Ablation for atrioventricular nodal reentrant tachycardia with a prolonged PR interval during sinus rhythm: the risk of delayed higher-degree atrioventricular block

Introduction: Delayed higher‐degree atrioventricular (AV) block can develop after slow pathway ablation for AV nodal reentrant tachycardia with a preexisting first‐degree AV block. Retrograde fast pathway ablation is considered as an alternative approach for patients with a markedly prolonged PR interval and no demonstrable anterograde fast pathway function at baseline. This study aimed to determine the long‐term reliability of AV conduction after retrograde fast pathway ablation in comparison to slow pathway ablation in patients with AV nodal reentrant tachycardia and a first‐degree AV block at baseline. Methods and Results: Among 43 patients with AV nodal reentrant tachycardia and a prolonged PR interval (defined as ≥200 msec), 10 patients without demonstrable dual pathway physiology underwent ablation of the retrograde fast pathway, and 33 patients with dual pathway physiology underwent slow pathway ablation. Persisting intraprocedural second‐ or third‐degree AV block requiring pacemaker implantation occurred in one patient (10%) after retrograde fast pathway ablation and in one patient (3%) after slow pathway ablation. During the long‐term follow‐up of 61 ± 39 months after retrograde fast pathway ablation, no delayed second‐ or third‐degree AV block occurred, and the PR interval remained unchanged (308 ± 60 msec vs 304 ± 52 msec) . During the follow‐up of 37 ± 25 months after slow pathway ablation, a delayed complete heart block developed in two patients, and a second‐degree AV block developed in two patients. Three patients aged 66, 75, and 76 years died suddenly of unknown cause 4, 16, and 48 months following slow pathway ablation, respectively. Conclusions: Slow pathway ablation was associated with a significant risk of a delayed higher‐degree AV block in patients with AV nodal reentrant tachycardia and a prolonged PR interval at baseline. Retrograde fast pathway ablation for patients with a first‐degree AV block and no demonstrable dual pathway physiology was associated with a higher intraprocedural risk of complete AV block but did not result in the development of higher‐degree AV block during the long‐term follow‐up of up to 9 years.     

Manifest and concealed AV nodal reentry in wenckebach type of AV conduction with AV junctional escape rhythm

An electrocardiogram was obtained that was characterized by sinus rhythm with progressive prolongation of the PR interval not followed by a blocked sinus impulse. After a critically long PR interval, the QRS complex was followed by a premature P′ wave, representing an echo beat, a manifest reentry in the atrioventricular (AV) node. The pause, occasioned by the premature P′ wave, was at times interrupted by an AV junctional escape beat, occurring with an escape interval of 1.21–1.24 seconds. On other occasions, however, the escape beat did not manifest on schedule, even though the pause was markedly longer than the escape cycle. This suggested that the manifest reentry was followed by a further concealed reentry, resulting in inapparent discharge of the AV junctional escape pacemaker, whose firing was postponed, thereby allowing the sinus impulse to capture the ventricles.     

Electrophysiology of the Atrio-AV Nodal Inputs and Exits in the Normal Dog Heart

Ablation of Atrionodal Connections. Introduction : We studied the effects of selective and combined ablation of the fast (FP) and slow pathway (SP) on AV and VA conduction in the normal dog heart using a novel epicardial ablation technique.
Methods and Results : For FP ablation, radiofrequency current (RFC) was applied to a catheter tip that was held epicardially against the base of the right atrial wall. SP ablation was performed epicardially at the crux of the heart. Twenty-three dogs were assigned to two ablation protocols: FP/SP ablation group (n = 17) and SP/FP ablation group (n = 6). In 12 of 17 dogs, FP ablation prolonged the PR interval (97 ± 10 to 149 ± 22 msec. P < 0.005) with no significant change in anterograde Wenckebach cycle length (WBCL), Subsequent SP ablation performed in 8 dogs further prolonged tbe PR interval and the anterograde WBCL (117 ± 22 to 193 ± 27, P < O.(M)5). Complete AV block was seen in I of 8 dogs, whereas complete or high-grade VA block was seen in 6 of 8 dogs. In the SP/FP ablation group, SP ablation significantly increased WBCL with no PR changes. Combined SP/FP ablation in A dogs prolonged the PR interval significantly, but no instance of complete AV block was seen. VA block was found in 50% of these cases. Histologic studies revealed that RFC ablation affected the anterior and posterior atrium adjacent to the undamaged AV node and His bundle.
Conclusion : Using an epicardial approach, combined ablation of tbe FP and SP AV nodal inputs can be achieved with an unexpectedly low incidence of complete A V block, although retrograde VA conduction was significantly compromised.     

Ventricular Echo Beats and Retrograde Atrioventricular Nodal Exits in the Dog Heart: Multiplicity in Their Electrophysiologic and Anatomic Characteristics

INTRODUCTION: A single ventricular echo beat frequently is induced in the dog heart by ventricular pacing, but it has not been investigated using a concomitant ablative technique. We studied the effects of ablating the anterior atrial input to the AV node on ventricular echo beats induced in the dog heart to evaluate their electrophysiologic characteristics, the anatomic reentrant circuit, and the retrograde AV nodal exits. METHODS AND RESULTS: In 20 dogs, an epicardial radiofrequency current was applied to the right anterior septum in an attempt to ablate the anterior input to the AV node. Ventricular programmed stimulation was performed to evaluate the ventricular echo beat and the retrograde AV nodal exit before and after ablation. The AV junction was examined with light microscopy. Seventeen dogs in which the PR interval was prolonged significantly from 108+/-17 msec to 153+/-19 msec (P < 0.001) were selected for ventricular echo evaluation; 3 dogs in which persistent second- or third-degree AV block was induced by ablation were excluded. Ventricular echo beats, which were induced in 13 of 17 dogs, were classified into the anterior type (n = 6) or posterior type (n = 7) according to the earliest atrial activation site during the echo beat. The retrograde AV nodal exit site showed anterior-exit only (n = 10), posterior-exit only (n = 2), and dual-exit (n = 5) patterns. After ablation, the anterior-type ventricular echo beat was noninducible in all 6 dogs, whereas the posterior-type ventricular echo beat was noninducible in only 3 of 7 dogs. In 17 dogs, VA conduction was not demonstrated after ablation in 3 dogs, all of which showed the anterior-exit only pattern. CONCLUSION: The effect of ablation on the ventricular echo beats and retrograde AV nodal exit site suggests multiplicity in their electrophysiologic and anatomic characteristics in the dog heart.     

Conventional and biventricular pacing in patients with first-degree atrioventricular block

Recent reports suggest that first-degree atrioventricular block is not benign. However, there is no evidence that shortening of the PR interval can improve outcome except for symptomatic patients with a very long PR interval ≥0.3 s. Because these patients require continual forced pacing, biventricular pacing should be used according to accepted guidelines for third-degree AV block. Functional atrial undersensing may occur in patients with conventional dual-chamber pacing and first-degree AV block because the sinus P-wave tends to be displaced into the post-ventricular atrial refractory period (PVARP) an arrangement that may cause a pacemaker syndrome. Prevention requires programming a shorter AV and PVARP that is feasible because retrograde conduction is rare in first-degree AV block patients. A relatively new pacing mode to minimize right ventricular stimulation has been designed by eliminating the traditional AV interval but with dual-chamber backup. This pacing mode permits the establishment of very long AV intervals that may cause pacemaker syndrome. About 50% of patients undergoing cardiac resynchronization therapy (CRT) have a PR interval ≥200 ms. The CRT patients with first-degree AV block are prone to develop electrical desynchronization more easily than those with a normal PR interval. The duration of desynchronization after exceeding the upper rate on exercise is also more pronounced. AV junctional ablation is rarely necessary in patients with first-degree AV block but should be considered for symptomatic functional atrial undersensing or when the disturbances caused by first-degree AV block during CRT cannot be managed by programming.     

Rate-Related and Autonomic Effects on Atrioventricular Conduction Assessed Through Beat-to-Beat PR Interval and Cycle Length Variability

Atrioventricular Conduction Variability. Introduction: Atrioventricular AV) conduction time varies on a beat-by-beat basis in response to the influences of cardiac efferent autonomic activity and rate-dependent electrical recovery processes. The goals of this study were to distinguish these effects on AV conduction time and to compare the variability in sinoatrial and AV nodal function. Methods and Results: The PR interval on the surface ECG served as an index of AV conduction time in this study of 14 adult human subjects undergoing a random interval breathing protocol. P and R waves were located by a template-matching algorithm. Spectral analysis allowed frequency-domain comparisons between PR and RR interval variability. Spectra of PR and RR intervals had similar power distributions, although the power of the RR interval spectra was much greater. Autonomic blockade with atropine plus propranolol reduced the power of both spectra. Standing significantly decreased the spectral power from 0.15 to 0.5 Hz for PR and RR spectra, and introduced a peak near 0.1 Hz in the mean PR and RR spectra, although the latter finding was significant only for the RR interval spectra. Propranolol had no significant effects on the PR and RR interval spectra. Linear regression analysis allowed quantification of the autonomic and recovery effects on AV conduction and showed which effect predominated. Simple linear regression confirmed in adults a previous finding in children that conduction time may be either positively or negatively correlated with cycle length. By multiple regression and transfer function analysis, the inverse relation seen in some subjects was attributed to the effect of recovery from the preceding cycle. With the preceding recovery period accounted for, the conduction time and cycle length of the current beat were positively correlated, presumably due to the parallel autonomic effects on the sinoatrial and AV nodes. The magnitude of the recovery effect predicted by the regression analysis was similar to published values. Conclusion: A noninvasive evaluation of the surface ECG can be used to compare variability in AV conduction time and cycle length and characterize the effects of autonomic efferent activity and rate-related recovery on AV nodal function.     

AV Nodal-His-Purkinje Reentry: A Novel Form of Tachycardia

AV Nodal-His-Purkinje Reentry. Introduction: Bundle branch reentry (BBR) typically occurs in patients with dilated cardiomyopathy and infra-Hisian conduction system disease. The macroreentrant circuit of BBR is confined to the His-Purkinje system (HPS) and ventricular myocardium. As such, the atrioventricular (AV) node plays no role in the tachycardia circuit. Methods and Results: In the present study, we identified a novel form of wide complex tachycardia in a patient with coronary disease and severe aortic regurgitation. The tachycardia morphology was right bundle branch block with a left superior axis. Ventriculoatrial block was present during tachycardia. An unusual feature of this rhythm was two sequential His-bundle deflections (H and H′) for each ventricular beat of tachycardia. The H′V interval was identical to the HV interval during supraventricular rhythm. Changes in the ventricular cycle length (VV) preceded changes in the HH interval, consistent with retrograde activation of the first His-bundle deflection. Changes in the H ‘H’interval preceded changes in the VV interval, consistent with anterograde activation of the second His-bundle deflection. Tachycardia could be terminated with ventricular extrastimuli that did not capture the proximal HPS as well as with ventricular extrastimuli that advanced the His deflection, consistent with block in the HPS and in the AV node, respectively. Reproducible termination of the tachycardia following the first His deflection was demonstrated with adenosine, consistent with an upper pivot in the AV node. Conclusions: We have identified a new form of reentrant tachycardia in which the AV node, HPS, and ventricular myocardium each obligatorily participates in the tachycardia circuit, with the left posterior fascicle and right bundle functioning as the anterograde and retrograde limbs, respectively. Unlike BBR, however, the His bundle is activated twice as the wavefront pivots in the AV node. This model requires longitudinal dissociation at the levels of the AV node and His bundle.     

Late occurrence of heart block after radiofrequency catheter ablation of the septal region: clinical follow-up and outcome

INTRODUCTION: There are few data regarding the occurrence of delayed heart block at least 24 hours after radiofrequency catheter ablation (RFCA) of AV nodal reentry or posteroseptal accessory pathways (APs). We investigated the late occurrence of heart block in this population, the clinical outcome, and whether findings at electrophysiologic study could have predicted its development. METHODS AND RESULTS: Two of 418 patients with AV nodal reentry undergoing RFCA using a posterior approach and 1 of 54 patients with RFCA of a posteroseptal AP developed late heart block. Anterograde and retrograde AV nodal conduction before and after RFCA were normal. Patients received 12, 15, and 32 RFCA lesions, respectively, using a mean maximum power of 44 W. The RFCA sites were the posterior septum for posteroseptal AP and the posterior and mid-septum for patients with AV nodal reentry, with no His electrogram ever recorded at the ablation site. During RFCA, junctional tachycardia occurred with 1:1 VA conduction in the patient with a posteroseptal AP, but occasional intermittent single retrograde blocked complexes were present in both patients with AV nodal reentry. No rapid junctional tachycardia or >1 consecutive retrograde blocked complex was ever observed during RFCA. Persistent high-degree AV block with junctional escape developed 2 days after RFCA in the posteroseptal AP patient. A permanent pacemaker was implanted, and normal conduction was noted 16 days after RFCA. Both patients with AV nodal reentry complained of fatigue, mainly on exertion, 3 to 4 days after RFCA, and ECG-documented exercise-induced variable AV block was obtained. Because heart block resolved in our initial patient, a prolonged monitoring period was allowed. Symptoms disappeared at 13 and 8 days, and a follow-up treadmill test showed normal PR interval and no heart block. No recurrence of heart block has been seen in any of these three patients. CONCLUSION: Late unexpected heart block after RFCA of AV nodal reentry and posteroseptal AP is rare, often resolves uneventfully in 1 to 2 weeks, and no specific electrophysiologic findings predicted its occurrence. Prolonged clinical observation is preferable to immediate pacemaker implantation in such patients.     

PR/RR Interval Ratio During Rapid Atrial Pacing:

Method for Confirming Slow Pathway Conduction. Introduction: Although the AV conduction curve in patients with AV nodal reentrant tachycardia (AVNRT) is usually discontinuous, many patients with this arrhythmia do not demonstrate criteria for dual AV nodal pathways. During rapid atrial pacing, the PR interval often exceeds the pacing cycle length when there is anterograde conduction over the slow pathway and AVNRT is induced. The purpose of this prospective study was to determine the diagnostic value of the ratio of the PR interval to the RR interval during rapid atrial pacing as an indicator of anterograde slow pathway conduction in patients undergoing electrophysioiogic testing. Methods and Results: The PR and RR intervals were measured during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction in four study groups: (1) patients with inducible AV nodal reentry and the classical criterion for dual AV nodal pathways during atrial extrastimulus testing (AVNRT Group 1); (2) patients with inducible AV nodal reentry without dual AV nodal pathways (AVNRT Group 2); (3) control subjects ≤ 60 years of age without inducible AV nodal reentry; and (4) control subjects > 60 years of age without inducible AV nodal reentry. For both groups of patients with inducible AV nodal reentry, AV conduction was assessed before and after radiofrequency ablation of the slow AV nodal pathway. Before slow pathway ablation, the PR/RR ratio exceeded 1.0 in 12 of 13 AVNRT Group 1 patients (mean 1.27 ± 0.21) and 16 of 17 AVNRT Group 2 patients (mean 1.18 ± 0.15, P = NS Group 1 vs Group 2). After slow pathway ablation, the maximum PR/RR ratio was < 1.0 in all AVNRT patients (Group 1 = 0.59 ± 0.08, P < 0. 00001 vs before ablation: Group 2 = 0.67 ± 0.11; P < 0.00001 vs before ablation). Among both groups of control subjects, the PR/RR ratio was > 1.0 in only 3 of 27 patients with no relation to patient age. Conclusion: The ratio of the PR interval to the RR interval during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction provides a simple and clinically useful method for determining the presence of slow AV nodal pathway conduction. This finding may be particularly useful in patients with inducible AV nodal reentry without dual AV nodal physiology on atrial extrastimulus testing.     

Morbitz type I second degree AV block during recovery from dengue hemorrhagic fever.

Two patients with serologically-proven dengue virus infection and Morbitz type I second degree atrioventricular (AV) block are described. A 7 years old boy (patient 1) with grade 2 and a 7 years old girl (patient 2) with grade 3 illness were admitted to the hospital on the 3rd and the 5th day of the illness, respectively. Both had typical resentation for dengue hemorrhagic fever including fever, hepatomegaly, thrombocytopenia and signs of extravascular leakage. The 7 year old girl also had epistaxis and anemia (Hct 24%). Morbitz type I second degree and 2:1 AV block developed on day 7 (patient 1) and day 8 (patient 2) of the illness, both during recovery periods. Patient 1 also had occasional monomorphic premature ventricular contraction (PVC). There was no other abnormality in the 12-lead EKGS and echocardiograms showed normal ventricular systolic function in both. Other than mild hypokalemia (3.3 and 3.4 mgq/l), serum electrolytes were normal. Neither patients had elevation of serum creatine phosphokinase (CPK). In patient 1, exercise (on day 10) normalized AV conduction and abolished the PVC. Follow up EKG and physical examination at 10 months after the illness was normal. The rhythm in patient 2 resolved to 1st degree AV block (with occasional morbitz type I second degree at night) on day 12. In this patient, exercise resulted in shortening of the PR interval and Valsalva maneuver resulted in further PR prolongation. The patient was well at 1-month follow up with a mormal EKG. Morbitz type I second degree AV block during recovery from dengue hemorrhagic fever may be a transient functional impairment of the AV node, in which altered autonomic tone may play a role.     

First-degree atrioventricular block

Marked first-degree AV block (PR≥0.30 s) can produce a clinical condition similar to that of the pacemaker syndrome. Clinical evaluation often requires a treadmill stress test because patients are more likely to become symptomatic with mild or moderate exercise when the PR interval cannot adapt appropriately. Uncontrolled studies have shown that many such symptomatic patients with normal left ventricular (LV) function improve with conventional dual chamber pacing (Class IIa indication). In contrast, marked first-degree AV block with LV systolic dysfunction and heart failure is still a Class IIb indication, a recommendation that is now questionable because a conventional DDD(R) pacemaker would be committed to right ventricular pacing (and its attendant risks) virtually 100% of the time. It would seem prudent at this juncture to consider a biventricular DDD device in this situation. Patients with suboptimally programmed pacemakers may develop functional atrial undersensing because the P wave tends to migrate easily into the postventricular atrial refractory period (PVARP). Retrograde vetriculoatrial conduction block is uncommon in marked first-degree AV block so a relatively short PVARP can often be used at rest with little risk of endless loop tachycardia. The usefulness of a short PVARP may be negated by special PVARP functions in some pulse generators designed to time out a long PVARP at rest and a gradually shorter one with activity. First-degree AV block during cardiac resynchronization therapy (CRT) predisposes to loss of ventricular resynchronization during biventricular pacing because it favors the initiation of electrical “desynchronization” especially in association with a relatively fast atrial rate and a relatively slow programmed upper rate. Patients with first-degree AV block have a poorer outcome with CRT than patients with a normal PR interval, a response that may involve several mechanisms. (1) The long PR interval may be a marker of more advanced heart disease. (2) Patients with first-degree AV block may experience more episodes of undetected “electrical desynchronization”. (3) “Concealed resynchronization” whereupon ventricular activation in patients with a normal PR interval may result from fusion of electrical wavefronts coming from the right bundle branch and the impulse from the LV electrode. The resultant hemodynamic response may be superior because the detrimental effects of right ventricular stimulation (required in the setting of a longer PR interval) are avoided.     

Spontaneous transition of 2:1 atrioventricular block to 1:1 atrioventricular conduction during atrioventricular nodal reentrant tachycardia: evidence supporting the intra-Hisian or infra-Hisian area as the site of block

INTRODUCTION: The incidence of spontaneous transition of 2:1 AV block to 1:1 AV conduction during AV nodal reentrant tachycardia has not been well reported. Among previous studies, controversy also existed about the site of the 2:1 AV block during AV nodal reentrant tachycardia. METHODS AND RESULTS: In patients with 2:1 AV block during AV nodal reentrant tachycardia, the incidence of spontaneous transition of 2:1 AV block to 1:1 AV conduction and change of electrophysiologic properties during spontaneous transition were analyzed. Among the 20 patients with 2:1 AV block during AV nodal reentrant tachycardia, a His-bundle potential was absent in blocked beats during 2:1 AV block in 8 patients, and the maximal amplitude of the His-bundle potential in the blocked beats was the same as that in the conducted beats in 4 patients and was significantly smaller than that in the conducted beats in 8 patients (0.49 +/- 0.25 mV vs 0.16 +/- 0.07 mV, P = 0.007). Spontaneous transition of 2:1 AV block to 1:1 AV conduction occurred in 15 (75%) of 20 patients with 2:1 AV block during AV nodal reentrant tachycardia. Spontaneous transition of 2:1 AV block to 1:1 AV conduction was associated with transient right and/or left bundle branch block. The 1:1 AV conduction with transient bundle branch block was associated with significant His-ventricular (HV) interval prolongation (66 +/- 19 ms) compared with 2:1 AV block (44 +/- 6 ms, P < 0.01) and 1:1 AV conduction without bundle branch block (43 +/- 6 ms, P < 0.01). CONCLUSION: The 2:1 AV block during AV nodal reentrant tachycardia is functional; the level of block is demonstrated to be within or below the His bundle in a majority of patients with 2:1 AV block during AV nodal reentrant tachycardia, and a minority are possibly high in the junction between the AV node and His bundle.     

A 2:1 atrioventricular block presenting paradoxical ventriculophasic response

Ventriculophasic response (VR) is defined as the shortening of the sinus cycle length in the setting of greater than second‐degree atrioventricular (AV) block. Typically, the PP intervals interposing a QRS complex are shorter than those without a QRS complex. Paradoxical VR is a rare clinical entity. We report about an 80‐year‐old man presenting with a 2:1 AV block, in whom typical and paradoxical VRs were observed.     

Efficacy and safety of radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia in the elderly

INTRODUCTION: Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common regular supraventricular tachycardia in the general population as well as in elderly patients. The purpose of the study was to investigate the success and complication rate particularly regarding the induction of an atrioventricular (AV) block by radiofrequency (RF) ablation in elderly patients with and without a preexisting AV block. METHODS AND RESULTS: Between February 1998 and July 2004, all patients with symptomatic AVNRT referred for slow-pathway ablation in our institution were included and divided into two groups: group 1 patients younger than 75 years (n = 508) and group 2 patients > or =75 years (n = 70). A preexisting prolonged PR interval was present in 17 (3.3%) patients of group 1 and in 26 (37%, P < 0.0001) patients of group 2. Following successful slow-pathway ablation (follow-up time group 1: 37 +/- 22, group 2: 37 +/- 24 months) no induction of an AV block was observed in group 2 but in four patients of group 1 (0.79%) a complete heart block was induced requiring a pacemaker implantation. In group 1, 15 (2.95%) patients with a recurrence of AVNRT were readmitted for a repeat ablation procedure. No recurrences occurred in group 2. CONCLUSION: Despite a higher incidence of preexisting prolonged PR intervals slow-pathway ablation in elderly patients is both effective and safe and should be considered as the first line therapy also in this patient population.     

Atypical Wenckebach periodicity simulating Mobitz II AV block.

Eleven patients were studied and a total of 144 Wenckebach cycles in the AV node and 118 Wenckebach cycles in the His-Purkinje system were analysed to determine the incidence of typical and atypical Wenckebach periodicity, with particular emphasis on one variant of atypical Wenckebach that may simulate a Mobitz type II block. This pseudo-Mobitz II pattern was defined as a long Wenckebach cycle in which, at least, the last three beats of the cycle show relatively constant PR intervals (variation of no more than 0.02 s in surface leads and no more than 10 ms in His bundle electrograms) and in which the PR interval immediately following the blocked beat is shorter than the PR interval before the block by 0.04 s or more. Atypical Wenckebach cycles were found to be more common than the typical variety at both the AV node (67%) and His-Purkinje system (69%). The pseudo-Mobitz II pattern was seen in 19 per cent of atypical AV nodal Wenckebach periods and in 17 per cent of atypical His-Purkinje system Wenckebach cycles. The need to discern a ''classical'' Mobitz II block from a pseudo-Mobitz II pattern, especially in the setting of an acute inferior myocardial infarction, is emphasised.     

Simplified "ATP test" for noninvasive diagnosis of dual AV nodal physiology and assessment of results of slow pathway ablation in patients with AV nodal reentrant tachycardia

INTRODUCTION: We recently reported that administration of adenosine triphosphate (ATP) during sinus rhythm identifies dual AV nodal physiology (DAVNP) in 76% of patients with inducible sustained AV nodal reentrant tachycardia (AVNRT) at electrophysiologic (EP) study. In that report, however, the ATP test was considered positive for DAVNP only when the results were reproducible at a given dose of ATP. The aim of the present study was to assess the value of a simplified ATP test for noninvasive diagnosis of DAVNP and abolition or modification of the slow pathway (SP) after radiofrequency ablation (RFA) in patients with inducible sustained AVNRT. METHODS AND RESULTS: The value of a single dose of ATP was studied in 105 patients with inducible sustained AVNRT and in 31 control patients before placement of EP catheters in the cardiac chambers. ATP (10 to 60 mg, in 10-mg increments) was injected during sinus rhythm until ECG signs of DAVNP (> or = 50 msec increase or decrease in PR interval in two consecutive beats, or occurrence of > or = 1 AV nodal echo beat) or > or = second-degree AV block was observed. DAVNP was observed in only 1 (3.2%) control patient. The test could be completed in 96 study patients. DAVNP was found by ATP test in 72 (75%) patients, whereas it was diagnosed by EP criteria in 82 (85%) patients. DAVNP by ATP test disappeared in 27 (96%) of 28 patients who underwent SP abolition and in 18 (60%) of 30 patients who underwent SP modification. In the 12 patients with persistent DAVNP determined by ATP test after SP modification, the number of beats conducted over the SP was significantly reduced (from 6.3+/-3.3 to 2.5+/-2.2 beats; P = 0.002). CONCLUSION: A single administration of ATP during sinus rhythm (at a given dose) enables noninvasive diagnosis of DAVNP in a high percentage of patients with inducible AVNRT and reliably confirms the results of RFA of the SP.     

Long-term safety and efficacy of slow pathway ablation in patients with atrioventricular nodal re-entrant tachycardia and pre-existing prolonged PR interval.

The association of atrioventricular nodal re-entrant tachycardia (AVNRT) and pre-existing prolonged PR interval is unusual. Radiofrequency (RF) ablation in such patients may be associated with an increased risk of immediate and delayed AV block. The aim of our study is to assess the long-term efficacy and safety of slow pathway ablation in this population. We studied 10 patients (4 males and 6 females) with pre-existing prolonged PR interval of 68 consecutive patients with AVNRT. All had slow-fast subtype of AVNRT. The mean PR interval was 222 +/- 15 ms before RF. The patients with pre-existing prolonged PR were older (69 +/- 15 vs. 54 +/- 17, P = 0.008) and their tachycardias were slower (387 +/- 102 vs. 323 +/- 73 ms; P < 0.05). Transient complete AV block (<5 s) occurred in two patients. None had permanent complete AV block. One patient had a significant increase in PR interval (from 220 to 320 ms). The mean post-RF PR interval was 232+/-37 ms (P = n.s.). Over a mean follow-up of 39 +/- 21 months, none had a recurrence of tachycardia nor developed higher degree AV block. In conclusion, in patients with AVNRT and pre-existing prolonged PR interval, a slow pathway ablation appeared efficient and safe. From our data, no delayed AV block developed on a long follow-up. Most of the patients with periprocedural transient AV block had no evidence of dual AV node physiology, suggesting that, in this population, absence of dual AV node physiology may be associated with a higher risk of AV block during slow pathway ablation.     

Evaluation of myocardial performance with conventional single-site ventricular pacing and biventricular pacing in a canine model of atrioventricular block

INTRODUCTION: The aim of this study was to evaluate epicardial biventricular pacing as a means of maintaining synchronous ventricular activation in an acute canine model of AV block with normal ventricular anatomy and function. Chronic single-site ventricular pacing results in dyssynchronous ventricular activation and may contribute to ventricular dysfunction. Biventricular pacing has been used successfully in adult patients with congestive heart failure. METHODS AND RESULTS: This was an acute study of open chest mongrel dogs (n = 13). ECG, left ventricular (LV), aortic, and pulmonary arterial pressures were measured. LV impedance catheters were used to assess cardiodynamics using instantaneous LV pressure-volume relations (PVR). Following radiofrequency ablation of the AV node, a temporary pacemaker was programmed 10 beats/min above the intrinsic atrial rate, with an AV interval similar to the baseline intrinsic PR interval. The pacing protocol consisted of 5-minute intervals with the following lead configurations: right atrium-right ventricular apex (RA-RVA), RA-LV apex (LVA), and RA-biventricular using combinations of four ventricular sites (RVA, RV outflow tract [RVOT], LVA, LV base [LVB]). RA-RVA was used as the experimental control. LV systolic mechanics, as measured by the slope of the end-systolic (Ees) PVR (ESPVR, mmHg/cc), was statistically greater (P < 0.05) with all modes of biventricular pacing (RA-RVA/LVA 20.0 +/- 2.9, RA-RVA/LVB 18.4 +/- 2.9, RA-RVOT/LVA 15.1 +/- 1.8, RA-RVOT/LVB 17.6 +/- 2.9) compared to single-site ventricular pacing (RA-RVA 12.8 +/- 1.6). Concurrent with this improvement in myocardial performance was a shortening of the QRS duration (RA-RVA 97.7 +/- 2.9 vs RA-RVA/LVA 75.7 +/- 4.9, RA-RVA/LVB 70.3 +/- 4.9, RA-RVOT/LVA 65.3 +/- 4.4, and RA-RVOT/LVB 76.7 +/- 5.9, P < 0.05). CONCLUSION: In this acute canine model of AV block, QRS duration shortened and LV performance improved with epicardial biventricular pacing compared to standard single-site ventricular pacing.     

Primo-implantation of a dual-chamber pacemaker in a patient with symptomatic first-degree AV block with proven AV dyssynchrony at an abnormally long PQ interval (pseudopacemaker syndrome)

First-degree atrioventricular block (first-degree AV block) is defined as a PR interval exceeding 200 ms [1]. The abnormally long PR interval may result in the condition resembling pacemaker syndrome, i.e. the collision of the atrial systole and the ventricular systole, being accompanied with similar symptoms including cardiac failure even if the systolic function of the left ventricle [2] is normal. This is called “pseudopacemaker syndrome” [3], [4], [5], [6], [7], [8], [9], [10]. This paper describes the case of a female patient with a significantly long PR interval after the replacement of the mitral valve, showing symptoms of pseudopacemaker syndrome. This is a relatively rare clinical condition. When it occurs, the implantation of a pacemaker in Class IIa [11] is recommended.     

Intra-His bundle blocks (102 cases).

Some intra-His bundle (intra-HB) blocks escape the routine exploration of the His bundle and are confused with supra- or infrahisian blocks. We believe that a more accurate exploration (recording of His bundle activity successively at the proximal end and the distal end of the His bundle, dynamic tests and drug injection) is needed to detect some concealed cases, mostly paroxysmal intra-HB blocks. In this series of 102 cases of intra-HB blocks, 20% had no criteria of AV block on the surface electrocardiogram, and only 4% had an intact conduction pattern (normal PR interval and normal QRS complexes.) A first degree intra-HB block was found in 35% (15 cases with a normal PR interval), a second degree intra-HB block in 23% and a thired degree intra-HB block in 42% of the cases (unidirectional in 4 cases). Of the 43% having an isolated intra-HB block, most were elderly women with a chronic third degree AV block.