Titration of Power Output During Radiofrequency Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia

Radiofrequency lesions in the anterior, superior aspect of the tricuspid annulus result in selective elimination of fast pathway function in patients with typical atrioventricular (AV) nodal reentry tachycardia. This technique is simple and effective, but has been associated with a significant risk of inadvertent complete AV block. The purpose of this study was to compare the safety and effectiveness of two different techniques for radiofrequency catheter ablation of the fast AV nodal pathway. Initially, a fixed power output was used at each target site. This method was compared retrospectively to a newer technique where power output was gradually incremented at each site. Radiofrequency power was initially applied at 10 watts for 10–15 seconds. If no junctional ectopy or a change in PR intervoi was seen, power output was incremented by 2 to 4 watts every 10 to 15 seconds up to a maximum of 30 watts. Thirty seven of 38 (96%) patients treated using this incremental power output were cured of their AV nodal reentry tachycardia. None of these patients developed inadvertent complete AV block. In contrast, 92% of historic controls treated with a fixed power output between 20 and 30 watts achieved a primary success and nine of these 89 (10%) historic controls developed inadvertent complete AV block (P = 0.04). There was no difference in the amplitudes of atrial, His, or ventricular electrograms at the effective sites between the two groups. Conclusions: (1) the anterior approach to radiofrequency catheter ablation of typical AV nodal reentry is associated with a significant risk of inadvertent complete AV block if a fixed power output is used; (2) starting at low power and gradually incrementing the output during radiofrequency energy application reduces the risk of complete AV block; (3) this incremental technique does not compromise efficacy.     

Radiofrequency Ablation of Idiopathic Left Anterior Fascicular Tachycardia

Left Anterior Fascicular Tachycardia. Introduction: A 45-year-old man with idiopathic ventricular tachycardia (VT) having a right bundle branch block configuration with right-axis deviation underwent au electrophysiologic test.
Methods and Results: Mapping demonstrated a site on the auterobasal wall of the left ventricle where there was an excellent pace map and an endocardial activation time of -20 msec, hut radiofrequency catheter ablation at this site was unsuccessful. At a nearby site, a presumed Purkinje potential preceded the QRS complex by 30 msec during VT and sinus rhythm, and catheter ablation was effective despite a poor pace map and an endocardial ventricular activation time of zero.
Conclusion: Idiopathic VT with a right bundle branch configuration and right-axis deviation may originate in the area of the left anterior fascicle. A potential presumed to represent a Purkinje potential may he more helpful than endocardial ventricular activation mapping or pace mapping in guiding ablation of this type of VT.     

Identification of ''short-lived'' and ''long-lived'' patients at presentation of idiopathic myelofibrosis

Mobilization of Philadelphia chromosome (Ph) negative blood progenitors was attempted in 23 newly diagnosed chronic myeloid leukaemia (CML) patients using a regimen of cyclophosphamide (CY) 5 g/m² and rHUG-CSF 150 μg/m² daily. This regimen was well tolerated with no major adverse events reported. More than 2 × 10⁶/kg CD34⁺ cells were collected in 21 patients (91%). Predominantly Ph-negative mobilization (0–25% Ph-positive) was seen in 30% of cases overall and was confined to patients with a Sokal prognostic score < 1 (7/11 with Sokal score <1; 0/12 with Sokal score ≥1). Within the low Sokal index group, a low WBC count pre-mobilization and a low WBC nadir both correlated strongly with Ph-negative mobilization ( P  =0.006 and 0.02 respectively). Five of 19 patients receiving at least 6 months of Roferon A therapy post mobilization achieved a major cytogenetic response; all five patients were Ph-negative mobilizers. Therefore CML patients can be divided into a good-prognosis group in whom predominantly Ph-negative progenitors can be mobilized using a regimen of moderate intensity if haematological control is achieved pre-mobilization, and a poor-prognosis group for whom predominantly Ph-positive cells are mobilized with this regimen regardless of haematological control.     

Inducibility of Atrial Fibrillation Before and After Radiofrequency Catheter Ablation of Accessory Atrioventricular Connections

Inducibility of Atrial Fibrillation. Introduction: The purpose of this study was to evaluate the inducihility of atrial fibrillation in patients with an accessory atriovcentricular connection (AAVC) and to determine if the inducibility of atrial fibrillation is altered after successfulradiofrequency catheter ablation of the AAVC.
Methods and Results: Thirty-seven patients with an AAVC and 36 control patients wereprospectively evaluated using a standardized atrial pacing protocol. The high right atrium waspaced using a 25-beat drive train, 1.5-second intertrain pause, 10-mA pulse amplitude, and 2-msec pulse duration at cycle lengths of 250 to 100 msec, in 10-msec decrements. Pacing wasperformed twice at each cycle length. Thirty patients with an AAVC underwent repeat atrialoverdrive pacing after successful radiofrequency ablation of the AAVC. Atrial fibrillation wasinduced in 26 (70%) patients with an AAVC and 22 (61 %) controls (P = NS). Atrial flutter wasinduced in 26 (70%) patients with an AAVC and 22 (61%) controls (P = NS). The cumulativepercentage of patients with atrial fibrillation/flutter induced at each pacing cycle length was thesame in each group. There was no difference in the duration of atrial fibrillation/flutterbetween control patients and patients with an AAVC. Among the 30 patients who underwentrepeat atrial overdrive pacing after radiofrequency ablation of an AAVC, there was no difference in the inducibility or duration of atrial fibrillation/atrial flutter after ablation compared tobaseline.
Conclusion: These findings indicate that the vulnerability of the atrium to fibrillate inresponse to atrial pacing is independent of the presence of an AAVC.     

Effect of the Atrioventricular Relationship on Atrial Refractoriness in Humans

Atrial arrhythmias occur frequently in the setting of increased atrial size and pressure. This may result from contraction-excitation feedback. The objective of this study was to investigate the effect of alterations in atrial pressure, induced by varying the atrioventricular (AV) interval, on atrial refractoriness, and on the frequency of induction of atrial fibrillation. Twenty-seven patients without structural heart disease participated in the study. In each patient the atrial effective (ERP) and absolute refractory period (ARP) were measured during AV pacing at a cycle length of 400 msec and AV intervals of 0, 120, and 160 msec. The ERP was defined as the longest extrastimulus coupling interval that failed to capture with an extrastimulus current strength of twice the stimulation threshold. The ARP was defined in a similar manner with an extrastimulus current strength of 10 mA. The ERP and ARP were determined during continuous pacing using the incremental extrastimulus technique. A subset of patients had the pacing protocol performed during autonomic blockade. As the AV interval was increased from 0 to 160 msec, the peak right atrial pressure decreased from 16 +/- 4 mmHg to 7 +/- 3 mmHg and the mean right atrial pressure decreased from 7 +/- 3 mmHg to 3 +/- 22 mmHg (P less than 0.001). The atrial ERP and ARP did not change with alterations in the AV interval. There was no difference in the frequency of induction of atrial fibrillation. Similar results were obtained during autonomic blockade. These findings suggests that the phenomenon of contraction-excitation feedback may not be of importance in the development of atrial arrhythmias in patients without structural heart disease.     

Impedance Monitoring During Radiofrequency Catheter Ablation in Humans

Radiofrequency catheter ablation of accessory pathways and the atrioventricular junction often requires multiple applications of energy. The inability to determine the effects of any given application on the underlying tissue may contribute to this problem. In the present study, impedance was monitored in 20 patients undergoing radiofrequency catheter ablation, and the relationship between an initial decrease in impedance and subsequent effects were examined. An initial fall in impedance of more than 10 omega was 78% sensitive and 88% specific for predicting subsequent evidence of tissue heating (interruption of conduction or an abrupt rise in impedance due to coagulum formation). In contrast, initial values of voltage, current, or impedance did not distinguish between effective and ineffective applications of radiofrequency energy. Continuous monitoring of impedance may facilitate radiofrequency catheter ablation.     

Comparison of Fixed Burst Versus Decremental Burst Pacing for Termination of Ventricular Tachycardia

The objective of this study was to compare prospectively the efficacy of fixed burst pacing with that of decremental hurst pacing in terminating VT. Forty-four patients with inducible sustained monomorphic VT were studied. The efficacy of fixed burst and decremental burst pacing in terminating 57 distinct types of VT were compared during 50 eiectrophysiology tests fmean VT cycle length = 334 ± 84 msec. Termination of each type of VT was attempted with fixed burst and decremental burst pacing, Both pacing algorithms were delivered in an adaptive fashion with an increasing number of stimuli with each successive attempt at VT termination. Seventy percent of VT episodes were successfully terminated with fixed burst pacing, The mean number of stimuli required for VT termination was 5 ± 2. Seventy-two percent of VT episodes were successfully terminated with decremental burst pacing. The mean number of stimuJi required for VT termination ivas 5 ± 2. For fixed burst and decremental burst pacing, the efficacy of VT termination was greater for VTs with a cycle length > 300 msec than for faster VTs (P < 0.05). The efficacy of VT termination and the incidence of VT acceleration were no different for the two pacing algorithms (P > 0.1). The results of this study demonstrate that fixed burst and decrementai burst pacing are equally effective in terminating VT and that a single adaptive pacing algorithm is effective in terminating nearly three fourths of VTs.     

Effects of An Acute Increase in Atrial Pressure on Atrial Refractoriness in Humans

Contraction-excitation feedback has been studied extensively in mammalian ventricles. In contrast, little is known about contraction-excitation feedback in mammalian atria. The objective of this study was to investigate the effect of acute alterations in atrial pressure, induced by varying the atrioventricular (AV) interval, on atrial refractoriness. Twenty patients without structural heart disease participated in the study. In each patient the atrial effective (ERP) and absolute refractory periods (ARP) were measured during AV pacing at a cycle length of 500 msec and an AV interval of 120 msec. Acute increases in atrial pressure were induced by pacing the atrium and ventricle simultaneously for the final two beats of the drive train. The ERP was defined as the longest extrastimulus coupling interval that failed to capture with an extrastimulus current strength of twice the stimulation threshold. The ARP was defined in a similar manner with an extrastimulus current strength of 10 mA. The ERP and ARP were determined using the incremental extrastimulus technique. A subset of patients had the pacing protocol performed during autonomic blockade. As the AV interval of the final two beats of the drive train was shortened from 120 msec to 0 msec, the peak right atrial pressure increased from 7 ± 3 mmHg to 15 ± 5 mmHg (P < 0.001). The increase in atrial pressure associated with simultaneous pacing of the atrium and ventricle resulted in shortening of the atrial ERP and ARP by 7.3 ± 5.2 and 6.2 ± 3.5 msec, respectively (P < 0.0011). Similar results were obtained during autonomic blockade. These findings confirm the presence of contraction-excitation feedback in normal human atria.     

Consumption of buprenorphine and other drugs among heroin addicts under ambulatory treatment: results from cross–sectional studies in 1988 and 1990

We assessed the prevalence of consumption of buprenorphine and other drugs among heroin addicts under ambulatory treatment in two cross-sectional studies conducted in 1988 (188 subjects) and in 1990 (197 subjects). Patients were enrolled in one of three different programmes: methadone maintenance programme (MMP), antagonist maintenance programme (AMP) and drug-free programme (DFP). Information given by participants was compared with results of urine screening for drugs. Urine samples were tested using enzyme immunoassay for the detection of heroin, cocaine, dextropropoxyphetie, cannabis and benzodiazopnies, and radioimmunoassay for buprenorphine. Sixty-six percent of patients in 1988 and 71% of patients in 1990 reported having consumed buprenorphine at some time during their history of drug dependence (period prevalence) and 5.9% and 6.1%, respectively, tested positive to the drug (point prevalence). In over 70% of these patients consumption was by the intravenous route. Consumption of cannabis, cocaine and benzodiazepines was also very high in the study population. Overall, patients in the DFP group consumed the largest number of the drugs tested, while those in the AMP group consumed the smallest number. Abuse of buprenorphine could be more widespread than previously reported.