Transvenous ablation with high frequency energy for atrioventricular junctional (AV nodal) reentrant tachycardia

We performed transcatheter AV junction ablation with high frequency energy in four patients with AV nodal reentrant tachycardia where extensive trials of several antiarrhythmic drugs failed to prevent further recurrences of tachycardia. Initially high frequency catheter ablation induced complete AV block in all patients. A recuperation of AV 1:1 conduction followed some time later, persisting in follow-up. No complications have been encountered in either the acute phase or the follow-up (from 6 to 8 months; mean +/- SD: 8.7 +/- 2.5 months). The electrophysiological study was carried out 6 weeks following ablation, and all patients showed AV 1:1 conduction. No dual nodal pathway was encountered and no tachycardia could be triggered. With refinement of the method, the potential application of high frequency energy to interrupt intranodal or perinodal connections responsible for reentrant supraventricular tachycardia or to retard AV nodal conduction appears promising.

[Induction of a double nodal pathway in dogs by transcatheter ablation with high frequency currents]

A dog weighing 15 kg and anesthetized with intravenous sodium thiopental was subjected to transcatheter ablation of the AV junction with high-frequency currents, in order to induce a partial alteration in AV conduction (first degree AV block). Two conventional bipolar electrode-catheters were introduced through the right femoral vein and used one for atrial pacing and the other for His bundle recording and current delivering. The catheter used for ablation was situated in the AV junction where the distal monopolar recording of the His bundle electrogram showed an A/V ratio close to one in the presence of His bundle deflection. Three discharges were delivered under continuous electrocardiographic monitoring. The output power used was 15 watts and current application time was up to five seconds after attaining complete AV block; 1:1 AV conduction was quickly restored on concluding discharge. After the second discharge, a discontinuous nodal function curve of the dual AV nodal pathway type was obtained (absent in control and after first discharge studies). Following the third discharge the conduction through the slow pathway was abolished. The study was repeated after four weeks, an a dual AV nodal pathway type curve similar to that found during the acute phase was obtained. The histologic findings showed a collagen scar partially replacing nodal tissue and creating a partial septation of the AV node. To conclude: The structural alterations of the AV node may induce a dual AV nodal pathway response.

[Experimental study of the effects of ATP on sinus automatism and atrioventricular node conduction]

A study was made of 14 thoracotomized dogs under i.v. sodium thiopental anesthesia; the effects of 1.5 mg/kg intravenous ATP on sinus node automatism and atrio-ventricular conduction were investigated. In 7 dogs (group A) ATP was administered under control conditions and following successive intravenous administrations of atropine (1 mg/kg), aminophylline (5 mg/kg) and propranolol (0.6 mg/kg). The remaining 7 dogs (group B) received ATP following atropine (1 mg/kg), isoproterenol (0.4 microgram/kg/min.), and aminophylline (5 mg/kg). An analysis was made of the percentage variations in cardiac cycle length during spontaneous rhythm and of the AH interval during atrial pacing at a fixed rate. In group A the negative dromotropic and chronotropic effects of ATP under control conditions decreased in 5 cases following atropine, although the average decrease was not statistically significant. On adding aminophylline, a statistically significant decrease was observed in the effects of ATP, and following propranolol the drop in negative chronotropic effect of ATP provoked by aminophylline was maintained. In group B, and following prior atropinization, the negative chronotropic and dromotropic effects of ATP were maintained in the presence of isoproterenol. As in group A, aminophylline significantly reduced the effects of ATP. To conclude: in the thoracotomized dog under sodium thiopental anesthesia, 1) atropine does not prevent the negative chronotropic and dromotropic actions of ATP, although the effect of the latter is decreased in a large percentage of cases; 2) sympathetic beta stimulation following prior atropinization does not prevent ATP action; 3) aminophylline in the atropinized dog noticeably reduces the effects of ATP, and 4) this action of aminophylline is effective in the presence of sympathetic beta stimulation.

Induction of complete AV block in dogs by transcatheter ablation using high-frequency current: an alternative to direct-current high energy shock

The utility of high-frequency current applied through the distal electrode of a conventional electrode-catheter for altering atrio-ventricular conduction was studied in 18 anaesthetized dogs. Following adequate unipolar His bundle recording, current was applied over periods of 20-30 s, with an output power of 30 W. Complete AV block was achieved in all dogs (four dogs on the third attempt, five on the second, and nine on the first). Ten of the dogs were killed after four hours of continuous ECG monitoring (Group I); examination revealed circumscribed spheroidal myocardial lesions at the base of the right atrium over the posterior tricuspid valve; no thrombus formation was encountered. The remaining eight dogs (Group II) were kept alive for three months during which complete block persisted in all cases. The histologic study showed partial replacement of AV nodal and His bundle tissues and myocardium by fibrous tissue. In conclusion, electro-catheter ablation using high-frequency energy is effective for producing complete AV block. The resulting lesions are circumscribed. This method may prove to be an alternative to the transcatheter DC shock for ablation of the AV conduction system.

[Prediction of the tachycardia cycle based on auriculoventricular re-entry. Experimental study in dogs]

Seven anaesthesized mongrel dogs subject to thoracotomy were used in a electronic simile of A-V accessory pathway with retrograde conduction to generate reentrant tachycardias with different ventriculo-atrial delays. This was done both under control conditions and following amiodarone i.v. administration. The ability to predict tachycardia cycle length was studied, using a mathematical model of the circuit, in which the cycle length is obtained from the function of nodal conduction and the time of extranodal conduction of the circuit. An analysis was made of the repercussions in using four different mathematical functions describing nodal conduction: three were non-linear (exponential and hyperbolic A and B) and one linear. In the case of the first three, the consequences of using a direct non-linear data-fitting procedure or an indirect procedure by linear transformations of the functions were studied. The exponential and hyperbolic B functions provide a better prediction of tachycardia cycle length on being used in the model; in the case of these functions, a mean value of the squared differences between the real and estimated values of 19.1 +/- 31.0 ms2 and 19.1 +/- 26.7 ms2, respectively, was obtained.

Inspiratory effort and occlusion pressure in triggered mechanical ventilation

We have studied eleven patients ventilated in the assisted mode during recovery from acute respiratory failure. We have measured the effort required to trigger the pressure demand valve for 3 different ventilators, and have measured the occlusion pressure as an index of neuromuscular inspiratory drive. We found a delay in the opening of the demand valve, as previously described by other authors. We also found a close correlation between the effort required to open the demand valve and the occlusion pressure. We conclude that the inspiratory effort required to open the demand valve, in the assist mode, is greater than the preset trigger level and that it is well correlated with the neuromuscular inspiratory drive. This inspiratory effort against the closed demand valve, allows the measurement of the occlusion pressure.

Observations on variability of atrioventricular nodal conduction in man and the dual-pathway response

A study was made of nodal conduction times of atrial stimuli with fixed coupling intervals, in 23 patients divided into two groups according to their atrial stimulus test response: Group I (continuous AV node function curve; 17 cases) and Group II (dual AV node pathway; six cases). The stimulation protocol involved the delivery of 75 stimuli with a fixed coupling interval 20 ms greater than the effective refractory period (ERP) of the AV node (Group I) or fast pathway (Group II). The atrial coupling intervals (A1A2) and node conduction times (A2H2) were measured. An evaluation was made of the dispersion of intervals with range (R) and of the distribution of A2H2 times (X2 test). In both Groups, R (A2H2) was greater than R(A1A2) (P less than 0.05); R(A2H2) in Group II was greater than R(A2H2) in Group I (P less than 0.001). In Group I the distribution of A2H2 was non-normal in four cases and bimodal in five; in Group II the distribution was non-normal and bimodal in all cases. It is concluded that: (1) the AV node generates a dispersion in its conduction times in the vicinity of its ERP, although the nodal conduction curve is continuous; and (2) the so-called dual pathway may constitute an exaggeration of AV node response inhomogeneity.

Induction of partial alterations in atrioventricular conduction in dogs by percutaneous emission of high-frequency currents

Ten anesthetized dogs were studied in an attempt to provoke partial alterations in atrioventricular (AV) conduction by high-frequency current (HFC) transcatheter ablation. A discharge power (10 to 15 W) was used for less than 5 seconds after reaching complete AV block (CAVB). The catheter was placed within an area having an A/V ratio = 1 with His bundle deflection. If following discharge, no appreciable lengthening an AH, AV nodal block cycle length (Wenckebach point, WP), and/or functional nodal refractory period (FRPAVN) was observed, the procedure was repeated. Four dogs (group I) were killed immediately, and the other six (group II) after 2 to 4 weeks. The AH interval, WP, and FRPAVN were found to prolong significantly following HFC, without variations in HV interval. In group II, two dogs progressed to CAVB, whereas the other four maintained 1:1 AV conduction with AH, WP, and FRPAVN greater than before the power discharge. In conclusion, HFC is an efficient technique to induce partial alterations in AV conduction, since the discharge can be adjusted and the ablation can be localized to specific regions.

Effect of body posture on respiratory impedance

The effects of posture on the mechanics of the respiratory system are not well known, particularly in terms of total respiratory resistance. We have measured respiratory impedance (Zrs) by the forced random noise excitation technique in the sitting and the supine position in 24 healthy subjects. Spirometry and lung volumes (He-dilution technique) were also measured in both postures. The equivalent resistance (Rrs), compliance (Crs), and inertance (Irs) were also calculated by fitting each measured Zrs to a linear series model. When subjects changed from sitting to the supine position, the real part of Zrs increased over the whole frequency band. The associated equivalent resistance, Rrs, increased by 28.2%. The reactance decreased for frequencies lower than 18 Hz and increased for higher frequencies. Consequently, Crs decreased by 38.7% and Irs increased by 15.6%. All of these parameter differences were significant (P less than 0.001). A covariance analysis showed that a significant amount of the postural change in Rrs and Crs can be explained by the reduction of functional residual capacity (FRC). This indicates that the observed differences on Zrs can in part be explained be a shift of the operating point of the respiratory system induced by the decrease in the FRC.

Diffusing lung capacity and cyclosporine in patients with heart transplants

Pulmonary function studies were performed in 10 patients undergoing surgery for heart transplantation. The study was repeated 6 to 12 months after surgery. The comparison between data before and after transplantation showed an overall improvement in lung function indices, except for the lung diffusing capacity (DLCO). A mean 14% reduction (p less than 0.01) of DLCO was observed. In the absence of evidence of other lung disease or rejection reaction in these patients, this finding may be related to a side effect of cyclosporine on the lung and deserves further investigation.

Spirometric reference values from a Mediterranean population

Maximal expiratory flow-volume (MEFV) curves were measured in 1044 healthy nonsmoking volunteers living in the Barcelona area, as part of a larger interhospital project to obtain reference values of pulmonary function tests. Forced vital capacity (FVC), one-second forced expiratory volume (FEV1), FEV1/FVC, %, forced maximal mid-expiratory flow (FEF25-75%), peak expiratory flow rate (PEF) and maximal expiratory flow at 50 and 75% of FVC (MEF50% and MEF25% respectively) were obtained and expressed at BTPS conditions. Techniques and equipments followed both the recommendations of the American Thoracic Society (ATS) and of the European Community for Coal and Steel (ECCS). Prediction equations for age 20 through 70 were calculated for both sexes from a final sample composed of 870 adult subjects, 443 males and 427 females. Simple linear equations using height, age and body weight predicted all spirometric variables as well as more complex equations except MEF25%. Logarithmic equations were proposed for MEF25% to correct for the heteroscedasticity shown in a simple linear model. To our knowledge, this study provides reliable spirometric equations from a large urban Mediterranean sample which were lacking so far in the literature.

Performance of a low flow O2 Venturi mask: diluting effects of the breathing pattern

To examine the performance of a new Venturi Mask (VM), PaO2 and PaCO2 were measured in 10 healthy volunteers before and while, breathing from a 0.24 O2 VM at 21/min of O2 flow for 20 min. FEO2, FECO2, VT, f, inspiratory (TI) and expiratory time (TE) and flow were also recorded during air breathing. Mean PaO2 increment observed during VM breathing was 1.8 kPa (SD 0.7). The FO2 measured at the face-piece of the VM while not in use was 0.247. The predicted increment of PaO2 corresponding to a FIO2 of 0.24 was calculated by the alveolar air equation and found to be 2.9 kPa (SD 0.2), indicating a diluting effect on the O2 concentration close to 40%, with an actual FIO2 of 0.228. The correlation coefficient (r) between dilution and a formula which includes initial acceleration of inspiration (VI 0.25), VT and the ratio TI/TT, was 0.94. Because the low O2 flow 0.24 VM model is markedly influenced by the patient's breathing, we conclude that it does not satisfactorily provide a stable and predictable concentration of supplementary oxygen. Theoretical considerations allow these results to be extended to other VM using low O2 flows for different O2 concentrations.

Spirometric response to a bronchodilator. Reference values for healthy children and adolescents

The spirometric response to inhaled salbutamol was assessed in 492 healthy volunteers 6 to 20 yr of age. Mean and standard deviation of the changes, expressed as percentage of prebronchodilator values, were as follows: forced vital capacity (FVC): 1.7 +/- 2.8; forced expiratory volume in one second (FEV1): 3.3 +/- 3.4; (FEV1/FVC): 3.1 +/- 3.2; peak expiratory flow: 6.4 +/- 8.6; maximal mid-expiratory flow: 10.1 +/- 8.8; maximum expiratory flow at 50% of FVC: 8.8 +/- 9.5 and maximum expiratory flow at 25% of FVC: 14.0 +/- 14.7. The changes were significant (p less than 0.005) for all parameters and similar to those observed in adults.

Evaluation of a new piston-type spirometer

A new dry spirometer (DS) incorporating a microcomputer for automatic calculation and direct read-out of spirometric parameters was compared to a calibrated Fleisch pneumotachograph (PT). Twenty-eight volunteers, including healthy subjects, obstructive and non-obstructive patients, performed a total of 48 spirometric tests with the two apparatuses randomly alternated. DS values for FVC were lower than those of the PT with a mean difference of 0.177 1 +/- 0.171 SD (p less than 0.0001). Mean FEV1 values were very similar in both apparatuses with a non significant difference of 0.003 1 +/- 0.182 FEF25-75 values were higher with the DS, showing a mean difference with the PT of 0.407 1 . s-1 +/- 0.324 (p less than 0.00001). The DS also gave slightly higher PEFR values than the PT, with a mean difference of 0.310 1 . s-1 +/- 0.830 (p less than 0.02). Differences in FVC readings between DS and PT were greater in severely obstructed patients (0.350 1 +/- 0.084, p less than 0.0001) than among healthy subjects (0.120 1 +/- 0.051, p less than 0.0002). On the contrary, in absolute figures DS values for FEF25-75 showed a greater difference with those of the PT in normals (0.547 1 . s-1 +/- 0.320, p less than 0.001) than in obstructed patients (0.288 1 . s-1 +/- 0.244, p less than 0.05). DS flow resistance was 2.67 cmH2). s. 1-1 for a flow of 8.8 1. s-1. Based on the spirometric differences observed, and on the high flow resistance and volume limitation imposed by its 6 1 capacity, we concluded that the apparatus tested cannot be recommended for clinical spirometry.

Distension of the operation site after posterior fossa surgery

In 130 posterior fossa operations 6 cases of progressive distension of the operation site have been recorded and documented. The possible causes of this complication and the surgical management are discussed. Isotope studies after injection of Ytterbium 169DTPA into the underlying cyst have shown abnormal patterns in CSF circulation and absorption. All the cases have resolved after ventriculo-peritoneal shunts.