摘要:

Characteristics of M Cells.Introduction: Recent studies have described the existence of M cells in the deep structures of the canine and human ventricle. The present study was designed to further characterize the M cell with respect to its distribution across the canine left ventricular free wall and the dependence of its action potential on [K+]0.Methods and Results: We used standard microelectrode techniques to record transmembrane activity from deep subepicardial or transmural strips isolated from the canine left ventricular free wall near the base as well as subendocardial Purkinje fibers. M cell behavior (steep APD‐rate relation) was observed at depths of 1 to 7 mm from the epicardial surface (deep subepicardium to mid‐myocardium). M cells were found to be distributed uniformly in the deep subepicardium and did not appear in discrete bundles. We observed transitional behavior throughout the wall. The maximum rate of rise of the action potential upstroke, Vmax, increased sharply between epicardium and deep subepicardium (176 ± 13 to 332 ± 61 V/sec), remained high throughout the mid‐myocardium and deep subendocardium, and returned to lower values only in the superficial layers of the endocardium (205 ± 21 V/sec). The relationship between Vmaxand takeoff potential in the M cell was fit by a Boltzmann equation with a V V0.5of ‐68.6 ± 1.5 mV and k of 3.4 ± 0.5. The relationship between resting membrane potential (RMP) and [K+]0in the M cell was exponential from 8 to 20 mmol/L (58 mV change in RMP per 10‐fold change in [K+]0), deviating from K+electrode behavior at [K+]0,<8 mmol/L. RMP in M cells continued to hyperpolarize at [K+]0<2.5 mmol/L, reaching potentials of approximately ‐110 mV at I+]0, of 1 mmol/L. In contrast, subendocardial Purkinje fibers depolarized at these low levels of [K+]0. Unlike endocardium and epicardium, M cells developed early afterdepolarizations at low [K+]0and slow rates.Conclusions: Our data indicate that the M cells are widely distributed in the intramural layers of the canine left ventricular free wall. M cells and transitional cells occupy 30% to 40% of the left ventricular wall and an estimated 20% to 40% of the mass of the ventricles of the normal canine heart. They display characteristics common to both myocardial and specialized conducting cells. Like Purkinje fibers, M cells exhibit a relatively large Vmaxand steep APD‐rute relations that are modulated by [K+]0. Unlike Purkinje fibers, M cells do not appear in bundles, they do not depolarize at [K+]0<2.5 mmol/L, nor do they exhibit phas

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00435.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Postshock Sensing in Transvenous Lead Systems.Introduction: The sensing performance of transvenous lead systems may be adversely affected by the delivery of high‐energy shocks. This may be due to the proximity of the sensing and energy‐delivery electrodes on transvenous leads.Methods and Results: The time required for detection of ventricular fibrillation and redetection after a failed first shock was compared in 93 patients with five different lead system‐pulse generator combinations: CadenceTM‐ EndotakTM60 series, Ventak PTM‐ EndotakTM60 series, JewelTM‐ TransveneTM, CadenceTM‐ TVLTM, and CadenceTM‐ TransveneTM. A total of 418 successful and 204 failed first shocks were delivered during induced ventricular fibrillation. Redetection times (RED) were consistently shorter than detection times (DET) in the Jewel‐Transvene (RED minus DET: 1.9 ± 0.8 sec, P<0.0001), the Cadence‐TVL (‐1.6 ± l.0sec, P<0.0001), and the Cadence‐Transvene combinations (‐2.0 ± 0.9 sec, P8.2 sec) were observed in the Cadence‐Endotak (7 [10%] of 73 episodes) and the Ventak‐Endotak (4 [10%]of 39 episodes), but not in the Jewel‐Transvene, the Cadence‐TVL, and the Cadence‐Transvene combinations.Conclusions: Redetection of ventricular fibrillation may be delayed in some transvenous lead‐pulse generator combinations. Successful redetection of ventricular fibrillation following a failed first shock should be demonstrated prior to hospital disch

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00436.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.tb00437.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Electrical Organization During VF.Introduction: Ventricular fibrillation is a most dangerous cardiac arrhythmia that has received considerable attention, yet its pattern of electrical activation remains controversial. The aim of this study was to investigate the degree of organization during the clinical arrhythmia and to examine the phase relationship between deflections in independent ECG leads.Methods and Results: Ten recordings of ventricular fibrillation were examined. Each had been provoked during routine electrophysiological study. The mean duration of ventricular fibrillation was 21 seconds (range 11 to 34). Independent and approximately orthogonal ECG leads I, aVF, and V2were recorded to computer at a sampling rate of 250 Hz. The phase relationship of each ECG lead pair was measured from the lag of peaks in their cross‐correlation function (CCF). In 61% of The 1‐second ECG epochs analyzed, CCF peak lag changed by<20 msec compared to The previous epoch. Thus, the overall phase relationship was stable most of the time. Changes in CCF peak lag tended to be either gradual or to punctuate periods of stability.Conclusions: This study provides evidence of organized myocardial activation during human ventricular fibrillat

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00438.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Histology of RF Lesions.Introduction: Radiofrequency (RF) ablation of ventricular tachycardia (VT) late after myocardial infarction may be difficult due to characteristics of the infarct containing the reentry circuit. RF lesions in these infarcts in humans have not been characterized.Methods and Results: Catheter mapping and ablation of VT originating from an anterior wall infarct was performed 8 days and again 12 hours prior to death. Pacing identified a region of abnormal conduction where RF ablation terminated VT. This region contained strips of myocytes sandwiched between endocardial fibrosis and dense scar. RF lesions ranged from 2 × 2 mm to 5 × 10 mm and were up to 3 mm in depth. Acute lesions showed superficial thrombus and early coagulation necrosis without inflammation. Older lesions showed coagulation necrosis, sparse neutrophil infiltrate, minimal granulation tissue, hemorrhage, and mixed inflammatory infiltrate along the lumen without re‐endothelialization.Conclusion: In this patient, RF lesions had sufficient depth but not width to interrupt the thin, but potentially broad, sheets of myocytes in the reentry circuit. In thinned areas, RF lesions can extend to the epicardium. Selecting sites with abnormal electrograms confines RF lesions to the infarct region. Inflammation and hemorrhage could conceivably cause delayed effects of

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00439.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Bradycardia‐Induced Polymorphic VT. In a patient with severe left ventricular dysfunction resulting from chronic nonparoxysmal sinus tachycardia, rate control and improvement in left ventricular function were achieved with atrioventricular junction ablation and ventricular pacemaker implantation. Within 12 hours after the ablation procedure, several episodes of polymorphic ventricular tachycardia that may have been triggered by the abruptly decreased heart rate occurred. Recurrence of polymorphic ventricular tachycardia was prevented by an increase in pacing rat

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00440.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Implantable Atrial Defibrillators. Due to the limited efficacy of antiarrhythmic drugs for atrial fibrillation, several nonpharmacologic therapeutic options have evolved. One of these is an implantable atrial defibrillator. Recent studies have shown that internal atrial defibrillation is feasible with relatively low energies. To date, the optimal electrode configuration involves large surface area catheters in the right atrium and coronary sinus. In humans, atrial defibrillation can generally be achieved with<2 J using this electrode configuration and a biphasic shock waveform. For shocks<5 J, there is no significant pathological damage to the atria or coronary sinus. Further investigation is needed to guarantee that atrial defibrillation shocks do not provoke ventricular arrhythmias. Preliminary data suggest that atrial defibrillation shocks synchronized to R waves that are not closely coupled are safe. In addition, the shocks are well tolerated if the shock energy is<1.5 J. With additional studies to confirm the safety of implantable atrial defibrillators, further reduce shock energy, and improve patient tolerance, an implantable atrial defibrillator can become an acceptable therapy for patients with symptomatic, paroxysmal atrial fibrillation.

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00441.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.tb00442.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.tb00443.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY