Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia (ARVC/D) - What We Have Learned after 40 Years of the Diagnosis of This Clinical Entity.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) was initially recognized as a clinical entity by Fontaine and Marcus, who evaluated a group of patients with ventricular tachyarrhythmia from a structurally impaired right ventricle (RV). Since then, there have been significant advances in the understanding of the pathophysiology, manifestation and clinical progression, and prognosis of the pathology. The identification of genetic mutations impairing cardiac desmosomes led to the inclusion of this entity in the classification of cardiomyopathies. Classically, ARVC/D is an inherited disease characterized by ventricular arrhythmias, right and / or left ventricular dysfunction; and fibro-fatty substitution of cardiomyocytes; its identification can often be challenging, due to heterogeneous clinical presentation, highly variable intra- and inter-family expressiveness, and incomplete penetrance. In the absence of a gold standard that allows the diagnosis of ARVC/D, several diagnostic categories were combined and recently reviewed for a higher diagnostic sensitivity, without compromising the specificity. The finding that electrical abnormalities, particularly ventricular arrhythmias, usually precede structural abnormalities is extremely important for risk stratification in positive genetic members. Among the complementary exams, cardiac magnetic resonance imaging (CMR) allows the early diagnosis of left ventricular impairment, even before morpho-functional abnormalities. Risk stratification remains a major clinical challenge, and antiarrhythmic drugs, catheter ablation and implantable cardioverter defibrillator are the currently available therapeutic tools. The disqualification of the sport prevents cases of sudden death because the effort can trigger not only the electrical instability, but also the onset and progression of the disease.

Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia (ARVC/D) - What We Have Learned after 40 Years of the Diagnosis of This Clinical Entity / Cardiomiopatia/Displasia Arritmogênica do Ventrículo Direito (C/DAVD) - O Que Aprendemos após 40 Anos do Diagnóstico desta Entidade Clínica

Abstract Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) was initially recognized as a clinical entity by Fontaine and Marcus, who evaluated a group of patients with ventricular tachyarrhythmia from a structurally impaired right ventricle (RV). Since then, there have been significant advances in the understanding of the pathophysiology, manifestation and clinical progression, and prognosis of the pathology. The identification of genetic mutations impairing cardiac desmosomes led to the inclusion of this entity in the classification of cardiomyopathies. Classically, ARVC/D is an inherited disease characterized by ventricular arrhythmias, right and / or left ventricular dysfunction; and fibro-fatty substitution of cardiomyocytes; its identification can often be challenging, due to heterogeneous clinical presentation, highly variable intra- and inter-family expressiveness, and incomplete penetrance. In the absence of a gold standard that allows the diagnosis of ARVC/D, several diagnostic categories were combined and recently reviewed for a higher diagnostic sensitivity, without compromising the specificity. The finding that electrical abnormalities, particularly ventricular arrhythmias, usually precede structural abnormalities is extremely important for risk stratification in positive genetic members. Among the complementary exams, cardiac magnetic resonance imaging (CMR) allows the early diagnosis of left ventricular impairment, even before morpho-functional abnormalities. Risk stratification remains a major clinical challenge, and antiarrhythmic drugs, catheter ablation and implantable cardioverter defibrillator are the currently available therapeutic tools. The disqualification of the sport prevents cases of sudden death because the effort can trigger not only the electrical instability, but also the onset and progression of the disease.

Resumo A cardiomiopatia/displasia arritmogênica do ventrículo direito (C/DAVD) foi inicialmente reconhecida como uma entidade clínica por Fontaine e Marcus que avaliaram um grupo de pacientes com taquiarritmia ventricular proveniente de um ventrículo direito (VD) estruturalmente comprometido. Desde então, houve avanços significativos na compreensão da fisiopatologia, manifestação e evolução clínica e prognóstico da patologia. A identificação de mutações genéticas comprometendo os desmossomos cardíacos levou a inclusão desta entidade na classificação das cardiomiopatias. Classicamente, a C/DAVD é uma doença hereditária que se caracteriza por arritmias ventriculares, disfunção ventricular direita e/ou esquerda; e substituição fibro-gordurosa dos cardiomiócitos; cuja identificação pode ser muitas vezes desafiadora, devido à apresentação clínica heterogênea, expressividade intra- e inter-familiar altamente variável e penetrância incompleta. Na falta de um padrão-ouro que permita o diagnóstico da C/DAVD, várias categorias diagnósticas foram combinadas e, recentemente revisadas buscando uma maior sensibilidade diagnóstica, sem comprometer a especificidade. A descoberta de que as anormalidades elétricas, particularmente as arritmias ventriculares, geralmente precedem anormalidades estruturais é extremamente importante para a estratificação de risco em membros genéticos positivos. Entre os exames complementares, a ressonância magnética cardíaca (RMC) possibilita o diagnóstico precoce de comprometimento ventricular esquerdo, mesmo antes das anormalidades morfofuncionais. A estratificação de risco continua a ser um grande desafio clínico e medicamentos antiarrítmicos, ablação de cateter e desfibrilador cardioversor implantável são as ferramentas terapêuticas atualmente disponíveis. A desqualificação do esporte previne casos de morte súbita uma vez que o esforço pode desencadear não só a instabilidade elétrica, mas também deflagrar o início e a progressão da doença.

Reentry mechanisms and ablation of ECG-typical atrial flutters involving the cavo-tricuspid isthmus and the proximal coronary sinus.

AIM: Reentry circuits of a rare typical atrial flutter (AFL) involving the cavo-tricuspid isthmus (CTI) and proximal coronary sinus (CS) are described based on electrophysiological data and effects of radiofrequency (RF). METHODS AND RESULTS: Twelve patients with ECG-typical AFL in whom entrainment demonstrated that CTI and proximal CS were both part of the circuit were included. Initial RF target was CTI in 8 patients and proximal CS in 4. Success was defined as AFL termination/noninducibility. After CTI ablation, AFL cycle length (CL) increased in all: AFL persisted in 3, while in the other 5 AFL was interrupted but subsequently induced with the same morphology; before induction CTI bi-directional block was validated; success was obtained at the CS, targeting fragmented atrial potentials (APs). In those with first ablation at CS, AFL was interrupted in 3 with no AFL inducibility; in 1 AFL persisted with CL prolongation and was terminated at CTI. Two reentry patterns were identified: in 5 patients the inter-atrial septum as well as the mid-distal CS were outside of the circuit, while the CTI, proximal CS and Bachmann's bundle zone were inside, suggesting a left atrial component; in 1 patient electrophysiological mapping suggested an intra-CS circuit component. RF was successful in all without recurrence. CONCLUSION: Electrophysiological mapping and RF effects suggest a continuum between the CTI and proximal CS in rare cases with ECG-typical AFL. RF inside the proximal CS, targeting fragmented APs, should be considered in any patient in whom CTI ablation failed to interrupt a typical AFL.

Long-term efficacy of low doses of quinidine on malignant arrhythmias in Brugada syndrome with an implantable cardioverter-defibrillator: a case series and literature review.

BACKGROUND: To prevent the recurrence of ventricular arrhythmias (VA) in Brugada syndrome (BrS), only quinidine has been consistently reported to have a beneficial effect. Recommended doses are ≥ 1 g/d. The efficacy of lower doses of quinidine has been suggested on the basis of a few isolated experiences. OBJECTIVES: To describe the efficacy and safety of doses ≤ 600 mg/d of quinidine after cardioverter-defibrillator implantation in BrS at 2 referral centers and to compare those results with a comprehensive review of the literature. METHODS: In a retrospective analysis of medical records from the 2 centers, 6 men with BrS who received ≤ 600 mg/d of quinidine sulfate or hydroquinidine after cardioverter-defibrillator implantation were identified. Quinidine was initiated after arrhythmic syncope or appropriate shocks, including arrhythmic storm in 4. A literature search was performed to find previous cases with symptomatic BrS reported as having received ≤ 600 mg/d of quinidine. RESULTS: Quinidine prevented recurrence of VA in all patients from our series without side effects during a median follow-up of 4 years (from 2 to 8 years). In the literature review, 14 additional adults were found. With the exception of 3, quinidine effectively suppressed arrhythmic events in all of them. Four subjects who discontinued the medication experienced VA recurrence, successfully treated by restarting quinidine. CONCLUSIONS: Low doses of quinidine were well tolerated and effective to prevent the recurrence of VA, including arrhythmic storm, in subjects with BrS with an implantable cardioverter-defibrillator. Effectiveness of quinidine or hydroquinidine in doses ≤ 600 mg/d is 85%.

Post-ablation prolongation of atrioventricular nodal refractory period is correlated with long-term success of cryoablation for atrioventricular nodal reentrant tachycardia in the case of the persistence of a residual jump.

PURPOSE: A residual slow pathway after successful cryoablation for atrioventricular nodal reentrant tachycardia (AVNRT) is correlated with a higher recurrence rate. We described determinants of recurrence in subjects with a residual jump. METHODS: We analyzed the data of subjects with acute successful slow pathway cryoablation for AVNRT using a 6-mm-tip cryocatheter. Success was defined as AVNRT non-inducibility. Patients with no baseline elicitable jump, no inducible AVNRT, and transient first atrioventricular (AV) block at the last site were excluded. RESULTS: From 371 patients who underwent cryoablation from May 2002 to March 2011, 303 fulfilled the entry criteria (mean age, 41 ± 16; 222 women). Baseline AV nodal effective refractory period (ERP) was 272 ± 57 ms, postprocedural 331 ± 64 (P < 0.001), and the mean of the difference (Δ ERP) 60 ± 41. At the end of the procedure, 64 patients (21 %) had a residual jump, of whom 22 with a single echo. At 12 months follow-up, the actuarial recurrence-free rate was 70.3 % in patients with a residual jump and 86 % in those without (P = 0.01). In patients with a jump, only Δ AV nodal ERP was correlated with recurrence (37 ± 41 vs. 68 ± 47 ms; P < 0.04) while a single echo was not. The actuarial rate of recurrence was 60.8 % in patients with a Δ AV nodal ERP ≤ 30 ms and 18.8 % in those with a Δ AV nodal ERP >30 ms (P < 0.01). CONCLUSIONS: Suppression of slow pathway conduction is the optimal endpoint for AVNRT cryoablation. A residual jump can be tolerated if AV nodal ERP postcryoablation is prolonged >30 ms.

Adverse effects of long-term right ventricular apical pacing and identification of patients at risk of atrial fibrillation and heart failure.

In patients needing a pacemaker (PM) for bradycardia indications, the amount of right ventricular (RV) apical pacing has been correlated with atrial fibrillation (AFib) and heart failure (HF) in both DDD and VVI mode. RV pacing was linked with left ventricular (LV) dyssynchrony in almost 50% of patients with PM implantation and atrioventricular (AV) node ablation for AFib. In patients with normal systolic function needing a PM, apical RV pacing resulted in LV ejection fraction (LVEF) reduction. These negative effects were prevented by cardiac resynchronization therapy (CRT). Algorithms favoring physiological AV conduction are possible useful tools able to maintain both atrial and ventricular support and limit RV pacing. However, when chronic RV pacing cannot be avoided, it appears necessary to reconsider the cut-off value of basic LVEF for CRT. In HF patients, RV pacing can induce greater LV dyssynchrony, enhanced by underlying conduction diseases. In this context, a more deleterious effect of RV pacing in implantable cardioverter-defibrillator (ICD) patients with low LVEF can be expected. In some major ICD trials, DDD mode was correlated with increased mortality/HF. This negative impact was attributed to unnecessary RV pacing >40-50%, virtually absent in VVI-40 mode. However, some data suggest that avoiding RV pacing may also not be the best option for patients requiring an ICD. In patients with impaired LV function, AV synchrony should therefore be ensured. The best pacing mode in ICD patients with HF should be defined on an individual basis.

Cryoablation of atrioventricular nodal reentrant tachycardia: a clinical review.

Slow-pathway ablation is the treatment of choice for atrioventricular nodal reentrant tachycardia (AVNRT). Cryoablation is effective and safe, but its widespread use seems to be limited by a slightly lower long-term clinical efficacy when compared to radiofrequency (RF) ablation. However, the occurrence of atrioventricular block requiring permanent pacing with RF remains clinically relevant (about 1%). This review summarizes current experiences accumulated during the last decade with cryotechnology in terms of acute and long-term results for AVNRT and compares it with those of RF ablation. We describe the advantages of cryo compared to RF ablation. Our data suggest that pursuing procedural endpoint up to slow pathway complete ablation may improve long-term clinical success of cryoablation. We also focus on potential benefit that can be expected by using cryocatheters leading to larger and deeper freeze. For high-risk ablations, cryoenergy should be used systematically.

Correlations between long-term results after cryoablation for atrioventricular nodal reentry tachycardia and a residual jump associated or not with a single echo.

AIMS: While in radiofrequency ablation for atrioventricular nodal reentry tachycardia (AVNRT) a residual jump and a single echo do not seem to substantially modify long-term results, in cryoablation procedures their effects are still under evaluation. The purpose of this study was to evaluate if a residual jump associated or not with an isolated echo is correlated with outcome. INCLUSION CRITERIA: acute successful slow pathway cryoablation for slow-fast AVNRT. EXCLUSION CRITERIA: use of a 4 mm tip cryocatheter, no baseline elicitable jump or inducible AVNRT, and unwanted persistent first degree atrioventricular (AV) block at the end of the procedure. Cryoablation (-80°C × 4 min) was applied after successful cryomapping. Atrioventricular nodal reentry tachycardia inducibility was checked 30 min later on and off isoproterenol. Acute success was defined as AVNRT non-inducibility. Among 332 patients (pts) who had undergone cryoablation from May 2002 to March 2010 in our institutions, 245 of them fulfilled the entry criteria (173 women, mean age 41 ± 16 years, ineffective drugs 1.3 ± 1.1). A 7-Fr 6-mm tip cryocatheter (CryoCath®) was used in all cases. Baseline AV nodal effective refractory period (ERP) was 271 ± 55 ms, post-procedural ERP 331 ± 60 ms (P< 0.001), and the mean of the difference between baseline and post-procedural ERP 63 ± 38 ms. A/V ratio at successful site was 1 ± 0.4. Forty-four pts (18%) had a residual jump at the end of the procedure, and 14 of them had an associated single echo. Global cryoapplication time was 993 ± 797 s. During a follow-up of 40 ± 10 months, 43 pts (17.5%) had recurrences. At 12 months follow-up, actuarial rate of recurrence-free pts was 85% in the group without residual jump (201 pts), 63.3% with residual jump and no echo (30 pts), and 60.6% with residual jump associated with a single echo (P< 0.003 among groups). Univariate predictors of recurrences were persistence of a residual jump (P< 0.001) and total cryoapplication time (P< 0.02). In a multivariate model, only residual jump was independently correlated with recurrences (P< 0.01). CONCLUSIONS: In patients undergoing AVNRT cryoablation, slow-pathway suppression is correlated with a better outcome. A single echo is associated with a recurrence risk similar to residual jump without echo. It may be suggested that pursuing a procedural endpoint up to slow pathway complete suppression may improve long-term success.

C-reactive protein levels in the brugada syndrome.

Background. Inflammation in the Brugada syndrome (BrS) and its clinical implication have been little studied. Aims. To assess the level of inflammation in BrS patients. Methods. All studied BrS patients underwent blood samples drawn for C-reactive protein (CRP) levels at admission, prior to any invasive intervention. Patients with a previous ICD placement were controlled to exclude those with a recent (<14 days) shock. We divided subjects into symptomatic (syncope or aborted sudden death) and asymptomatic groups. In a multivariable analysis, we adjusted for significant variables (age, CRP ≥ 2 mg/L). Results. Fifty-four subjects were studied (mean age 45 ± 13 years, 49 (91%) male). Twenty (37%) were symptomatic. Baseline characteristics were similar in both groups. Mean CRP level was 1,4 ± 0,9 mg/L in asymptomatic and 2,4 ± 1,4 mg/L in symptomatic groups (P = .003). In the multivariate model, CRP concentrations ≥ 2 mg/L remained an independent marker for being symptomatic (P = .018; 95% CI: 1.3 to 19.3). Conclusion. Inflammation seems to be more active in symptomatic BrS. C-reactive protein concentrations ≥ 2 mg/L might be associated with the previous symptoms in BrS. The value of inflammation as a risk factor of arrhythmic events in BrS needs to be studied.

Catheter cryoablation of atrio-ventricular nodal reentrant tachycardia. A clinical review.

Cryoablation is a new method in interventional cardiac electrophysiology for percutaneous catheter ablation of cardiac arrhythmias. Cryothermal mapping enables the functional assessment of a particular site before permanent ablation. In this way, the targeted tissue may be confirmed as safe for ablation. This is useful in high risk ablation, for example, nex to the His bundle or the compact AV node. In the last decade, several studies have been addressed to AV-nodal reentry tachycardia (AVNRT) cryoablation. Current experiences indicate that cryoablation for AV-nodal reentry tachycardia is effective and safe. However, its wide use seems to be somewhat limited by a slightly lower efficacy when compared to radiofrequency. Further studies evaluating long-term success of cryothermal ablation versus radiofrequency are warranted. However, for high-risk ablations, cryoenergy is very helpful and should be systematically used. This article is a review of acute and long-term effects of cryoablation in patients suffering of AV-nodal reentry tachycardia episodes.

Catheter cryoablation of atrio-ventricular nodal reentrant tachycardia. A clinical review / Crioablación con catéter de la taquicardia por reentrada intranodal. Una revisión clínica

Cryoablation is a new method in interventional cardiac electrophysiology for percutaneous catheter ablation of cardiac arrhythmias. Cryothermal mapping enables the functional assessment of a particular site before permanent ablation. In this way, the targeted tissue may be confirmed as safe for ablation. This is useful in high-risk ablation, for example, next to the His bundle or the compact AV node. In the last decade, several studies have been addressed to AV-nodal reentry tachycardia (AVNRT) cryoablation. Current experiences indicate that cryoablation for AV-nodal reentry tachycardia is effective and safe. However, its wide use seems to be somewhat limited by a slightly lower efficacy when compared to radiofrequency. Further studies evaluating long-term success of cryothermal ablation versus radiofrequency are warranted. However, for high-risk ablations, cryoenergy is very helpful and should be systematically used. This article is a review of acute and long-term effects of cryoablation in patients suffering of AV-nodal reentry tachycardia episodes.

La crioablación es un nuevo método en la electrofisiología cardiaca intervensionista para la ablación percutánea de las arritmias cardiacas. El mapeo criotérmico permite la evaluación funcional de un sitio en particular antes de la ablación permanente; de esta manera, el tejido blanco puede confirmarse como seguro para el procedimiento. Esto es útil en la ablación de alto riesgo, por ejemplo, cerca del haz de His o del nodo AV compacto. En la última década, varios estudios se han orientado a la crioablación para la taquicardia de reentrada del nodo AV (TRNAV). Las experiencias actuales indican que la crioablación de la taquicardia de reentrada del nodo AV es efectiva y segura. Sin embargo, la apertura para ampliar su uso está parcialmente limitada por su eficacia ligeramente menor al compararla con el empleo de la radiofrecuencia. Se justifican ensayos clínicos futuros con objeto de evaluar el éxito a largo plazo de la ablación criotérmica en comparación con la radiofrecuencia. Para las ablaciones de alto riesgo, la crioenergía es muy útil y debería ser usada sistemáticamente. Este artículo consiste en una revisión sobre los efectos inmediatos y a largo plazo de la crioablación en pacientes que presentan episodios de taquicardia por reentrada del nodo AV.

Radiofrequency ablation of coronary sinus-dependent atrial flutter guided by fractionated mid-diastolic coronary sinus potentials.

BACKGROUND: The efficacy of radiofrequency (RF) ablation of an uncommon coronary sinus (CS)-dependent atrial flutter (AFL) was evaluated using conventional electrophysiological criteria in a highly selected subset of patients with typical and atypical AFL. METHODS: Fourteen patients with atrial flutter (11 males, mean age 69 ± 9 years) without previous right or left atrial RF ablation were included. Heart disease was present in eight patients. Baseline ECG suggested typical AFL in 12 patients and atypical AFL in two. Mean AFL cycle length was 324 ± 64 ms at the time of RF ablation in the CS. Lateral right atrium activation was counterclockwise (CCW) in 13 patients and clockwise in one. CS activation was CCW in all. Criteria for CS ablation included the presence of CS mid-diastolic fractionated atrial potentials (APs) associated with concealed entrainment with a postpacing interval within 20 ms. Success was defined as termination of AFL and subsequent noninducibility. RESULTS: The initial target for ablation was the cavotricuspid isthmus (CTI) in 11 patients and the CS with further CTI ablation in three. AP duration at the CS target site was 122 ± 33 ms, spanning 40 ± 12% of the AFL cycle length. CS ablation site was located 1-4 cm from the CS ostium. Ablation was successful in all patients. Mean time to AFL termination during CS ablation was 39 ± 52 s (<20 s in eight patients). No recurrence of ablated arrhythmia occurred during a follow-up of 18 ± 8 months. CONCLUSIONS: The CS musculature is a critical part of some AFL circuits in patients with typical and atypical AFL. AFL can be terminated in patients with CS or CTI/CS AFL reentrant circuits by targeting CS mid-diastolic fragmented APs.

A case of inappropriate sinus tachycardia after atrio-ventricular nodal reentrant tachycardia cryoablation successfully treated by ivabradine.

We illustrate a case of persistent inappropriate sinus tachycardia after slow pathway atrio-ventricular (AV) nodal reentrant tachycardia cryoablation, and inadvertent fast pathway lesion with residual first-degree AV block in a 72-year-old man with a small Koch's triangle. At the end of the cryoprocedure, the patient presented with sinus tachycardia 100 b.p.m., while PR was 300 ms. An accelerated sinus rhythm and a PR prolongation persisted over time. The patient was successfully treated with ivabradine with no effect on atrioventricular node conduction.

Three-dimensional electroanatomical mapping of right periatriotomy tachycardias after interatrial defect correction.

BACKGROUND: Pericicatricial right intra-atrial reentrant tachycardias occur frequently in patients who have undergone surgical correction of an interatrial defect. AIM: To characterize the tachycardia circuits using three-dimensional electroanatomical mapping. METHODS: Twelve tachycardias were analysed in 11 patients who had undergone surgical correction of an interatrial defect. Patients were divided into two groups: atrial flutter with typical sawtooth flutter waves in inferior leads, atrial tachycardia with clearly delimited P waves separated by an isoelectric line. RESULTS: Seven tachycardias were classified as atrial flutter; three-dimensional mapping identified a peritricuspid circuit with inferior vena cava-tricuspid annulus isthmus involvement in all cases. All atrial flutters were terminated by linear ablation of this isthmus. Five tachycardias were classified as atrial tachycardia; three-dimensional mapping identified periatriotomy loops. All atrial tachycardias were ablated successfully between two scars or between a scar and an anatomical barrier. CONCLUSION: Periatriotomy loops were always associated with an atrial tachycardia electrocardiogram pattern. Three-dimensional electroanatomical mapping appeared to be particularly useful for circuit identification and for ablation of these complex arrhythmias.

Effects of inadvertent atrioventricular block on clinical outcomes during cryoablation of the slow pathway in the treatment of atrioventricular nodal re-entrant tachycardia.

AIMS: The study aimed at evaluating the long-term effects of transient atrioventricular (AV) block on clinical outcomes during atrioventricular nodal re-entrant tachycardia (AVNRT) cryoablation. METHODS AND RESULTS: In 150 consecutive patients (39 +/- 14 years, ineffective anti-arrhythmic drugs 1.9 +/- 1.3), slow-pathway cryoablation for AVNRT was performed. A 7 Fr 6 mm-tip cryocatheter was used. After successful cryomapping (-30 degrees C), defined as jump abolition or AV nodal refractory period prolongation, cryoablation (-80 degrees C for 4 min) was applied if no AV block occurred. Atrioventricular nodal re-entrant tachycardia inducibility was checked after 30 min. Acute success (AVNRT non-inducibility) was achieved in 142 patients (95%). Overall, after a follow-up of 18 +/- 10 months, 118 of 150 patients (79%) were recurrence-free (including 2 patients for whom the procedure was unsuccessful). Among successful procedures, 116 of 142 (82%) patients were recurrence-free. During cryoablation, inadvertent transient AV block of varying degrees occurred in 34 patients (22.7%), namely, increased PR in 17 patients and a 2nd-3rd AV block in the remaining 17. In 24 patients, AV block occurred at the last effective site (increased PR in 13 patients and a 2nd-3rd AV block in 11). In the study population as a whole, univariate predictors of recurrence in the follow-up were AVNRT inducibility (P < 0.001), increased PR at the last effective site (P < 0.001), residual jump (P < 0.02), and small Koch's triangle (X-ray distance < 11 mm between the His and coronary sinus ostium catheters; P < 0.02). Atrioventricular nodal re-entrant tachycardia inducibility (P < 0.03), increased PR (P < 0.01), and small Koch's triangle (P< 0.04) were independently significant. For attempts at the last effective site, 3 groups of patients were compared: 13 patients with increased PR duration (Group A), 11 with a 2nd-3rd AV block (Group B), and 126 without AV block (Group C). Cryo-application time was 277 +/- 203 s in Group A, 75 +/- 87 s in Group B, and 253 +/- 135 s in Group C (A vs. B, P < 0.01; B vs. C, P < 0.001; and C vs. A, P= NS). There was no statistical difference among groups in the atriogram/ventriculogram amplitude ratio at the site of the last attempt, unsuccessful acute procedure, small Koch's triangle, and residual jump. Actuarial incidence of recurrence-free status at 12 months was 38% in A, 82% in B, and 82% in C (A vs. B, P < 0.05; B vs. C, P = NS; and C vs. A, P < 0.001). CONCLUSION: All AV blocks occurring during cryoablation were transient, confirming the safety of this method. An increased PR duration at the last effective site is associated with a higher recurrence rate, whereas a 2nd-3rd degree AV block has a recurrence rate similar to that of patients without AV block despite a shorter cryo-application time at the last site.