ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01347.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01348.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Radiofrequency Ablation of Pseudo‐Mahaim Fibers.Introduction:A young woman with refractory recurrent supraventricular tachycardia was referred for catheter ablation.Methods and Results:Electrophysiologic studies revealed the mechanism of tachycardia to be atrioventricular (AV) reentry, utilizing a decrementally conducting atriofascicular accessory pathway as the anterograde limb of the circuit and the normal intraventricular conducting system as the retrograde limb. Pace mapping in the right atrium during sinus rhythm suggested an atrial origin of the accessory pathway several centimeters distant from the AV node. Multiple radiofrequency lesions at the distal insertion of the accessory pathway in or near the right bundle branch failed to abolish preexcitation. In contrast, radiofrequency current applied to the ventricular side of the anterolateral tricuspid ring, adjacent to the atrial origin of the accessory pathway, was successful in abolishing preexcitation and inducible supraventricular tachycardia without affecting AV nodal conduction.Conclusion:Radiofrequency ablation can provide curative therapy for intractable supraventricular tachycardia due to decrementally‐conducting atriofascicular accessory pathways. The risk of AV block in such patients as a consequence of the procedure should be quite

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01349.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Adrenergic Afterdepolarizations in Ventricular Cells.Introduction:The purpose of these studies was to expose canine multicellular ventricular endocardial preparations and disaggregated myocytes to adrenergic agonists and antagonists, and to investigate the generation of delayed afterdepolarizations and triggered action potentials.Methods and Results:We used multicellular preparations and disaggregated myocytes from canine ventricles. The threshold concentration for induction of delayed afterdepolarizations in isolated myocytes for norepinephrine was between 1 × 10−8M and 5 × 10−5M, with 50% of the cells showing delayed afterdepolarizations at 4.3 × 10−8M. Higher concentrations of epinephrine are required with 50% of the cells responding to 8.3 × 10−8M. The threshold concentrations for induction of delayed afterdepolarizations in myocardial cells of multicellular preparations were an order of magnitude higher. Delayed afterdepolarizations could not be induced in Purkinje fibers with concentrations up to 10−4M with norepinephrine. Adrenergic delayed afterdepolarizations were inhibited promptly by reduction of pO2in superfusate that was equilibrated with N2(95%) in place of O2. The amplitudes of adrenergic delayed afterdepolarizations and the propensity to triggered action potentials were inversely related to cycle length down to the shortest cycle length tested (330 msec). Adrenergic delayed afterdepolarizations were induced by isoproterenol but not byα‐adrenergic agonists (methoxamine or phenylephrine). They were inhibited by aβantagonist (propranolol) but not byαantagonists (prazosin or yohimbine). Delayed afterdepolarizations induced by isoproterenol were inhibited byαagonists (methoxamine or phenylephrine). Theα‐adrenergic inhibitory effects onβ‐adrenergic delayed afterdepolarizations could be reversed by prazosin, but not by yohimbine.Conclusions:We conclude the natural catecholamines norepinephrine and epinephrine generate delayed afterdepolarizations in myocardial cells, but not in Purkinje cells, by activatingβreceptors, but activation ofα1receptors inhibits adrenergic delayed afterdepolarizations. Individual myocytes exhibit widely varying sensitivities for induction of adrenergic delayed afterdepolarizations, but some cells respond to concentrations similar to those that may exist in vivo. Therefore, sympathetic activation in vivo may generate delayed afterdepolarizations, triggered action

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01350.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Potassium and Anisotropy.Introduction:The purpose of this study was to investigate the effects of potassium on anisotropic conduction in rabbit ventricles.Methods and Results:In Langendorff perfused rabbit hearts, a two‐dimensional epicardial layer of anisotropic myocardium was created by cryodestruction of the endocardial four fifths of the left ventricle. The heart was paced at 0.5 Hz and the epicardial spread of activation was recorded with a high‐resolution mapping electrode (240 points). In ten experiments, we studied the effects of stepwise increased concentrations of extracellular potassium on epicardial conduction, longitudinal and transverse to the fiber direction. At 6.2 mM of K+, longitudinal conduction velocity (θL) was 61 ± 6.2 and transverse conduction velocity (θT) 25 ± 4.6 cm/sec with a ratioθL/θTof 2.6. At a high concentration of 12.5 ± 1.1 mM, conduction slowed down to 29 ± 6.0 and 11 ± 4.4 cm/sec, respectively, with a slightly increased ratio of 3.2 (NS). The amount of depression ofθLandθTvaried considerably from experiment to experiment and from region to region. On the average, no statistical difference in the depression of conduction velocity in relation to the fiber orientation was found. At K+concentrations of more than 12.5 ± 1.1 mM, local conduction was seriously impaired at various sites. Lines of functional conduction block appeared in longitudinal and transverse direction.Conclusion:We conclude that during slow heart rates, depression of the fast sodium channels by high extracellular K+causes no detectable differential effects on conduction velocity or on occurrence of conduction block, longitudinal or transverse to the general fi

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01351.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Bandwidth of Late PotentialsIntroduction:Limited bandwidth systems such as Holter recorders are being used to record cardiac late potentials. Standard late potential systems have a low‐pass frequency of 300 Hz. This suggests that Holter tape systems may significantly distort the late potential measurements, when compared to standard late potential systems.Methods and Results:Signal‐averaged recordings were obtained with an analog bandwidth of 0.05‐300 Hz. Digital filters were then used to do high‐pass filtering and low‐pass filtering. All XYZ signal‐averaged recordings were low‐pass filtered at frequencies of 250, 150, 100, 75, 50, and 25 Hz using a second order Butterworth filter. A fourth order 40 Hz bidirectional high‐pass filter was then applied to each set of recordings. The QRS duration (QRSd) was measured in the filtered vector magnitude. Thirty‐eight syncope patients who had negative electrophysiologic studies for ventricular tachycardia, no prior infarction, normal ejection fractions (>50%), and a QRSd120 msec served as the positive late potential group.Conclusions:A statistically significant lengthening of the QRSd (P<0.05) was observed in the patients with late potentials between the 250 Hz and 25 Hz low‐pass filter. There was a statistically significant shortening of the QRSd in the negative late potential patients between 250 Hz and 25 Hz, as well as between 250 Hz and 50 Hz, with P<0.05 in both cases. Thus, significant changes in late potentials are seen in limited bandwidth recordings that may limit the clinical usefu

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01352.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Determinants of Radiofrequency Lesion Size.Introduction:Radiofrequency (RF) catheter ablation is a promising modality in the management of cardiac arrhythmias, but the optimum protocol for energy delivery has not yet been determined. The purpose of this study was to examine the effects of varying electrode‐tissue contact pressure and varying duration of RF energy delivery on the size of the resultant lesion in an in vitro model of isolated perfused and superfused canine myocardium.Methods and Results:RF power (500 kHz) was delivered through the tip of a specially‐designed thermistor‐tipped 1.6‐mm diameter electrode mounted on an adjustable fulcrum so that contact force could be varied. RF power was adjusted to maintain a constant electrode‐tissue interface temperature of 80°C during lesion production. Seventy‐nine lesions were created with a 90‐second RF energy delivery, and a contact force that was varied between 0 and 400 newtons (N) (0‐41 g). Lesions produced with a small contact force (10 N) were significantly larger than those with a contact force of zero (width 5.5 mm vs 3.8 mm, P<0.0002), but not significantly different from those produced with the maximum contact force of 400 N (width 6.5 mm, P = NS). However, the greater contact force significantly decreased the power required to maintain a constant electrode‐tissue interface temperature. Ninety‐six lesions were then created using a constant contact force, but duration of energy delivery was varied from 10 to 600 seconds. Lesion size grew monoexponentially with time. The t1/2of lesion growth was 7.6 and 9.6 seconds for depth and width, respectively.Conclusion:Thus, close electrode‐tissue contact is essential for adequate lesion formation during RF ablation of myocardium, but increasing contact force does not significantly increase lesion size if power is adjusted to maintain a constant electrode‐tissue interface temperature. In order to approach steady‐state and maximize lesion size, duration of RF energy delivery sho

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01353.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Arrhythmias in Hypertrophic Cardiomyopathy.Arrhythmias, particularly atrial fibrillation and nonsustained ventricular tachycardia, are common in adult patients with hypertrophic cardiomyopathy. Atrial fibrillation has long been thought to herald an ominous prognosis, but this is probably not the case, and in the majority of patients atrial fibrillation can be controlled without accelerated symptomatic deterioration. Uncontrolled observations indicate that low dose amiodarone may be the most useful drug in paroxysmal and chronic atrial fibrillation. The detection of nonsustained ventricular tachycardia on ambulatory electrocardiogram monitoring remains the single most useful indicator of the risk of sudden death in the adult patient, and the treatment of choice is again low dose amiodarone. The mechanism of sudden death, and the mode of action of amiodarone in preventing it, are not known for certain in the majority of patients. The risk of sudden death is higher in children and adolescents, but arrhythmias are less common, and no useful predictive marker of increased risk has been found. The role of invasive electrophysiological studies and the place of the implantable cardioverter‐defibrillator in hypertrophic cardiomyopathy have not yet been establishe

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01354.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01355.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Ionic Current in Sinoatrial Node Cells. In this article, we report our current understanding of ionic mechanisms of the spontaneous rhythm of the mammalian sinoatrial pacemaker cells obtained from whole‐cell voltage clamp studies. Various ionic currents that underlie the pacemaker potential are discussed. Calcium (Ca) current, delayed‐rectifier potassium (K) current, and hyperpolarization‐activated inward current were found to be the major time‐dependent currents responsible for the pacemaker depolarization. Together with these time‐dependent currents, a time‐independent background current may also contribute to generation of pacemak

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1991.tb01356.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY