Permanent Atrioventricular Block Research Articles

Retrograde catheterization of the right heart in patients with occluded femoral veins

Occlusion of the femoral veins is a frequent complication of cardiac catheterization in small children. If the venous femoral approach is not available, a jugular approach is generally used for catheterization of the right heart. To describe and evaluate an alternative retrograde approach for catheterization of the right heart in small children with a ventricular septal defect or single ventricle. Between January 2004 and January 2007 we attempted retrograde catheterization of the right heart via the femoral artery using a 4 French sheath in eight children with occluded femoral veins. The procedure was planned under awake sedation. Median age was five months (range 4-60) and median weight was 5 kg (range 4-10). Diagnoses were as follows: single ventricle (n = 6); pulmonary atresia and ventricular septal defect (n = 1); complex transposition of the great arteries (n = 1). The procedure was successful in six patients, enabling measurement of pulmonary arterial pressure and pulmonary angiography. The procedure was abandoned in two patients because of ventricular arrhythmias. One patient had concomitant dilatation of aortic recoarctation and one had embolization of aortopulmonary collaterals. With the exception of transient ventricular arrhythmias, no acute or late complications occurred. In particular, transient or permanent atrioventricular block, occurrence of new aortic insufficiency, and acute or late thrombosis of the femoral artery were not observed. Retrograde catheterization of the right heart in small children is feasible and relatively safe. This technique can be performed without general anaesthesia and avoids a jugular approach.

Cryoablation of junctional tachycardia at high risk of atrio-ventricular block

Transcatheter cryoablation is an alternative option for the treatment of supraventricular tachycardia, due to its very low risk of permanent atrio-ventricular block. However, the overcost of cryocatheter and the high recurrence rate of this emerging technology braked its large use. This study reports the results of an approach using cryoablation for the treatment of junctional tachycardia (JT) in selected patients at high risk of atrio-ventricular (AV) block. Out of a series of 199 patients with JT treated by catheter ablation, 26 benefited from cryoablation (mean age 32.8+/-15 years, 15 males). The indications were the presence of an accessory pathway with a high risk of atrio-ventricular block (n=7), a slow pathway difficult to ablate, with a risk of atrio-ventricular block (n=7), a recurrence after a RF procedure, during which a transient atrio-ventricular block has occurred (n=4), and finally patients at young age (n=8). The primary success rate was 92%. No permanent AV block has been reported, neither with RF nor with cryoablation. The recurrence rate at 9+/-10 months was at 29% after cryoablation and 8.6% after RF. In case of AV nodal reentrant tachycardia, the additional cost of cryotherapy catheter has been avoided in 76.85% of cases. The use of a cryotherapy catheter and RF catheter has been necessary for the remaining cases. This study demonstrates that an approach, reserving cryoablation in selected patients at high risk of AV block is an alternative strategy to "the systematic use" of cryotherapy in the ablation of JT with a high efficacy, an excellent safety and a reduced cost.

Transcatheter Cryoablation Part I: Preclinical Experience

The concept of cooling to treat medical disorders dates back to the ancient Egyptian Edwin Smith Papyrus on surgical trauma, written between 3000 and 2500 B.C. Hypothermic therapy was recommended for abscesses that were “oily, like fluid under thy hand, [which] produce some clamminess of the surface.”1 Modern forms of cryothermal tissue ablation have been used surgically for decades in numerous organ systems and for various pathologies. Unlike heat that destroys cells by coagulation and tissue necrosis with potential for thrombus formation and aneurysmal dilatation, cryoablation involves a distinct pathophysiological process. As such, it carries a unique safety and efficacy profile. While not novel as an energy modality, harnessing cryoenergy into a steerable transcatheter format represents a more recent landmark in the history of arrhythmia therapy. In Part I of this two-part series, we will focus on the body of knowledge underlying the development of a transcatheter cryoablation system. Pertinent features related to biophysics and mechanisms of cryothermal tissue injury will be highlighted, key historical developments considered, and experience gained from cryosurgery with hand-held probes summarized. Preclinical studies with transcatheter cryoablation will be detailed, setting the framework for human applications. Part II of this series will review the current state of knowledge regarding clinical experience with transcatheter cryoablation.

Abstract 2349: Cryoablation for Atrioventricular Nodal Reentrant Tachycardia (AVNRT) in 154 Young Patients: 4mm vs. 6mm Catheter Tip Sizes

Introduction : Cryoablation of AVNRT has a high initial success rate and an excellent safety profile; however, there is a risk of recurrence. We hypothesized that the transition from a 4mm to a 6mm cryoablation catheter tip size would decrease recurrences without compromising safety. Methods/Results : We retrospectively reviewed all patients (n=154) who underwent cryoablation for AVNRT at the UCSF/Stanford Pediatric Arrhythmia Center from 1/04 –2/07. Initially, we used the 4mm tip, and then transitioned to a 6mm tip except for younger and smaller children. The majority of the patients had a structurally normal heart. 10 patients had congenital heart disease (3 ASDs, 3 aortic valve abnormalities, 1 Ebstein’s, 1 PDA, 1 unbalanced AV canal defect, 1 L-TGA). Typical AVNRT was inducible in 123 patients (80%), atypical in 13 (9%), and both typical and atypical in 1 patient. 17 (11%) had presumed AVNRT. Additional arrhythmias were documented in 18 patients (7 WPW, 6 AET, 4 atrial fibrillation, 1 JET). There was no difference in initial outcomes between the 4mm and 6mm tips. There was no permanent AV block. Recurrence rates were lower with the 6mm tip, but this did not reach statistical significance. The median time to recurrence was 2 (0.25–20) months. Follow-up time was longer in the 4mm group but did not significantly impact recurrence rate (p=0.61). Recurrences were not associated with any patient variable (age, size, heart disease, AVNRT inducibility, additional arrhythmias) or any procedural variable (fluoroscopy time, duration of cryoablation, transient AV block, presence of residual slow AV nodal pathway or echo beats). Conclusions : Initial outcomes of the 6mm cryoablation catheter tip for AVNRT are excellent and early recurrence rates are promising. However, we have yet to demonstrate a convincing advantage for the 6mm tip. Further improvements in cryoablation technique are necessary to reduce recurrences without sacrificing the safety profile. Cryoablation for AVNRT

Tachycardia after pacemaker implantation in a patient with complete atrioventricular block

The atrioventricular (AV) node allows ante- and retrograde conduction between atria and ventricles. It is commonly assumed that these AV nodal conduction properties go hand in hand. However, ante- and retrograde AV conduction can be completely independent from each other in individual patients. We report about a patient with permanent AV block III degrees requiring implantation of a pacemaker. As soon as a dual-chamber device was connected to the implanted leads, a tachycardia started at the maximum tracking rate, which was subsequently reprogrammed from 120 to 170 bpm. Non-invasive electrophysiologic testing showed that this patient demonstrated 1:1 ventriculoatrial (VA) conduction up to 170 bpm leading to endless loop tachycardia (ELT) while the antegrade AV block III degrees persisted. This case impressively illustrates that one has to take into account that patients with antegrade AV block III degrees may still have a high VA conduction capacity leading to ELT. Dual-chamber devices therefore have to be programmed accordingly, activating dedicated reactions after ventricular premature beats and automatic ELT detection and termination algorithms.

Performance evaluation of permanent conventional vs bifocal stimulation in permanent atrial fibrillation and atrioventricular block patients using peak endocardial acceleration

Performance evaluation of permanent conventional vs bifocal stimulation in permanent atrial fibrillation and atrioventricular block patients using peak endocardial acceleration

Transvenous cryo-ablation of the slow pathway for the treatment of atrioventricular nodal re-entrant tachycardia: a single-centre initial experience study

Within the last several years, transvenous cryo-ablation has become an alternative method to perform ablation of the slow-pathway. This study evaluated the acute and long-term safety and effectiveness of atrio-ventricular nodal re-entrant tachycardia (AVNRT) cryo-ablation. The first 69 consecutive patients with AVNRT (60 slow-fast, 4 fast-slow, and 5 slow-slow) who underwent slow-pathway cryo-ablation were included. Mean age was 37 +/- 15, body weight 68 +/- 14 kg, symptom duration 125 +/- 104 months, and number of ineffective antiarrhythmic (AA) drugs 1.8 +/- 1.4. A 7 Fr cryo-catheter (Cryocath(A)) was used, with initially 4-mm-tip and later with 6-mm-tip electrode. Cryo-mapping (n = 7.9 +/- 8.4 per pt) was performed at the temperature of -30 degrees C to test the effect on the target ablation site. Successful cryo-mapping was defined as abolition of nodal conduction jump or AV nodal refractory period prolongation. Cryo-ablation (n = 5.1 +/- 4.9 per pt) was then applied by freezing to -75 degrees C for 4 min in duration if no AV-block occurred. Acute procedural success (defined as AVNRT non-inducibility) after the first cryo-ablation attempt was achieved in 60/69 patients (87%). During cryo-ablation, inadvertent transient AV-block was encountered in 14 patients (five I AV-block and nine II-III AV-block). A mid-septal target site was the only variable correlated with inadvertent AV-block occurrence during cryo-ablation (P < 0.02). Long-term clinical success after cryo-ablation was globally achieved in 56/66 (85%) with a mean follow-up of 18 +/- 9 months (3 pts dropped-out). After the first procedure, 41/66 (62%) had no relapse, eight had a dramatic reduction in AVNRT duration-frequency and considered themselves cured, and five needed previously ineffective AA (with no relapse in three, drastic reduction in AVNRT duration-frequency in two). The five last patients needed one or more procedures, after which one had no recurrence and one had reduction in duration-frequency. Absence of recurrence after the first procedure was positively correlated with 6-mm-tip cryo-catheter use (<0.001) and negatively with acute procedural success (<0.001). At multivariate analysis, both were independently significant (<0.04 and <0.008, respectively). Long-term clinical success was correlated only with 6-mm-tip cryo-catheter use (<0.001). Slow pathway cryo-ablation is associated with an acute success but a higher recurrence rate. A 6-mm-tip cryo-catheter seems to assure during cryo-ablation a large acute and long-term success. AV-block seems non-guaranteed by a negative cryo-mapping, stressing on need of a careful surveillance. Nevertheless, the theoretical advantage of avoiding the risk of permanent AV-block when compared with radiofrequency needs larger series to be demonstrated.

15. Folge: Verschlechterung der Herzinsuffizienz unter kardialer Resynchronisationstherapie: Was ist der Grund?

A 74 year old patient with cardiac resynchronization therapy (CRT) since 12 months presents with cardiac decompensation and dyspnea NYHA III-IV after improvement of cardiac symptoms for 9 months. Her history is remarkable for left ventricular hypertrophy, aortic valve replacement 14 years earlier, a left ventricular ejection fraction of 35-40%, and permanent third degree AV block. The 12 lead standard ECG reveals the cause of cardiac deterioration which is confirmed by telemetry. This case demonstrates the importance of optimized programming of CRT systems which differs from conventional programming of dual-chamber devices in some aspects.

AAIsafeR Limits Ventricular Pacing in Unselected Patients

Dedicated pacing modes, such as AAIsafeR, prevent ventricular (V) pacing in selected patients. We report our experience in consecutive unselected patients. All data collected in recipients of Symphony DR 2550 pacemakers (ELA Medical, Montrouge, France) were retrospectively analyzed. At each visit, the percentage of V and atrial (A) pacing and the number of endless-loop tachycardia (ELT) episodes detected by the device were retrieved. Data were pooled according to pacing mode and compared with non-paired Student's t-test. Between April 2004 and July 2005, our center recruited 147 patients (mean age = 80 +/- 9 years, 54% men) treated for AV block (n = 58), sinus node dysfunction (n = 48) or other indications (n = 41). Mean age at implant was 80 +/- 9 years, and 54% were men. AAIsafeR(R) was programmed in 96 patients, DDD(R) in 43, DDI in 7, and DDD/AMC in 1 patient. In DDD mode, the mean resting AV delay was set at 150 +/- 17 ms. Patients were seen 1 month after implantation of the pacing system to verify its proper function, and every 6 months thereafter. At each follow-up, the percentage of ventricular and atrial pacing, and the number of ELT detected by the device, were recorded. The mean follow-up was 7 +/- 6 months (range 1-21). No device was reprogrammed from AAIsafeR(R) to DDDI(R) because of permanent AF. Only 6 devices (6.25%) were automatically reprogrammed from AAIsafeR(R) to DDD(R) during follow-up due to permanent AV block. An empirical choice of AAIsafeR pacing mode at the time of implantation was effective in 94% of patients, allowing a significant decrease in the percentage of V pacing. AAIsafeR versions 1 or 2 significantly decreased the percentage of V pacing (9 +/- 21%) compared with DDD (95 +/- 14%), DDD/AMC (31 +/- 34%), and DDI (87 +/- 20%) pacing (P < 0.00001). The mean percentage of V pacing was 12 +/- 24% (median 0%, range 0-94) in AAIsafeR1 versus 4 +/- 12% (median 0%, range 0-52) in AAIsafeR2 (P = .055). In 16 devices upgraded from AAIsafeR version 1 to version 2, with follow-up analyzable in both modes, the mean percentage of V pacing decreased from 6.4 +/- 15.1% to 2.6 +/- 9.7% (ns). No adverse effect related to the AAIsafeR modes was observed. No patient reported palpitation, dyspnea, or lightheadedness attributable to overdrive pacing by the AF prevention algorithms, and there was no rehospitalization, need for cardioversion, device-related complication, or death. In unselected pacemaker recipients, AAIsafeR reliably prevented V pacing compared with other pacing modes. No adverse effects were reported by any patient. Furthermore, maintaining spontaneous AV conduction protected the patients against ELT episodes.

Acute and long-term outcome of transvenous cryothermal catheter ablation of supraventricular arrhythmias involving the perinodal region

Cryoenergy is a new valuable treatment option to perform ablation close to the atrioventricular (AV) node in the cure of supraventricular tachycardias because of its favourable properties, such as the possibility of creating reversible lesions. The aim of this study was to report our experience on the effectiveness and safety of catheter cryoablation performed in "critical areas" to treat a large cohort of patients with supraventricular arrhythmias. One hundred and thirty-one patients suffering from supraventricular tachycardias underwent catheter cryoablation using a 7F catheter. Eighty-seven patients presented with AV nodal re-entrant tachycardia (AVNRT), 39 had accessory pathways (APs) either manifest or concealed (15 midseptal, 24 parahissian), three had ectopic right atrial tachycardia (AT), and two patients had a permanent junctional reciprocating tachycardia (PJRT). When the optimal parameters were recorded, ice mapping at -30 degrees C was performed for 80 s to validate the ablation site. If the expected result occurred, cryoablation was carried out by lowering the temperature to -75 degrees C for 4 min. In two patients cryoablation was not performed because of technical reasons. Cryoablation was acutely successful in 84 out of 85 patients with AVNRT, in 37 of 39 with APs and in all patients with AT and PJRT. No complications occurred in any patient. Transient AV conduction impairment occurred in seven patients with midseptal APs and in two patients with AVNRT. In particular, in these patients no late permanent AV block was observed at follow-up. At a mean follow-up of 27 +/- 12.9 months, clinical success rate was 87%. Cryoablation is a safe and effective technique with a high success rate in the long term. It may be particularly useful when performing ablation close to the AV node or His bundle owing to the possibility of validating the ablation site with ice mapping, which creates only a reversible lesion, mainly in the midseptal APs.

Percutaneous septal ablation for symptomatic hypertrophic obstructive cardiomyopathy: Managing the risk of procedure-related AV conduction disturbances

Aim To provide tools for predicting the course of AV conduction disturbances after ethanol-induced septal ablation (PTSMA) for hypertrophic obstructive cardiomyopathy (HOCM). Methods and Results Based on a scoring system developed 1996–1998 and including parameters from baseline ECG, heart rate profile, severity of outflow obstruction (LVOTO), peri-interventional enzyme kinetics, and peri-interventional conduction problems, the risk of permanent AV block following PTSMA was assessed in 155 consecutive HOCM patients (pts.; mean age: 53 ± 13 years) between 1999 and 2004. During PTSMA with 2.1 ± 0.5 ml of ethanol, transient complete AV block occurred in 71 pts. (46%). Pts. were grouped into a low, intermediate, and high risk group for permanent conduction damage, and treated accordingly (early discharge from monitoring, prolonged monitoring, early DDD-PM implantation). Permanent pacing was necessary in 11 cases (7%), 0/116 of these (0%) in the low, 4/31 (13%) in the intermediate, and 7/8 (87%) in the high-risk group. While a new right bundle branch block was the most frequent ECG finding after PTSMA, a left bundle branch block at baseline was associated with 4 of the 11 DDD-PM implantations ( p < 0.0001). In-hospital mortality was 0%, short-term (3-months) follow up was complete. During follow-up, AV conduction recovered in 4 pts. (46%) with a DDD-PM. New onset AV blocks did not occur. Significant improvement of symptoms was reported by 141 pts. (91%). Conclusions Catheter-based septal ablation is an effective non-surgical technique for reducing symptoms and outflow gradients in HOCM. The proposed scoring system appears to reliably discriminate pts. with a high risk for permanent PM dependency from those with stable AV conduction after PTSMA. Pts. with left bundle branch block at baseline should undergo DDD-PM implantation prior to ablation.

Cryoablation versus radiofrequency ablation for treatment of pediatric atrioventricular nodal reentrant tachycardia: Initial experience with 4-mm cryocatheter

Initial reports have shown cryoablation to be safe and efficacious for treatment of atrioventricular nodal reentrant tachycardia (AVNRT). No direct comparisons of cryoablation vs radiofrequency (RF) catheter ablation in pediatric patients have been made. The purpose of this study was to compare the outcomes of cryothermal vs RF catheter ablation for treatment of AVNRT in pediatric patients. We retrospectively reviewed consecutive ablation procedures for treatment of AVNRT at a single arrhythmia center. The RF group consisted of patients who underwent RF ablation from 2002 until cryothermy became available. The cryoablation group consisted of patients who underwent cryothermal ablation from 2004 to 2005. The groups were compared for procedural and electrophysiologic outcomes. RF (n = 60, age 14 +/- 4 years) and cryoablation (n = 57, age 14 +/- 4 years) groups had similar demographic and baseline parameters. Procedural times were shorter in the RF group (RF ablation 112 +/- 31 minutes vs cryoablation 148 +/- 46 minutes, P < .001). Fluoroscopy times were comparable (RF ablation 21 +/- 15 minutes vs cryoablation 20 +/- 13 minutes, P = .77). In an intention-to-treat analysis, success of the procedure was 100% for RF ablation and 95% for cryoablation (P = .11). No permanent AV block occurred in either group. Recurrence rates were higher for the cryoablation group, but this did not reach statistical significance (RF ablation 2% vs cryoablation 8%, P = .19). Cryoablation appears to be similar to RF for ablation of AVNRT with respect to short-term efficacy and safety of the procedure in a pediatric population. Recurrence rates are higher with cryoablation.

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.

Slow pathway ablation in children with documented reentrant supraventricular tachycardia not inducible during invasive electrophysiologic study

Radiofrequency catheter ablation (RFA) has become the procedure of choice for permanent therapy of atrioventricular nodal reentrant tachycardia (AVNRT). This report presents our experience with atrio-ventricular node (AVN) modification in patients with documented narrow complex reentrant SVT, but no evidence for an accessory pathway, and no inducible tachyarrhythmia during invasive electrophysiology (EP) study. The study population consists of nine children, age range 6-13 years (median 9) with previously documented SVT who had no tachyarrhythmia inducible during EP study (at baseline and following isoprenaline infusion). Eight of the 9 EP studies were performed under general anesthesia, and one under conscious sedation. An accessory pathway was excluded in all patients by appropriate atrial and ventricular extrastimulus pacing techniques. Eight of the nine patients had dual AV nodal physiology, and one had single AV nodal echo beats. The slow AV nodal pathway was empirically ablated, by applying RF lesions in the right inferoseptal AV groove, achieving catheter tip temperature of 50 degrees C. The appearance of an accelerated junctional rhythm during RF application was deemed to denote a successful application site. AV conduction during RF application was confirmed by incremental atrial pacing. The catheter position, and its relation to the compact AV node was constantly monitored using the LocaLisa navigation system. The end-point was absence of dual AVN physiology, and/or AV nodal echo beats. Successful slow pathway ablation was achieved in all patients. One patient appeared to have two separate slow pathways with different locations and two AH-jumps, which were both successfully ablated. None of the patients had evidence of temporary or permanent AV block at follow-up (median duration 9 months, range 4 to 36 months); none has had recurrence of symptoms or documented tachyarrhythmia. In children with structurally normal hearts, a previously documented SVT, absence of an accessory pathway and noninducibility of SVT during EP study, empirical slow pathway ablation appears to be justified.

Radiofrequency catheter septal ablation for hypertrophic obstructive cardiomyopathy in childhood

Two patients, a 5 year old boy with progressive hypertrophic obstructive cardiomyopathy and increasing symptoms despite appropriate pharmacologic therapy and an 11 year old girl with symptoms of tiredness and peak instantaneous LVOT gradient of 80 and 90 mmHg respectively were considered for radiofrequency catheter septal ablation, to relieve the left ventricular outflow tract obstruction. Via a femoral arterial approach, the His bundle was initially plotted and marked using the LocaLisa navigation system. Subsequently, using a cooled tip catheter a series of lesions was placed in the hypertrophied septum, commencing distally in the ventricle and proceeding towards the aortic valve, taking care to stay away from the His bundle. The procedure was deemed to be completed when the entire extent of the hypertrophied septum had been treated. In the boy the procedure was complicated by two episodes of ventricular fibrillation, requiring DC cardioversion, but without any neurologic sequelae. The peak to peak gradient between left ventricle and aorta was 50 mmHg and 60 mmHg respectively pre-ablation, and remained unchanged immediately after. Both patients were discharged from the hospital 48 hours later. Serial measurement of serum Troponin T and CK-MB isoenzyme confirmed significant myocardial necrosis. Follow-up echocardiography at 7 days and at 6 weeks post-ablation respectively confirmed a beneficial hemodynamic result, with reduction of left ventricular outflow obstruction and relief of symptoms. In young children, in whom alcohol induced septal ablation is not an option, radiofrequency catheter ablation offers an alternative to surgery, with the benefits of repeatability and a lower risk of procedure-related permanent AV block.

Usefulness of myocardial contrast echocardiographic quantification of risk area for predicting postprocedural complications in patients undergoing septal ethanol ablation for obstructive hypertrophic cardiomyopathy

Septal ethanol ablation (SEA) is an alternative to surgical myectomy in patients who have drug-refractory obstructive hypertrophic cardiomyopathy. However, permanent atrioventricular conduction block is seen more frequently with SEA. To determine whether septal infarction risk area (SIRA) predicts outcome in patients who have obstructive hypertrophic cardiomyopathy and are undergoing SEA, we evaluated 51 patients (mean age 60 +/- 16, 53% women) who had a successful SEA at Toronto General Hospital (November 1998 to June 2003). Intracoronary myocardial contrast echocardiography that targeted the contact area between the septum and the anterior mitral leaflet was performed before ethanol injection. End-systolic myocardial contrast echocardiographic frames were color coded for better delineation of contrast borders, and myocardial contrast echocardiographic area was calculated by planimetry. Patients were assigned to 1 of 2 groups by median SIRA value (3.51 cm(2), range 0.4 to 7.8). The 2 groups did not differ significantly in age, medication before SEA, electrocardiographic characteristics, left ventricular function, left atrial diameter, volume of intracoronary ethanol injected, peak creatine kinase after ablation, and baseline and follow-up left ventricular outflow tract gradients at rest. Patients in the large SIRA group had greater hypertrophy and a larger septal artery than did patients in the small SIRA group. In the small SIRA group, 3 patients (11.5%) had pacemaker implantation; in the large SIRA group, 12 patients (48.0%) had complications after SEA (pacemaker in 5 patients, implantable defibrillator in 5 patients, death in 2 patients; p = 0.008). We conclude that patients who have hypertrophic cardiomyopathy with a small, well-localized SIRA benefit similarly from SEA as patients who have a larger SIRA but with significantly fewer serious complications.

Role of force--frequency relation during AV-block, sinus node block and beta-adrenoceptor block in conscious animals.

Myocardial contractility is regulated by adrenergic stimulation, the strength-length relationship and the force-frequency relationship or Bowditch effect. The latter mechanism was clearly demonstrated in muscle strips, in the isolated heart as well as in in-vivo experiments. The aim of this study was to further investigate the role of the force-frequency effect on the contractile response to exercise or isoproterenol infusion in conditions of restricted increases in heart rate i.e., AV-block, sinus node block and beta-adrenoceptor block. Nineteen dogs were instrumented with a left ventricular miniature pressure gauge, catheters in the aorta, pulmonary artery and left atrium and pacing leads on the left atrium and left ventricle. In order to control the chronotropic response during sympathetic stimulation, permanent AV-block was induced in nine dogs, sinus node block using UL-FS 49 and beta-adrenoceptor block using propranolol was studied in ten dogs. Adrenergic stimulation (isoproterenol 0.4 micro g/kg or exercise) after total AV-block failed to increase LVdP/dt. However, increasing LV pacing rate (from 50 up to 200 bpm) prior to adrenergic stimulation elicited a significant increase in LVdP/dt (4762 +/- 166 mmHg/s vs. 6485 +/- 381 mmHg/s, p < 0.05). In dogs in sinus rhythm, heart rate and LVdP/dt response to isoproterenol and exercise following pre-treatment with UL-FS 49 is significantly reduced, with heart rate increasing from 103 +/- 7 up to 154 +/- 5 bpm and LV dP/dt(max) from 2925 +/- 171 mmHg/s to 6249 +/- 400 mmHg/s compared to the response in control conditions (HR 220 +/- 3 bpm and LV dP/dt(max) 7473 +/- 616 mmHg/s) (p < 0.05). When heart rate is matched using atrial pacing, the LVdP/dt(max) response reached comparable values as observed in control conditions (7310 +/- 550 mmHg/s). Similar responses were obtained during exercise. Beta-adrenoceptor blockade attenuates considerably the heart rate and LVdP/dt response to sympathetic stimulation. Adjusting heart rate with atrial pacing restores only partially LVdP/dt(max). During sympathetic stimulation, the chronotropic response plays a major role for the concomitant full expression of the inotropic response. In conditions where increases in heart rate are absent or severely restricted such as in permanent AV-block, sinus node block and beta-adrenoceptor block, the inotropic response will also be impaired.

19.2 Mechanisms of syncope in arrhythmogenic right ventricular dysplasia-cardiomyopathy

In patients with arrhythmogenic right ventricular dysplasia-cardiomyopathy (ARVD/C) syncopes are frequent events with in most cases a bad prognosis. In most cases the cause of syncope is non-sustained monomorphic VT. In 27 patients (9 males, mean age 46.3 years) with ISFC/ESC criteria of ARVD/C without documented or inducible monomorphic VT several other features could be found. Permanent AV Block IIIo in 3 cases, an intermittant AV block IIIo in 2 cases, an isolated HV interval of 80 msec in one case and isolated pathological atrioventricular conduction (<100 bpm) in 4 cases. In a young female patient a short polymorphic VT with degeneration into VF was inducible. In four patients positive Brugada phenomenon was provocable by ajmaline testing. Tilt table testing was done in 7 cases; neurocardiogenic syncope was found in 2 cases. Conclusions: Besides non-sustained monomorphic VT other mechanisms of syncope must be discussed in ARVD/C. There seems to be an association of ARVD/C to progressive conduction disease, catecholaminergic polymorphic ventricular tachycardia and Brugada syndrome.

Síncope de origen desconocido en pacientes con bloqueo auriculoventricular permanente sintomático después del implante de un marcapasos definitivo. Utilidad de la prueba de mesa basculante

Four female patients aged 26 to 71 years, with permanent complete AV heart block and an implanted pacemaker had syncope or presyncope after the pacemaker implantation. As part of the study protocol the tilt table test was done. Neurological disease, arrhythmias, pacemaker syndrome or dysfunction of the stimulation system were ruled out. A head up tilt was performed, isosorbide was used as pharmacological challenge, since the basal test was negative. In three patients this test was positive: in one patient possibly caused by postural orthostatic tachycardia syndrome, and two with neurally mediated syncope. In one patient it was not possible a diagnosis. The head-up tilt test is a useful procedure to identify the etiology of the appearance of syncope or presyncope after a pacemaker implantation in patients with complete and permanent AV block.

Techniques to avoid atrioventricular block during radiofrequency catheter ablation of septal tachycardia substrates in young patients.

Radiofrequency catheter ablation (RFCA) has proven safe for most young patients, but the risk of inadvertent atrioventricular (AV) block remains. The purpose of this report is to describe techniques to avoid inadvertent AV block during effective RFCA in young patients with septal tachycardia substrates. The techniques included intubation and apnea during RFCA, coronary sinus pacing during RFCA to observe intact AV conduction during junctional ectopy, localizing the optimal His electrogram prior to RFCA, not ablating during tachycardia and titrating power output with temperature monitoring. In the period January 1995-June 2001, RFCA of 424 tachycardia substrates was performed. A total of 217 consecutive septal tachycardia substrates are included in this report. Apnea eliminated a mean catheter tip displacement of 5.4 +/- 2.5 mm seen during respiration. No patient experienced transient or permanent complete AV block after any of the 217 substrate ablation procedures. All of the patients had normal PR intervals following ablation without development of any degree of AV block in 194 patients at latest follow-up. RFCA success for substrates with septal accessory pathways was 87/96 (91%), permanent junctional reciprocating tachycardia (PJRT) 15/16 (94%), typical atrioventricular node reentry tachycardia (AVNRT) 82/85 (96%), atypical AVNRT 6/7 (86%) and intra-atrial reentry tachycardia (IART) 10/13 (77%). Fluoroscopy time averaged 10.8 minutes. For patients with accessory pathway, 8 (7.9%) developed a recurrence. Catheter stability is paramount to safe and effective RFCA in septal locations. Use of these techniques resulted in acceptable success rates and low recurrence rate for RFCA of septal tachycardia substrates while avoiding inadvertent AV block in these young patients.