obtained at a site relatively basal to the exit of the reentrant circuit and it is considered that this is a useful marker in terms of the successful ablation of ILVT.

Slow-fast form of atrioventricular nodal reentrant tachycardia with eccentric retrograde left-sided activation

A case of atypical AV nodal reentrant tachycardia (AVNRT) with eccentric retrograde left-sided activation, masquerading as tachycardia using a left-sided accessory pathway, is reported. Initially, it appeared that the tachycardia was a typical slow-fast form of AVNRT. The earliest retrograde activation, however, was registered at a site approximately 3 cm from the coronary sinus orifice (left atrial free wall), indicating atypical AVNRT. Atrial tachycardia and orthodromic AV reciprocating tachycardia using an accessory AV pathway were excluded. Slow pathway ablation at the posteroseptal right atrium eliminated the tachycardia. It was suggested that the anterograde limb of the tachycardia circuit was a slow AV nodal pathway with typical posteroseptal location, whereas the retrograde limb was a long atrionodal pathway connecting the compact AV node and the left atrial free wall near the mid-coronary sinus.

The response of the slow atrioventricular nodal pathway to temperature

The present study attempted to determine the lowest temperature at which the slow atrioventricular nodal pathway responds to heating and the temperature necessary for successful ablation of the slow pathway in patients with atrioventricular nodal reentrant tachycardia (AVNRT). The study group comprised 23 consecutive patients (14 women, 9 men) with symptomatic AVNRT. Radiofrequency current was delivered at the slow pathway potential recording site using a HAT 200S catheter ablation system. Successful radiofrequency ablation of the slow pathway was achieved in all 23 patients. Junctional beats, suggesting the response of the slow pathway to temperature, were detected in 62 of the total 136 applications. The temperature measured at the first junctional beat was 45.4+/-4.2 degrees C. The maximum temperature required for the successful ablation of AVNRT ranged from 45 to 88 degrees C. There were no complications except for 1 patient with transient atrioventricular (AV) block. There were no recurrences of AVNRT during follow-up. The lowest temperature at which the slow pathway was responsive to heat was quite similar to that for accessory pathways or the AV junction. However, the temperature required for the successful ablation of AVNRT differed markedly among the patients.

Intermittent bundle branch blocks in a patient with uncommon-type atrioventricular nodal reentrant tachycardia and enhanced atrioventricular nodal conduction

We report on a patient with uncommon-type atrioventricular (AV) nodal reentrant tachycardia with a short tachycardia cycle length (235-270 ms), in whom transient wide QRS tachycardia with both left bundle branch block and right bundle branch block aberrancy were followed by narrow QRS complexes. In addition, His-ventricular (H-V) block and a sudden prolongation of the H-V interval occurred during the tachycardia. As the determinant of these unusual findings, the possibility that the anterograde limb of the reentry circuit has an enhanced AV nodal conduction property is discussed, as is the clinical significance of this type of tachycardia.

New diagnostic finding to assess para-Hisian pacing observed in a patient with a permanent form of junctional reciprocating tachycardia

Para-Hisian pacing, a useful method to differentiate conduction over an accessory pathway from conduction over the AV node, is assessed essentially by comparing the timing of local atrial electrograms between His-bundle captured beats and His-bundle noncaptured beats. We describe the case of a patient with a permanent form of junctional reciprocating tachycardia, in whom an atrial double potential was recorded only during the tachycardia at the right posterior septum. During para-Hisian pacing, a morphologic change in the atrial electrogram at the posterior septum was also identified, as well as a change in the retrograde atrial sequence. Since the morphologic change of atrial electrograms during para-Hisian pacing cannot be demonstrated in a patient without an accessory pathway, this new finding could be considered a new additional diagnostic criterion suggesting the presence of an accessory pathway.

Heterogeneity of anterograde fast-pathway and retrograde slow-pathway conduction patterns in patients with the fast-slow form of atrioventricular nodal reentrant tachycardia: electrophysiologic and electrocardiographic considerations

OBJECTIVES

This study sought to define the electrophysiologic and electrocardiographic characteristics of fast-slow atrioventricular nodal reentrant tachycardia (AVNRT).

BACKGROUND

In fast-slow AVNRT the retrograde slow pathway (SP) is located in the posterior septum, whereas the anterograde fast pathway (FP) is located in the anterior septum; however, exceptions may occur.

METHODS

Twelve patients with fast-slow AVNRT were studied. To determine the location of the retrograde SP, atrial activation during AVNRT was examined while recording the electrograms from the low septal right atrium (LSRA) on the His bundle electrogram and the orifice of the coronary sinus (CS). Further, to investigate the location of the anterograde FP, single extrastimuli were delivered during AVNRT both from the high right atrium and the CS.

RESULTS

The CS activation during AVNRT preceded the LSRA in six patients (posterior type); LSRA activation preceded the CS in three patients (anterior type), and in the remaining three both sites were activated simultaneously (middle type). In the anterior type, CS stimulation preexcited the His and the ventricle without capturing the LSRA electrogram (atrial dissociation between the CS and the LSRA), suggesting that the anterograde FP was located posterior to the retrograde SP. In the posterior and middle types, high right atrial stimulation demonstrated atrial dissociation, suggesting that the anterograde FP was located anterior to the SP. In the posterior and middle types, retrograde P waves in the inferior leads were deeply negative, whereas they were shallow in the anterior type.

CONCLUSIONS

Fast-slow AVNRT was able to be categorized into posterior, middle and anterior types according to the site of the retrograde SP. The anterior type AVNRT, where an anteriorly located SP is used in the retrograde direction and a posteriorly located FP in the anterograde direction, appears to represent an anatomical reversal of the posterior type which uses a posterior SP for retrograde and an anterior FP for anterograde conduction. Anterior type AVNRT should be considered in the differential diagnosis of long RP (RP > PR intervals) tachycardias with shallow negative P waves in the inferior leads.

Coronary sinus pacing initiates counterclockwise atrial flutter while pacing from the low lateral right atrium initiates clockwise atrial flutter. Analysis of episodes of direct initiation of atrial flutter

INTRODUCTION

Rapid atrial pacing in sinus rhythm may directly induce atrial flutter without provoking intervening atrial fibrillation, or initiate atrial flutter indirectly, by a conversion from an episode of transient atrial fibrillation provoked by rapid atrial pacing. The present study was performed to examine whether or not the direct induction of clockwise or counterclockwise atrial flutter was pacing-site (right or left atrium) dependent.

METHODS AND RESULTS

We analyzed the mode of direct induction of atrial flutter by rapid atrial pacing. In 46 patients with a history of atrial flutter, rapid atrial pacing with 3 to 20 stimuli (cycle length = 500 - 170 ms) was performed in sinus rhythm to induce atrial flutter from 3 atrial sites, including the high right atrium, the low lateral right atrium, and the proximal coronary sinus, while recording multiple intracardiac electrograms of the atria. Direct induction of atrial flutter by rapid atrial pacing was a rare phenomenon and was documented only 22 times in 15 patients: 3, 11, and 8 times during stimulation, respectively, from the high right atrium, low lateral right atrium, and the proximal coronary sinus. Counterclockwise atrial flutter (12 times) was more frequently induced with stimulation from the proximal coronary sinus than from the low lateral right atrium (8 vs 1, P = .0001); clockwise atrial flutter (10 times) was induced exclusively from the low lateral right atrium (P = .0001 for low lateral right atrium vs proximal coronary sinus, P = .011 for low lateral right atrium vs high right atrium).

CONCLUSIONS

Direct induction of either counterclockwise or clockwise atrial flutter was definitively pacing-site dependent; low lateral right atrial pacing induced clockwise, while proximal coronary sinus pacing induced counterclockwise atrial flutter. Anatomic correlation between the flutter circuit and the atrial pacing site may play an important role in the inducibility of counterclockwise or clockwise atrial flutter.

Nonfluoroscopic guidance for catheter placement into the coronary sinus under direct vision using a balloon-tipped cardioscope

The right atrial posterior septum, including the coronary sinus (CS) ostium, is an important landmark in radiofrequency catheter ablation therapy for supraventricular tachycardia or atrial flutter. The anatomical findings around the CS ostium would be useful to determine a target site or line during catheter ablation. The aim of the study was to test the ability of the imaging catheter to identify structures in the posterior septal area of the right atrium and to evaluate the feasibility of guidance for catheter placement in the CS using a cardioscope that we recently developed. In 12 anesthetized dogs, the cardioscope, consisting of a deflectable 7 Fr fiberoptic endoscope with an inflatable and transparent balloon, was introduced into the right atrium via the femoral vein. The cardioscope was manipulated to observe the right atrial posterior septum. A deflectable electrode catheter was inserted via the jugular vein and positioned in the CS under cardioscopic guidance. In 10 of 12 dogs, the right atrial posterior septum, including the CS ostium, and the tendon of Todaro could be anatomically identified by cardioscopy. It was possible to position an electrode catheter in the CS in all 10 dogs under direct vision without fluoroscopy. But the CS ostium could not be detected in the remaining two dogs, although the cardioscope was placed at as many sites as possible. No complication occurred. The balloon-tipped cardioscope appears to be useful in observing the right atrialposterior septum and in guiding an electrode catheter into the CS.

Shortening of the intraventricular conduction time in premature ventricular beats during ventricular extrastimulation: possible role of dimensional shortening of the conducting distance during ventricular systole

INTRODUCTION

Conduction time (CT) is given by the formula: conducting distance divided by conduction velocity. Based on this formula, we hypothesized that CT shortening (i.e., supernormal conduction) may result from dimensional shortening of the distance of impulse propagation, which naturally occurs during ventricular systole.

METHODS AND RESULTS

To test the above, two separate groups of patients were studied, group A (14 patients) for electrophysiologic study and group B (12 patients) for echocardiographic study. In group A patients, CT from the stimulus artifact to the basal lateral wall of the left ventricle (LV) (S-LV interval) was measured using right ventricular (RV) apical extrastimulus testing. S-LV interval shortening in premature RV beats was demonstrated in all 14 patients. The maximum shortening was 20 +/- 9 msec (range 10 to 40), and the maximum % shortening was 16% +/- 6% (7% to 27%). In group B patients with implanted pacemakers, the major (long) and minor (short) axis dimensions of the LV were measured with echocardiography. The major axis dimension was used as an approximate measure of the linear length from the RV apex to the basal lateral wall of LV. The maximum % shortening of the major axis dimensions was 15% +/- 4%, 16% +/- 2%, and 11% +/- 4% during VVI pacing, respectively, at paced cycle lengths of 1,000 (11 patients), 800 (5 patients), and 600 msec (12 patients). The maximum % shortening of the S-LV intervals was comparable in magnitude with that of the major axis dimensions: 20% versus 15% +/- 4%, 15% +/- 7% versus 16% +/- 2% and 16% +/- 6% versus 11% +/- 4%, respectively, at paced cycle lengths of 1,000, 800, and 600 msec. There was also a good temporal correlation between the electrophysiologic (CT shortening) versus echocardiographic (dimensional shortening) parameters. Thus, the intraventricular CT and the major axis dimension of the LV were shortened in a similar magnitude and also at a similar timing in the cardiac cycle.

CONCLUSION

These findings suggest the possibility that supernormal conduction may result, at least in part, from dimensional shortening of the pathway length of impulse propagation from the stimulating to recording electrodes, which naturally occurs during ventricular systole.

Experimental study of catheter ablation using ultrasound energy in canine and porcine hearts

We examined the efficacy and safety of ultrasound energy in eliminating the arrhythmogenic substrates of atrial as well as ventricular tissue using a newly developed instrument in both in vivo and in vitro experiments. Ultrasound (US) applicators were tested on 79 lesions created on a beating heart in canine cardiac tissue, and on 64 lesions in porcine heart specimens. US lesions were created by using transducers with frequencies around 5-10 MHz. In the in vivo study, we observed a significant decrease in the amplitude of the electrograms recorded from the tip of the ablation catheter during the US application (p < 0.01). In some sites transmural lesions could be created which were well demarcated. Blood coagulum formation was observed on the tip of the ablation catheter on several occasions. In one dog ventricular fibrillation was provoked by the delivery of ultrasound energy to the left ventricle. In the in vitro study, lesion depth increased significantly with a longer duration of energy delivery when the temperature was maintained table (p < 0.001), and the lesion depth increased significantly with higher temperatures of energy delivery when the duration of US application was maintained (p < 0.05). In both cases, no significant change in surface area was observed. The maximum depth of the lesion was 10.3 mm.

CONCLUSIONS

An ultrasound energy system is relatively safe and effective for creating lesions large enough to eliminate arrhythmogenic substrates deep in the ventricular myocardium. Although the US system is free from pop phenomenon, the problem of blood coagulation on the catheter tip remains to be settled.

Atypical form of the fourth criterion for transient entrainment

The typical fourth criterion for transient entrainment is defined when both a sudden shortening in conduction interval to and a distinct change in electrogram morphology at a bipolar recording site are demonstrated while performing overdrive pacing of a reentrant tachycardia from a single pacing site at two different constant rates. The purpose of this article was to test the hypothesis that if an intracardiac recording site showing both orthodromic and antidromic capture with entrainment pacing is located suitably distant from the circuit, sudden shortening in conduction interval to that site may occur without any significant change in the bipolar electrogram morphology (i.e., atypical form of the fourth criterion). Atrial overdrive pacing of orthodromic tachycardia was performed in 20 patients with either left anterior (12 patients) or left posterior (8 patients) accessory pathways. We investigated the effects of overdrive pacing from the proximal or distal coronary sinus, specifically effects on the electrogram interval and the electrogram morphology at the right atrial appendage. Overdrive pacing of orthodromic tachycardia from the proximal coronary sinus was performed in 10 of the 12 patients with left anterior accessory pathways; those 10 patients demonstrated the first entrainment criterion at the right atrial appendage site. Overdrive pacing of orthodromic tachycardia at still shorter cycle lengths demonstrated a sudden shortening in conduction interval to the right atrial appendage site. Despite shortening in conduction interval the morphology of the right atrial appendage electrogram was completely or almost identical to that during orthodromic tachycardia, indicating an atypical form of the fourth criterion. This criterion was not demonstrated in patients with left posterior accessory pathways. Thus, atypical fourth entrainment criterion was demonstrated during overdrive pacing of orthodromic tachycardia from the proximal coronary sinus only in patients with left anterior accessory pathways. Demonstration of atypical fourth criterion seems largely dependent on the location of the accessory pathway, the pacing, and the recording sites.

New electrophysiologic features and catheter ablation of atrioventricular and atriofascicular accessory pathways: evidence of decremental conduction and the anatomic structure of the Mahaim pathway

INTRODUCTION

Several modalities of catheter ablation have been proposed to eliminate Mahaim pathway conduction. However, limited research has been reported on the electrophysiologic nature of this pathway in its entity.

METHODS AND RESULTS

In seven patients, electrophysiologic study was performed, and radiofrequency energy was applied to investigate the electrophysiologic clues for successful ablation. In all seven patients, the Mahaim pathway was diagnosed as a right-sided atriofascicular or atrioventricular pathway with decremental properties. In two patients, two different kinds of electrograms were recorded through the ablation catheter positioned at the Mahaim pathway location: one was suggestive of conduction over the decremental portion, demonstrating a dulled potential; and the other of nondecremental conduction, demonstrating a spiked potential. All but one of the Mahaim pathways were eliminated successfully at the atrial origin where the spiked Mahaim potential was recorded. Radiofrequency energy application was performed at the slow potential site resulting in failure to eliminate the conduction over the Mahaim pathway. Conduction block at the site between the slow and fast potential recording sites was provoked by intravenous administration of adenosine, concomitant with a decrease in the amplitude of the Mahaim potential. In one patient, the clinical arrhythmia was a sustained monomorphic ventricular tachycardia originating from the ventricular end of the Mahaim fiber.

CONCLUSION

The identification of Mahaim spiked potentials may be the optimal method to permit their successful ablation. Detailed electrophysiologic assessment is indispensable for successful ablation of tachycardias associated with Mahaim fibers because tachycardias unassociated with Mahaim fibers can occur despite complete elimination of the Mahaim fiber.

Transcatheter neodymium-yttrium-aluminum-garnet laser coagulation of canine ventricle using a balloon-tipped cardioscope

The feasibility of transcatheter laser ablation of the canine left ventricle (LV) was tested using a newly developed cardioscope. In 17 anesthetized dogs, a combined laser-endoscope catheter, consisting of an endoscope encased in a 7-French flexible catheter with an inflatable and transparent balloon at the distal end, was introduced into the LV via the carotid artery. A 1064-nm neodymium-yttrium-aluminum-garnet (Nd:YAG) laser was delivered by laser optic fiber, which was introduced through the transport channel and positioned inside the saline-filled balloon. In 16 of 17 dogs, the endocardial surface of the LV was clearly observed. Laser energy totaling 500-5,000 J was applied sequentially in 13 dogs and laser irradiation was completed in all but 2 of the dogs. The excised hearts revealed well-demarcated oval-shaped lesions 2.5-9.5 mm deep in 7 of 11 dogs. Histologic sections revealed coagulation necrosis surrounded by a rim of contraction band necrosis. Thus, transballoon laser photocoagulation of the beating LV is feasible. The newly combined laser-endoscope catheter, which is still in its preliminary stages and needs to be improved to increase the success rate of photocoagulation, appears to be a promising alternative modality for catheter ablative therapy for ventricular tachycardia.

Quantitative analysis of concealed conduction into accessory atrioventricular pathways in Wolff-Parkinson-White syndrome

Concealed conduction is demonstrated to occur in an accessory AV pathway (AP). To test the hypothesis that anterograde and retrograde concealed conduction in the AP would have different characteristics, 35 consecutive patients with single APs were studied. The anterograde or retrograde ERP of the AP could be determined in 23 of those patients. Anterograde concealed conduction in the AP was assessed in the first 13 patients with retrograde AP conduction (6 APs with retrograde conduction only and 5 with both directions) (group A). Retrograde concealed conduction in the AP was evaluated in the remaining 10 patients with anterograde AP conduction (6 APs with anterograde conduction only and 4 with both directions) (group B). The concealed conduction in the AP was quantified by determining the ERP of the AP using a "probe" extrastimulus (Sp) introduced in the opposite chamber. The ERP was determined both during conventional extrastimulus (S1S2 method; ERPc) and during that with an Sp (S1SpS2 method; ERPp). The Sp was delivered before or after the last S1 with various S1Sp intervals. The ERPp was determined at each S1Sp interval. Three distinct patterns in concealed conduction in the AP were noted. In the first pattern, the ERPp was always shorter than the ERPc, whereas the reverse relation was noted in the second pattern. The third pattern showed a combination of the two. In group A, only the first pattern was noted. In group B, the first, second, and third patterns were noted in 4, 2, and 4 patients, respectively. The first pattern was noted only in septal APs and the second and third were seen only in left free-wall APs. The second pattern was seen in patients with retrograde AP conduction, whereas the third one was mainly noted in patients without retrograde AP conduction. These observations indicate that anterograde and retrograde concealed conduction in the AP have different characteristics. Shortening of the ERPp might be due to the "peeling back" phenomenon, and its lengthening might be caused by the presence of the inhomogeneous refractory periods of the AP.

Conversion of recent-onset Atrial Fibrillation by a single oral dose of Pilsicainide (Pilsicainide Suppression Trial on atrial fibrillation). The PSTAF Investigators

The efficacy and safety of a single oral dose of 150-mg pilsicainide, a new class Ic antiarrhythmic drug, in converting recent-onset atrial fibrillation to sinus rhythm were evaluated in 75 patients (51 men, 24 women; age 23 to 74 years). Conversion to sinus rhythm was achieved within 90 minutes in 45% of patients given pilsicainide and in 8.6% of those on placebo (p < 0.01), with no major adverse effects.

Atypical antidromic resetting during programmed extrastimulation of reentrant ventricular tachycardia

A patient with reentrant ventricular tachycardia exhibited both the orthodromic and antidromic resetting responses at a single intracardiac recording site during programmed extrastimulation of ventricular tachycardia. The transition from orthodromic to antidromic resetting with extrastimulation demonstrated a sudden shortening in conduction interval to an electrogram recording site and unexpected identical morphology of the spontaneous and captured electrograms at that site, indicating atypical antidromic resetting. This newly observed resetting phenomenon with programmed extrastimulation suggests that the fourth entrainment criterion with overdrive pacing may likely be demonstrated in an atypical form; that is, a sudden shortening in conduction interval to an electrogram recording site may occur without any significant change in the bipolar electrogram morphology at that site when overdrive pacing is performed during tachycardia from a single pacing site at two different constant rates.

Earlier activation of the distal than the proximal site of the coronary sinus may represent retrograde conduction through AV node: significance of recording of far distal coronary sinus

During retrograde conduction through an accessory pathway (AP) or the atrioventricular (AV) node, earlier activation of the distal recording site than a more proximal site of the coronary sinus (CS) generally indicates retrograde conduction via a distally located AP. Thus, after successful ablation of a left-sided AP, if the distal CS recording site is activated earlier than a more proximal site retrogradely, it is considered to suggest-in the absence of His-bundle recording or more frequently in the setting of poor recording of the low septal right atrial electrogram-a conduction via a second AP (located more distally), and not conduction via the AV node. Yet, we hypothesized that retrograde conduction through the AV node may activate the far distal site of the CS (CSD) earlier than a more proximal site, as the anterior atrial wavefront, coming retrogradely from the AV node and traveling along the anterior mitral annulus, could reach the CSD earlier than a more proximal site. To test this we studied 18 patients with intact retrograde conduction via the AV node, but without evidence of an AP. The CSD was recorded by means of a quadripolar catheter (interelectrode distance of 2-5 mm); retrograde activation sequence at the distal (CSD1-2) versus proximal (CSD3-4) bipolar recording site was determined during ventricular stimulation. In 12 of 18 patients the CSD1-2 recording site was activated 5-10 ms earlier than the CSD3-4 recording site, in 3 of 18 patients the CSD1-2 site was activated 5 ms later than the CSD3-4 site; in the remaining 3 patients both recording sites were depolarized simultaneously. The results indicate that the CSD was often depolarized earlier than a more proximal site by impulses that conducted to the atria retrogradely via the AV node while the quadripolar recording catheter was placed at the CSD. This observation, although not well documented previously, suggests that the sequence of retrograde atrial activation in the CS should be studied carefully in consideration of the actual location of the mapping catheter in order to correctly diagnose the presence or absence of conduction via an AP.

Bradycardia-dependent activation delay of the atrial tissue in a patient with sick sinus syndrome

Bradycardia-dependent block or activation delay of the atrial tissue has not been documented in the literature. A patient with sick sinus syndrome in whom bradycardia-dependent, as well as tachycardia-dependent, activation delay in the atria was elucidated is reported on. The phenomenon of bradycardia-dependent activation delay was reproducibly demonstrated, both during atrial extrastimulation and incremental atrial pacing from the high right atrium, in the setting of an abnormally prolonged activation interval from the distal stimulating electrodes to the proximal recording electrodes of a quadripolar catheter, which was localized in the high right atrial region. Supernormal conduction seemed to be an unlikely explanation for the observed phenomenon.

The response of atrioventricular junctional tissue to temperature

To determine the optimal temperature for catheter heat mapping without damaging cardiac tissue, we studied the electrophysiologic and histologic responses of the atrioventricular (AV) conduction system exposed to a specific range of temperatures. In 18 closed-chest dogs, an electrode catheter with a thermistor, tip was positioned transvenously at the AV junction. Radiofrequency current (RFC) was applied in incremental temperature steps until transient 2nd-degree AV block was induced. Catheter tip temperature (CTT) was measured at each step. RFC was immediately discontinued when AV block occurred. AV conduction was evaluated before and 4 weeks after the procedure. Acute transient 2nd-degree AV block was induced in 45 applications, during which the average CTT was 48.7 +/- 2.7 degrees C. In another 40 applications in which 2nd degree AV block was not induced, the average CTT was significantly lower [46.3 +/- 2.5 degrees C] (p < 0.001). Eleven of 16 dogs showed acute 2nd-degree AV block, but had normal AV conduction at 4 weeks (Group A). In the other 5 dogs, 1st-degree AV block was seen at 4 weeks (Group B). The lowest CTTs in Groups A and B were 45 and 49 degrees C, respectively. Histologic findings in 2 dogs from Group A revealed that 10-15% (by area) of the AV node was fibrotic. These findings suggest that the induction of fully reversible AV block can be achieved by titration of RFC, during the application of RFC to the AV junction. In conclusion, RF energy was used to produce a tip temperature of between 45 degrees C and 49 degrees C, which induced reversible and significant interruption of conduction of in tissue in the AV junction, and presumably also in target sites in clinical RF ablation.

Double ventricular responses during extrastimulation of atrioventricular nodal reentrant tachycardia

In patients with dual atrioventricular (AV) nodal pathways, double ventricular responses to a single atrial depolarization have been shown to occur, but virtually only during atrial pacing in sinus rhythm. We report on a patient with a slow-fast form of AV nodal reentrant tachycardia who exhibited double ventricular responses following extrastimulation during AV nodal reentrant tachycardia. The phenomenon of double ventricular responses during the tachycardia was demonstrated by extrastimulation from the proximal coronary sinus. Retrograde unidirectional block in the slow pathway, and an anterograde effective refractory period that was shorter in the fast pathway than that in the slow pathway, are suggested.

"Paradoxical" AH shortening caused by proximal coronary sinus stimulation during orthodromic reciprocating tachycardia

INTRODUCTION

During extrastimulation or entrainment of orthodromic atrioventricular (AV) reciprocating tachycardia (ORT), the atrium-His (AH) interval as measured at the His-bundle recording site is expected to lengthen due to extrastimulation-dependent or pacing rate-dependent slowing of AV nodal conduction by impulses that penetrate the tachycardia circuit. We report 6 patients in whom the AH interval "paradoxically" shortened during ORT in response to extrastimulation and rapid pacing from the proximal coronary sinus.

METHODS AND RESULTS

Accessory pathway location was right anterior (1 patient), right anteroseptal (1 patient), and left anterior (4 patients). Cycle length of ORT was stable (variation < or = 5 msec) and ranged from 325 to 410 msec. During ORT, extrastimulation and rapid pacing were performed from the proximal coronary sinus and the right atrium. Extrastimulation from the proximal coronary sinus late in diastole caused significant shortening of AH interval in all patients by a mean of 18 +/- 3 msec (range 15 to 20 msec). AH shortening was demonstrated without a change of either the timing or morphologic appearance of the low septal right atrium at the His-bundle recording site. This phenomenon was not observed during right atrial extrastimulation. Rapid pacing from the proximal coronary sinus at cycle lengths of 305 to 390 msec (i.e., 15 to 20 msec shorter than the cycle length of each ORT) again demonstrated shortening of AH interval in all patients by a mean of 15 +/- 3 msec (range 10 to 20 msec). By contrast, rapid pacing from the right atrium demonstrated classical AH prolongation at any paced cycle length.

CONCLUSION

AH shortening without a change of either the timing or morphologic appearance of the low septal right atrium at the His-bundle recording site confirms the existence of a distinct posterior atrial input to the AV node. In this setting low septal right atrial activation is not requisite for AV nodal conduction. Whether activation of the low septal right atrium is essential for, or contributes to, AV nodal conduction of atrial impulses from locations other than the proximal coronary sinus needs to be determined.

Nonuniformity of AH intervals during stimulation at different left atrial sites

Studies in humans have found left atrial stimulation via the coronary sinus (CS) to elicit significantly shorter atrium-His (AH) intervals as compared to right atrial stimulation, but whether pacing at different left atrial sites (anterior vs posterior left atrium, i.e., far distal vs proximal CS) affects the AH interval has not been studied. Hence, in 22 patients, we compared the effects of stimulation from various atrial sites, including anterior high right atrium (HRA), distal CS, mid-CS, and proximal CS, on: stimulus-atrium (SA), AH, and stimulus-His intervals on the His bundle electrogram. Paced cycle length differed for each patient (range 900-350 msec, mean 532 +/- 140 msec), but conduction intervals from different atrial sites were compared using identical cycle length in each patient. The mean SA intervals were 34 +/- 10 msec, 57 +/- 10 msec, 44 +/- 11 msec, and 32 +/- 8 msec with stimulation, respectively, from HRA, distal CS, mid-CS, and proximal CS (each significantly different except for HRA vs proximal CS). The mean AH intervals were 123 +/- 23 msec, 104 +/- 28 msec, 95 +/- 15 msec, and 90 +/- 18 msec with stimulation, respectively, from HRA, distal CS, mid-CS, and proximal CS (each significantly different except for mid-CS vs proximal CS). In 13 patients, the discrepancy in AH intervals during distal versus proximal CS stimulation was > or = 15 msec; in 9 patients this difference was only < or = 10 msec, considered within the range of measurement error. Thus, in a significant portion of patients, discrepant AH intervals were demonstrated during stimulation from the distal versus proximal CS. These previously undescribed observations suggest that electrophysiological studies on atrioventricular nodal conduction that involve left atrial stimulation must take into account actual location of the stimulation site (anterior or posterior) in order to properly interpret the findings.

The relationship between early afterdepolarization and the occurrence of torsades de pointes--an in vivo canine model study

The relationship between early afterdepolarization (EAD) and the occurrence of torsades de pointes (TdP) was studied in a canine model. Twelve dogs of both sexes, weighing 9.9-16 Kg, were studied. After reducing the concentration of serum potassium to 3.0-4.0 mEq/l, by administration of calcium polystyrene sulfonate at 15-20 g/day for 1 or 2 weeks, a 6F electrode catheter was introduced via the femoral vein and positioned at the atrioventricular (AV) junction. Complete AV block was produced by catheter ablation using a high frequency current. A Franz 6F catheter was introduced into the right ventricle to record monophasic action potentials (MAPs) using the contact electrode technique. After a stable recording of the MAPs was achieved, cesium chloride (CsCl; 1 mM/Kg) was administered as an intravenous bolus over 15 sec. The MAPs and electrocardiogram (ECG) changes were simultaneously recorded for 30 min after the administration of CsCl. The administration was repeated several times at intervals 30 min. Sustained or non-sustained ventricular tachycardia was produced in all dogs. EAD appeared in 8 of 12 dogs. When EAD developed sufficiently high amplitude, ventricular premature beats occurred near the peak of EAD and TdP was induced in 3 of 8 EAD-positive dogs. TdP was not induced in EAD-negative dogs. Although TdP was comparatively difficult to induce, EAD-triggered activity was suggested to be one of the necessary conditions for TdP, because TdP occurred only when EAD reached a sufficiently high amplitude to produce ventricular premature beats.

Retrograde supernormal conduction, gap phenomenon in concealed accessory atrioventricular pathways

We present four patients with the Wolff-Parkinson-White syndrome who exhibited retrograde supernormal conduction or gap phenomenon in concealed accessory pathways. In the first patient, ventricular extrastimulus testing revealed retrograde block at the coupling interval of 520 msec and reappearance of conduction at the coupling interval of 370 msec. In a second patient, 1:1 retrograde conduction was not present but supernormal conduction was demonstrated at coupling intervals of 360 msec to 310 msec during the ventricular extrastimulus testing when the basic drive consisted of atrioventricular (AV) simultaneous pacing. In a third patient, ventricular extrastimulus testing demonstrated retrograde conduction through the accessory pathway only at coupling intervals of 400 msec to 360 msec. In a fourth patient, retrograde block occurred at the coupling interval of 340 msec and retrograde "slow" conduction reappeared at coupling intervals of 300 msec to 250 msec (gap phenomenon) only when the basic drive consisted of AV simultaneous pacing. Thus, concealed accessory pathways may exhibit retrograde supernormal conduction or gap phenomenon. Ventricular extrastimulus testing consisting of AV simultaneous pacing during the basic drive may facilitate demonstration of these unusual properties.

[Progress in clinical electrophysiologic study (EPS): recent tendency]

About twenty years have passed since the clinical introduction of electrophysiologic study (EPS). The mechanism of arrhythmias can be understood by EPS, and EPS-guided therapy is available theoretically. Of course, not all arrhythmia needs EPS, because other non-invasive tests are available. Clinically, reentry is the most frequently observed mechanism. Therefore, EPS is most suitable for the reentrant arrhythmias which can be repeatedly initiated and terminated by programmed stimulation. In many tachyarrhythmias, slow conduction pathway or area essential for reentry are demonstrated. On the other hand, triggered activity and abnormal automatism have been less frequently observed clinically. Today, application of EPS has been extended to catheter ablation for which precise mapping is required.

Atrioventricular nodal reentrant tachycardia with retrograde block induced by aprindine

Two patients are described who had atrioventricular nodal reentrant tachycardia (AVNRT) with 1:1 relationship in the control state, but in whom a varying degree of VA block during AVNRT was observed during therapy with aprindine. Aprindine, however, did not cause anterograde blockade of conduction over the slow AV nodal pathway during tachycardia. These observations support the conclusion that the bulk of atrial muscle is not a requisite part of the tachycardia circuit in AVNRT and that antiarrhythmic drugs may have disparate effects on conduction in the retrograde and anterograde limbs of the circuit.

Experimental study on the electrophysiological effects of the combination of the antiarrhythmic drugs aprindine and verapamil

The acute electrophysiological effects of the antiarrhythmic drugs aprindine and verapamil, injected intravenously either alone or in combination, were studied in 14 dogs during invasive electrophysiology. The AH and HV intervals during sinus rhythm were significantly prolonged, especially in the aprindine and the aprindine plus verapamil groups. The cycle lengths of the antegrade and retrograde atrio-ventricular block were most prolonged in the combination group. The effective refractory period and the functional refractory period of the atrial tissue, as well as the functional refractory period of the atrio-ventricular node, the effective refractory period of ventricular tissue and the ventriculo-atrial conduction system were most prolonged when the combination of the agents was given. The effective refractory period of the atrio-ventricular node was prolonged in the groups receiving verapamil and verapamil plus aprindine. There was no significant difference in the serum concentration of each agent given alone or in combination. These results suggest that the efficacy of the combination of verapamil and aprindine may be due to additive or synergistic effects of these antiarrhythmic agents.

Demonstration of right and left atrial dissociation by atrial rapid pacing or extrastimulation during fast-slow (uncommon) form of atrioventricular nodal reentrant tachycardia

Some recent works suggest that extranodal atrial fibers may form part of the reentry circuit in the atrioventricular (AV) nodal reentrant tachycardia (AVNRT). This hypothesis is based on the fact that the perinodal dissection successfully abolished AVNRT while preserving intact AV conduction. Apart from the surgical success, the electrophysiological evidence supporting this hypothesis has not been demonstrated, especially in the uncommon (fast-slow) form of AVNRT. We present some electrophysiological evidence suggesting atrial participation in eight patients with the fast-slow form of AVNRT. During the tachycardia, rapid pacing or extrastimulation was done from the orifice of the coronary sinus (CS) and the right atrium (RA), while recording the electrograms of the CS and the low septal RA. In seven patients, right and left atrial dissociation was demonstrated during pacing from the RA, while in the remaining one this was demonstrated from the CS. The interatrial dissociation will be unlikely if the intranodal reentry circuit connects with the atria via a single upper common pathway. This suggests that the upper turnaround of the reentry circuit involves atrial tissue and that the extranodal accessory pathway with long conduction times may form the ascending limb of the circuit (atrionodal reentry). Alternatively, the reentry circuit is entirely intranodal and two or more connecting pathways are present between the atria and the circuit.

Combination therapy with aprindine and verapamil for paroxysmal supraventricular tachycardia as assessed by transesophageal atrial pacing

To assess the efficacy of combination therapy of aprindine (40 mg/day) and verapamil (160 mg/day), transesophageal programmed atrial stimulation was performed on 21 patients with paroxysmal supraventricular tachycardia (including 12 patients with atrioventricular nodal reentrant tachycardia and nine patients with atrioventricular reentrant tachycardia) under four conditions: a) control, b) aprindine alone, c) verapamil alone, and d) aprindine + verapamil.

RESULTS

a) Aprindine, verapamil, and aprindine + verapamil prevented paroxysmal supraventricular tachycardia induction in 2/21, 3/21, and 9/21 patients, respectively; b) aprindine + verapamil prolonged the cycle length of paroxysmal supraventricular tachycardia more than aprindine or verapamil alone; c) aprindine, verapamil, and aprindine + verapamil decreased the AV blocking rate by 15, 23, and 35 beats/min, respectively, in comparison with the control state; d) aprindine, verapamil, and aprindine + verapamil prolonged the effective refractory period of atrioventricular conduction system by 20, 34, and 76 msec, respectively, compared with the control state. In conclusion, aprindine + verapamil appear to be more effective than aprindine or verapamil alone in preventing paroxysmal supraventricular tachycardia with nodal reentry, but there was less benefit in those without nodal reentry (Wolff-Parkinson-White group).