Search PubMed⌕ Search

Biomedical subjects

G N Kay

Publications and source records attributed to G N Kay.

At least 55 records · Page 3Linked to original sources
PubMed1997

Defibrillation efficacy with endocardial electrodes is influenced by reductions in cardiac preload.

Little is known about the effects of cardiac preload and cardiac geometry on defibrillation efficacy with endocardial electrodes. We studied nine pigs implanted with an endocardial lead system in the normal and reduced preload state. In the reduced preload state, a balloon catheter was inflated in the inferior vena cava (IVC) for 20 seconds prior to the induction of ventricular fibrillation (VF). Complete occlusion of the IVC and reductions in preload were confirmed by observing deformation of the contrast-filled balloon, a reduction in cardiac size by fluoroscopy, and reductions in ventricular pressures. Biphasic shocks were delivered after 10 seconds of VF using a recursive up-down protocol. VF was induced 20 times for each preload state, and the 50% effective doses (ED50) for energy, current, and voltage were estimated by averaging all shocks for that state. At reduced preloads, energy decreased from 12.1 +/- 3.0 J (+/- SD) to 10.5 +/- 2.9 J (p < 0.01), voltage decreased from 415 +/- 51 V to 390 +/- 51 V (p < 0.05), and current decreased from 8.6 +/- 1.5 A to 7.6 +/- 1.5 A (p < 0.01), while impedance rose from 49.2 +/- 3.8 omega to 52.8 +/- 4.4 omega (p < 0.001). We conclude that reducing cardiac preload and cardiac size significantly lowers ED50 defibrillation energy, current, and voltage. This outcome may be caused directly by the decrease in blood volume as evidenced by increased impedance and/or may be due to changes in heart geometry and stretch.

Animals↗
PubMed1997

The effects of ventricular fibrillation duration and a preceding unsuccessful shock on the probability of defibrillation success using biphasic waveforms in pigs.

INTRODUCTION: While the defibrillation threshold has been reported to increase with ventricular fibrillation (VF) duration for monophasic waveforms, the effect of VF duration for biphasic waveforms is unknown. METHODS AND RESULTS: The ED 50 requirements (the 50% probability of defibrillation success) for an endocardial lead system, which included a subcutaneous array, were determined by logistic regression using a recursive up-down algorithm for a biphasic waveform (6/6 msec). The study was performed in two parts, each with eight pigs. In part 1, ED 50 was compared for shocks delivered after 10 seconds of VF and for shocks delivered after 20 seconds of VF following a failed first shock at 10 seconds. Energy at ED 50 decreased from 6.5 +/- 0.9 J for shocks delivered after 10 seconds of VF to 4.9 +/- 0.8 J (P < 0.01) for shocks delivered after 20 seconds. To determine if improved second shock efficacy was a result of preconditioning by the failed first shock or a function of VF duration, part 2 of the study compared defibrillation efficacy between shocks delivered after 10 seconds of VF with shocks delivered after 20 seconds of VF with and without a failed first shock at 10 seconds. Mean energy at ED 50 decreased from 10.1 +/- 2.4 J for shocks delivered after 10 seconds of VF to 7.9 +/- 2.4 J (P < 0.01) and 7.5 +/- 3.2 J (P < 0.01) for shocks delivered after 20 seconds of VF with and without a failed first shock, respectively. The mean energy at ED 50 for shocks delivered after 20 seconds of VF with and without a failed first shock was not significantly different (P = 0.53). A strong linear correlation for energy at ED 50 was found between shocks delivered after 10 seconds of VF and shocks delivered after 20 seconds of VF following a failed first shock (r = 0.95, P < 0.01). CONCLUSION: (1) As opposed to monophasic shocks, ED 50 is significantly lower for biphasic shocks delivered after 20 seconds of VF compared with shocks delivered after 10 seconds of VF in pigs. (2) An unsuccessful biphasic shock in pigs does not affect the defibrillation efficacy for a subsequent shock. (3) ED 50 for a biphasic shock delivered after 20 seconds of VF is linearly related to ED 50 for a shock delivered after 10 seconds of VF.

Animals↗
PubMed1997

Determination of 3D positions of pacemaker leads from biplane angiographic sequences.

In vitro and in vivo analyses of stress on pacemaker leads and their components during the heart cycle have become especially important because of incidences of failure of some of these mechanical components. For stress analyses, the three-dimensional (3D) position, shape, and motion of the pacemaker leads must be known accurately at each time point during the cardiac cycle. We have developed a method for determination of the in vivo 3D positions of pacemaker leads during the entire heart cycle. Sequences of biplane images of patients with pacemakers were obtained at 30 frames/s for each projection. The sequences usually included at least two heart cycles. After patient imaging, biplane images of a calibration object were obtained from which the biplane imaging geometry was determined. The centerlines of the leads and unique, identifiable points on the attached electrodes were indicated manually for all acquired images. Temporal interpolation of the lead and electrode data was performed so that the temporal nonsynchronicity of the image acquisition was overcome. Epipolar lines, generated from the calculated geometry, were employed to identify corresponding points along the leads in the pairs of biplane images for each time point. The 3D positions of the lead and electrodes were calculated from the known geometry and from the identified corresponding points in the images. Using multiple image sets obtained with the calibration object at various orientations, the precision of the calculated rotation matrix and of the translation vector defining the imaging geometry was found to be approximately 0.7 degree and 1%, respectively. The 3D positions were reproducible to within 2 mm, with the error lying primarily along the axis between the focal spot and the imaging plane. Using data obtained by temporally downsampling to 15 frames/s, the interpolated data were found to lie within approximately 2 mm of the true position for most of the heart cycle. These results indicate that, with this technique, one can reliably determine pacemaker lead positions throughout the heart cycle, and thereby it will provide the basis for stress analysis on pacemaker leads.

Calibration↗
PubMed1996

Effect of radiofrequency catheter ablation on health-related quality of life and activities of daily living in patients with recurrent arrhythmias.

BACKGROUND: Although radiofrequency catheter ablation can be used to effectively treat a variety of arrhythmias, the effects of this procedure on health-related quality of life have not been systematically studied. METHODS AND RESULTS: The SF-36 (a measure of general health status), the Symptom Checklist-Frequency and Severity Scale (an instrument specific for cardiac arrhythmias), and an Activities of Daily Living questionnaire were used to assess quality of life in 161 patients before radiofrequency catheter ablation. These same instruments were used to measure quality of life 1 and 6 months after ablation with complete data in 159 of the original 161 patients. Before ablation, SF-36 scores of the study population were low compared with the US normative data base reflecting significant impairment in physical functioning and well-being. The lowest scores were reported by patients with atrial fibrillation and atrial flutter. Catheter ablation was associated with significant improvement in quality of life that was sustained over the 6 months after ablation. Improvements were measured in both the generic SF-36 health status questionnaire and the disease-specific Symptom Checklist-Frequency and Severity Scale. Catheter ablation was followed by improved performance of activities of daily living and a marked decrease in the number of visits to physicians and emergency rooms in the 6 months after ablation compared with the 6 months before ablation. CONCLUSIONS: Radiofrequency catheter ablation improves the health-related quality of life for patients with a variety of cardiac arrhythmias.

Activities of Daily Living↗
PubMed1996

The present role of radiofrequency catheter ablation in the management of cardiac arrhythmias.

Radiofrequency catheter ablation can be used to treat a variety of cardiac arrhythmias. Yet while the spectrum of arrhythmias amenable to catheter ablation continues to expand, the protocol for whether or not catheter ablation should be recommended for the management of an individual patient has not been firmly established. This article summarizes the experience of one medical center with radiofrequency catheter ablation. The varieties of arrhythmias that may be effectively treated with catheter ablation, the probability of success, and the attendant risks of these procedures in the series are presented. In addition, the future applications of catheter ablation to cardiac arrhythmias are discussed.

Atrial Flutter↗
PubMed1996

Posterior left thoracic cardiac sympathectomy by surgical division of the sympathetic chain: an alternative approach to treatment of the long QT syndrome.

Although high thoracic left sympathectomy via an anterior surgical approach is a highly efficacious treatment for refractory ventricular arrhythmias in patients with the long QT syndrome, the degree of sympathetic denervation has been variable, success of the operation is influenced by anatomical differences between patients, and Horner's syndrome may result. We hypothesized that interruption of sympathetic input to the heart could be accomplished using a posterior thoracic approach to this variable and often complex anatomy by division of the sympathetic chain rather than by direct destruction of the stellate and superior thoracic ganglia with the more conventional anterior, supraclavicular approach. In addition, the posterior approach should decrease the risk of Horner's syndrome by avoiding the ocular sympathetic efferent nerves. This posterior approach is described in five patients with the long QT syndrome and recurrent ventricular arrhythmias. After a mean follow-up of 18 +/- 12 months, all are alive without Horner's syndrome.

Adult↗
PubMed1996

PR/RR interval ratio during rapid atrial pacing: a simple method for confirming the presence of slow AV nodal pathway conduction.

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

Adult↗
PubMed1995

The risk of atrial fibrillation following radiofrequency catheter ablation of atrial flutter.

BACKGROUND: Although radiofrequency catheter ablation of atrial flutter is associated with a high rate of initial success, several clinical issues regarding this therapy remain to be defined. For example, the risks of recurrent atrial flutter and of developing atrial fibrillation after flutter ablation are unknown. In addition, it is not known whether elimination of atrial flutter will modify the natural history of atrial fibrillation in patients who experience both of these arrhythmias. The purpose of the present study was to determine the actuarial freedom from recurrent or new atrial arrhythmias in patients with atrial flutter undergoing catheter ablation. METHODS AND RESULTS: The study population consisted of 59 consecutive patients (mean age, 61.9 +/- 12.6 years) with typical atrial flutter who underwent catheter ablation of the reentrant circuit. Catheter ablation was not advised for patients in whom paroxysmal atrial fibrillation had been a major clinical problem. The inducibility of atrial fibrillation and atrial flutter was assessed after successful atrial flutter ablation with programmed atrial stimulation and rapid atrial pacing to a cycle length of 180 ms or 2:1 atrial capture. Atrial flutter was successfully ablated and rendered noninducible in 53 of 59 patients (90%). Over a mean follow-up period of 13.2 +/- 6.6 months, atrial flutter recurred in 5 patients (9.4%). Atrial fibrillation occurred in 14 of 53 patients after successful ablation (26.4%). Four clinical variables were associated by univariate analysis with the late occurrence of atrial fibrillation: (1) the presence of structural heart disease, (2) a history of atrial fibrillation before ablation of atrial flutter, (3) inducible sustained atrial fibrillation after ablation, and (4) a greater number of failed antiarrhythmic drugs. By multivariate analysis, only the persistent inducibility of sustained atrial fibrillation predicted the later development of atrial fibrillation. CONCLUSIONS: Although atrial flutter ablation is highly effective and associated with a low risk of recurrent atrial flutter, atrial fibrillation continues to be a long-term risk for individuals undergoing this procedure. The risk of later atrial fibrillation is especially high for patients in whom sustained atrial fibrillation remains inducible after ablation of atrial flutter.

Aged↗
PubMed1995

Relationship between heart rate and oxygen kinetics during constant workload exercise.

BACKGROUND: Oxygen uptake during constant workload exercise increases exponentially from its resting value before reaching a steady state. The difference between the actual rate of oxygen consumption at the onset of exercise and the steady state is an oxygen deficit. Similarly, the normal sinus node increases its rate at the onset of exercise before achieving a steady state, thereby producing a heart rate deficit. The purpose of this study was to test the hypothesis that elimination of the heart rate deficit by an instantaneous increase in heart rate at the onset of constant workload exercise to the steady-state level would reduce the oxygen deficit and improve the perceived difficulty of exertion as compared with the chronotropic response of the normal sinus node. METHODS AND RESULTS: Ten subjects with normal sinus node function who had DDD pacemakers implanted for AV block completed a symptom-limited maximal treadmill exercise test using the Chronotropic Assessment Exercise Protocol (CAEP) to assess sinus node function, maximal heart rate, and VO2max. The subjects then performed constant workload exercise tests (6-min duration) at a workload equal to approximately 50% of metabolic reserve with the pacemaker randomly programmed to each of three patterns of chronotropic response: (1) DDD (lower rate 60 beats/min); (2) Fast (lower rate abruptly programmed to the expected value at 50% metabolic reserve); and (3) Overpaced (lower rate at least 80% of the age predicted maximum). The oxygen deficit was lower with the fast chronotropic response (434 +/- 238 mL O2) than with either the DDD (512 +/- 233; P = 0.02), or overpaced chronotropic patterns (488 +/- 238; P = 0.02 vs fast). The rate constant for change in VO2 was highest with the fast chronotropic pattern (2.85 +/- 1.38) compared with either the DDD (2.25 +/- 0.64; P = 0.01) or overpaced (2.38 +/- 0.43; P = 0.02) patterns. The Borg perceived exertion rating was lowest with the fast chronotropic response (P = 0.02 vs DDD and P = 0.02 vs overpaced). CONCLUSIONS: The results of this study suggest that oxygen kinetics and exertional symptoms are improved by an abrupt increase in pacing rate at the onset of exercise to a value that is appropriate for metabolic demand as compared with the DDD pacing mode in patients with normal sinus node function. In contrast, an overly aggressive chronotropic response was not associated with improved oxygen kinetics or exertional symptoms.

Adult↗
PubMed1995

Elevated defibrillation threshold when right-sided venous access is used for nonthoracotomy implantable defibrillator lead implantation. The Endotak Investigators.

INTRODUCTION: Although myriad factors influence the defibrillation threshold, the relation between the site of transvenous lead entry into the vascular system and the defibrillation threshold has not been reported. This study examines the influence that venous entry site has on defibrillation success for a transvenous implantable cardioverter defibrillator lead with two defibrillating coils. METHODS AND RESULTS: The study population comprised 345 patients. Their mean age was 61 +/- 13 years and, left ventricular ejection fraction was 0.33 +/- 0.13. A left-sided approach was used in 324 (93.9%) of the patients, and a right-sided approach was used in the remaining 21 (6.1%) patients. There was no difference in the gender, age, left ventricular ejection fraction, or underlying cardiac disease in the two groups. For all patients, with a transvenous lead used either alone or with a submuscular or subcutaneous patch, the biphasic defibrillation threshold was 9.9 +/- 4.8 J when a left-sided approach was used, and 14.0 +/- 7.3 J when a right-sided approach was used (P = 0.02). When a transvenous lead was used with a submuscular or subcutaneous patch (115 patients), the biphasic defibrillation threshold was 9.5 +/- 4.3 J when a left-sided approach was used, and 12.0 +/- 10.0 J when a right-sided approach was used (P = 0.98). When a transvenous lead was used without a submuscular or subcutaneous patch (230 patients), the biphasic defibrillation threshold was 10.1 +/- 5.0 J when a left-sided approach was used, and 14.6 +/- 6.6 J when a right-sided approach was used (P < 0.01). For the entire group of patients and for each specific lead arrangement, there was no significant difference in the defibrillating lead system impedance when right-sided versus left-sided approaches were compared. CONCLUSION: Left-sided approaches to implant transvenous leads with two coils for defibrillation result in lower biphasic defibrillation thresholds than when right-sided approaches are used.

Defibrillators, Implantable↗
PubMed1994

Predictors of recurrent atrioventricular nodal reentry after selective slow pathway ablation.

Although radiofrequency catheter ablation of the slow atrioventricular (AV) nodal pathway is highly effective for the management of AV nodal reentrant tachycardia (AVNRT), this arrhythmia may recur in some patients after an ablation procedure that initially renders AVNRT noninducible. A retrospective study examined the factors that are associated with the recurrence of AVNRT after selective radiofrequency catheter ablation of the slow pathway. Patients were included in the study if they had initially inducible, typical slow-fast AVNRT that was noninducible at the end of the ablation session. Selective ablation of the slow pathway was performed using radiofrequency energy applied along the tricuspid annulus near the coronary sinus ostium. AVNRT recurred after initially successful slow pathway ablation in 10 of 136 patients (7.4%) over a mean follow-up period of 20.1 +/- 5.0 months; the time to recurrence ranged from 1 to 411 days. Despite the absence of inducible AVNRT, dual anterograde AV nodal conduction properties persisted after slow pathway ablation in 10 patients. AVNRT recurred in 4 of 10 patients who had evidence of residual slow pathway conduction compared with only 6 of 126 who had no residual slow pathway conduction (p = 0.003). All patients with persistent slow pathway conduction and recurrent AVNRT also had residual AV nodal echo beats. AVNRT recurred in 3 of 6 patients without accelerated junctional tachycardia during radiofrequency application compared with only 7 of 109 with accelerated junctional tachycardia (p = 0.003). Thus, AVNRT infrequently recurs after successful selective radiofrequency ablation of the slow pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrioventricular Node↗
PubMed1994

Effect of chronotropic response pattern on oxygen kinetics.

BACKGROUND: The sinus node is considered to be the model of chronotropic response for pacemakers that use artificial rate modulating sensors. Maximal metabolic exercise testing with measurement of oxygen consumption (VO2) is frequently used to evaluate chronotropic response. Since activities of daily living are generally transient and involve submaximal effort, maximal exercise testing may not provide the most clinically relevant method of assessing rate modulation. The purpose of this study was to determine if an abrupt increase in heart rate (HR) at the onset of submaximal exercise provides improved oxygen kinetics compared with a linear response. METHODS AND RESULTS: Thirteen patients with complete heart block and permanent rate modulating pacemakers implanted following catheter ablation of the atrioventricular junction for refractory atrial fibrillation were chosen for study. The patients first completed a maximal treadmill exercise test using the chronotropic assessment exercise protocol with breath-by-breath analysis of expired gases. The expected HR at 50% of metabolic reserve was calculated for each patient. Three submaximal constant workload exercise tests were then performed at 50% of each patient's metabolic reserve, with the pacemaker randomly programmed to provide three different patterns of chronotropic response: linear (in which HR increased from 70 beats/min to the expected HR at 50% of metabolic reserve), fast (in which HR was abruptly increased to the expected HR at 50% of metabolic reserve), and slow (VVI at 70 beats/min). Oxygen kinetics were compared for the three patterns of chronotropic response. Cumulative oxygen (O2) consumption was significantly greater for the fast pattern (3610 mL) as compared with the linear (3487 mL, P = 0.004) or slow pattern (3277 mL). The O2 deficit was lower for the fast (361 +/- 139 mL) than for the linear (539 +/- 225 mL, P = 0.003) or slow chronotropic pattern (559 +/- 194). Similar improvements in the rate constant of O2 uptake and Borg perceived exertion scores were observed with the fast chronotropic response pattern. CONCLUSION: A rapid increase in pacing rate at the onset of exercise improves oxygen kinetics and results in less perceived exertion as compared to a more gradual rate increase that is more characteristic of sinus node behavior.

Adult↗
PubMed1994

Rate modulated pacing based on right ventricular dP/dt: quantitative analysis of chronotropic response.

Right ventricular contractility increases in response to catecholamine stimulation and greater ventricular preload, factors that increase with exercise workload. Thus, the maximum systolic dP/dt may be a potentially useful sensor to control the pacing rate of a permanent pacing system. The present study was designed to test the long-term performance of a permanent pacemaker that modulates pacing rate based on right ventricular dP/dt and to quantitatively analyze the chronotropic response characteristics of this sensor in a group of patients with widely varying structural heart diseases and degrees of hemodynamic impairment. A permanent pacing system incorporating a high fidelity pressure sensor in the lead for measurement of right ventricular dP/dt was implanted in 13 patients with atrial arrhythmias and AV block, including individuals with coronary artery disease, hypertension, severe obstructive pulmonary disease with prior pneumonectomy, atrial septal defect, dilated cardiomyopathy, restrictive cardiomyopathy, and mitral stenosis. Patients underwent paired treadmill exercise testing in the VVI and VVIR pacing modes with measurement of expired gas exchange and quantitative analysis of chronotropic response using the concept of metabolic reserve. The peak right ventricular dP/dt ranged from 238-891 mmHg/sec with a pulse pressure that ranged from 19-41 mmHg. There was a positive correlation between the right ventricular dP/dt and pulse pressure (r = 0.70, P = 0.012). The maximum pacing rate and VO2max were 72 +/- 6 beats/min and 12.61 +/- 4.0 cc O2/kg per minute during VVI pacing and increased to 124 +/- 18 beats/min and 15.89 +/- 5.9 cc O2/kg per minute in the VVIR pacing mode (P < 0.0003 and P < 0.002, respectively). The integrated area under the normalized rate response curve was 96.7 +/- 45.7% of expected during exercise and 100.1 +/- 43.4% of expected during recovery. One patient demonstrated an anomalous increase in pacing rate in response to a change in posture to the left lateral decubitus position. Thus, the peak positive right ventricular dP/dt is an effective rate control parameter for permanent pacing systems. The chronotropic response was proportional to metabolic workload during treadmill exercise in this study population with widely varying forms of structural heart disease.

Adult↗
PubMed1994

Treatment of patients with prior exit block using a novel steroid-eluting active fixation lead. Model 4068 Investigators.

An increased interest has developed in active fixation leads for several reasons. Exit block is an uncommon complication that is seen with both active and passive fixation leads. Exit block has not been a significant problem with passive fixation steroid-eluting leads and has been treated with these leads. A new steroid-eluting active fixation lead was examined for its performance in patients in whom exit block had previously occurred. The lead function was evaluated prospectively in 24 patients with a history of exit block (15 ventricular and 9 atrial). The results in patients with atrial exit block are encouraging with an average chronic stimulation threshold of 0.19 msecs at 2.5 volts. Results in the ventricle are less encouraging with 3 occurrences of recurrent exit block in 15 patients; however, the remaining patients had a good mean threshold of 0.21 +/- 0.11 msecs at 2.5 volts. There were a remarkable number of non-lead related complications suggesting that this is a substantially different group than routine implantations.

Cardiac Pacing, Artificial↗
PubMed1994

Differential effect of esmolol on the fast and slow AV nodal pathways in patients with AV nodal reentrant tachycardia.

INTRODUCTION: AV nodal reentrant tachycardia (AVNRT) usually involves anterograde conduction over a slowly conducting ("slow") pathway and retrograde conduction over a rapidly conducting ("fast") pathway. A variety of drugs, such as beta blockers, digitalis, and calcium channel blockers, have been reported to prolong AV nodal refractoriness in both the anterograde and retrograde limbs of the circuit. However, few data are available that address whether the fast and slow pathways respond in a quantitatively different manner to drugs such as beta-adrenergic antagonists. In addition, it is not known whether the effects of these agents on refractoriness parallel the effects on conduction in the fast and slow pathways. The present study was performed to measure the effect of the intravenous beta-adrenergic agent, esmolol, on refractoriness and conduction in both the fast and slow AV nodal pathways in patients with AVNRT. METHODS AND RESULTS: Thirteen patients with discontinuous AV nodal conduction properties and typical AVNRT were studied. Anterograde and retrograde AV nodal functional assessment was performed at baseline and following steady-state drug infusion of intravenous esmolol at a dose of 500 micrograms/kg for 1 minute, 150 micrograms/kg per minute for the next 4 minutes, followed by a continuous maintenance infusion of 50 to 100 micrograms/kg per minute. The anterograde effective refractory period of the fast pathway increased from 381 +/- 75 msec at baseline to 453 +/- 92 msec during the infusion of esmolol (P = 0.003). The anterograde effective refractory period of the slow pathway was also prolonged by esmolol, from 289 +/- 26 msec to 310 +/- 17 msec (P = 0.005). However, the absolute magnitude of the change in the anterograde effective refractory period of the fast pathway (+72 +/- 59 msec) was significantly greater than the change in anterograde effective refractory period of the slow pathway (+21 +/- 16 msec, P = 0.01). The mean retrograde effective refractory period of the fast pathway increased from 276 +/- 46 msec to 376 +/- 61 msec during esmolol infusion (P = 0.03). Retrograde slow pathway conduction that could not be demonstrated at baseline became manifest in three patients during esmolol infusion. In contrast to the effects of esmolol on refractoriness, the AH interval during anterograde slow pathway conduction prolonged to a far greater extent (+84 msec) than the HA interval associated with retrograde fast pathway conduction (+5 msec, P = 0.04). CONCLUSION: The beta-adrenergic antagonist, esmolol, has a quantitatively greater effect on anterograde refractoriness of the fast than the slow AV nodal pathway. However, the effects on conduction intervals during AVNRT are greater in the anterograde slow pathway than in the retrograde fast pathway. These observations suggest that the fast and slow pathways may have differential sensitivities to autonomic influences. This difference in the response to beta-adrenergic antagonists may be exploited as a clinically useful method for demonstrating slow pathway conduction in some individuals with AVNRT.

Adrenergic beta-Antagonists↗
PubMed1993

Radiofrequency ablation for treatment of primary atrial tachycardias.

OBJECTIVES: The purpose of this study was to determine the safety and efficacy of radiofrequency ablation as definitive therapy for primary atrial tachycardias. BACKGROUND: Primary atrial tachycardias are often difficult to control with antiarrhythmic medications and frequently require nonpharmacologic interventions for definitive therapy. Despite isolated reports of successful treatment of primary atrial tachycardias with radiofrequency ablation, the safety and efficacy of this technique have not been established in a larger series with long-term follow-up. METHODS: The immediate procedural success rate, associated complications and follow-up data of radiofrequency ablation were evaluated in 15 consecutive patients (11 adults and 4 children) with primary atrial arrhythmias that were refractory to medical management. RESULTS: The clinical arrhythmia was ectopic atrial tachycardia in 11 patients and sinus node reentry in 4. The site of origin of the tachycardia was in the right atrium in 14 patients and in the left atrium in 1 patient (with two distinct foci) where the local atrial electrogram preceded the onset of the P wave by 10 to 30 ms. Radiofrequency energy successfully terminated the primary atrial tachycardia in each of the patients, and all were discharged from the electrophysiology laboratory in sinus rhythm without inducible atrial tachycardia. A mean of 10.8 +/- 9.9 radiofrequency applications were delivered using 30 W of power for 30 s. The local intracardiac activation time (relative to the P wave in the surface electrocardiogram) was a mean of -21 +/- 5 ms at the successful ablation site and -15 +/- 6 ms at unsuccessful sites (p < 0.001). No complications were observed, although one patient with incessant ectopic atrial tachycardia had sinus pauses after ablation. During a mean follow-up period of 277 +/- 133 days, the clinical arrhythmia recurred in three patients (20%, 95% confidence intervals 3% to 37%) including two patients with ectopic atrial tachycardia and one patient with sinus node reentry. One of these patients was successfully treated in a second ablation session. CONCLUSIONS: Thus, radiofrequency catheter ablation appears to be a safe and effective technique for the treatment of primary atrial arrhythmias that are refractory to antiarrhythmic medications.

Adolescent↗