Radiofrequency ablation for atrioventricular node reentrant tachycardia: comparison between fast (anterior) and slow (posterior) pathway ablation

OBJECTIVES: We compared the electrophysiologic effects on atrioventricular (AV) node physiology of selective "fast" versus selective "slow" pathway radiofrequency ablation in 42 patients with drug-resistant AV node reentrant tachycardia who underwent 51 ablation attempts to prevent tachycardia recurrence while preserving AV conduction. BACKGROUND: The recent introduction of radiofrequency ablation to treat AV node reentrant tachycardia allows the opportunity to study the effects of selective elimination of the different limbs involved in AV node reentrant tachycardia. METHODS: Selective fast pathway ablation was attempted in 13 patients by delivering radiofrequency energy anteriorly across the tricuspid valve anulus. Selective slow pathway ablation was attempted in 29 patients by delivering radiofrequency energy posteriorly across the tricuspid valve anulus at sites where putative slow pathway potentials were recorded. RESULTS: Selective fast pathway ablation eliminated AV node reentrant tachycardia without AV block in 6 (46%) of 13 patients after one ablation session and in an additional 3 patients (69% of total) after repeat ablation sessions. Slow pathway ablation eliminated AV node reentrant tachycardia without AV block in 26 (90%) of 29 patients after one radiofrequency ablation session and in an additional 2 patients (97% of total) after repeat ablation sessions. Selective fast pathway ablation increased the PR interval (140 to 220 ms, p = 0.0001) and AH interval (66 to 153 ms, p = 0.0001), whereas slow pathway ablation did not change these intervals. Fast pathway radiofrequency ablation caused retrograde block in 7 (64%) of 11 patients, whereas no patients undergoing slow pathway ablation developed selective retrograde block. Single AV node echo beats were commonly induced after slow but not fast pathway ablation (17 of 29 patients vs. 1 of 11 patients, respectively, p = 0.01) and did not predict recurrence of AV node reentrant tachycardia. CONCLUSIONS: Successful selective radiofrequency ablation of fast or slow pathways in patients with AV node reentrant tachycardia resulted in different electrophysiologic properties after ablation. Slow pathway ablation produced more successful outcomes, with a decreased prevalence of recurrent AV node reentrant tachycardia or AV block.     

A simple technique for selective radiofrequency ablation of the slow pathway in atrioventricular node reentrant tachycardia

OBJECTIVES: A simple technique was designed for radiofrequency ablation therapy of atrioventricular (AV) node reentrant tachycardia. BACKGROUND: This technique was based on the hypothesis that slow pathway conduction reflects conduction through the compact node and its posterior atrial input. METHODS: A total of 100 consecutive patients were studied; there were 37 men and 63 women, with a mean age of 48 +/- 15 years. All 100 patients had induction of sustained tachycardia with (51 patients) or without (49 patients) administration of isoproterenol or atropine, or both. The ablation catheter was initially manipulated to record the largest His bundle deflection from the apex of Koch's triangle. It was then curved downward and clockwise to the area of the compact node when His deflection was no longer visible and the ratio of atrial to ventricular electrogram was < 1. The radiofrequency current was delivered from the 4-mm tip electrode a mean of 5 +/- 7 times at a power of 25 +/- 4 W for a duration of 21 +/- 4 s. The total fluoroscopic time was 19 +/- 11 min. RESULTS: Selective ablation (56 patients) or modification (26 patients) of the slow pathway without affecting anterograde and retrograde fast pathway conduction was achieved in 82 patients. Ablation or modification of both the retrograde fast pathway and the slow pathway but with preservation of anterograde fast pathway conduction was noted in 12 patients. Ablation or modification of the retrograde fast pathway alone or both anterograde and retrograde fast pathway conduction was noted in three patients. Complete AV node block occurred in three patients. Seventy-three patients had no induction of echo beats or tachycardia and 24 patients had induction of a single echo beat after ablation. Follow-up study was performed in 62 patients 76 +/- 18 days after ablation. Thirty-nine patients had no induction of echo beats or tachycardia, 22 had induction of echo beats alone and 1 patient had induction of sustained tachycardia. CONCLUSION: Selective ablation of the slow AV node pathway can be achieved by a simple procedure with a high success rate and few complications.     

Successful slow pathway ablation in a patient with atrioventricular nodal reentrant tachycardia having a proximal common pathway

Radiofrequency catheter ablation was attempted in a patient with atrioventricular nodal reentrant tachycardia (AVNRT). AVNRT was easily inducible but an intermittent loss of the atrial activation was observed during AVNRT suggesting the presence of a proximal common pathway. During sinus rhythm, a relatively delayed activation that was compatible with a slow potential, was recorded anterior to the ostium of coronary sinus, and radiofrequency catheter ablation application (20 watts) to the site induced junction tachycardia. After an additional radiofrequency catheter ablation application to close the site, AVNRT became noninducible without deterioration of atrioventricular conduction through a fast pathway. This is the first case in which radiofrequency catheter ablation application to the slow potential recording site has been successful, even in AVNRT having a proximal common pathway.     

Induction of atrioventricular node reentrant tachycardia with adenosine: differential effect of adenosine on fast and slow atrioventricular node pathways

OBJECTIVES: This study sought to evaluate the sensitivity of fast and slow atrioventricular (AV) node pathways to incremental doses of adenosine in patients with typical AV node reentrant tachycardia. BACKGROUND: Although adenosine is known to depress conduction through the AV node, the relative sensitivity to adenosine of the anterograde fast and slow pathways in patients with dual AV node pathways and typical AV node reentrant tachycardia has not previously been studied. METHODS: Sixteen patients with dual AV node physiology and typical AV node reentrant tachycardia and 10 control patients were given incremental doses of adenosine during atrial pacing. RESULTS: In 14 of 16 patients with dual-AV node physiology, administration of small doses of adenosine during atrial pacing led consistently to transient block of impulse conduction in the fast pathway before block in the slow pathway, resulting in abrupt prolongation of the AH interval with continued 1:1 AV conduction. The mean (+/- SD) doses of adenosine required to cause conduction block in the fast and slow pathways were 2.7 +/- 3.0 and 7.2 +/- 4.7 mg, respectively (p = 0.004). In 9 of 16 patients, administration of low dose adenosine led to initiation of AV node reentrant tachycardia. The control patients showed no abrupt increases in AH interval with administration of adenosine during atrial pacing. CONCLUSIONS: In most patients with dual AV node pathways and typical AV node reentrant tachycardia, the fast pathway is more sensitive than the slow pathway to the effects of adenosine.     

Randomized comparison of anatomic and electrogram mapping approaches to ablation of the slow pathway of atrioventricular node reentrant tachycardia

OBJECTIVES: The purpose of this study was to prospectively compare in random fashion an anatomic and an electrogram mapping approach for ablation of the slow pathway of atrioventricular (AV) node reentrant tachycardia. BACKGROUND: Ablation of the slow pathway in patients with AV node reentrant tachycardia can be performed by using either an anatomic or an electrogram mapping approach to identify target sites for ablation. These two approaches have never been compared prospectively. METHODS: Fifty consecutive patients with typical AV node reentrant tachycardia were randomly assigned to undergo either an anatomic or an electrogram mapping approach for ablation of the slow AV node pathway. In 25 patients randomly assigned to the anatomic approach, sequential radiofrequency energy applications were delivered along the tricuspid annulus from the level of the coronary sinus ostium to the His bundle position. In 25 patients assigned to the electrogram mapping approach, target sites along the posteromedial tricuspid annulus near the coronary sinus ostium were sought where there was a multicomponent atrial electrogram or evidence of a possible slow pathway potential. If the initial approach was ineffective after 12 radiofrequency energy applications, the alternative approach was then used. RESULTS: The anatomic approach was effective in 21 (84%) of 25 patients, and the electrogram mapping approach was effective in all 25 patients (100%) randomly assigned to this technique (p = 0.1). The four patients with an ineffective anatomic approach had a successful outcome with the electrogram mapping approach. On the basis of intention to treat analysis, there were no significant differences between the electrogram mapping approach and the anatomic approach with respect to the time required for ablation (28 +/- 21 and 31 +/- 31 min, respectively, mean +/- SD, p = 0.7) duration of fluoroscopic exposure (27 +/- 20 and 27 +/- 18 min, respectively, p = 0.9) or mean number of radiofrequency applications delivered (6.3 +/- 3.9 vs. 7.2 +/- 8.0, p = 0.6). With both the anatomic and electrogram mapping approaches, the atrial electrogram duration and number of peaks in the atrial electrogram were significantly greater at successful target sites than at unsuccessful target sites. CONCLUSIONS: The anatomic and electrogram mapping approaches for ablation of the slow AV nodal pathway are comparable in efficacy and duration. If the anatomic approach is initially attempted and fails, the electrogram mapping approach may be successful at sites outside the areas targeted in the anatomic approach. With both the anatomic and electrogram mapping approaches, there are significant differences in the atrial electrogram configuration between successful and unsuccessful target sites.     

A randomized comparison of fixed power and temperature monitoring during slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia

In the present study, using sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Western blot techniques, the patterns of proteins extracted from C. neoformans yeast cells were analysed. A major 105 kilodalton (kDa) antigen that binds to Concanavalin A and cross-reacts with anti-mannan antibodies was identified. The 105 kDa mannoprotein, highly expressed in the acapsular mutant of C. neoformans with respect to the encapsulated strain, is involved in the lymphoproliferative response of T lymphocytes to Cryptococcus-sensitized monocytes.     

Differential effect of adenosine on anterograde and retrograde fast pathway conduction in patients with atrioventricular nodal reentrant tachycardia

INTRODUCTION: Several studies have shown that the fast pathway is more responsive to adenosine than the slow pathway in patients with AV nodal reentrant tachycardia. Little information is available regarding the effect of adenosine on anterograde and retrograde fast pathway conduction. METHODS AND RESULTS: The effects of adenosine on anterograde and retrograde fast pathway conduction were evaluated in 116 patients (mean age 47 +/- 16 years) with typical AV nodal reentrant tachycardia. Each patient received 12 mg of adenosine during ventricular pacing at a cycle length 20 msec longer than the fast pathway VA block cycle length and during sinus rhythm or atrial pacing at 20 msec longer than the fast pathway AV block cycle length. Anterograde block occurred in 98% of patients compared with retrograde fast pathway block in 62% of patients (P < 0.001). Unresponsiveness of the retrograde fast pathway to adenosine was associated with a shorter AV block cycle length (374 +/- 78 vs 333 +/- 74 msec, P < 0.01), a shorter VA block cycle length (383 +/- 121 vs 307 +/- 49 msec, P < 0.001), and a shorter VA interval during tachycardia (53 +/- 23 vs 41 +/- 17 msec, P < 0.01). CONCLUSION: Although anterograde fast pathway conduction is almost always blocked by 12 mg of adenosine, retrograde fast pathway conduction is not blocked by adenosine in 38% of patients with typical AV nodal reentrant tachycardia. This indicates that the anterograde and retrograde fast pathways may be anatomically and/or functionally distinct. Unresponsiveness of VA conduction to adenosine is not a reliable indicator of an accessory pathway.     

Junctional tachycardia during radiofrequency ablation of the slow pathway in patients with AV nodal reentrant tachycardia: effects of autonomic blockade

BACKGROUND: Exogenous surfactant treatment of hyaline membrane disease is known to modify the pattern of radiological changes on the chest radiograph. OBJECTIVES: To analyse and attempt to explain the radiological changes observed after exogenous surfactant treatment. Materials and methods. Thirty-nine premature infants with typical hyaline membrane disease. RESULTS: Transient asymmetrical clearing with better aeration of the right lung in the absence of malposition of the tip of the endotracheal tube was observed in nine cases (23 %). This asymmetry was patchy in one case. It was due to a complication of mechanical ventilation in three cases [pneumothorax (n = 2) and pneumomediastinum (n = 1)]. In the other six cases, asymmetrical clearing could be related to the anatomical position of the right main bronchus, which facilitates distribution of surfactant to the right lung. However, the course of these premature infants was similar to that of infants with symmetrical chest radiological findings after treatment. CONCLUSIONS: Asymmetrical clearing of chest radiographs, sometimes patchy, after surfactant treatment requires exclusion of pneumothorax or infection but has no influence on clinical outcome.     

Complex electrophysiological characteristics in atrioventricular nodal reentrant tachycardia with continuous atrioventricular node function curves

BACKGROUND: Although typical atrioventricular nodal reentrant tachycardia (AVNRT) with discontinuous AV node function curves has been well studied, there has been a lack of any significant information about AVNRT without evidence of dual AV nodal pathway physiology during atrial extrastimulus testing or atrial pacing. METHODS AND RESULTS: Group 1 included 9 patients with continuous curves during atrial extrastimulus testing but without a jump (> or = 50 ms) of the atrial-His bundle (AH) interval during incremental atrial pacing. The maximal AH interval during atrial pacing (266 +/- 61 versus 168 +/- 27 ms, P = .007) or extrastimulus testing (290 +/- 60 versus 176 +/- 18 ms, P = .005) shortened significantly after ablation. Antegrade and retrograde AV node properties were similar before and after ablation. Group 2 included 14 patients with continuous curves and a jump of the AH interval during incremental atrial pacing. The atrial pacing cycle length with 1:1 AV conduction and effective refractory period (ERP) of the antegrade AV node increased significantly, whereas the maximal AH interval during atrial pacing (358 +/- 70 versus 203 +/- 28 ms, P = .001) or extrastimulus testing (338 +/- 75 versus 196 +/- 34 ms, P = .002) shortened significantly after ablation. Group 3 included 24 patients with discontinuous curves. The maximal AH interval during atrial pacing or extrastimulus testing and the ERP of the antegrade fast AV node shortened, whereas the ERP of the antegrade AV node increased significantly after ablation. The maximal AH interval before ablation, extent of decrease in maximal AH interval after ablation, ERP of the retrograde AV node before ablation, and tachycardia cycle length were significantly shorter in group 1 than groups 2 and 3. CONCLUSIONS: In AVNRT with continuous AV node function curves, dual AV nodal pathway physiology may or may not be demonstrated during atrial pacing. Significant shortening of the maximal AH interval during atrial pacing after radiofrequency ablation suggests successful elimination of AVNRT.     

Randomized comparison of slow pathway modification within the posteroseptal versus the midseptal area in patients with atrioventricular nodal reentrant tachycardia

A total of 332 local electrogram recordings including 62 successful and 270 unsuccessful sites were analyzed. Univariate analysis revealed that there was a longer duration and more peaks of the atrial electrogram with a lower atrioventricular ratio and a higher incidence and shorter onset time of junctional ectopy during energy delivery at successful than at unsuccessful target sites.     

Absence of junctional rhythm during successful slow-pathway ablation in patients with atrioventricular nodal reentrant tachycardia

BACKGROUND: The presence of junctional rhythm has been considered to be a sensitive marker of successful slow-pathway ablation. However, in rare cases, junctional rhythm was absent despite multiple radiofrequency applications delivered over a large area in the Koch's triangle, and successful ablation was achieved in the absence of a junctional rhythm. METHODS AND RESULTS: This study included 353 patients with AV nodal reentrant tachycardia (143 men and 210 women; mean age, 50+/-17 years) who underwent catheter ablation of the slow pathway. Combined anatomic and electrogram approaches were used to guide ablation. Inducibility of AV nodal reentrant tachycardia was assessed after each application of radiofrequency energy. Successful sites were located in the posterior area in 18 (90%) of 20 patients without junctional rhythm during slow-pathway ablation compared with 200 (60%) of 333 patients with junctional rhythm (P<0.001). The fast-slow form of tachycardia was more common in patients without than in those with junctional rhythm (30% versus 3%; P=0.001). At the successful ablation sites, patients with junctional rhythm had a higher incidence of a multicomponent or slow-pathway potential (51% versus 10%; P<0.001), a longer duration of the atrial electrogram (64+/-8 versus 50+/-9 ms; P=0.04), and a smaller atrial/ventricular electrogram amplitude ratio (0.29+/-0.18 versus 0.65+/-0.27; P<0. 001) than those without junctional rhythm. Mean temperatures at successful sites (56+/-6 degreesC versus 58+/-9 degreesC; P=0.57) and incidence of transient AV block (2% versus 0%; P=0.86) were similar between patients with and without junctional rhythms. By multivariate analysis, location of ablation sites, atrial/ventricular electrogram amplitude ratio, absence of a multicomponent or slow-pathway potential, and occurrence of the fast-slow form of tachycardia were independent predictors of the absence of a junctional rhythm during successful slow-pathway ablation. CONCLUSIONS: In some rare cases, successful slow-pathway ablation is possible in the absence of a junctional rhythm.     

Radiofrequency ablation in a patient with tachycardia incorporating triple free wall accessory pathways and atrioventricular nodal reentrant tachycardia

Bone marrow cells from 15 patients with normal deoxyuridine (dU) suppression test results, 3 healthy subjects, and 11 patients with megaloblastic anemia caused by vitamin B12 or folate deficiency were examined for misincorporation of uracil into DNA. Cells were incubated with [5-3H] uridine for 2 hours and their DNA extracted. The DNA was hydrolyzed to deoxyribonucleosides with DNase 1, phosphodiesterase and alkaline phosphatase, and any dU present was separated from other deoxyribonucleosides by Aminex A6 chromatography. The quantity of dU/mg DNA and the radioactivity in the dU peak/mg DNA were then calculated. The results clearly showed that there was markedly increased uracil misincorporation into the DNA of vitamin B12- or folate-deficient marrow cells. Misincorporation of uracil into DNA may be an important biochemical lesion underlying both the megaloblastic change and the ineffectiveness of hematopoiesis in vitamin B12 and folate deficiency.     

Catheter ablation for the common type of atrioventricular nodal reentrant tachycardia

Radiofrequency (RF) catheter ablation of the slow AV nodal pathway was attempted in 34 patients with common type of AV nodal reentrant tachycardia (AVNRT). Radiofrequency energy of 18-32 watts was applied for 30-60 seconds at sites exhibiting atrial-slow pathway potentials or slow potentials. These potentials were recorded at the mid or posterior septum, anterior to the coronary sinus ostium. A mean of two radiofrequency applications successfully eliminated AVNRT in all patients. The incidence of junctional ectopy was significantly higher during 34 effective applications of radiofrequency energy than during 36 ineffective applications (100% versus 17%). Thus, the recording of atrial-slow pathway potentials or slow potentials, and the development of junctional ectopy can be used as a marker for successful ablation. Slow AV nodal conduction was eliminated in 22 patients and persisted without inducible AVNRT in 12. None of the patients had recurrences of AVNRT over a mean follow-up interval of 12 months, and all had preserved AV conduction. Long-term follow-up studies with an electrophysiological method confirmed that the ablation was effective. Transient AV block was observed in only 1 patient, and no major complications were noted. Thus, radiofrequency catheter ablation of the slow AV nodal pathway is highly effective and safe, with a low rate of complication, for the treatment of common type of AVNRT.     

Radiofrequency catheter ablation of atrioventricular junctional ("AV nodal") reentrant tachycardia in patients with implantable cardioverter defibrillators

Catheter ablation of tachycardias has been undertaken successfully in patients with ICDs without damage to the ICD or lead. Ablation of the slow AV nodal pathway, however, is technically challenging because the lead of the ICD lies close to the ablation site. We report successful ablation of AV junctional reentrant tachycardia (AVJRT) in three patients with ICDs. In all cases, the ablation site was within a few millimeters of the ICD lead. The ablation was successful in all cases and did not cause damage to the ICD or lead. The patients have remained free of recurrence of AVJRT during a mean follow-up of 12 months.     

Case report: radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia in a patient with heart transplantation

We have assessed hepatocellular integrity in patients anaesthetized with desflurane or isoflurane using glutathione transferase Alpha (GSTA) as a sensitive indicator. Volatile anaesthetic was administered to 72 women at 0.7 MAC for 25 min and thereafter at 1.0 MAC. GSTA was measured with a time-resolved immunofluorometric assay in serum samples. Mild or moderate increases in GSTA were found in approximately 40% of patients immediately after anaesthesia. In the desflurane group (n = 30) the increase in GSTA concentration was from a baseline value of the geometric mean of 1.3 microgram litre-1 (95% confidence interval 0.9-1.9 microgram litre-1) to a peak of 2.6 (1.8-3.8) micrograms litre-1. The corresponding increase in the isoflurane group (n = 31) was from 1.3 (0.9-1.9) microgram litre-1 to 3.0 (2.2-4.2) micrograms litre-1. The change in GSTA concentration was significant in both groups but not between groups. No predictive factors for the increase in GSTA concentrations were found. Increased GSTA concentrations were not accompanied by increases in amino-transferases. We conclude that desflurane and isoflurane anaesthesia were associated with a mild subclinical disturbance of hepatocellular integrity.     

Atrioventricular nodal reentry tachycardia in patients with sinus node dysfunction: electrophysiologic characteristics, clinical presentation, and results of slow pathway ablation

BACKGROUND AND PURPOSE: The purposes of this study were to describe the use of ultrasound by Dutch physical therapists and to address the question of whether this use is what would be considered correct. SUBJECTS AND METHODS: Physical therapists in the Dutch primary health care system gathered data on 17,201 patients, addressing reasons for referral, treatment goals (in terms of impairments and disabilities), and physical therapy interventions. Patients treated with ultrasound (n = 3,959) were compared with a reference group of patients who were not treated with ultrasound (n = 13,242). RESULTS: Physical therapists applied ultrasound for soft tissue injuries of recent onset, mainly aiming to reduce pain and swelling. Ultrasound was used in all phases of treatment and was not restricted to the first 3 weeks of treatment. Ultrasound was combined relatively infrequently with exercise and relatively frequently with massage. CONCLUSION AND DISCUSSION: Regarding the indications for referral and treatment goals chosen, the actual use of ultrasound corresponds to assumptions about expected use. The timing of its application and the combination with other forms of therapy do not correspond in all aspects to the assumptions made.     

Difficulties with pharmacologic treatment of a patient with atrioventricular nodal reentrant tachycardia

A case history of a 38 year old teacher with AVNRT is described. She had been treated for 11 years with 11 antiarrhythmic drugs in various combinations. No treatment prevented recurrence of arrhythmia. During long term treatment with class IA, IC, II, III and IV antiarrhythmic drugs, various side effects occurred. There was also suspicion of proarrhythmic effect, especially of prajmaline. Some of the drugs terminated tachycardia while administered intravenously. But often deep hypotonia, heart automatism disturbances and even asystole occurred, MAS syndrome occurred 5 times. The patient was referred to our laboratory to perform percutaneous radiofrequency ablation of the slow pathway. The procedure was performed without any complications. Efficacy of the ablation was proved by electrophysiologic study before and after intravenous atropine administration. During the 11 months follow-up the patient had no tachycardia. She is on no antiarrhythmic medication and continues her normal activity.     

Dimension and related anatomical distance of Koch's triangle in patients with atrioventricular nodal reentrant tachycardia

INTRODUCTION: The dimension of Koch's triangle in patients with AV nodal reentrant tachycardia has not been well described. Understanding the dimension and anatomical distance related to Koch's triangle might be useful in avoiding accidental AV block during ablation of the slow pathway. The purposes of this study were to define the dimension of Koch's triangle and its related anatomical distance and correlate these parameters with the successful ablation sites in patients with AV nodal reentrant tachycardia. METHODS AND RESULTS: We studied 218 patients with AV nodal reentrant tachycardia. The distance between the presumed proximal His-bundle area and the base of the coronary sinus orifice (DHis-OS) measured in the right anterior oblique view was used to define the dimension of Koch's triangle. The distance of the proximal His-bundle recording site from the successful ablation site (DHis-Ab) and the distance as a fraction of the entire length of Koch's triangle (DHis-Ab/DHis-Os) were determined. The mean DHis-Os and DHis-Ab were 25.9 +/- 7.9 and 13.4 +/- 3.8 mm, respectively. DHis-Os negatively correlated with patient age (r = -0.41, P < 0.0001) and body mass index (r = -0.18, P = 0.004). Among the patients with successful ablation sites in the medial area, DHis-Os was longer (27.2 +/- 6.6 vs 24.6 +/- 8.4 mm, P < 0.005), DHis-Ab was similar (12.9 +/- 3.1 vs 13.9 +/- 4.0, P > 0.05) and DHis-Ab/DHis-Os was smaller (0.48 +/- 0.04 vs 0.74 +/- 0.11, P < 0.05). Furthermore, the patients with successful ablation sites in the medial location needed more radiofrequency pulse numbers than those in the posterior location (6 +/- 4 vs 4 +/- 3, P < 0.05). CONCLUSION: The site of successful slow pathway ablation was consistently about 13 mm from the site recording the proximal His-bundle deflection in patients with AV nodal reentrant tachycardia despite marked variability in the dimensions of Koch's triangle; therefore, patients with large triangles required ablation in the medial region rather than the posterior region. Care should be taken when delivering radiofrequency energy to the posteroseptal area in patients with shorter DHis-Os to avoid injury to AV node.     

Effects of pharmacological autonomic blockade on dual atrioventricular nodal pathways physiology in patients with slow-fast atrioventricular nodal reentrant tachycardia

The purpose of this study was to investigate the atrioventricular AV nodal physiology and the inducibility of AV nodal reentrant tachycardia (AVNRT) under pharmacological autonomic blockade (AB). Seventeen consecutive patients (6 men and 11 women, mean age 39 +/- 17 years) with clinical recurrent slow-fast AVNRT received electrophysiological study before and after pharmacological AB with atropine (0.04 mg/kg) and propranolol (0.2 mg/kg). In baseline, all 17 patients could be induced with AVNRT, 5 were isoproterenol-dependent. After pharmacological AB, 12 (71%) of 17 patients still demonstrated AV nodal duality. AVNRT became noninducible in 7 of 12 nonisoproterenol dependent patients and remained noninducible in all 5 isoproterenol dependent patients. The sinus cycle length (801 +/- 105 ms vs 630 +/- 80 ms, P < 0.005) and AV blocking cycle length (365 +/- 64 ms vs 338 +/- 61 ms, P < 0.005) became shorter after AB. The antegrade effective refractory period and functional refractory period of the fast pathway (369 +/- 67 ms vs 305 +/- 73 ms, P < 0.005; 408 +/- 56 ms vs 350 +/- 62 ms, P < 0.005) and the slow pathway (271 +/- 30 ms vs 258 +/- 27 ms, P < 0.01; 344 +/- 60 ms vs 295 +/- 50 ms, P < 0.005) likewise became significantly shortened. However, the ventriculoatrial blocking cycle length (349 +/- 94 ms vs 326 +/- 89 ms, NS) and effective refractory period of retrograde fast pathway (228 +/- 38 ms vs 240 +/- 80 ms, NS) remained unchanged after autonomic blockade. Pharmacological AB unveiling the intrinsic AV nodal physiology could result in the masking of AV nodal duality and the decreased inducibility of clinical AVNRT.