Atrioventricular nodal reentry. Clinical, electrophysiological, and therapeutic considerations

Atrioventricular re-entrant tachycardia and atrioventricular node re-entrant tachycardia in a patient with cancer under chemotherapy: a case report and literature review

Cardio-oncology is a new field of interest in cardiology focusing on the detection and treatment of cardiovascular diseases, such as arrhythmias, myocarditis, and heart failure, as side-effects of chemotherapy and radiotherapy. The association between chemotherapeutic agents and arrhythmias has previously been established. Atrial tachyarrhythmias, particularly atrial fibrillation, are most common, but ventricular arrhythmias, including those related to treatment-induced QT prolongation, and bradyarrhythmias can also occur. However, the association between chemotherapeutic agents and atrioventricular re-entrant tachycardia (AVRT)/atrioventricular node re-entrant tachycardia (AVNRT) remains poorly understood. Here, we report a patient with new-onset AVRT/AVNRT and lung cancer who underwent chemotherapy. We considered that chemotherapy or cancer itself may have been a trigger for the initiation of paroxysmal AVRT/AVNRT, and that radiofrequency catheter ablation was effective in treating this type of tachycardia. Here, possible mechanisms and potential genes (mostly ion channels) involved in AVRT/AVNRT are summarized and the mechanisms underlying the possible regulatory patterns of cancer cells and chemotherapy on ion channels are reviewed. Finally, we considered that ion channel abnormalities may link cancer or chemotherapy to the onset of AVRT/AVNRT. The aim of the present study was to highlight the association between chemotherapeutic agents and AVRT/AVNRT and to provide new insights for future research. Understanding the intermediate mechanisms between chemotherapeutic agents and AVRT/AVNRT may be beneficial in preventing chemotherapy-evoked AVRT/AVNRT (and/or other arrhythmias) in future.

Three-dimensional electroanatomically guided slow pathway elimination is associated with procedural improvements and clinical benefit in atrioventricular node reentrant tachycardia patients

Background

Slow pathway (SP) ablation, in the context of atrioventricular node reentrant tachycardia (AVNRT) treatment could result in either complete elimination or only modification of the SP with ambiguity regarding associated benefits. Three-dimensional electroanatomical mapping (3D-EAM) may be used adjunctively aiming to complete SP elimination. Our purpose was to compare a 3D-EAM-based strategy targeting SP elimination to the conventional fluoroscopic approach with respect to clinical outcomes.

Methods

One hundred and two consecutive AVNRT patients (36 males, mean age 53.2 ± 13.7 years) underwent in two successive periods a conventional fluoroscopic ablation approach (n = 42) or a 3D-EAM-guided ablation focusing on complete SP elimination (n = 60).

Results

Several procedural parameters improved with 3D-EAM use, including fluoroscopy time (2.4 ± 4.7 min vs. 13 ± 4.5 min), dose-area product (1061 ± 3122 μGy × m2 vs. 5002 ± 3032 μGy × m2) and slow pathway elimination frequency (95% vs. 50%, all p < .001). Procedural time was slightly prolonged in the 3D-EAM group (101 ± 31 min vs. 87 ± 24 min, p = .013). Two major complications occurred in the conventional group. Altogether, over a mean follow-up of approximately 2.7 years, recurrence occurred in 6 of 42 (14.3%) in the conventional group as compared to 1 of 62 (1.7%) in the EAM-based group (p = .019). In the Kaplan-Meier analysis, time-to-event was significantly longer for the EAM-based patients (p < .030). Moreover, the EAM-based strategy was associated with less redo procedures' rates (9.5% in the non-EAM group vs. 0% in the EAM group, p = .026).

Conclusions

The present study showed that an EAM-based SP elimination strategy is not only feasible and safe but it is also accompanied by improved clinical outcomes in the setting of AVNRT ablation.

Integrative Analyses Identify Potential Key Genes and Calcium-Signaling Pathway in Familial Atrioventricular Nodal Reentrant Tachycardia Using Whole-Exome Sequencing

Background

Atrioventricular nodal reentrant tachycardia (AVNRT) is a common arrhythmia. Growing evidence suggests that family aggregation and genetic factors are involved in AVNRT. However, in families with a history of AVNRT, disease-causing genes have not been reported.

Objective

To investigate the genetic contribution of familial AVNRT using a whole-exome sequencing (WES) approach.

Methods

Blood samples were collected from 20 patients from nine families with a history of AVNRT and 100 control participants, and we systematically analyzed mutation profiles using WES. Gene-based burden analysis, integration of previous sporadic AVNRT data, pedigree-based co-segregation, protein-protein interaction network analysis, single-cell RNA sequencing, and confirmation of animal phenotype were performed.

Results

Among 95 related reference genes, seven candidate pathogenic genes have been identified both in sporadic and familial AVNRT, including CASQ2, AGXT, ANK2, SYNE2, ZFHX3, GJD3, and SCN4A. Among the 37 reference genes from sporadic AVNRT, five candidate pathogenic genes were identified in patients with both familial and sporadic AVNRT: LAMC1, ryanodine receptor 2 (RYR2), COL4A3, NOS1, and ATP2C2. To identify the common pathogenic mechanisms in all AVNRT cases, five pathogenic genes were identified in patients with both familial and sporadic AVNRT: LAMC1, RYR2, COL4A3, NOS1, and ATP2C2. Considering the unique internal candidate pathogenic gene within pedigrees, three genes, TRDN, CASQ2, and WNK1, were likely to be the pathogenic genes in familial AVNRT. Notably, the core calcium-signaling pathway may be closely associated with the occurrence of AVNRT, including CASQ2, RYR2, TRDN, NOS1, ANK2, and ATP2C2.

Conclusion

Our pedigree-based studies demonstrate that RYR2 and related calcium signaling pathway play a critical role in the pathogenesis of familial AVNRT using the WES approach.

AH jump duration is associated with elimination of slow pathway during ablation of atrioventricular nodal reentrant tachycardia

Introduction

Ablating the slow pathway (SP) is the superior treatment for atrioventricular nodal reentrant tachycardia (AVNRT) with a low complication rate. However, the ablation of the SP could result in either complete elimination or modification of the SP. We aimed to investigate whether the duration of AH jump pre-ablation associated with the outcome of elimination of SP.

Methods

We included 56 patients with typical AVNRT (slow-fast), 20 males and 36 females, aged 44.2 ± 15.1 years. Slow pathway ablation was performed using classical approach. Univariate and multivariate analysis was performed for potential predictors of SP elimination.

Results

Typical AVNRT was inducible in all patients. Post-ablation, non-inducibility of AVNRT was obtained in all 56 (100%) patients, with SP elimination in 33 (61%) patients and SP modification in 23 (39%) patients. Patients with SP elimination had significantly longer AH jump than patients with SP modification. Cox regression analysis showed that AH jump duration was the independent predictor of SP elimination, in which every 20 ms increase in AH jump duration was associated with 1.30 higher rate of SP elimination. Furthermore, ROC curve analysis indicated that the AH jump duration of ≥100 ms had 6.14 times higher probability for complete elimination of the SP with a sensitivity of 79%, specificity of 70%, PPV of 79% and NPV of 70%.

Conclusions

AH jump duration pre-ablation is associated with complete elimination of slow pathway during AVNRT ablation.

Identification of potential candidate genes and pathways in atrioventricular nodal reentry tachycardia by whole-exome sequencing

Background

Atrioventricular nodal reentry tachycardia (AVNRT) is the most common manifestation of paroxysmal supraventricular tachycardia (PSVT). Increasing data have indicated familial clustering and participation of genetic factors in AVNRT, and no pathogenic genes related to AVNRT have been reported.

Methods

Whole‐exome sequencing (WES) was performed in 82 patients with AVNRT and 100 controls. Reference genes, genome‐wide association analysis, gene‐based collapsing, and pathway enrichment analysis were performed. A protein‐protein interaction (PPI) network was then established; WES database in the UK Biobank and one only genetic study of AVNRT in Denmark were used for external data validation.

Results

Among 95 reference genes, 126 rare variants in 48 genes were identified in the cases (minor allele frequency < 0.001). Gene‐based collapsing analysis and pathway enrichment analysis revealed six functional pathways related to AVNRT as with neuronal system/neurotransmitter release cycles and ion channel/cardiac conduction among the top 30 enriched pathways, and then 36 candidate pathogenic genes were selected. By combining with PPI analysis, 10 candidate genes were identified, including RYR2, NOS1, SCN1A, CFTR, EPHB4, ROBO1, PRKAG2, MMP2, ASPH, and ABCC8. From the UK Biobank database, 18 genes from candidate genes including SCN1A, PRKAG2, NOS1, and CFTR had rare variants in arrhythmias, and the rare variants in PIK3CB, GAD2, and HIP1R were in patients with PSVT. Moreover, one rare variant of RYR2 (c.4652A > G, p.Asn1551Ser) in our study was also detected in the Danish study. Considering the gene functional roles and external data validation, the most likely candidate genes were SCN1A, PRKAG2, RYR2, CFTR, NOS1, PIK3CB, GAD2, and HIP1R.

Conclusion

The preliminary results first revealed potential candidate genes such as SCN1A, PRKAG2, RYR2, CFTR, NOS1, PIK3CB, GAD2, and HIP1R, and the pathways mediated by these genes, including neuronal system/neurotransmitter release cycles or ion channels/cardiac conduction, might be involved in AVNRT.

Supraventricular Tachycardia

The term paroxysmal supraventricular tachycardia encompasses a heterogeneous group of arrhythmias with different electrophysiologic characteristics. Knowledge of the mechanism of each supraventricular tachycardia is important in determining management in the office, at the bedside, and in the electrophysiology laboratory. Paroxysmal supraventricular tachycardias have an abrupt onset and offset, typically initiating and terminating with premature atrial ectopic beats. In the acute setting, both vagal maneuvers and pharmacologic therapy can be effective in arrhythmia termination. Catheter ablation has revolutionized therapy for many supraventricular tachycardias, and newer techniques have significantly improved ablation efficacy and decreased periprocedural complications and procedure times.

Next-generation sequencing of AV nodal reentrant tachycardia patients identifies broad spectrum of variants in ion channel genes

Atrioventricular nodal reentry tachycardia (AVNRT) is the most common form of regular paroxysmal supraventricular tachycardia. This arrhythmia affects women twice as frequently as men, and is often diagnosed in patients <40 years of age. Familial clustering, early onset of symptoms and lack of structural anomaly indicate involvement of genetic factors in AVNRT pathophysiology. We hypothesized that AVNRT patients have a high prevalence of variants in genes that are highly expressed in the atrioventricular conduction axis of the heart and potentially involved in arrhythmic diseases. Next-generation sequencing of 67 genes was applied to the DNA profile of 298 AVNRT patients and 10 AVNRT family members using HaloPlex Target Enrichment System. In total, we identified 229 variants in 60 genes; 215 missenses, four frame shifts, four codon deletions, three missense and splice sites, two stop-gain variants, and one start-lost variant. Sixty-five of these were not present in the Exome Aggregation Consortium (ExAC) database. Furthermore, we report two AVNRT families with co-segregating variants. Seventy-five of 284 AVNRT patients (26.4%) and three family members to different AVNRT probands had one or more variants in genes affecting the sodium handling. Fifty-four out of 284 AVNRT patients (19.0%) had variants in genes affecting the calcium handling of the heart. We furthermore find a large proportion of variants in the HCN1-4 genes. We did not detect a significant enrichment of rare variants in the tested genes. This could be an indication that AVNRT might be an electrical arrhythmic disease with abnormal sodium and calcium handling.

Human His-Purkinje System: Abnormalities of Conduction, Rhythm Disorders and Case Studies

This review covers many of the arrhythmias and conduction abnormalities related to His-Purkinje System. These include junctional premature complexes, junctional and fascicular tachycardias, bundle branch reentry (BBR), and the role of apparent conduction in various forms of supraventricular tachycardias (SVT) with or without involvement of accessory pathways (AP).

Effectiveness of the Valsalva Manoeuvre for reversion of supraventricular tachycardia

BACKGROUND

People with the cardiac arrhythmia supraventricular tachycardia (SVT) frequently present to clinicians in the prehospital and emergency medicine settings. Restoring sinus rhythm by terminating the SVT involves increasing the refractoriness of atrioventricular nodal tissue within the myocardium by means of vagal manoeuvres, pharmacological agents, or electrical cardioversion. A commonly used first-line technique to restore the normal sinus rhythm (reversion) is the Valsalva Manoeuvre (VM). This is a non-invasive means of increasing myocardial refractoriness by increasing intrathoracic pressure for a brief period, thus stimulating baroreceptor activity in the aortic arch and carotid bodies, resulting in increased parasympathetic (vagus nerve) tone.

OBJECTIVES

To assess the evidence of effectiveness of the VM in terminating SVT.

SEARCH METHODS

We updated the electronic searches of the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 7); MEDLINE Ovid (1946 to August week 3, 2014); EMBASE Classic and EMBASE Ovid (1947 to 27 August 2014); Web of Science (1970 to 27 August 2014); and BIOSIS Previews (1969 to 22 August 2014). We also checked trials registries, the Index to Theses, and the bibliographies of all relevant publications identified by these strategies.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) that examined the effectiveness of VM in terminating SVT.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted the data using a standardised form. We assessed each trial for internal validity, resolving any differences by discussion. We then extracted and entered data into Review Manager 5.

MAIN RESULTS

In this update, we did not identify any new RCT studies for inclusion. We identified two RCT studies as ongoing that we are likely to include in future updates. Accordingly, our results are unchanged and include three RCTs with a total of 316 participants. All three studies compared the effectiveness of VM in reverting SVT with that of other vagal manoeuvres in a cross-over design. Two studies induced SVT within a controlled laboratory environment. Participants had ceased all medications prior to engaging in these studies. The third study reported on people presenting to a hospital emergency department with an episode of SVT. These participants were not controlled for medications or other factors prior to intervention.The two laboratory studies demonstrated reversion rates of 45.9% and 54.3%, whilst the clinical study demonstrated reversion success of 19.4%. This discrepancy may be due to methodological differences between studies, the effect of induced SVT versus spontaneous episodic SVT, and participant factors such as medications and comorbidities. We were unable to assess any of these factors, or adverse effects, further, since they were either not described in enough detail or not reported at all.Statistical pooling was not possible due to heterogeneity between the included studies.

AUTHORS' CONCLUSIONS

We did not find sufficient evidence to support or refute the effectiveness of VM for termination of SVT. Further research is needed, and this research should include a standardised approach to performance technique and methodology.

Empiric slow pathway ablation in non-inducible supraventricular tachycardia

BACKGROUND

The data supporting the practice of empiric slow pathway ablation (ESPA) in patients with documented supraventricular tachycardia (SVT) who are non-inducible at electrophysiology study (EPS) is limited. The aim of this study is to assess the efficacy of ESPA in adults.

METHODS

A multi-center cohort study of patients who had ESPA between January 2008 and October 2013 was performed. Patients were identified by screening sequential SVT ablation procedures.

RESULTS

Forty-three (5%) out of 859 SVT ablation procedures were identified as ESPA. The median age was 53 (IQR: 24) years; 63% were female. All patients had pre-EPS documentation of SVT (either strip or ECG). In 23 (53.5%) cases, pre-EPS ECG showed short RP tachycardia. Thirty-two (74.4%) patients had dual atrioventricular nodal physiology (DAVNP) plus echo beats. Junctional rhythm (JR) as procedural endpoint was noted in 39 (90.7%) patients. In 18 (41.9%) patients, the abolishment of DAVNP was achieved. No complications were encountered. A median follow-up of 17 months (range: 6 to 31 months) revealed 83.7% (36 of 43) success rate, defined as the absence of pre-procedural symptoms and any documented sustained arrhythmia. As compared to patients with recurrence (n=7), patients with no recurrence (n=36) had significantly higher prevalence of clinical short RP tachycardia (61.1% vs. 14.3%, p=0.038), and EPS finding of DAVNP plus echo beats (80.6% vs. 42.9%, p=0.034).

CONCLUSIONS

ESPA is a reasonable approach in patients with documented SVT, in particular in short RP tachycardia, who are not inducible at EPS. Larger studies are required to assess this practice.

[Dual AV nodal nonreentry tachycardia (DAVNNT): unrecognized differential diagnosis with far-reaching consequences]

BACKGROUND

The dual atrioventricular nodal nonreentry tachycardia (DAVNNT) is a rare form of tachycardia which occurs due to a time delayed double antegrade conduction via the slow and fast atrioventricular nodal pathways. Its epidemiology is not known so far. The aim of this article is to present the clinical findings in a series of patients with DAVNNT.

MATERIALS AND METHODS

We retrospectively analyzed our database of patients who successfully underwent radiofrequency catheter ablation between January 2012 and March 2013 due to diagnosed supraventricular tachycardia.

RESULTS

In 3 out of 231 patients DAVNNT could be successfully treated by slow pathway modulation/ablation. Patients presented with widely varying symptoms including syncope, palpitations which had been mistaken as atrial fibrillation, and inappropriate defibrillator shocks due to suspected ventricular tachycardia.

CONCLUSIONS

The DAVNNT seems to be more common than previously thought. This important differential diagnosis needs to be taken into consideration as slow pathway modulation can be curative while a misdiagnosis, such as atrial fibrillation or ventricular tachycardia might result in over-treatment in patients with this arrhythmia.

Slow pathway ablation for typical atrioventricular nodal re-entrant tachycardia significantly alters the autonomic modulation of atrioventricular conduction

PURPOSE

Atrioventricular (AV) conduction turbulence, biphasic dromotropic response of AV node to single ventricular premature contraction (VPC), consists of early shortening and later prolongation of AV conduction intervals due to the direct electrophysiological mechanisms and perturbation in autonomic modulation. We investigated the acute effect of radiofrequency catheter ablation of slow pathway on AV turbulence.

METHODS

The electrophysiological study was performed in 18 patients (7 men, mean age 49 ± 15 years) undergoing catheter ablation for AV nodal reentrant tachycardia. The stimulation protocol consisting of series of isolated VPC (coupling interval of 273 ± 23 ms) delivered from right ventricle apex during constant atrial pacing at 100 bpm was performed immediately prior to and 8 ± 4 min after successful slow-pathway ablation. Averaged post-VPCs profiles of AV conduction intervals were analyzed by purpose-written software. The descriptors of AV turbulence, turbulence onset (TOAV), turbulence slope (TSAV), and AV recovery (R AV) were assessed.

RESULTS

Slow-pathway ablation suppressed the AV nodal responsiveness to VPC as evidenced by significant reduction of AV turbulence indices: TOAV: -6.4 ± 7.5 % vs. -4.3 ± 6.1 % (p < 0.05); TSAV: 2.0 ± 2.6 ms/RRi vs. 1.0 ± 0.7 ms/RRi (p < 0.05); and R AV: -13.8 ± 7.3 % vs. -6.5 ± 12.7 % (p < 0.05).

CONCLUSIONS

Slow-pathway ablation significantly attenuated both vagal and non-autonomic modulation of AV nodal conduction. This effect is likely due to direct thermal injury of AV node associated with the change of properties of AV nodal fast-pathway although specific alteration of peri-AV nodal ganglionated plexi or their neural inputs into the AV node cannot be excluded.

Are patients admitted to emergency departments with regular supraventricular tachycardia (SVT) treated appropriately?

Regular supraventricular tachycardia (SVT) is frequently encountered in clinical practice. Guidelines are available from the National Service Framework (NSF) for the treatment of patients attending emergency departments (ED) with SVT. These recommend a thyroid-function test (TFT) and arrhythmia electrocardiography (ECG), and referral to a heart-rhythm specialist on discharge. Hospital admission is rarely required. In our multicentre study, we examined the implementation of these guidelines among patients attending the ED with SVT. Only 34% of patients had specialist referrals, with an average wait of 50.3 days (the majority of delays resulted from referral requests from general practitioners). A history of previous SVT, the mode of tachycardia termination, patient age and/or comorbidities were similar for the 27 (23.5%) patients who were admitted overnight. Of these, 15 (13%) of the total 115 patients who attended ED with regular SVT were referred for Holter monitoring despite having ECGs demonstrating arrhythmia. Low referral rates, unnecessary investigations and admissions indicate a need for improvement for better patient care and to minimise healthcare costs. We have formulated a standard operating procedure, which will be available via the College of Emergency Medicine website.

Effectiveness of the Valsalva Manoeuvre for reversion of supraventricular tachycardia

BACKGROUND

Patients with the cardiac arrhythmia supraventricular tachycardia (SVT) frequently present to clinicians in the prehospital and emergency medicine settings. Restoring sinus rhythm by terminating the SVT involves increasing the refractoriness of AV nodal tissue within the myocardium by means of vagal manoeuvres, pharmacological agents or electrical cardioversion. A commonly used first-line technique to restore the normal sinus rhythm (reversion) is the Valsalva Manoeuvre (VM). This is a non-invasive means of increasing myocardial refractoriness by increasing intrathoracic pressure for a brief period, thus stimulating baroreceptor activity in the aortic arch and carotid bodies, resulting in increased parasympathetic (vagus nerve) tone.

OBJECTIVES

To assess the evidence of effectiveness of the Valsalva Manoeuvre in terminating supraventricular tachycardia.

SEARCH METHODS

We electronically searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (Issue 1 of 12, 2012); MEDLINE Ovid (1946 to January 2012); EMBASE Ovid (1947 to January 2012); Web of Science (1970 to 27 January 2012); and BIOSIS Previews (1969 to 27 January 2012). Trials registries, the Index to Theses and the bibliographies of all relevant publications identified by these strategies were also checked.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) that examined the effectiveness of the Valsalva Manoeuvre in terminating SVT.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted the data using a standardised form. Each trial was assessed for internal validity with differences resolved by discussion. Data were then extracted and entered into Review Manager 5.1 (RevMan).

MAIN RESULTS

We identified three randomised controlled trials including 316 participants. All three studies compared the effectiveness of VM in reverting SVT with that of other vagal manoeuvres in a cross-over design. Two studies induced SVT within a controlled laboratory environment. Participants had ceased all medications prior to engaging in these studies. The third study reported on patients presenting to a hospital emergency department with an episode of SVT. These patients were not controlled for medications or other factors prior to intervention.The two laboratory studies demonstrated reversion rates of 45.9% and 54.3%, whilst the clinical study demonstrated reversion success of 19.4%. This discrepancy may be due to methodological differences between studies, the effect of induced SVT versus spontaneous episodic SVT, and participant factors such as medications and comorbidities. We were unable to assess any of these factors further, nor adverse effects, since they were either not described in enough detail or not reported at all.Statistical pooling was not possible due to heterogeneity between the included studies.

AUTHORS' CONCLUSIONS

We did not find sufficient evidence to support or refute the effectiveness of the Valsalva Manoeuvre for termination of SVT. Further research is needed and this should include a standardised approach to performance technique and methodology.

Supraventricular tachycardias: proposal of a diagnostic algorithm for the narrow complex tachycardias

The narrow complex tachycardias (NCTs) are defined by the presence in a 12-lead electrocardiogram (ECG) of a QRS complex duration less than 120ms and a heart rate greater than 100 beats per minute; those are typically of supraventricular origin, although rarely narrow complex ventricular tachycardias have been reported in the literature. As some studies document, to diagnose correctly the NCTs is an arduous exercise because sometimes those have similar presentation on the ECG. In this paper, we have reviewed the physiopathological, clinical, and ECG findings of all known supraventricular tachycardias and, in order to reduce the possible diagnostic errors on the ECG, we have proposed a quick and accurate diagnostic algorithm for the differential diagnosis of NCTs.

Pediatric tachyarrhythmia and radiofrequency catheter ablation: results from 1993 to 2011

BACKGROUND AND OBJECTIVES

We performed a retrospective study to elucidate the frequency of tachycardia mechanisms and the characteristics of accessory pathways (APs), confirmed by radiofrequency catheter ablation (RFCA) in pediatric tachycardia. In addition, we analyzed the efficacy and safety of pediatric RFCA.

SUBJECTS AND METHODS

The authors retrospectively reviewed the records of a total of 260 patients (aged 2 to 18 years) who had undergone RFCA between August 1993 and July 2011 at two medical centers in Daegu.

RESULTS

Two hundred and sixty patients underwent 272 RFCAs at less than 18 years of age. Of these 260 patients, 9 patients (3%) were younger than 6 years, and 175 patients (67%) were older than 12 years. The tachycardia mechanisms observed were atrioventricular reentry tachycardia (AVRT) in 175 patients (65%), atrioventricular nodal reentry tachycardia (AVNRT) in 83 patients (30%), ventricular tachycardia in 12 patients (4%), and atrial tachycardia in 2 patients (0.7%). Among the patients with AVRT, there were 94 concealed APs and 81 manifest APs. Left-side APs were more common in concealed APs than in manifest APs (72/94, 77% vs. 33/81, 41%, p<0.001). Sixty-six percent (55/83) of AVNRT cases were located at the M1 and/or M2 sites. Four patients had multiple tachycardia mechanisms (AVNRT+AVRT) and 9 patients had multiple APs. The recurrence rate was 5% (13/272). Of these recurrent cases, 12 patients had AVRT. The overall success rate was 95%.

CONCLUSION

Pediatric RFCA provides a good success rate and an acceptable recurrence. In addition, we suggest that the APs location may be associated with concealed or manifest property of APs.

Antiarrhythmic Drug Therapy of Supraventricular Tachycardia

Pharmacologic therapy is commonly used for the acute treatment and termination of paroxysmal supraventricular tachycardia (SVT) and continues to be an important long-term option for some patients. Drug choice depends on the correct diagnosis of the arrhythmia and an understanding of its mechanism. Pharmacologic agents commonly used in the acute and chronic treatment of SVT are reviewed along with their effect on the various types of SVT. Drugs that are well tolerated with minimal side effects are preferred over agents with perhaps more efficacy but higher risk of toxicity.

Clinical and electrophysiological characteristics, and relatively benign outcome, of typical atrioventricular nodal reentrant tachycardia in children and adolescents

BACKGROUND

Atrioventricular nodal re-entrant tachycardia is an uncommon arrhythmia in children. The natural history of this disturbance is poorly known in young patients.

METHODS

We analyzed the clinical and electrophysiological features, and the final outcome, in 19 children affected by typical atrioventricular nodal re-entrant tachycardia diagnosed by a transoesophageal electrophysiological study.

RESULTS

Of the cohort, 12 patients were female and 7 male, with a mean age of 11 years. Dual atrioventricular nodal physiology was demonstrated in 14 children (73%). The mean length of the tachycardia cycle was 297 milliseconds, with periods of 2 to 1 atrioventricular block during tachycardia noted in 5 children (26%). The mean cycle length was significantly shorter in the children who presented episodes of 2 to 1 atrioventricular block than in those who did not. After diagnosis, 12 children were not treated, 6 were treated with medical therapy, and 1 was submitted to radiofrequency transcatheter ablation. During a mean follow-up period of 41 months, 2 children with rare, but sustained, episodes of tachycardia that initially had not been treated were submitted to radiofrequency transcatheter ablation. Among children treated pharmacologically, 1 teenager was submitted to radiofrequency transcatheter ablation on the basis of parental choice, 3 children have discontinued medical therapy recording only sporadic episodes of tachycardia, and 2 children are still treated with antiarrhythmic drugs. At the last follow-up visit, 13 children (68%) were without any treatment, 4 had been successfully ablated, and 2 were still on medical treatment.

CONCLUSIONS

Our data indicates a relatively benign outcome in this group of children and adolescents with atrioventricular nodal re-entrant tachycardia.

Comparison of the cardiac electrophysiological effects between doxazosin and bunazosin

In Langendorff-perfused adult rat heart with constant pressure at 80 mmHg, we found doxazosin, an alpha(1) adrenoceptor blocker, at 10 muM prolonged PR interval and induced occasional arrhythmia followed by complete inhibition of the sinus rhythm, whereas bunazosin, another alpha(1)-blocker, at same concentration did not. The results of voltage-clamp study showed that, at the concentration of 10 muM, doxazosin inhibited I (Na), I ( (Ca,L) ), I (to), and Iss without changing I (k1) but bunazosin only inhibited I ( (Ca,L) ) about 30%. Doxazosin also caused markedly negative shift of the I (Na) inactivation curve. In current-clamp study, doxazosin prolonged action potential duration in association with the decreased action potential amplitude and upstroke velocity, whereas bunazosin did not. We hypothesize that doxazosin-induced arrhythmia may result from the heterogeneous or different level of I ( (Ca,L) ) blockade of AV nodal tissue. In conclusion, the present study suggests that bunazosin is safer than doxazosin for long-term treatment in view of electrophysiological effect. However, the underlying mechanism of doxazosin induced nodal arrhythmia is still needed to be determined.

Supraventricular tachycardia and the struggle to be believed

BACKGROUND

Little research exists examining patient experiences of life with supraventricular tachycardia (SVT). Realistic expectations of symptoms, patient management strategies, and treatment options are important components of patient education and treatment decisions.

AIM

This descriptive qualitative study explored patients' experiences living with SVT.

METHODS

Grounded theory methodology was used with semi-structured interviews of 25 SVT patients undergoing radiofrequency ablation treatment.

RESULTS

The main core category that emerged from the data was the "struggle to be believed". The struggle or work of living with SVT entails: (1) living with the uncertainty of the occurrence and duration of an episode, (2) "covering up" to manage symptoms and appear normal, (3) searching for causative factors to prevent further episodes, and (4) experimenting with management techniques to shorten or end episodes.

CONCLUSION

Clinical diagnosis and referral for ablation treatment were more difficult for women suggesting existence of a gender bias. As with many other chronic conditions, the illness trajectory work is formidable. Patients in this study with SVT, however, reported facing the additional difficulty of being believed. Disruptions in self-esteem and personal relationships are the effects of not being believed. Providers could avoid minimizing women's symptoms by listening seriously and offering realistic expectations; including insight into patient experiences and the trajectory of the dysrhythmia; and efficacy of drug and ablation treatments.

Successful ablation of atrioventricular node reentry tachycardia in a patient with crisscross heart and situs inversus levocardia

Crisscross heart is a complex congenital anomaly that is rarely seen in the absence of important associated structural defects. We describe a 41-year-old woman with recurrent dizziness and tachycardia but no previous cardiovascular symptoms. Narrow-QRS tachycardia was detected, and magnetic resonance imaging showed situs inversus levocardia with a circulatory pattern typical of crisscross heart. Electrophysiologic study revealed atypical atrioventricular (AV) node reentry tachycardia of the "fast-slow" type. Despite the unusual anatomy, we successfully modified the AV node physiology by ablating the "slow AV node inputs" with the guidance of a multielectrode basket catheter in the anatomic right atrium.

Long-term outcome of patients with atrioventricular node reentrant tachycardia

BACKGROUND

Little information is available on the natural history of patients with AVNRT. The purpose of this study was to compare the outcome of patients with Atrioventricular node reentrant tachycardia (AVNRT) who underwent ablation with those on antiarrhythmic therapy and those not receiving drugs.

METHODS

93 consecutive patients (mean age=33.5+/-18.1 years) with AVNRT referred to our institution from 1988 to 1993 were prospectively followed-up for a mean of 13.2+/-2.0 years (range=11.4-16.1 years).

RESULTS

18 patients underwent ablation (group 1), 24 received antiarrhythmic therapy (group 2), 38 received no drugs or remained on drug therapy for only few months (group 3), 3 died and 10 were lost to follow-up. The frequency of symptoms at the baseline was higher in group 1 than in groups 2 and 3 (7.8+/-3.7, 3.5+/-2.3, 2.3+/-1.9 episodes/month, respectively; p<0.02 in group 1 vs. group 3). At the end of the follow-up 18/18 (100%) of group 1, 14/23 (61%) of group 2 and 17/38 of group 3 (44.7%) reported being asymptomatic for the previous 3 years. Group 3 patients who became asymptomatic had a shorter duration of symptoms before enrolment (3.7+/-1.5 vs. 7.1+/-3.6 years, p<0.05) and a shorter mean length of the tachycardia episodes (3.8+/-2.4 vs. 42.6+/-17.8 min, p<0.02) than patients from the same group who remained symptomatic.

CONCLUSIONS

The main result of this study is that during a long-term follow-up a considerable number of untreated patients with AVNRT become asymptomatic. This finding should be considered for choosing treatment modality and for calculating healthcare costs of ablation vs. medical therapy.

Incidence and clinical relevance of supraventricular tachyarrhythmias in pulmonary hypertension

BACKGROUND

In patients with severe pulmonary hypertension (PH), right ventricular function is a main determinant of clinical stability and outcome. Supraventricular tachyarrhythmias (SVTs) may compromise cardiac function and threaten prognosis in patients with PH, but the incidence and clinical relevance of SVTs in PH and chronic right ventricular failure have not been evaluated.

METHODS

In a 6-year retrospective single-center analysis, 231 consecutive patients followed for pulmonary arterial hypertension, or inoperable chronic thromboembolic PH were studied for SVTs. Analysis included incidence, clinical consequences, treatment, and outcome.

RESULTS

Thirty-one episodes of SVT were observed in 27 of 231 patients (cumulative incidence 11.7%, annual risk 2.8% per patient), including atrial flutter (n = 15), atrial fibrillation (n = 13), and AV nodal reentry tachycardia (n = 3). Supraventricular tachyarrhythmia onset was almost invariably associated with marked clinical deterioration and right ventricular failure (84% of SVT episodes). Outcome was strongly associated with the type of SVT and restoration of sinus rhythm. During follow-up, cumulative mortality was low (6.3%, follow-up 26 +/- 23 months) when sinus rhythm was restored (all cases of AV nodal reentry tachycardia and atrial flutter). In contrast, 9 of 11 patients with sustained atrial fibrillation died from right ventricular failure (cumulative mortality 82%, follow-up 11 +/- 8 months).

CONCLUSIONS

In patients with PH, SVTs constitute a relevant problem, often resulting in clinical deterioration. Sustained atrial fibrillation may be associated with a high risk of death from right ventricular failure.

Atrioventricular nodal reentrant tachycardia in children

The purpose of this study was to identify the clinical and electrophysiological characteristics of children with atrioventricular reentry tachycardia (AVNRT) and to define the prognosis and the treatment strategy. Sixty-two children (28 males and 34 females mean age, 10.2 +/- 3.2 years) with AVNRT ("slow-fast" type) were included in the study. Patients were divided into two groups: 47 patients with severe symptoms (group A) and 15 with mild symptoms (group B). The severity of the symptoms was not related to the electrophysiological parameters. Females were more symptomatic than males. Patients in group B did not receive any treatment (except 1 because of parents' choice) nor did they develop symptoms, and 5 patients had resolution of palpitations. Forty-one of 46 patients in group A were successfully treated with medical therapy as initial treatment. Thirty-one patients in group A underwent slow pathway ablation. There were late recurrences of AVNRT in 6 patients. Typical AVNRT in young patients does not appear to be life threatening. Patients with mild or no symptoms do well without therapy. Medical therapy and slow pathway ablation appear to be effective in the more symptomatic patients. Age and electrophysiological variables are not related to the symptoms or response to treatment. Females with AVNRT are more symptomatic and more likely to present with syncope.

Characterizing Dual Atrioventricular Nodal Physiology in Pediatric Patients with Atrioventricular Nodal Reentrant Tachycardia

INTRODUCTION

Dual atrioventricular (AV) nodal physiology, defined as an AH jump > or =50 msec with a 10 msec decrease in A1A2, is the substrate for atrioventricular nodal reentrant tachycardia (AVNRT) and yet it is present in a minority of pediatric patients with AVNRT. Our objective was to characterize dual AV nodal physiology as it pertains to a pediatric population.

METHODS/RESULTS

We retrospectively reviewed invasive electrophysiology studies in 92 patients with AVNRT (age12.1 +/- 3.7 yrs) and in 46 controls without AVNRT (age 13.3 +/- 3.7 yrs). Diagnoses in controls: syncope (N = 31), palpitations (N = 6), atrial flutter (N = 3), history of atrial tachycardia with no inducible arrhythmia (N = 3), and ventricular tachycardia (N = 3). General anesthesia was used in 49% of AVNRT and 52% of controls, P = 0.86. There were no differences in PR, AH, HV, or AV block cycle length. With A1A2 atrial stimulation, AVNRT patients had a significantly longer maximum AH achieved (324 +/- 104 msec vs 255 +/- 67 msec, P = 0.001), and a shorter AVNERP (276 +/- 49 msec vs 313 +/- 68 msec P = 0.0005). An AH jump > or =50 msec was found in 42% of AVNRT versus 30% of controls (P = 0.2). Using a ROC graph we found that an AH jump of any size is a poor predictor of AVNRT. With atrial overdrive pacing, PR > or = RR was seen more commonly in AVNRT versus controls, (55/91(60%) vs 6/46 (13%) P = 0.000).

CONCLUSIONS

Neither the common definition of dual AV nodes or redefining an AH jump as some value <50 msec are reliable methods to define dual AV nodes or to predict AVNRT in pediatric patients. PR > or = RR is a relatively good predictor of AVNRT.