摘要:

Right/Left‐Sided ICD Implantation.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

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00374.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

QTc Dispersion.Introduction: QTc dispersion has traditionally been calculated from all 12 leads of a standard electrocardiogram (ECG). It is possible that alternative, quicker methods using fewer than 12 leads could be used to provide the same information.Methods and Results: We have previously shown a difference in QTc dispersion from ECGs recorded at least 1 month after myocardial infarction between patients who subsequently died and long‐term survivors. In the current study, we recalculated QTc dispersion in these ECGs using different methods to determine if the observed difference in QTc dispersion measurements between the two groups, as calculated from 12‐lead ECGs, persisted when using smaller sets of leads. QTc dispersion was recalculated by four methods: (1) with the two extreme QTc intervals excluded: (2) from the six precordial leads; (3) from the three leads most likely to contribute to QTc dispersion (aVF, V1V4); and (4) from the three quasi‐orthogonal leads (aVF, I, V). For each of the 270 12‐lead ECGs examined, a mean of 9.9 leads (SD 1.5 leads) had a QT interval analyzed; the QT interval could not be accurately measured in the remaining leads. Using the standard 12‐lead measurement of QTc dispersion, there was a difference in the fall in QTc dispersion from early to late ECG between the groups: 9.1 (SD 60.8) msec for deaths versus 34.4 (55.2) msec for survivors (P = 0.016). This difference in QTc dispersion between early and late ECGs was maintained using either three‐lead method (quasi‐orthogonal leads: ‐2.6 [56.2] msec for deaths vs 26.9 [54.3]msec for survivors [P = 0.003]; “likeliest” leads: 8.6 [64.9]msec vs 29.5 [50.2] msec [P = 0.05]), but not when using the other two methods (precordial leads: 19.1 [55.5] msec vs 22 [50.8]msec [P = 0.76]; extreme leads removed: 9.2 [50.1]msec vs 21.8 [42] msec [P = 0.13]).Conclusion: QTc dispersion calculated from three leads may be as useful a measurement as QTc dispersion calculated from all leads of a standard ECG. Its advantages over the standard measurement are its simplicity and the lack of problems w

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00375.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Autonomic Modulation of Sinus and AV Nodes.Introduction: Evidence from animal experiments indicates that the autonomic nervous system may influence the sinus (SA) and atrioventricular (AV) nodes differently. We investigated, therefore, whether there are spontaneous functional differences in the innervation of the SA and AV nodes in man.Methods and Results: This study was performed in 10 healthy males (ages 21 to 26 years) during strict bed rest from 10 pm to 6 am. Three ECG leads were digitized on‐line. PR and PP intervals were determined on a heat‐to‐beat basis off‐line using a correlation algorithm with an accuracy of ± 2 msec and were verified visually. During; major body movements, there were sudden decreases in PP intervals of 36 to 827 msec (mean 335) for periods of 6 to 265 seconds (mean 24), During these phases of heart rate (HR) acceleration, PR intervals showed either concomitant shortening (9 to 30 msec), no change, or lengthening (6 to 25 msec). Furthermore, tonic changes in the PR interval occurred over 15‐minute periods during which the range of PP intervals was constant. Additionally, recovery‐adjusted PR interval (PR ‐ b2/RP) and cycle length were negatively correlated for some periods, which confirmed independent autonomic effects on SA node and A V node.Conclusion: Beat‐to‐beat measurement of PR intervals allows for evaluation of autonomic effects on the human AV node. The different patterns in PR intervals during sudden spontaneous increases in HR and the tonic changes in PR interval indicate that the autonomic inputs to the SA and AV nodes are, in principle, indepen

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00376.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Calcium Channel in Infarct‐Induced Hypertrophied Rat Ventricle.Introduction: The present investigation was aimed at characterization of: (1) action potential parameters; and (2) L‐type calcium channels in the hypertrophied ventricular tissue surviving an extensive healed myocardial infarction in the rat.Methods and Results: Myocardial infarction was produced in Wistar rats by ligation of the left coronary artery. One to 2 months later, their hearts were subjected to electrophysiologic study. The main difference in subendocardial transmembrane potentials recorded with intracellular microelectrodes was an increase in action potential duration (APD). In the left ventricle, the infarcted/sham‐operated APD ratio ranged from 2.7 to 7.2, whereas in the right ventricle it ranged from 1.6 to 2.3 in different regions. When compared with control ceils, ventricular myocytes from infarcted hearts were found to be larger (P<0.01) and showed a reduction (P<0.05) in L‐type calcium current (ICa,L) density obtained by whole cell, patch clamp (at 0 mV: 4.44 ± 0.41 in infarcted vs 8.03 ± 1.22 pA/pF in normal). The time course of decay of the currents could be fitted by two exponential functions in both normal and infarcted hearts. There was a tendency toward an increase in the time constant of the slower component of inactivation, T2, significant only at +20 mV (215 ± 25 vs 151 ± 15 msec).Conclusions: Cardiac hypertrophy of healed infarction in rats is associated with lengthening of the action potential in both ventricles. The main alteration observed in ICa,Lwas a decrease in the current density. Thus, alteration of the calcium channel is not the determinant factor of

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00377.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Radiofrequency Ablation of Multiple VTs.Introduction: As treatment options for ventricular tachycardia (VT) continue to evolve, the use of radiofrequency catheter ablation is rapidly expanding. However, in the presence of multiple morphologies of VT, achieving successful results may seem less likely. We report two patients with multiple morphologies of VT who underwent successful radiofrequency ablation by application of adiofrequency energy to a single region in the left ventricle.Methods and Results: Two patients, each without any apparent cardiac dysfunction and a history of documented VT, were referred to our institution for further management. They underwent an electrophysiologic study and were found to have easily inducible VT, of three morphologies in one patient and two in the other. Using a transaortic approach, left ventricular mapping was performed for detecting a site with presystolic potentials, earliest ventricular activation, or both. Application of radiofrequency energy to a single area in the left ventricle resulted in the elimination of all previously inducible VT in each patient.Conclusion: VTs with distinctly different morphologies can occur in patients with no detectable structural heart disease. These VT circuits may share a common pathway and, therefore, may readily be amenable to therapy with radiofrequency catheter ablation.

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00378.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Long QT Syndrome. Competing theories to explain the congenital long QT syndrome have included an imbalance in sympathetic innervation of the heart or a defect in repolarizing ion currents. Recent studies have identified at least four chromosomal loci at which mutations cause the congenital long QT syndrome in different families. The specific genes mutated in affected individuals have been identified at two of these loci, and both encode cardiac ion channels. The affected genes are SCN5A, the cardiac sodium channel gene, and HERG, whose protein product likely underlies IKr, the rapidly activating delayed rectifier. Thus, currently available evidence indicates that the congenital long QT syndrome is a primary disease of cardiac ion channels. Abnormalities in either inward or outward currents can cause the disease. Ongoing studies are evaluating the function of the mutant ion channels and the relationship between individual mutations and the clinical manifestations of the syndrome.

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00379.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

TdP and Complete Heart Block.Introduction: To determine whether an increased female gender susceptibility to torsades de pointes (TdP) may exist in a clinical model of bradycardia‐ induced long QT syndrome, we investigated reported cases of TdP associated with acquired complete heart block.Methods and Results: Seventy‐two cases reported in the medical literature dating from 1941 through 1993 were identified, all describing TdP or “transient ventricular tachycardia/fibrillation” (to include those cases reported prior to the use of TdP terminology) in the setting of acquired complete heart block unassociated with QT prolonging drugs. Expected female prevalence in complete heart block was estimated at 52%, based on projections derived from 206,016 hospital discharges in the National Inpatient Profile (Commission on Professional and Hospital Activities, Ann Arbor, MI), over the years 1985 through 1992. During complete heart block, mean heart rate was 37 beats/min in both sexes (combined n = 43), and absolute QT interval ranged from 0.52 to 0.88 seconds, with a mean of 0.68 seconds (n = 25). Female prevalence among patients with TdP during complete heart block was greater than expected: 72% for all studied cases (P<0.001); 70% (P<0.04) and 74% (P<0.02) among those reported prior to (n = 35) and during or alter (n = 37) 1980, respectively; 73% (P<0.03) among those with documented normokalemia (n = 26); and 68% (P = 0.2) among those with a prolonged QT interval and known polymorphic VT (i.e., unequivocal TdP; n = 25).Conclusion: Despite inherent limitations of this retrospective study, the data are consistent in suggesting a greater than expected female prevalence among patients with TdP related to complete heart block. This finding lends support to a broadening concept of increased susceptibility of women to the development of TdP in various settings of QT prolo

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00380.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Myocardial Ischemia. Myocardial ischemia leads to significant changes in the intracellular and extracellular ionic milieu, high‐energy phosphate compounds, and accumulation of metabolic by‐products. Changes are measured in extracellular pH and K+and intracellular pH, Ca2+, Na+Mg2+, ATP, ADP, and inorganic phosphate. Alterations of membrane currents occur as a consequence of these ionic changes, adrenergic receptor stimulation, and accumulation of lactate, amphipathic compounds, and adenosine. Changes in the volume of the extracellular and intracellular spaces contribute further to the ultimate perturbations of active and passive membrane properties that underlie alterations in excitability, abnormal automaticity, refractoriness, and conduction. These characteristic changes of electrophysiologic properties culminate in loss of excitability and failure of impulse propagation and form the substrate for ventricular arrhythmias mediated through abnormal impulse formation and reentry. The ability to detail the changes in ions, metabolites, and high‐energy phosphate compounds in both the extracellular and intracellular spaces and to correlate them directly with the simultaneously occurring electrophysiologic changes have greatly enhanced our understanding of the electrical events that characterize the ischemic process and hold promise for permitting studies aimed at developing interventions that may lessen the lethal consequences of isc

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00381.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY