Destructive device removal - sparks and deletion of therapy history from an implantable cardioverter defibrillator

A 74-year-old female with a diagnosis of idiopathic dilated cardiomyopathy and ventricular tachycardia died suddenly 9 years after an implantation of an implantable cardioverter-defibrillator (ICD). The destructive removal of an ICD generator and the leads by an uninformed coroner resulted in the loss of the fragile electrograms during the terminal episodes of VT/VF and caused severe charring on the surface of the ICD generator. In order to observe the conditions in which the shock deliveries occurred during the noise detection, we programmed the ICD to deliver the maximum shock energy via a programmer while keeping continuous contact between the device surface and shock lead. The maximum shock energy of 31 Joules produced significant sparks from the surface of the ICD. To avoid the loss of data from an ICD and injury to the patient, widespread notification and education through appropriate scientific societies about the functions of ICDs are highly recommended.

Neurally mediated syncope as a cause of syncope in patients with Brugada electrocardiogram

INTRODUCTION

Patients with type 1 Brugada electrocardiogram (ECG) and an episode of syncope are diagnosed as symptomatic Brugada syndrome; however, all episodes of syncope may not be due to ventricular tachyarrhythmia.

METHODS AND RESULTS

Forty-six patients with type 1 Brugada ECG (all males, 51 +/- 13 years, 29 spontaneous, 17 Ic-drug induced), 20 healthy control subjects (all males, 35 +/- 11 years), and 15 patients with suspected neurally mediated syncope (NMS; 9 males, 54 +/- 22 years) underwent the head-up tilt (HUT) test. During the HUT test, 12-lead ECGs were recorded in all patients, and the heart rate variability was investigated in some patients. Sixteen (35%) of 46 patients with Brugada ECG, 2 (10%) of 20 control subjects, and 10 (67%) of 15 patients with suspected NMS showed positive responses to the HUT test. Although no significant differences were observed in HUT-positive rate among Brugada patients with documented VT (7/14; 50%), syncope (5/19; 26%) and asymptomatic patients (4/13; 31%), the HUT-positive rate was significantly higher in patients with documented VT (50%) and those with VT or no symptoms (11/27, 41%) compared to that in control subjects (10%) (P < 0.05). Augmentation of ST-segment amplitude (> or =0.05 mV) in leads V1-V3 was observed in 11 (69%) of 16 HUT-positive patients with Brugada ECG during vasovagal responses, and was associated with augmentation of parasympathetic tone following sympathetic withdrawal.

CONCLUSION

Thirty-five percent of patients with Brugada ECG showed vasovagal responses during the HUT test, suggesting that some Brugada patients have impaired balance of autonomic nervous system, which may relate to their syncopal episodes.

Long-term prognosis of probands with Brugada-pattern ST-elevation in leads V1-V3

BACKGROUND

The prognosis of patients with saddleback or noncoved type (non-type 1) ST-elevation in Brugada syndrome is unknown. The purpose of this study was to clarify the long-term prognosis of probands with non-type 1 ECG and those with coved (type 1) Brugada-pattern ECG.

METHODS AND RESULTS

A total of 330 (123 symptomatic, 207 asymptomatic) probands with a coved or saddleback ST-elevation > or = 1 mm in leads V(1)-V(3) were divided into 2 ECG groups-type 1 (245 probands) and non-type 1 (85 probands)-and were prospectively followed for 48.7+/-15.0 months. The absence of type 1 ECG was confirmed by drug provocation test and multiple recordings. The ratio of individuals with a family history of sudden cardiac death (14%) was lower than previous studies. Clinical profiles and outcomes were not notably different between the 2 groups (annual arrhythmic event rate of probands with ventricular fibrillation; type 1: 10.2%, non-type 1: 10.6%, probands with syncope; type 1: 0.6%, non-type 1: 1.2%, and asymptomatic probands; type 1: 0.5%, non-type 1: 0%). Family history of sudden cardiac death at age <45 years and coexistence of inferolateral early repolarization with Brugada-pattern ECG were independent predictors of fatal arrhythmic events (hazard ratio, 3.28; 95% confidence interval, 1.42 to 7.60; P=0.005; hazard ratio, 2.66; 95% confidence interval, 1.06 to 6.71; P=0.03, respectively, by multivariate analysis), although spontaneous type 1 ECG and ventricular fibrillation inducibility by electrophysiological study were not reliable parameters.

CONCLUSIONS

The long-term prognosis of probands in non-type 1 group was similar to that of type 1 group. Family history of sudden cardiac death and the presence of early repolarization were predictors of poor outcome in this study, which included only probands with Brugada-pattern ST-elevation.

QRS prolongation is associated with high defibrillation thresholds during cardioverter-defibrillator implantations in patients with hypertrophic cardiomyopathy

BACKGROUND

Although high defibrillation threshold (DFT) is a major and unavoidable clinical problem after implantation of an implantable cardioverter defibrillator (ICD), little is known about the cause and management of a high DFT in patients with hypertrophic cardiomyopathy (HCM). The purpose of this study was to assess the predictors of a high DFT in patients with HCM.

METHODS AND RESULTS

Twenty-three patients with non-dilated HCM who underwent ICD implantation were included. The DFT at the time of the device implantation was measured in all patients. The patients were divided into 2 groups, a high DFT group (DFT >or=15J, n=13) and a low DFT group (DFT <15J, n=10); and their baseline characteristics were compared. The QRS duration was longer in the high than in the low DFT group (128 +/-31 vs 103 +/-12 ms, respectively; P=0.02). QRS duration, left ventricular (LV) end-systolic diameter, and LV ejection fraction were significant predictors of DFT in univariate analysis. However, in multivariate analysis, the only factor significantly associated with DFT was QRS duration (P=0.002).

CONCLUSIONS

QRS duration is the most consistent predictor of a high DFT in HCM patients undergoing ICD implantation.

Mitral isthmus pathology of re-entrant ventricular tachycardia in a patient with idiopathic dilated cardiomyopathy

A 68-year-old woman with idiopathic dilated cardiomyopathy suffered from drug-resistant monomorphic ventricular tachycardia (VT). Electrophysiological study revealed a re-entrant VT circuit located just beneath the inferior mitral valve annulus. The VT was considered to be related to the mitral valve isthmus and was abolished by radiofrequency ablation. The patient died 2 years after the ablation due to worsening of heart failure and an autopsy was performed. Pathological examination revealed ablation scar tissue on the localized myocardial bundle running parallel to the mitral valve annulus. Therefore, this bundle appeared to comprise the slow conduction area of the re-entrant VT in this case.

Efficacy of DynaCT digital angiography in the detection of the fistulous point of dural arteriovenous fistulas

BACKGROUND AND PURPOSE

Identifying the precise hemodynamic features, including the fistulous point, is essential for treatments of dural arteriovenous fistulas (DAVFs). This study illustrates the efficacy of DynaCT digital angiograms obtained from a 3D C-arm CT to directly visualize the location of the fistulous points in DAVFs.

MATERIALS AND METHODS

This retrospective study observed 14 consecutive patients with DAVFs, which included 7 cavernous sinuses, 4 transverse-sigmoid sinuses, 2 convexity-superior sagittal sinuses, and 1 tentorial sinus. In the assessment of the practical applicability for the diagnosis of DAVFs, images obtained from 2D digital subtraction angiography (DSA) and DynaCT were comparatively evaluated.

RESULTS

In all patients, DynaCT digital angiography could clearly demonstrate the feeding arteries, the fistulous points, and the draining veins. Significant anatomic landmarks for the fistulous points with relationships to osseous structures were also provided. Compared with 2D DSA, DynaCT digital angiograms demonstrated 12 additional findings in 8 patients (57%), including the detection of the fistulous points (n = 7), the feeders (n = 1), the retrograde leptomeningeal drainage (n = 1), the draining veins (n = 1), and the venous anomaly (n = 2).

CONCLUSIONS

In comparison with 2D DSA, DynaCT may provide more detailed information to evaluate DAVFs. DynaCT digital angiograms have a high contrast and isotropic spatial resolution, allowing a reliable visualization of small vessels and fine osseous structures. Such detailed information, especially for the location of the fistulous points, could be very useful for either the endovascular or the surgical treatments of DAVFs.

Seasonal and circadian distributions of ventricular fibrillation in patients with Brugada syndrome

BACKGROUND

It is well-known that the incidence of ventricular tachyarrhythmias is the highest in winter and during the daytime in patients with structural heart disease. However, little is known about the seasonal and circadian distributions of ventricular fibrillation (VF) in patients with Brugada syndrome.

OBJECTIVE

The aim of this study was to investigate seasonal and circadian distributions of VF in patients with Brugada syndrome.

METHODS

We analyzed the data of appropriate shock episodes for VF recorded by an implantable cardioverter-defibrillator (ICD) in patients with Brugada syndrome.

RESULTS

Among 62 consecutive Brugada syndrome patients with an ICD (48 +/- 14 years, 58 males), 19 patients had at least one episode of an appropriate ICD shock due to VF during a mean follow-up of 70 +/- 36 months, and 98 episodes were evaluated as isolated VF. There was a significant peak between March and June (P = .03). As for the circadian variation, significantly more VF occurred from midnight to 6:00 (P <.0001). Electrical storms of VF occurred in seven patients. The seasonal and circadian variations of electrical storms were similar to those of the isolated VF episodes.

CONCLUSIONS

In patients with Brugada syndrome, there was a significant seasonal peak from spring to early summer and a significant circadian peak from midnight to early morning in terms of the occurrences of VF.

Comparison of long-term follow-up of electrocardiographic features in Brugada syndrome between the SCN5A-positive probands and the SCN5A-negative probands

To investigate changes of electrocardiographic parameters with aging and their relation to the presence of SCN5A mutation in probands with Brugada syndrome (BS), we measured several electrocardiographic parameters prospectively during long-term follow-up (10 +/- 5 years) in 8 BS probands with SCN5A mutation (SCN5A-positive group, all men; age 46 +/- 10 years) and 36 BS probands without SCN5A mutation (SCN5A-negative group, all men; age 46 +/- 13 years). Throughout the follow-up period, depolarization parameters, such as P-wave (lead II), QRS (leads II, V(2), V(5)), S-wave durations (leads II, V(5)), and PQ interval (leads II) were all significantly longer and S-wave amplitude (II, V(5)) was significantly deeper in the SCN5A-positive group than in the SCN5A-negative group. The SCN5A-positive group showed a significantly longer corrected QT interval (lead V(2)) and higher ST amplitude (lead V(2)) than those in the SCN5A-negative group. The depolarization parameters increased with aging during the follow-up period in both groups; however, the PQ interval (lead II) and QRS duration (lead V(2)) were prolonged more prominently and the QRS axis deviated more to the left with aging in the SCN5A-positive group than in the SCN5A-negative group. In conclusion, conduction slowing was more marked and more progressively accentuated in Brugada probands with SCN5A mutation than in those without SCN5A mutation.

Implications of 2:1 atrioventricular block during typical atrioventricular nodal reentrant tachycardia

OBJECTIVE

The effects of 2:1 AV block (AVB) on AV nodal reentrant tachycardia (AVNRT) remain to be elucidated. This study was performed to localize the site of 2:1 AVB and elucidate the effects of 2:1 AVB on typical AVNRT.

METHODS

The His bundle (HB) electrograms during typical AVNRT with 2:1 AV block were reviewed in 24 patients. It was hypothesized that if 2:1 AVB at the HB or below changed tachycardia cycle length (TCL), the lower turnaround point of the reentrant circuit (RC) might be located within the HB and parts of the HB might be involved in the RC.

RESULTS

A HB potential was absent in blocked beats during 2:1 AVB in four patients (supra-Hisian block), and the maximal amplitude of the HB potential in blocked beats was the same as that in conducted beats in four patients (infra-Hisian block), and was significantly smaller than that in conducted beats (0.1 +/- 0.1 versus 0.5 +/- 0.2 mV, P < 0.05) in 16 patients (intra-Hisian block). Eight patients (33%) with intra-Hisian block had a nearly identical prolongation of the H-A and A-A intervals in blocked beats (12 +/- 3 and 13 +/- 2 ms, respectively) with unchanged A-H intervals, while the remaining 16 patients (67%) exhibited invariable A-A and/or H-A intervals.

CONCLUSION

The site of 2:1 AVB during typical AVNRT was estimated to be at the HB or below in 83% of the cases. Two-to-one intra-Hisian block transiently prolonged TCL, possibly indicating involvement of the proximal HB in the RC in one-third of typical the AVNRT cases with 2:1 AVB.

Participation of a concealed atriohisian tract in the reentrant circuit of the slow–fast type of atrioventricular nodal reentrant tachycardia

BACKGROUND

The retrograde fast pathway in typical atrioventricular nodal reentrant tachycardia (AVNRT) exhibits marked variation in its electrophysiologic properties.

OBJECTIVE

The purpose of this study was to characterize the retrograde fast pathway and localize the lower turnaround site of the reentrant circuit in typical AVNRT.

METHODS

Seventy-four patients with typical AVNRT were divided into two groups according to the response of the retrograde fast pathway to intravenous administration of adenosine triphosphate (ATP) during ventricular pacing: ATP-S [n = 47 (63.5%)] with and ATP-R without [n = 27 (36.5%)] His-atrial (H-A) block. H-A intervals were measured from the most proximal His-bundle electrogram to the earliest atrial activation during the tachycardia (HAt) and entrainment pacing from the parahisian right ventricular region (HAe). It was postulated that the HAt was the difference in conduction time between the lower common pathway (x) and retrograde fast pathway (y) (HAt = y - x), whereas HAe was the sum of the two (HAe = y + x). Hence, x = (HAe-HAt)/2. x >0 suggested the presence of a lower common pathway, whereas x <0 suggested the absence of a lower common pathway and lower turnaround site within the His bundle.

RESULTS

x was significantly smaller in ATP-R than ATP-S (-6 +/- 5 vs 4 +/- 4 ms, P <.05) and was <0 in 23 (85%) of 27 ATP-R patients. The maximal increment in H-A interval during ventricular pacing was significantly longer in ATP-S than ATP-R (35 +/- 33 vs 2 +/- 2 ms, P <.05).

CONCLUSION

A concealed atriohisian tract totally bypassing the atrioventricular node constituted the retrograde fast pathway in one third of all typical AVNRT cases.

Sex Hormone and Gender Difference?Role of Testosterone on Male Predominance in Brugada Syndrome

INTRODUCTION

The clinical phenotype is 8 to 10 times more prevalent in males than in females in patients with Brugada syndrome. Brugada syndrome has been reported to be thinner than asymptomatic normal controls. We tested the hypothesis that higher testosterone level associated with lower visceral fat may relate to Brugada phenotype and male predominance.

METHODS AND RESULTS

We measured body-mass index (BMI), body fat percentage (BF%), and several hormonal levels, including testosterone, in 48 Brugada males and compared with those in 96 age-matched control males. Brugada males had significantly higher testosterone (631 +/- 176 vs 537 +/- 158 ng/dL; P = 0.002), serum sodium, potassium, and chloride levels than those in control males by univariate analysis, and even after adjusting for age, exercise, stress, smoking, and medication of hypertension, diabetes, and hyperlipidemia, whereas there were no significant differences in other sex and thyroid hormonal levels. Brugada males had significantly lower BMI (22.1 +/- 2.9 vs 24.6 +/- 2.6 kg/m(2); P < 0.001) and BF% (19.6 +/- 4.9 vs 23.1 +/- 4.7%; P < 0.001) than control males. Testosterone level was inversely correlated with BMI and BF% in both groups, even after adjusting for the confounding variables. Conditional logistic regression models analysis showed significant positive and inverse association between Brugada syndrome and hypertestosteronemia (OR:3.11, 95% CI:1.22-7.93, P = 0.017) and BMI (OR:0.72, 95% CI:0.61-0.85, P < 0.001), respectively.

CONCLUSIONS

Higher testosterone level associated with lower visceral fat may have a significant role in the Brugada phenotype and male predominance in Brugada syndrome.

Acute and chronic management in patients with Brugada syndrome associated with electrical storm of ventricular fibrillation

BACKGROUND

Some patients with Brugada syndrome experience an electrical storm of ventricular fibrillation (VF).

OBJECTIVE

The purpose of this study was to investigate the clinical, laboratory, electrocardiographic, and electrophysiologic characteristics, acute and subsequent chronic treatment, and follow-up data of patients with Brugada syndrome associated with electrical storm of VF.

METHODS

Sixty-seven patients with Brugada syndrome (65 men and 2 women, age 46 +/- 14 years) were divided into three groups: 7 patients with a history of electrical storm of VF (group I), 39 symptomatic patients with documented VF and/or syncope (group II), and 21 asymptomatic patients (group III). Electrical storm was defined as three or more episodes of VF per day recorded by the memory of an implantable cardioverter-defibrillator.

RESULTS

No significant differences were observed among the three groups with regard to clinical (age at diagnosis, familial history of sudden cardiac death), laboratory (SCN5A mutation and serum potassium level), electrocardiographic and electrophysiologic characteristics, and follow-up duration after diagnosis. However, arrhythmic events during follow-up after diagnosis and number of arrhythmic events per patient were significantly higher in group I compared with groups II and III. Isoproterenol infusion (0.003 +/- 0.003 microg/kg/min for 24 +/- 13 days) completely suppressed electrical storm of VF in all five patients treated and was successfully replaced with oral medications, including denopamine, quinidine, isoproterenol, cilostazol, and bepridil alone or in combination.

CONCLUSION

No specifically clinical, laboratory, electrocardiographic, and electrophysiologic characteristics were recognized in patients with Brugada syndrome associated with electrical storm of VF. Isoproterenol infusion was effective as an acute treatment in suppressing electrical storm of VF and was successfully replaced with chronic oral medications.

Diagnostic and prognostic value of a type 1 Brugada electrocardiogram at higher (third or second) V1 to V2 recording in men with Brugada syndrome

To evaluate the diagnostic and prognostic value of an electrocardiogram (ECG) recorded at a higher (third or second) intercostal space, 98 men (17 to 76 years of age, mean +/- SD 47 +/- 13; with documented ventricular fibrillation [VF] in 22 and syncope in 32) were categorized into 3 groups; 68 men had a spontaneous type 1 ECG in standard leads V(1) and V(2) (S group), 19 had a spontaneous type 1 ECG only in the higher V(1) and V(2) leads (H group), and 11 had a type 1 ECG only after receiving class Ic sodium channel blockers (Ic group). There were no significant differences in baseline clinical characteristics, including VF episodes, syncope, atrial fibrillation, family history, late potentials, and inducibility of VF during electrophysiologic study across the 3 groups. During prospective follow-up periods (779 +/- 525, 442 +/- 282, and 573 +/- 382 days, respectively), subsequent cardiac events occurred in 11 men (16%) within the S group, in 2 men (11%) in the H group, and in 0 men (0%) in the Ic group (p = NS, S vs H group). In men with previous episodes of VF, subsequent cardiac events occurred in 7 (44%) within the S group and in 2 (50%) in the H group (p = NS). In conclusion, men with a spontaneous type 1 Brugada ECG recorded only at higher leads V(1) and V(2) showed a prognosis similar to that of men with a type 1 ECG in using standard leads V(1) and V(2).

Catheter ablation of stable and unstable ventricular tachycardias in patients with arrhythmogenic right ventricular dysplasia

INTRODUCTION

A reentrant circuit within an area of abnormal myocardium is suspected as the origin of ventricular tachycardia (VT) in patients with arrhythmogenic right ventricular dysplasia (ARVD).

OBJECTIVES

To examine the relationship between the reentrant circuits of VT and the abnormal electrograms in ARVD, and to assess the feasibility of a block line formation in the reentrant circuit isthmus utilizing electroanatomical mapping system (CARTO) guidance.

METHODS AND RESULTS

An electrophysiological study and catheter ablation (CA) were performed in 17 ARVD patients (13 men, 47 +/- 17 year) using CARTO. Endocardial mapping during sinus rhythm demonstrated electrogram abnormalities extended from the tricuspid annulus (TA) or the right ventricular outflow tract in 16 of 17 patients. In 13 hemodynamically stable VTs, the reentrant circuits and critical slow conduction sites for the CA were investigated during VTs. The entire macro-reentrant pathway was identified in 6/13 stable VTs (figure-of-8 in 4, single loop in 2). In the remaining seven VTs, a focal activation pattern was found in four and an unidentifiable pattern in three. CA successfully abolished all the macro-reentrant and focal tachycardias, however, not effective in three unidentifiable VTs. In the 13 cases with unstable VT, the linear conduction block zone was produced between the sites with abnormal electrograms and the TA. Ultimately, 23/26 VTs (88%) became noninducible after the CA. During follow-up (26 +/- 15 months), 13/17 patients remained free from any VT episodes.

CONCLUSIONS

CARTO is useful for characterizing the anatomical and electrophysiological substrates, and for identifying the optimal ablation sites for VT associated with ARVD.

Spatial Distribution of Repolarization and Depolarization Abnormalities Evaluated by Body Surface Potential Mapping in Patients with Brugada Syndrome

BACKGROUND

Mutations in sodium channel gene, SCN5A, have been identified in Brugada syndrome, but it is still unclear as to how sodium channel dysfunction relates to arrhythmogenesis. We examined spatial distribution of both repolarization and depolarization abnormalities in patients with Brugada syndrome by using 87-leads body surface potential mapping (BSPM).

METHODS

BSPM was recorded under baseline condition and after pharmacological interventions in 28 patients with Brugada syndrome (27 males, 49 +/- 14 years). The ST-segment amplitude 20 ms after the end of QRS (ST20), QRS duration, and corrected recovery time (RTc) were measured in all 87-leads, and averaged among 6-leads (D-F, 5-6) reflecting right ventricular outflow tract (RVOT) potentials and the other 81-leads.

RESULTS

The ST20 was elevated at baseline, normalized by isoproterenol, and augmented by pilsicainide in only the RVOT. The RTc was longer at baseline and increased by pilsicainide in only the RVOT. On the other hand, the QRS duration was slightly widened at baseline, further increased by pilsicainide, but not changed by isoproterenol in both leads.

CONCLUSIONS

The ST-segment elevation and the RTc prolongation were localized and modulated by agents only in the RVOT region, while the slight QRS widening at baseline and further increase by pilsicainide were observed homogeneously. Our data suggest that depolarization abnormalities are distributed homogeneously, whereas repolarization abnormalities are localized in the RVOT.

"Left-variant" atypical atrioventricular nodal reentrant tachycardia: electrophysiological characteristics and effect of slow pathway ablation within coronary sinus

INTRODUCTION

Recent anatomical and electrophysiological studies have demonstrated the presence of leftward posterior nodal extension (LPNE); however, its role in the genesis of atrioventricular nodal reentrant tachycardia (AVNRT) is poorly understood. This study was performed to characterize successful slow pathway (SP) ablation site and to elucidate the role of LPNE in genesis of atypical AVNRT with eccentric activation patterns within the coronary sinus (CS).

METHODS AND RESULTS

Among 45 patients with atypical AVNRT (slow-slow/fast-slow/both = 20/22/3 patients) with concentric (n = 37, 82%) or eccentric CS activation (n = 8, 18%), successful ablation site was evaluated. Among 35/37 patients (95%) with concentric CS activation, ablation at the conventional SP region outside CS eliminated both retrograde SP conduction and AVNRT inducibility. Among eight patients with eccentric CS activation, the earliest retrograde atrial activation was found at proximal CS 16 +/- 4 mm distal to the ostium during AVNRT. The earliest retrograde activation site was located at inferior to inferoseptal mitral annulus, consistent with the presumed location of LPNE. Ablation at the conventional SP region with electroanatomical approach only rendered AVNRT nonsustained without elimination of retrograde SP conduction in seven of eight patients (88%). Ablation targeted to the earliest retrograde atrial activation site within proximal CS (15 +/- 4 mm distal to the ostium); however, eliminated retrograde SP conduction and rendered AVNRT noninducible in six of eight patients (75%).

CONCLUSION

In 75% of "left-variant" atypical AVNRT, ablation within proximal CS was required to eliminate eccentric retrograde SP conduction and render AVNRT noninducible, suggesting LPNE formed retrograde limb of reentrant circuit.

Site-Specific Influence of Transversal Conduction Across Crista Terminalis on Recognition of Isthmus Block

BACKGROUND

Transversal conduction across crista terminalis (CT) is commonly observed during low-rate coronary sinus (CS) pacing after isthmus ablation and sometimes mimics incomplete clockwise isthmus block (IB). Site-specific influence of trans-cristal conduction gap on recognition of clockwise IB has been poorly understood.

METHODS

Forty-five patients with common-type atrial flutter underwent mapping of CT and free wall lateral to CT during CS pacing of 100 ppm using CARTO after verification of IB, while duodecapolar catheter was positioned along tricuspid annulus to map periannular activation.

RESULTS

A total of 43 gaps were demonstrated at upper (n = 15, 35%), middle (n = 17, 40%), and lower one-thirds of CT (n = 11, 25%) in 36 of 45 patients (80%). Gaps were single in 31 (69%) and multiple in 5 patients (11%). Activation patterns of free wall lateral to CT in CARTO maps were descending pattern without gaps (n = 9, 20%), collision pattern with a single gap (n = 31, 69%), and simultaneous pattern with multiple gaps (n = 5, 11%). Activation sequence of duodecapolar catheter was complete block pattern in 41 (91%) and incomplete block pattern in 4 patients (9%), masquerading as persistent clockwise isthmus conduction. The incomplete block pattern in duodecapolar catheter was exclusively associated with a gap at the lower CT (0/15, 0/17, and 4/11 gaps at upper, middle, and lower CT, respectively; P < 0.01) and was attributable to faster conduction across CT gaps than in complete block pattern.

CONCLUSIONS

Trans-cristal conduction was commonly observed during low-rate CS pacing. Rapid transversal conduction exclusively across lower CT masqueraded as incomplete clockwise IB.