摘要:

Defibrillation with Small Capacitance.Introduction:The size of current implantable cardioverter defibrillators (ICD) is still large in comparison to pacemakers and thus not convenient for pectoral implantation. One way to reduce ICD size is to defibrillate with smaller capacitors. A trade‐off exists, however, since smaller capacitors may generate a lower maximum energy output.Methods and Results:In a prospective randomized cross‐over study, the step‐down defibrillation threshold (DFT) of an experimental 90‐μF biphasic waveform was compared to a standard 125‐μF biphasic waveform. The 90‐μF capacitor delivered the same energy faster and with a higher peak voltage but provided only a maximum energy output of 20 instead of 34 J. DFTs were determined intraoperatively in 30 patients randomized to receive either an endocardial (n = 15) or an endocardial‐subcutaneous array (n = 15) defibrillation lead system. Independent of the lead system used, energy requirements did not differ at DFT for the experimental and the standard waveforms (10.3 ± 4.1 and 9.5 ± 4.9 J, respectively), but peak voltages were higher for the experimental waveform than for the standard waveform (411 ± 80 and 325 ± 81 V, respectively). For the experimental waveform the DFT was 10 J or less using an endocardial lead‐alone system in 10 (67%) of 15 patients and in 12 (80%) of 15 patients using an endocardial‐subcutaneous array lead system.Conclusions: A shorter duration waveform delivered by smaller capacitors does not increase defibrillation energy requirements and might reduce device size. However, the smaller capacitance reduces the maximum energy output. If a 10‐J safety margin between DFT and maximum energy output of the ICD is required, only a subgroup of patients will benefit from 90‐μF ICDs with DFTs feasible using curren

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Ventricular Rate During AF.Introduction:The mechanisms of the ventricular response during atrial fibrillation (AF) remain uncertain. The parameters obtained during an electrophysiologic study, including atrial rates during AF, were analyzed to clarify further the determinants of the ventricular rate during AF.Methods and Results:Thirty patients without manifest preexcitation in whom AF was induced during electrophysiologic study were divided into two groups, Group I consisted of 20 patients (ages 55 ± 10 years) without a dual AV nodal pathway. Group 2 consisted of 10 patients (ages 53 ± 13 years) having a dual AV nodal pathway. The correlation coefficient between the mean RR interval during AF (mRR) and the mean intra‐atrial potential interval during AF (mff) was positive (0.05 [P<0.05] in group 1 and 0.37 [P = NS]in group 2). The correlation coefficient of the mRR against the functional refractory periods of the AV node (AVFRP) was 0.73 (P<0.001) in group 1. The correlation coefficients between mRR and the fast AV nodal pathway functional refractory periods and the slow AV nodal pathway effective refractory periods (SPERP) were 0.58 (P = NS) and 0.7 (P<0.05) in group 2, respectively. The correlation coefficients between mRR against (mff × AVFRP)1/2in group 1 and (mff × SPERP)1/2in group 2 were 0.8 (P<0.001) and 0.72 (P<0.05), respectively.Conclusions:This clinical study did not indicate an inverse relation between the atrial and ventricular rates that had been reported by the previous experimental study. The ventricular rate during AF appeared to be quantitatively related to the atrial rate via AV node function. The importance of the slow pathway in determining the ventricular rate during AF was obs

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00406.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Validation of Accessory Pathway Potentials. Four pacing maneuvers have been proposed to validate an anterograde accessory pathway potential (APP): (1) atrial pacing to induce complete block between the atrial electrogram and the APP; (2) ventricular pacing to advance the APP without altering the timing of the atrial electrogram; (3) atrial pacing to induce complete block between the APP and the ventricular electrogram; and (4) ventricular pacing to advance the ventricular electrogram without altering the timing of the APP. The purpose of this study was to assess these validation techniques by applying them to electrograms that simulated APPs but which were known to be atrial in origin. In 32 patients undergoing an electrophysiology procedure, a split atrial electrogram containing two components separated by at least 30 msec (mean 54 ± 15 msec) was recorded. Using an atrial extrastimulus tecbnique, complete block between the two components of the atrial electrogram (criterion 1) could never be induced, but complete block between the second component of the atrial electrogram and the ventricular electrogram (criterion 3) consistently was induced. Using a ventricular extrastimulus technique, the second component of the atrial electrogram consistently could be advanced by 10 to 40 msec without altering the timing of the first component (criterion 2). In addition, with ventricular pacing, the ventricular electrogram consistently was advanced without altering the timing of the two components of the atrial electrogram (criterion 4). In conclusion, among the four pacing maneuvers used to validate an anterograde APP, the only one that may be specific for an APP is the ability to induce complete block between the atrial electrogram and the APP

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Circadian Variation of HRV.Introduction:Determination of heart rate variability (HRV) is widely used for noninvasive assessment of cardiac autonomic tone. A decreased HRV is associated with an increased mortality in patients surviving an acute myocardial infarction. There are, however, only sparse data about the circadian variation of different components of HRV that may be linked to the well‐known circadian fluctuations in the occurrence of sudden death. In addition, the potential prognostic impact of circadian variations of HRV has not been examined.Methods and Results:The present study compared the circadian variation of HRV from 14 postinfarction patients who had survived at least one episode of out‐of‐hospital cardiac arrest (cardiac arrest group) with that of 14 age‐ and sex‐matched patients without a history of malignant arrhythmias after their index infarct (control group). Several time‐ and frequency‐domain measures of HRV were assessed from 24‐hour Holter recordings. Circadian variations of high‐ (HF), low‐ (LF), and total‐frequency (TF) components were determined by calculating for each parameter the hourly difference from the day's mean. The average of these differences was calculated for every hour as well as for predefined day and night periods. There was no significant difference between the two groups with regard to HRV indices that predominantly reflect vagal tone, such as SDNN (78 ± 25 vs 96 ± 24 msec), pNN50 (2.7%± 4.6% vs 4.9%± 4.2%), or HF (6.3 ± 3.0 vs 7.8 ± 3.2 msec; cardiac arrest vs control group). There was also no significant difference in the circadian variation of LF or TF between the two groups during daytime and nighttime. However, a significant difference in circadian variation of HF was found during daytime (0.02 ± 0.5 vs ‐0.6 ± 0.5 msec; P = 0.006) and nighttime (0.19 ± 0.64 vs 1.5 ± 0.75 msec; P = 0.0002). In cardiac arrest survivors, there was no difference in the mean deviation of HF between the day‐and the nighttime periods.Conclusions:These results show an almost complete abolition in circadian variation of parasympathetic tone in postinfarction patients surviving an episode of out‐of‐hospital cardiac arrest, whereas circadian variation of sympathetic tone is comparable to that of postinfarction patients without arrhythmic episodes. These findings indicate that determination of diurnal variation of HRV may add to the prognostic value of HRV with respect to identifyin

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00408.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.tb00409.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Compression Affects Defibrillation and ULV.Introduction:We determined the effects of decreasing the ventricular blood volume and altering cardiac geometry on defibrillation, the upper limit of vulnerability (ULV), and the relationship between them.Methods and Results:In six pigs, fibrillation/defibrillalion trials were performed with a left ventricular apex patch to a superior vena cava catheter electrode configuration and a biphasic waveform. Thirty trials each were performed on a compressed versus noncompressed (normal) heart. Compression was achieved using direct mechanical ventricular actuation. Dose‐response curves were constructed, and the 50% probability points (KD50) were compared for leading edge voltage (LEV), leading edge current (LEI), and total energy (TE). In another 12 pigs, triplicate defibrillation thresholds (DFTs) and ULVs were determined for each heart state. The T wave was scanned with shocks in 10‐msec steps for determining the ULV. Compression resulted in decreased ED50s for LEV (δ= 138 ± 77 V, P<0.05, mean ± SD), LEI (A = 1.57 ± 0.7 A, P<0.05), and TE (δ= 4.9 ± 3.6 J, P<0.05) compared to normal. In the second study, compression significantly reduced DFT (P<0.02) and ULV (P<0.02) for LEV, LEI, and TE compared to normal. The ULV tended to be lower than the DFT for the normal heart state (δ= 23 ± 46 V LEV; P = NS). However, the ULV was significantly greater than the DFT for the compressed heart state (A = 19 ± 25 V LEV; P<0.03).Conclusions:Shock delivery during cardiac compression improves defibrillation efficacy. Additionally, cardiac compression decreases both DFT and ULV, which supports the ULV hypothesis of defibrillation. Finally, maintaining the heart's geometric and volumetric state during ULV testing in paced rhythm and DFT testing in ventricular fibrillation moves the ULV higher than the DFT—the position predicted by the ULV hypothesis for

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00410.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Transmembrane Current Estimation.Introduction:A mathematical/computer model of cardiac tissue was used to study the estimation of transmembrane current (EIm) from extracellular potential recordings.Methods and Results:The simulatedEImof transmembrane current was compared with the simulated transmembrane current (Im), and both simulated values were compared with experimentally derivedEImobtained during sinus rhythm and ventricular fibrillation in dogs. We found that althoughEImmeasurements slightly overestimate the duration of theImwaveform, they provide a reasonable approximation ofImduring normal conduction and during decremental conduction and conduction block.Conclusions:There is a very clear linear correlation between the time spent at or below 25% of the peak inward transmembrane current (Im25), its corresponding estimate (EI25), the peak inwardImandEImand the peak ionic current, providing some evidence thatEIm25may be a suitable in vivo measure of peak ionic current.

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00411.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Tachycardia‐Induced Cardiomyopathy.Introduction:Two years after orthotopic cardiac transplantation, a 60‐year‐old man presented with unexplained congestive heart failure and an incessant atrial tachycardia.Methods and Results:Electrophysiologic evaluation identified the underlying arrhythmia as automatic atrial tachycardia with site of origin at the high anterior lateral right atrial wall. Radiofrequency catheter ablation successfully eliminated the tachycardia, which resulted in prompt improvement of this patient's congestive heart failure.Conclusion:This is the first reported case of tachycardia‐induced cardiomyopathy in a cardiac transplant patient. Radiofrequency catheter ablation can he used successfully in this patient pop

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00412.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Spontaneous Echo Contrast. Spontaneous echo contrast has never been described in association with cardiac defibrillation. In this report, we present a patient who developed dense echo contrast as a result of a shock delivered from a transvenous defibrillator system.

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00413.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AV Nodal‐His‐Purkinje Reentry.Introduction:Bundle branch reentry (BBR) typically occurs in patients with dilated cardiomyopathy and infra‐Hisian conduction system disease. The macroreentrant circuit of BBR is confined to the His‐Purkinje system (HPS) and ventricular myocardium. As such, the atrioventricular (AV) node plays no role in the tachycardia circuit.Methods and Results:In the present study, we identified a novel form of wide complex tachycardia in a patient with coronary disease and severe aortic regurgitation. The tachycardia morphology was right bundle branch block with a left superior axis. Ventriculoatrial block was present during tachycardia. An unusual feature of this rhythm was two sequential His‐bundle deflections (H and H′) for each ventricular beat of tachycardia. The H′V interval was identical to the HV interval during supraventricular rhythm. Changes in the ventricular cycle length (VV) preceded changes in the HH interval, consistent with retrograde activation of the first His‐bundle deflection. Changes in the H ‘H’interval preceded changes in the VV interval, consistent with anterograde activation of the second His‐bundle deflection. Tachycardia could be terminated with ventricular extrastimuli that did not capture the proximal HPS as well as with ventricular extrastimuli that advanced the His deflection, consistent with block in the HPS and in the AV node, respectively. Reproducible termination of the tachycardia following the first His deflection was demonstrated with adenosine, consistent with an upper pivot in the AV node.Conclusions:We have identified a new form of reentrant tachycardia in which the AV node, HPS, and ventricular myocardium each obligatorily participates in the tachycardia circuit, with the left posterior fascicle and right bundle functioning as the anterograde and retrograde limbs, respectively. Unlike BBR, however, the His bundle is activated twice as the wavefront pivots in the AV node. This model requires longitudinal dissociation at the levels of the A

ISSN:1045-3873    

DOI:10.1111/j.1540-8167.1995.tb00414.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY