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Biomedical subjects

G N Kay

Publications and source records attributed to G N Kay.

At least 73 records · Page 4Linked to original sources
PubMed1993

Role of radiofrequency ablation in the management of supraventricular arrhythmias: experience in 760 consecutive patients.

INTRODUCTION: Several reports have demonstrated that radiofrequency catheter ablation provides effective control of a variety of supraventricular tachycardias. However, the efficacy, complications, risk of arrhythmia recurrence, and follow-up survival analysis have not been reported in a large series of consecutive patients with supraventricular arrhythmias with diverse electrophysiologic mechanisms. This report details the results of radiofrequency catheter ablation in 760 consecutive patients (386 males, 374 females) with a wide variety of supraventricular tachycardias treated at one center. METHODS AND RESULTS: Arrhythmias were associated with the presence of an accessory pathway in 363 patients (384 accessory pathways), including four patients with Mahaim fibers and eight patients with the permanent form of junctional reciprocating tachycardia. The mechanism of the clinical arrhythmia was AV nodal reentrant tachycardia in 245 patients, and a primary atrial tachycardia in 20 patients (ectopic atrial tachycardia in 16 patients and sinus nodal reentry in 4 patients). Ablation of the reentrant circuit of atrial flutter within the right atrium was attempted in 13 patients. AV node ablation and permanent pacemaker implantation were performed in 119 patients with medically refractory atrial fibrillation or flutter. Radiofrequency catheter ablation was successful in 346 of 363 patients (95.3%, CI 93.1%-97.5%) with accessory pathways (367 of 384 pathways, 95.6%, CI 93.5%-97.6%) with a complication rate of 1.1% and a recurrence rate of 5.5%. Successful accessory pathway ablation was achieved for 179 of the first 192 pathways treated (93.2%, CI 89.7%-96.6%) and increased to 188 of 192 pathways (97.9%, CI 95.9%-99.9%) over the second half of the series. AV nodal reentry was successfully abolished in 244 of 245 patients (99.6%, CI 98.8%-100%) by selective ablation of the slow pathway in 234 patients and the fast pathway in 10 patients. The complication rate in this group was 2.0% with a recurrence rate of 6.5%. All 20 primary atrial tachycardias were successfully ablated with no complications and a recurrence rate of 15%. The reentrant circuit of atrial flutter was ablated successfully in 10 of 13 patients (77%) with recurrent atrial flutter in one additional patient. Complete AV block was achieved in 117 of 119 (98.3%, CI 96.0%-100%) patients with atrial fibrillation or flutter treated by AV nodal ablation with a complication rate of 0.8% and recurrence of AV conduction in 6%. The median duration of fluoroscopy exposure for the population was 23.4 minutes. The overall primary success rate for the entire population was 97.0% (737 of 760 patients, CI 95.8%-98.2%). CONCLUSION: Thus, the results of this large series of patients demonstrates the safety and efficacy of radiofrequency ablation for the treatment of a wide variety of supraventricular arrhythmias. It also appears that increasing experience with these procedures increases the rate of successful ablation and decreases the risk of complications.

Adolescent↗
PubMed1993

Evaluation of the acute hemodynamic and electrophysiologic effects of intravenous amlodipine alone and in combination with a beta-blocker in patients with angina pectoris.

The acute hemodynamic and electrophysiologic effects of intravenous amlodipine (2 x 10 mg), administered either alone or on a background of beta-blocker therapy, were studied in 25 patients with angina pectoris. Hemodynamic assessments showed that amlodipine produced significant decreases in systemic vascular resistance and systemic blood pressure, and increases in stroke volume and cardiac output in both treatment groups. Electrophysiologic evaluation revealed that neither sinus node function, nor HIS ventricular conduction, were altered with amlodipine. Therefore, acute intravenous administration of amlodipine alone or in combination with a beta-blocker does not appear to compromise left ventricular performance, sinus node function, or intracardiac conduction.

Adrenergic beta-Antagonists↗
PubMed1992

Intracoronary ethanol ablation for the treatment of recurrent sustained ventricular tachycardia.

The selective infusion of ethanol into the coronary circulation supplying the site of origin of incessant ventricular tachycardia has been demonstrated to abolish this arrhythmia in selected patients. The present study was designed to evaluate the efficacy and safety of the intracoronary ethanol ablation technique in patients with paroxysmal ventricular tachycardia related to prior myocardial infarction. Twenty-three patients with sustained monomorphic ventricular tachycardia that was refractory to conventional antiarrhythmic drug therapy were prospectively studied. After induction of ventricular tachycardia by programmed electrical stimulation, the response of the arrhythmia to the infusion of radiographic contrast medium or saline solution into the ostia of the native coronary arteries and coronary artery bypass grafts was assessed. If ventricular tachycardia was reliably interrupted by injections into the proximal coronary artery or bypass graft, the vessel was cannulated with a steerable guide wire and 2.7F infusion catheter to determine the smallest arterial branch that would result in termination of the arrhythmia with selective injections. If reliable interruption of ventricular tachycardia was observed with saline or contrast injections, ethanol (2 ml) was then delivered through the infusion catheter. Ventricular tachycardia could be terminated by injections of saline solution or contrast medium in 11 of 21 patients in whom the protocol could be completed. Ethanol was infused in 10 of these patients. Ventricular tachycardia was inducible in only 1 of 10 patients immediately after ethanol infusion. At a follow-up electrophysiologic study performed 5 to 7 days after ablation, ventricular tachycardia became inducible in two other patients, in one of whom the arrhythmia substrate was successfully ablated after three sessions. The mean left ventricular ejection fraction was 0.33 +/- 0.1 before and 0.35 +/- 0.11 after ablation. Complications of the procedure included complete atrioventricular block in four patients and pericarditis in one patient. Thus, intracoronary ethanol ablation is associated with a moderate degree of efficacy but the potential for important complications. Despite these limitations, this technique may provide effective long-term control of ventricular tachycardia for some patients.

Aged↗
PubMed1992

Quantitation of chronotropic response: comparison of methods for rate-modulating permanent pacemakers.

OBJECTIVES: The aim of this study was to develop a technique for quantitating chronotropic response. BACKGROUND: Although the importance of chronotropic response for optimizing cardiac output during exercise is widely recognized, methods for quantitating the rate-modulating behavior of permanent pacemakers have not been developed. For a method of quantitating chronotropic response to be clinically useful, the rate-modulating characteristics of a pacing system should be defined at the onset of exertion, over a variety of exercise work loads and during recovery. METHODS: Three methods for quantitation of rate modulation were assessed in 10 patients during treadmill exercise testing using the chronotropic assessment exercise protocol with expired gas exchange analysis. To compare the observed chronotropic response with a standard, the "expected" heart rate throughout exercise was calculated by using the concept of heart rate reserve as described by Wilkoff. The pacing rate observed during exercise was analyzed with 1) standard linear regression analysis, 2) comparison of observed and expected pacing rates at the midpoint and end of each quartile of exercise, and 3) integration of the area under the rate-response curve with comparison with the area under the expected curve. RESULTS: With use of a normalized scale relating change in heart rate to change in metabolic work load, with values of heart rate and metabolic work load at rest set to 0 and those at maximal exertion set to a value of 1, the mean y intercept for the study group was 0.10 +/- 0.20 (range -0.14 to +0.45), with a mean slope of 0.81 +/- 0.25 (range 0.31 to 1.19). The correlation coefficient relating change in heart rate to change in exercise work load was a mean of 0.90 +/- 0.09 (range 0.63 to 0.98). Integration of the area under the rate-response curve observed during exercise yielded a mean area that was 101 +/- 36% of that expected. When the range of exercise work loads was divided into quartiles, the area under the observed rate-response curve was 151 +/- 114% of that expected during the first quartile of exercise, 113 +/- 70% during the second, 96 +/- 38% during the third and 92 +/- 20% during the fourth. The mean area under the curve during recovery was 93 +/- 29% of that expected. Although calculation of the observed heart rate as a percent of that expected at the midpoint and end of each quartile of exercise used fewer observations, it provided similar results. CONCLUSIONS: Quantitation of the rate-response curve with comparison with the expected heart rate curve provides accurate methods for quantitation of chronotropic response. Adoption of this method would facilitate comparisons of artificial sensors and provide a framework to address issues of optimal rate modulation.

Age Factors↗
PubMed1992

Modification of late potentials by intracoronary ethanol infusion.

Antiarrhythmic drugs have no consistent effects on the signal-averaged electrocardiogram (ECG) while successful surgical ablation of ventricular tachycardia is known to abolish late potentials. Ten patients with prior myocardial infarction had successful ablation of recurrent sustained ventricular tachycardia by selective ethanol infusion into a small coronary vessel supplying the tachycardia origin. Signal-averaged ECGs were performed before and after initially successful ablation in patients without pacemaker dependence or intraventricular conduction delay to assess the effects on late potentials and to determine if the signal-averaged ECG could predict ventricular tachycardia recurrence. Only four of ten patients were eligible for study and all four had late potentials prior to ethanol ablation. Late potentials were abolished in one patient who has not had an arrhythmia recurrence in 25 months. One patient with sudden death and another patient with ventricular tachycardia recurrence had persistent late potentials post procedure that were modified by a reduction in terminal voltage and lengthening of terminal low amplitude signal. The fourth patient who receives chronic amiodarone had no arrhythmia recurrence in spite of persistent but modified late potentials. Thus, the abolition of late potentials after ethanol ablation may predict freedom from arrhythmia recurrence.

Cardiac Pacing, Artificial↗
PubMed1992

Can the heart be chronically paced with electrodes on the pericardial surface?

During implantable defibrillator (ICD) operations, we measured acute and chronic transpericardial bipolar pacing thresholds through standard myocardial surface electrodes sewn on the pericardium for chronic ICD QRS rate-sensing use. We compared observations in 24 patients on day 0 with chronic measurements in seven patients at 27.4 +/- 12.1 (median 31.7) months. The leads were used only for QRS rate-sensing, not for pacing, during the time between acute and chronic measurements. Acute transpericardial pacing threshold at 0.5-msec stimulus duration on day 0 was 4.5 +/- 2.19 V (standard deviation), median 3.5 V, and at median time 964 days postimplantation was 3.8 +/- 2.07 V, median 3.5 V. Mean acute pacing current threshold was 3.7 +/- 1.90 mA, n = 23, and chronic was 2.7 +/- 1.79 mA, n = 6. Acute bipolar impedance was 1,209 +/- 383 ohms, median 1,138 ohms, and chronic was 1,550 +/- 358 ohms, median 1,410 ohms, n = 7. Acute bipolar QRS amplitude was 12.3 +/- 5.93 mV, median 12.1 mV, n = 24, and chronic was 13.5 +/- 8.5 mV, median 17.2 mV, n = 7. None of the changes between the acute and chronic states was statistically significant, with the exception of bipolar impedance (P = 0.054). We concluded that: (1) transpericardial pacing threshold did not increase with time; (2) initial and chronic pacing impedances were high and current low; (3) QRS amplitudes were highly satisfactory for defibrillator rate-sensing; and (4) this approach to ICD implantation left the surgically virgin heart unscarred to make future transplantation easier, and enhanced safety when previous cardiac operations had been done.

Cardiac Pacing, Artificial↗
PubMed1992

Gross and microscopic changes associated with a nonthoracotomy implantable cardioverter defibrillator.

The pathology associated with an investigational transvenous defibrillating and sensing lead is described. The lead system had delivered a total of 865 J from the time of implantation to the time of patient death from a noncardiac cause 7 months after implantation and 1 month after his last defibrillator shock. There was mild, superficial fibrous thickening on the endothelial surface of the superior vena cava adjacent to the proximal spring electrode, which did not extend into the vessel wall. The distal portion of endocardial lead was embedded in the interventricular septum near the apex of the right ventricle, surrounded by fibrous thickening, and partially covered by endocardial tissue. Microscopically, there was a thick bed of fibrous connective tissue surrounding the lead with extensive interstitial fibrous connective tissue radiating into the adjacent myocardium. Since this pattern is different from the more generalized fibrotic scarring produced by myocardial infarction, we speculate that the mechanism for the observed interstitial fibrosis is replacement fibrosis following acute myocyte injury that resulted from prior defibrillator shocks and possibly from the trauma produced by the lead compressing adjacent myocardium during systole. Potential effects on device efficacy of these fibrotic changes at the bioelectric interface include their representing a new arrhythmia substrate, the possibility that fibrosis could increase both defibrillation and pacing thresholds, and that the inflammatory reaction may cause deterioration of intracardiac electrograms and interfere with sensing and tachycardia recognition.

Aged↗
PubMed1992

Selective radiofrequency ablation of the slow pathway for the treatment of atrioventricular nodal reentrant tachycardia. Evidence for involvement of perinodal myocardium within the reentrant circuit.

BACKGROUND: The circuit of atrioventricular (AV) nodal reentrant tachycardia may include perinodal atrial myocardium. Furthermore, in patients with dual AV nodal pathways, the atrial insertion of the slow pathway is likely to be located near the ostium of the coronary sinus, caudal to the expected location of the AV node. The present study was designed to evaluate the safety and efficacy of selective catheter ablation of the slow pathway using radiofrequency energy applied along the tricuspid annulus near the coronary sinus ostium as definitive therapy for AV nodal reentrant tachycardia. METHODS AND RESULTS: Among 34 consecutive patients who were prospectively enrolled in the study, the slow pathway was selectively ablated in 30, and the fast pathway was ablated in four. Antegrade conduction over the fast pathway remained intact in all 30 patients after successful selective slow pathway ablation. There was no statistically significant change in the atrio-His interval (68.5 +/- 21.8 msec before and 69.6 +/- 23.9 msec after ablation) or AV Wenckebach rate (167 +/- 27 beats per minute before and 178 +/- 50 beats per minute after ablation) after selective ablation of the slow pathway. However, the antegrade effective refractory period of the fast pathway decreased from 348 +/- 94 msec before ablation to 309 +/- 79 msec after selective slow pathway ablation (p = 0.005). Retrograde conduction remained intact in 26 of 30 patients after selective ablation of the slow pathway. The retrograde refractory period of the ventriculo-atrial conduction system was 285 +/- 55 msec before and 280 +/- 52 msec after slow pathway ablation in patients with intact retrograde conduction (p = NS). There were three complications in two patients, including an episode of pulmonary edema and the development of spontaneous AV Wenckebach block during sleep in one patient after slow pathway ablation and the late development of complete AV block in another patient after fast pathway ablation. Over a mean follow-up period of 322 +/- 73 days, AV nodal reentrant tachycardia recurred in three patients, all of whom were successfully treated in a second ablation session. CONCLUSIONS: Radiofrequency ablation of the slow AV pathway is highly effective and is associated with a low rate of complications.

Adult↗
PubMed1992

Clinical characteristics and outcome of patients with high defibrillation thresholds. A multicenter study.

BACKGROUND: Successful defibrillation by an implantable cardioverter-defibrillator (ICD) depends on its ability to deliver shocks that exceed the defibrillation threshold. This study was designed to identify clinical characteristics that may predict the finding of an elevated defibrillation threshold and to describe the outcome of patients with high defibrillation thresholds. METHODS AND RESULTS: The records of 1,946 patients from 12 centers were screened to identify 90 patients (4.6%) with a defibrillation threshold greater than or equal to 25 J. Excluding three patients who received ICDs that delivered greater than 30 J, there were 81 men and six women with a mean age of 59.5 +/- 10.1 years, a mean left ventricular ejection fraction of 0.32 +/- 0.14, and a 76% prevalence of coronary artery disease. Sixty-one patients (70%) were receiving antiarrhythmic drugs, and 45 (52%) were receiving amiodarone. Seventy-one patients (82%) received an ICD. Death occurred in 27 patients--19 of the 71 (27%) with an ICD (eight arrhythmic), and eight of the 16 (50%) without an ICD (four arrhythmic). Actuarial survival for all patients at 5 years was 67%. Actuarial survival rates at 2 years for patients with and without an ICD were 81% and 36%, respectively (p = 0.0024). Actuarial survival at 5 years for the ICD patients was 73%; no patient without an ICD has lived longer than 32 months. Actuarial survival free of arrhythmic death in the ICD patients at 5 years was 84%. Although the only variable to predict survival was ICD implantation (p = 0.003), it is entirely possible that in this retrospective analysis, clinical selection decisions to implant or to not implant an ICD differentiated patients destined to have better or worse outcomes, respectively. CONCLUSIONS: Antiarrhythmic drug use may be causally related to the finding of an elevated defibrillation threshold. When patients with high defibrillation thresholds receive an ICD, arrhythmic death remains an important risk (42% of deaths in these patients were arrhythmia related, with 16% actuarial incidence at 5 years). Vigorous testing to optimize patch location can potentially benefit patients by enhancing the margin of safety for effective defibrillation.

Adult↗
PubMed1992

Wolff-Parkinson-White syndrome. A quantitative morphometric analysis of surgical anatomy.

Previous descriptions of the four anatomic regions of dissection in Wolff-Parkinson-White syndrome have been largely qualitative. In this study quantitative data describing this anatomy are presented, together with statistical analysis of selected anatomic relationships. Fourteen human hearts were dissected. The borders of the posteroseptal dissection along the mitral anulus, tricuspid anulus, and epicardium were measured. A positive correlation between the mitral and tricuspid annular dimensions was found (r = 0.55; p = 0.04); however, the length of epicardial dissection was more variable. The dimensions of the anteroseptal space and the position of the right coronary artery within this space were measured. These measurements emphasize the proximity of the aortic sinuses of Valsalva to the right atrial endocardium near the posteromedial extent of the dissection. The dimensions of the right and left free walls and the position of the coronary arteries within these spaces were measured. A positive correlation was found between the width of the atrioventricular groove and the length of the dissection necessary to separate the atrioventricular groove fat from the ventricular surface (r = 0.89; p = 0.0001, right free wall; r = 0.87; p = 0.0001, left free wall). The quantitative data presented in this article are intended to enhance the surgeon's appreciation of the anatomy relevant to the treatment of Wolff-Parkinson-White syndrome. The knowledge gained from this quantitative analysis may improve accuracy in the electrophysiologic localization and surgical disruption of accessory atrioventricular connections.

Autopsy↗
PubMed1991

Intermediate septal accessory pathways: electrocardiographic characteristics, electrophysiologic observations and their surgical implications.

Intermediate septal accessory pathways are located in close proximity to the atrioventricular (AV) node and His bundle, have unique features that distinguish them from typical anterior and posterior accessory pathways and have been associated with a high risk for unsuccessful pathway division and the production of complete AV block after surgery. Between July 1986 and May 1990, 4 of 70 patients (3 men and 1 woman; mean age 33 +/- 13 years) undergoing surgery for accessory pathway division were found to have an intermediate septal accessory pathway. The presenting arrhythmia was atrial fibrillation with rapid anterograde conduction over the accessory pathway in two patients and recurrent orthodromic reciprocating tachycardia in two patients. In all patients, the delta wave on the electrocardiogram (ECG) was inverted in lead V1, but two patterns of delta wave configuration were observed. In three patients (type 1 intermediate septal accessory pathway), the delta wave was upright in lead II, inverted in lead III and isoelectric in lead a VF; the transition from a negative to an upright delta wave occurred in lead V2. The fourth patient exhibited a different delta wave pattern (type 2 intermediate septal accessory pathway). The delta wave was upright in each of leads II, III and aVF; the transition from a negative to an upright delta wave occurred at lead V3. Intraoperative electrophysiologic study localized the atrial insertion of type 1 pathways to the midpoint of Koch's triangle close to the AV node.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

A prospective evaluation of intracoronary ethanol ablation of the atrioventricular conduction system.

The clinical efficacy and complications associated with ablation of the atrioventricular (AV) conduction system by the selective infusion of ethanol into the AV node artery were prospectively assessed in 12 consecutive patients with medically refractory atrial arrhythmias. Six of the patients had previously failed to have permanent complete AV block created with direct current or radiofrequency catheter ablation. The AV node artery was cannulated with a 0.016 in. (0.041 cm) guide wire in all 12 patients. It was also possible to advance a 2.7F infusion catheter into the AV node artery in all patients. Transient AV block was induced by selective injections into the AV node artery of iced saline solution (8 patients) and of radiographic contrast agent (ioxaglate) (10 patients). The infusion of 2 ml of ethanol (96%) induced immediate complete AV block in all 10 patients who demonstrated AV block with ioxaglate. The escape rhythm exhibited a narrow QRS complex preceded by a His bundle deflection in nine patients and left bundle branch block in one patient. The immediate mean rate of the escape rhythm was 45.3 +/- 13.4 beats/min. In two patients who demonstrated reflux of contrast agent into the distal right coronary artery with selective injections into the AV node artery, transient ST segment elevation developed in the inferior electrocardiographic leads with the infusion of ethanol. There was no change in the left ventricular ejection fraction from the baseline value (0.53 +/- 0.12) to that measured after ablation (0.55 +/- 0.11) and no patient developed wall motion abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Inability of the signal-averaged electrocardiogram to determine risk of arrhythmia recurrence in patients with implantable cardioverter defibrillators.

Signal-averaged electrocardiography has been used to identify patients at risk for arrhythmic death after myocardial infarction. Since patients with implantable cardioverter defibrillators (ICDs) are at high risk for arrhythmic events, they should also be expected to have a high incidence of abnormal signal-averaged electrocardiograms (SAECGs). However, whether the SAECG can discriminate patients who will have arrhythmia recurrence and receive appropriate ICD shocks from those who will have no recurrence and no shocks is unknown. This study examines the usefulness of the SAECG to separate appropriate users from non-users of the ICD. Fifty patients with ICDs participated in this study. Those who received a shock preceded by symptoms, a shock without preceding symptoms but with electrocardiographic documentation of ventricular fibrillation or ventricular tachycardia, or a shock while asleep were classified as ICD users. All other patients were classified as nonusers. The SAECG was classified as normal if the QRS duration on the standard electrocardiogram was less than or equal to 110 msec and if the total filtered QRS duration was less than 120 msec, the root-mean square voltage of the terminal 40 msec was greater than 25 muV, and the terminal low amplitude signal duration measured less than 38 msec. The SAECG was classified as abnormal if the QRS duration on the standard electrocardiogram was less than or equal to 110 msec and any one of these three criteria were outside the "normal range." The SAECG was classified as indeterminate if the QRS duration on the standard 12-lead electrocardiogram was greater than 110 msec. For the entire group of 50 patients, 8 (16%), 12 (24%), and 30 (60%) had normal, abnormal, and indeterminate SAECGs, respectively. Of the 22 ICD users, 1 (5%), 5 (23%), and 16 (73%) patients had normal, abnormal, and indeterminate SAECGs, respectively. Of the 28 ICD nonusers, 7 (25%), 7 (25%), and 14 (50%) patients had normal, abnormal, and indeterminate SAECGs, respectively. ICD users had lower left ventricular ejection fractions (P = 0.0002), a higher incidence of ventricular tachycardia (P = 0.04), prior exposure to a greater number of antiarrhythmic drugs (P = 0.04), and a lower likelihood for survival (P = 0.02) compared to the ICD nonusers. There was no statistically significant difference between the ICD users and nonusers as stratified by SAECG classification regardless of whether or not the interminate studies were included or excluded from the analysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Arrhythmias, Cardiac↗
PubMed1990

Evidence for a central site of action to explain the negative chronotropic effect of atropine: studies on the human transplanted heart.

The chronotropic response to atropine is biphasic; low doses cause slowing of the sinus rate and high doses cause acceleration. Although it is accepted that atropine functions as a competitive antagonist at high doses, the mechanism of the negative chronotropic response at low doses is controversial. Specifically, it is unclear whether the effect is mediated centrally or peripherally. Since at the time of cardiac replacement all central nervous system connections to the heart are severed, the transplanted heart is a unique model for separating these effects. Graded doses of atropine sulfate (0.5, 1.0, 2.0, 4.0, 8.0 and 40.0 micrograms/kg body weight) were administered to 12 human heart transplant recipients to test the hypothesis that the bradycardiac effect of low dose atropine is centrally mediated. The baseline sinus cycle lengths of the decentralized donor and innervated native sinus nodes were 694 +/- 20 and 733 +/- 27 ms, respectively. At the 0.5 and 1.0 microgram/kg doses, the cycle lengths of the native sinus node increased by 29.1 +/- 13.5 and 23.1 +/- 14.2 ms, respectively. At the 2.0 micrograms/kg dose the sinus cycle length again shortened to control. At the maximal dose of atropine the sinus cycle length shortened by 138.3 +/- 29.7 ms compared with control. In contrast, the decentralized donor sinus node exhibited a flat dose response to atropine. High dose atropine (40 micrograms/kg) caused no change in the donor heart's atrial effective refractory period, corrected sinus node recovery time, or sinoatrial conduction time measured by either the Strauss or the Narula method.(ABSTRACT TRUNCATED AT 250 WORDS)

Atropine↗
PubMed1990

Effect of pacing rate on the human atrial strength-duration curve.

The effect of rapid pacing on the atrial constant voltage stimulation threshold in humans has not been defined at rates applicable to those of antitachycardia pacing. The effect of pacing rate on the atrial strength-duration relation was determined in 10 patients at pacing rates between 125 and 300 beats/min to explore excitability over the range of rates used for permanent antitachycardia pacing systems. Two points that define the strength-duration curve were measured at each pacing rate: rheobase voltage--the lowest stimulus voltage that results in capture at a pulse duration of 2 ms; and chronaxie pulse duration--the threshold pulse duration at twice rheobase voltage. A permanent, tined, J-shaped pacing lead with a high current density and low polarization electrode was positioned in the right atrial appendage for cathodal stimulation. A constant voltage output, incorporating a fast recharge pulse designed to minimize electrode polarization, was used for stimulation. There was a significant increase in rheobase voltage (p = 0.009), chronaxie pulse duration (p = 0.001) and minimal threshold stimulus energy (p = 0.05) at pacing rates greater than 225 beats/min. A rheobase voltage greater than 5 V occurred in three patients at pacing rates greater than or equal to 275 beats/min. At a pacing rate of 300 beats/min, rheobase voltage had increased in 8 of 10 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1990

Significance of ventricular tachyarrhythmias complicating cardiac catheterization: a CASS Registry Study.

Ventricular tachycardia and ventricular fibrillation are recognized complications of cardiac catheterization. Despite numerous reports documenting the frequency of these occurrences, their significance has not been systematically examined. Accordingly, the outcome of 108 patients who experienced either ventricular tachycardia or ventricular fibrillation during coronary angiography between 1975 and 1979 in the Coronary Artery Surgery Study (CASS) Registry were examined. There were 20,142 patients analyzed. Patients with ventricular tachyarrhythmias had more objective evidence of left ventricular impairment, clinical heart failure, and ventricular arrhythmia recorded as a clinical symptom. The overall 5-year survival rates were 83% and 88% for patients with and without ventricular tachyarrhythmias, respectively (p = 0.07). When ventricular function, age, gender, angina, and previous myocardial infarction were added in a stepwise Cox survival analysis, the presence of arrhythmias was not significant (p = 0.66). At 5 years, 80% of the medically treated patients and 82% of the surgically treated patients remained alive (p = 0.95). The only statistically significant differences in the patients with ventricular arrhythmias who were treated medically or surgically were age (medically treated patients 52 +/- 10 years, surgical patients 57 +/- 9 years, p = 0.01) and number of diseased vessels (p less than 0.001). In a stepwise Cox survival analysis, functional impairment secondary to congestive heart failure was the only significant covariate to affect survival in the medical and surgical groups (p = 0.0001). Surgical therapy itself was not significant (p = 1.00). The incidence of sudden death during 5 years for patients with and without ventricular tachyarrhythmias during catheterization was 5% and 4%, respectively (p = 0.28).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Catheterization↗