心房颤动患者收缩期肺静脉血流特征的超声研究

目的 探讨心动周期变化对不同病因心房颤动(房颤)患者肺静脉收缩期血流的影响。方法 对照组20例；房颤组74例(非瓣膜病房颤16例，风湿性心脏病二尖瓣轻中度狭窄22例，二尖瓣重度狭窄36例)。应用经食管超声心动图测量肺静脉血流频谱曲线收缩早期逆向R波峰值流速(PVR)和收缩期S波峰值流速(PVS)，分析PVR和PVS与其前心电图R-R间期的关系。结果 所有房颤患者均可检出收缩早期逆向R波，二尖瓣重度狭窄组PVR明显减低，PVR与其前的R-R间期显著负相关；房颤患者的PVS减低，二尖瓣重度狭窄组尤为明显，PVS与其前的RR间期显著正相关。结论 房颤患者的PVR和PVS与其前的RR间期长短密切相关，连续观察PVR和PVS的变化，为动态评价房颤时左心房血流动力学异常提供了重要信息。     

组织多普勒成像技术评估慢性房颤患者左室壁运动

目的 应用组织多普勒成像技术（DTI）探讨慢性房颤患者的室壁运动特点,为临床诊治提供重要的信息,方法,将研究分为三组,A组为18例正常对照,B组为15例心房大小正常的房颤患者,C组为16例心房扩大的房颤患者,所有患者均无严重瓣膜病或节段性室壁运动异常,采用HP SONOS 5500超声显像仪和脉冲DTI,分别在心尖四腔心切面和胸骨旁长轴切面测定左室侧壁和后壁收缩期峰值速度（VS）,舒张期峰值速度（VE）,心电图QRS波起始至收缩期峰值速度的平均时间T1,心电图QRS波起始至舒张期峰值速度的平均时间T2,平均心率为R－R,结果 （1）A组正常人均有舒张早期和晚期两个波峰（E峰和A峰）,B组和C组房颤患者均只有一个舒张期波峰（E峰）,（2）A组与B组这间的DTI测值差异均无显著性意义（均为P＞0．05）,（3）C组左室侧的VS显著小于A组（P＜0．05）,C组左室后壁的VS,VE均显著大于A组（P均＜0．05）,C组侧壁的T1／（R－R）^1/2,Ts/(R-R)1/2显著高于A组（P均＜0．05）,C组后壁的T1／（R－R）^1/2,T2/(R-R)^1/2与A组比较差异无显著性意义（P均＞0．05）,结论 左房增大的房颤患者左室壁在长轴方向收缩活动减弱,舒张期峰值速度延迟,在短轴方向舒缝活动增强,DTI技术能精确地定量分析房颤患者的室壁活动,可成为评价房颤患者心肌舒缩功能的无创伤性新方法。     

Mitral annulus velocity in the evaluation of left ventricular diastolic function in atrial fibrillation.

This study assessed the clinical utility of mitral annulus velocity in the evaluation of left ventricular diastolic function in patients with atrial fibrillation. Atrial fibrillation is the most common sustained arrhythmia encountered in clinical practice. The clinical usefulness of conventional Doppler indexes is limited in atrial fibrillation because of the altered left atrial pressure and loss of synchronized atrial contraction. Mitral inflow and mitral annulus velocities were measured simultaneously with tau in 27 patients with nonrheumatic atrial fibrillation at the cardiac catheterization laboratory. Among deceleration time of mitral inflow, peak mitral inflow velocity (E), and peak diastolic mitral annulus velocity (E), only E correlated with tau (r = 0.51, P =.007). Prolonged tau (>/=50 ms) could be predicted by E <8 cm/s with a sensitivity of 73% (16 of 22) and a specificity of 100% (5 of 5). The E/E ratio correlated with left ventricular filling pressure (r = 0.79, P <.001). The E/E ratio of >/=11 could predict elevated left ventricular filling pressure (>/=15 mm Hg) with a sensitivity of 75% (9 of 12) and a specificity of 93% (14 of 15). Mitral annulus velocity is useful in the detection of impaired left ventricular relaxation and estimation of filling pressure even in patients with atrial fibrillation.     

Tachycardia during the valsalva maneuver: a sign of normal diastolic filling pressures.

Alteration of the loading conditions during the Valsalva maneuver is a helpful ancillary method in the noninvasive assessment of diastolic filling of the heart by Doppler echocardiography. When tachycardia is induced by the maneuver, mitral inflow velocity curves may become uninterpretable because of E velocity (the initial early diastolic velocity on the transmitral flow velocity curve) and A velocity (the velocity at atrial contraction on the transmitral flow velocity curve) wave fusion. To determine the clinical significance of the E velocity and A velocity wave fusion, our study assessed the relation between the heart rate response induced by the Valsalva maneuver and the left ventricular filling pressures measured during cardiac catheterization. In all, 77 patients performed the maneuver during continuous hemodynamic and electrocardiographic monitoring. The ratio between the baseline R-R interval and the shortest R-R interval during the maneuver was calculated. A ratio value higher than 1.1 was predictive of a pre-A pressure of less than 18 mm Hg (94% positive predictive value). Reflex tachycardia during the Valsalva maneuver and subsequent fusion of the E velocity and A velocity waves on the mitral velocity curves is a sign of normal left ventricular filling pressures.     

Single-beat determination of Doppler-derived aortic flow measurement in patients with atrial fibrillation.

The clinical assessment of left ventricular systolic function in patients with atrial fibrillation is unreliable and difficult because of beat-to-beat variation. We initially evaluated an index that is on the basis of the ratio of preceding R-R (RR1) to pre-preceding R-R (RR2) intervals (RR1/RR2) for the measurement of Doppler aortic flow (peak flow velocity [Vp] and time-velocity integral [TVI] proportional to stroke volume) in 20 patients (aged 65 +/- 9.6 years) with atrial fibrillation. We obtained each parameter for >13 cardiac cycles, and the relationship between each parameter at a given cardiac beat and the RR1/RR2 ratio were evaluated by linear regression analysis. The value of each parameter at RR1/RR2 = 1 was calculated from the equation of linear regression line and compared with measured average value over all cardiac cycles. Both parameters showed a significant positive correlation with the RR1/RR2 ratio (Vp, r = 0.98, y = 1.01x + 0.61; TVI, r = 0.99, y = 1.01x + 0.26). The calculated value of each parameter at RR1/RR2 = 1 was quite similar to the average value (Vp, 97.4 +/- 30.8 vs 95.7 +/- 29.8 cm/s; TVI, 17.7 +/- 6.8 vs 17.3 +/- 6.7 cm, respectively). In the additional 20 patients (aged 77.4 +/- 15.2 years), Doppler aortic flow parameters of a single beat with identical RR1 and RR2 intervals were compared with measured average value over all cardiac cycles and showed similar results (Vp, r = 0.99, y = 0.99x + 3.4, P <.0001, bias -0.5 cm/s; TVI, r = 0.99, y = 0.92x + 1.5, P <.0001, bias 0.1 cm). In conclusion, the Doppler aortic flow at RR1/RR2 = 1 allows the left ventricular systolic parameters to be accurately evaluated during atrial fibrillation and obviates the less reliable process of averaging multiple irregular beats.     

VDD Pacing at Short Atrioventricular Intervals Does Not Improve Cardiac Output in Patients with Dilated Heart Failure

Atrial synchronous pacing with short, nonphysiologicai atrioventricular (AV) intervals has been reported to increase cardiac output in selected patients with severe dilated heart failure. The aim of this study was to determine the acute effect of atrial synchronous pacing with short AV intervals in a consecutive series of patients with dilated heart failure. Twelve patients with a mean ejection fraction of 21 %± standard error 2.5% were studied. Pacing catheters were placed in the high right atrium and right ventricular apex and a balloon flotation catheter in the pulmonary artery for measurement of cardiac output. Simultaneous transthoracic echocardiography was performed for measurement of left ventricular filling time and mitral regurgitation. In a randomized crossover design, measurements were made during VDD pacing at programmed AV intervals of 100 and 60 msec and during a control period in sinus rhythm. Left ventricular filling time increased at AV intervals of 100 and 60 msec (mean difference 37 ± 9 and 34 ± 11 msec, respectively, both P < 0.01 compared to control). Despite increases in ventricular filling time, stroke, and cardiac index declined with short atrioventricular intervals (at an AV interval of 60 msec, stroke index fell by 2.1 ± 0.5 mL/m², P < 0.05 and cardiac index by 125 ± 45 mL/m²; P = NS). Heart rate was unchanged at both AV intervals (78 ± 4.9 at control, 78 ± 5.2 at 100 msec and 79 ± 4.9 beats/min at 60 msec; P = NS). The decrease in stroke index at an AV Interval of 60 msec was inversely related to control left ventricular filling time (r = 0.74; P = 0.01) and ejection fraction (r = 0.69; P = 0.02) and directly related to heart rate (r = 0.77; P < 0.01). The change in stroke index at an AV delay of 60 msec was also inversely related to the change in mitral regurgitation induced by pacing (r = 0.84; P = 0.01). Thus, in a group of patients with stable dilated heart failure, atrial synchronous pacing with short AV intervals did not improve cardiac output. The change in cardiac output with pacing was inversely related to baseline left ventricular function and to the change in mitral regurgitation induced by pacing.     

Beat-to-beat variability of echocardiographic measurements of left ventricular end diastolic diameter and performance.

Echocardiographic measurements of left ventricular dimensions and performance correlate well with similar data from other sources. However, little attention has been paid to the beat-to-beat variations in these parameters in individual subjects. Considerable variability in measurements of left ventricular end diastolic diameter (EDD), R-R interval, mean circumferential fiber shortening velocity (V_cf), and ejection fraction (EF) has been demonstrated in subjects in both sinus rhythm and atrial fibrillation. The coefficients of variation have varied from 2.5 to 9 percent, 2.1 to 11.2 percent, 4.4 to 11.0 percent, and 3.4 to 7.8 percent, respectively, in different individuals in sinus rhythm and from 2.0 to 7.9 percent, 2.1 to 20.7 percent, 4.9 to 30.0 percent, and 1.9 to 90.0 percent, respectively, in different patients in atrial fibrillation. Recent ultrasound studies of the interrelationships among preload, afterload, cycle length, and indices of left ventricular performance have yielded variable results. In this study the relationships between both EDD and R-R interval and echocardiographic measurements of left ventricular function were analyzed in individual subjects in both sinus rhythm and atrial fibrillation. Changes in EDD and, to a lesser extent, cycle length were shown to be accompanied by predictable changes in indices of left ventricular function. EDD correlated better than did R-R interval with V_cf and EF in 8 of 10 and 10 of 10 normal subjects, respectively, and in 9 of 11 and 7 of 11 patients in atrial fibrillation, respectively. The data suggest that preload has a more important effect than cycle length on left ventricular performance.     

Left ventricular diastolic dysfunction in end-stage dilated cardiomyopathy: simultaneous Doppler echocardiography and hemodynamic evaluation

Left ventricular diastolic dysfunction is an integral component of end-stage dilated cardiomyopathy. To better characterize this disorder we studied 15 patients undergoing catheterization during cardiac transplant screening evaluation. Pulsed-wave Doppler echocardiographic recordings of mitral inflow were obtained with simultaneous high-fidelity left ventricular and phase-corrected pulmonary capillary wedge pressures. Doppler-derived isovolumic relaxation times were within normal limits, despite a prolonged coefficient of relaxation (tau), and correlated with pulmonary capillary wedge--left ventricular crossover pressure. Peak velocity of early diastolic filling was similar to that reported in normal subjects and did not correlate with crossover pressure or tau. Early diastolic acceleration and deceleration times were shortened compared with reported normal values. Acceleration time correlated with mean negative dP/dt from mitral valve opening to left ventricular minimum pressure and with crossover pressure, and deceleration time correlated with mean dP/dt from left ventricular minimum pressure to the peak of the rapid filling wave. Late diastolic filling at atrial contraction was absent in 12 patients, all of whom had a significant early diastolic rapid filling wave and an elevated end-diastolic pressure. Despite an increase in pulmonary capillary wedge pressure during atrial contraction, the failing ventricles were unable to generate detectable forward transmitral flow. Poor cardiac pump function was shown by low left ventricular stroke volume, which correlated with the diastolic flow velocity integral. Thus, in end-stage cardiomyopathy, the transmitral flow velocity pattern is characterized by normal peak early filling velocity, low normal isovolumic relaxation time, shortened acceleration and deceleration times of early diastolic flow, decreased early flow velocity integral, and absent or decreased filling during atrial contraction. This pattern reflects interaction between elevated transmitral driving pressure and the compromised relaxation and compliance of a left ventricle functioning on an elevated pressure-volume curve.     

An Analysis of Post-Pacing R-R Intervals During Atrial Fibrillation

Bursts of ventricular pacing at cycle lengths of 350-260 ms were introduced during atrial fibrillation in nine patients, and the post-pacing R-R intervals were compared to the R-R intervals of spontaneous QRS complexes. In eight of nine patients, the mean post-pacing R-R interval was 126-199 ms longer than the mean spontaneous R-R interval (p less than 0.005). Spontaneous runs of aberrantly conducted supraventricular complexes were recorded during atrial fibrillation in one patient. The mean R-R interval following the runs of aberrantly conducted supraventricular complexes was significantly longer than the mean R-R interval of spontaneous narrow QRS complexes (p less than 0.001), but not significantly different than the mean post-pacing R-R interval. The findings of this study suggest that the R-R interval that follows a wide-complex tachycardia during atrial fibrillation is unlikely to be of value in differentiating ventricular tachycardia from aberrantly conducted supraventricular complexes. Analysis of R-R intervals that follow bursts of ventricular pacing suggests that there is likely to be considerable overlap between the R-R intervals that follow runs of ventricular tachycardia and the spontaneous R-R intervals during atrial fibrillation. Furthermore, even when the post-tachycardia R-R interval clearly exceeds the longest spontaneous R-R interval during atrial fibrillation, this is still of little diagnostic value, because a long pause may occur after either a run of ventricular tachycardia or a run of aberrantly conducted QRS complexes of supraventricular origin.     

Pressure-flow studies in man: effect of atrial systole on left ventricular function

In order to evaluate the effects of atrial contraction on left ventricular function, the pressure gradient technique was used to measure instantaneous aortic blood flow and pressure in nine patients, six having complete heart block and three having normal sinus rhythm. From these data both left ventricular stroke volume and stroke work were calculated. Ventricular rate was controlled by transvenous right ventricular pacing over a range of 50-158 beats/min. At each heart rate, beats which were not preceded by a P wave served as controls. The other beats were divided into six groups according to the duration of the preceding PR interval. The results indicated that stroke volume and stroke work were always affected similarly. In one patient the presence of a P wave did not alter the subsequent stroke volume significantly. In the other patients, beats preceded by P waves had stroke volumes greater than the controls. In general, there was no difference in stroke volume for beats preceded by a P wave having a PR interval within the range of 0.05-0.20 sec. As the PR interval lengthened beyond 0.20 sec stroke volume tended to decrease, especially at more rapid heart rates. The absolute increase in stroke volume after a beat preceded by a P wave (PR interval 0.05-0.20 sec) was quite variable among the patients. For a given patient the absolute increase in stroke volume was essentially independent of heart rate. The percentage change in stroke volume, however, was always greater as the heart rate increased.These data indicate that in most patients atrial systole is important in augmenting ventricular stroke volume and stroke work especially at high heart rates, but the magnitude of these effects are quite variable among patients.     

用多普勒超声心动图研究心房纤颤患者左室充盈的变化

本文报告用多普勒超声心动图研究特发性房颤(AF)、冠心病AF及二尖瓣狭窄(MS)并AF患者心动周期长度与左室充盈量的关系。结果表明,MS并AF心动周期与左室充盈量的相关性明显优于冠心病AF及特发性AF;初始充盈时间稳定且完成充盈时间很长。提示MS并AF的左室充盈强烈地依赖于心动周期的长度,心率代偿能力非常有限;冠心病AF的充盈速率和心率代偿能力较特发性AF稍差。     

64排螺旋CT不同R-R间期间隔法在评估左心室功能中的对比研究

目的 探讨在使用多排螺旋CT评估左心功能时,采用不同R-R间期间隔会对统计结果产生怎样的影响.方法 50例临床怀疑冠心病的患者,行64排螺旋CT冠状动脉血管造影检查.扫描结束后,将原始数据分别按照2％、5％、10％和15％的R-R间期间隔进行重建,所得数据导人工作站中,利用心功能分析软件,测量左心室舒张末期容积、收缩末期容积、每搏输出量和左室射血分数.以2％R-R间期间隔所得数据为标准,并利用统计软件,观察5％、10％和15％的R-R同期间隔重建的数据是否具有统计差异.结果 5％、10％R-R间期间隔重建的数据会在一定程度上高估左心室收缩末期容积,同时低估舒张末期容积、每搏输出量和左室射血分数,但无显著性差异,均可用于左心功能评估;15％R-R间期间隔重建所得的四种心功能参数与2％间期之间形成明显差异,具有统计学意义,不能用于心功能的评估.结论 以10％R-R间期重建评定心功能,工作量最小(仅为2％R-R间期重建1/5;5％R-R同期重建的1/2),虽然每搏输出量和左室射血分数会较实际情况略小,但无统计学差异,临床可以广泛应用.     

A new method describing cross-sectional blood flow velocity profiles in the left ventricular outflow tract of patients with atrial fibrillation with the use of high-frame rate 2-dimensional color flow imaging.

A new Doppler method was developed to evaluate the instantaneous cross-sectional velocity profile variability in the left ventricular outlet tract in patients with atrial fibrillation. Blood flow velocities acquired at a high frame rate (>90 frames/s) from a single heart cycle were used to display the velocity profile. In 9 patients, 2 heart cycles with different R-R interval lengths were recorded in color flow mode in a transthoracic apical 5-chamber and long-axis view. Raw digital ultrasound data were analyzed with an external personal computer. The data indicated a variable skew in the profiles with the highest velocities and velocity-time integral (VTI) most often located in the center and toward the septum. The maximum VTI overestimated the mean VTI by approximately 40%. No significant difference existed between the two heartbeats. Thus the VTI can be averaged from heartbeats of different R-R lengths in atrial fibrillation.     

Left Ventricular Systolic Wall Motion Velocities Along the Long and Short Axes Measured by Pulsed Tissue Doppler Imaging in Patients with Atrial Fibrillation

Pulsed tissue Doppler imaging was performed to measure systolic left ventricular (LV) posterior wall motion velocity along the long and short axes and to evaluate the relationships between the systolic variables and the maximum first derivative (peak dP/dt) of the LV pressure curve and the 2 preceding R-R intervals in 39 patients with atrial fibrillation (AF). The study group consisted of 22 patients with AF only, 17 patients with dilated or ischemic cardiomyopathy and AF, and 25 healthy control subjects in sinus rhythm. The systolic component of the LV posterior wall motion velocity was divided into the first (Sw₁ ) and second (Sw₂ ) systolic waves. The peak Sw₁ along the long axis was greater than either that along the short axis or the peak Sw₂ s along the long and short axes in the control and AF-only groups. The peak Sw₁ along the long axis was lower in the AF-only group than in the control group, and those along the short and long axes were lower in the dilated AF group than in the other groups. The peak Sw₁ almost coincided with the peak dP/dt. The peak Sw₁ along the long axis correlated closely with the peak dP/dt, and the ratio of the preceding R-R interval to the interval before the preceding (“prepreceding”) R-R interval in both AF groups, particularly in the dilated AF group, and the slopes of their relationships were steeper in the dilated AF group than in the AF-only group. The peak Sw₂ along the short axis was greater than that along the long axis in the control and AF-only groups. The peak Sw₂ along the long axis was lower in the AF-only group than in the control group, and those along the short and long axes were lower in the dilated AF group than in the other groups. The peak dP/dt was lower and the LV end-diastolic pressure was higher in the dilated AF group than in the other groups. In conclusion, peak Sw₁ along the long axis is useful for the evaluation of isovolumic myocardial LV contractility, and the interval-force relation and the Frank-Starling mechanism are important factors of beat-to-beat variability in systolic LV function in patients with AF. (J Am Soc Echocardiogr 1999;12:121-8.)     

Shorter AV Delays Provide Improved Echocardiographic Hemodynamics during Exercise in Patients Receiving Cardiac Resynchronization Therapy

Background: Although atrial ventricular (AV) intervals are often optimized at rest in patients receiving cardiac resynchronization therapy (CRT), there are limited data on the impact of exercise on optimal AV interval.
Methods: In 15 patients with CRT, AV intervals were serially programmed while patients were supine and at rest, and during exercise with heart rates that averaged 20 and 40 beats per minute above their resting rates. Echocardiographic Doppler images were acquired at each programmed AV interval and each rate. Three independent echocardiographic criteria were retrospectively used to determine each patient's optimal AV interval as a function of exercise-induced increased heart rates: the duration of left ventricular filling, stroke volume, and a clinical assessment of left ventricular function.
Results: A negative correlation between the optimal AV interval and heart rate was observed across all patients using all three independent criterion: the maximum left ventricular filling time (slope =–0.77, intercept = 151.9, r = 0.55, P < 0.001), maximum stroke volume (slope =–0.93, intercept = 183.3, r = 0.50, P = 0.002), or the subjective clinical assessment (slope =–1.06, intercept = 182.0, r = 0.72, P < 0.001). Consistent trends were observed between all three parameters for 12 out of the 15 patients.
Conclusions: These results suggest that in patients indicated for CRT, rate-adaptive functions may be useful to shorten AV intervals with increased rate, in order to maximize left ventricular filling, stroke volume, and clinical left ventricular function. Further studies are necessary to determine the clinical impact of these rate-adaptive algorithms.     

Hemodynamic Effect of Physiological Dual Chamber Pacing in a Patient with End-Stage Dilated Cardiomyopathy: A Case Report

I report a case of end-stage dilated cardiomyopathy with first-degree atrioventricular (AV) block, which had been resistant to intensive medical therapy and was eventually treated by DDD pacemaker. The optimal AV interval setting was decided using invasive right-heart catheterization and Doppler echocardiography. At a pacing rate of 92/minute, an AV interval setting of between 200 and 100 msec increased left ventricular filling and enhanced myocardial contractility. An AV interval setting of 50 msec increased the left ventricular filling further. However, this resulted in deteriorated left ventricular function. Based on these findings, the pacemaker was programmed at an optimal AV delay of 100 msec, a rate of 82-150 beats/min and a DDD mode, resulting in a good clinical course for 4 months after the therapy. Thus, it is suggested that in patients with end-stage dilated cardiomyopathy and first-degree AV block, an optimal AV delay setting using a DDD pacemaker can improve deteriorated myocardial function probably by increasing the left ventricular filling, and thus promote utility of the Frank-Starling mechanism.     

心房颤动患者冷冻消融联合左心耳封堵术后左心房结构和功能的超声心动图评价

目的应用超声心动图评价阵发性心房颤动患者冷冻消融联合左心耳封堵（CA+LAAC）术前、术后左心房结构和功能的变化。 方法选取2019年9月至2021年3月于辽宁省人民医院行“一站式”手术（CA+LAAC）的患者26例。所有患者分别于术前1周内、术后3个月行超声心动图检查评价左心房的结构和功能。行常规超声心动图检查，测量常规超声心动图参数：左心房前后径（LAD）、左心房最大容积（LAVmax）、左心房最小容积（LAVmin）、左心室射血分数（LVEF）、左心室舒张早期二尖瓣口血流速度（E峰）、二尖瓣环侧壁和房间隔侧舒张早期运动速度的平均值（e'）。并计算左心房最大容积指数（LAVImax）、左心房最小容积指数（LAVImin）、左心房射血分数（LAEF）、左心房扩张指数（LAEI）及E/e'。应用二维斑点追踪超声心动图（2D-STI）在心尖四腔心和心尖两腔心切面测量左心房应变参数：心室收缩期左心房储备期纵向峰值应变（PALSres），心室舒张早期左心房管道期纵向峰值应变（PALScond）及心室舒张晚期左心房泵功能期纵向峰值应变（PALSpump）。采用配对样本t检验比较术前与术后3个月超声心动图参数。 结果与术前相比，CA+LAAC手术后3个月，LAD、LAVmax、LAVmin、LAVImax、LAVImin减小，差异均有统计学意义（P均＜0.05），LAEF、LAEI、LVEF，PALSres、PALScond、PALSpump与术前相比均增大，差异均有统计学意义（P均＜0.05）。 结论CA+LAAC术后3个月，阵发性心房颤动患者左心房的结构和功能均得到改善和恢复，超声心动图对于评估心房颤动患者左心房结构和功能具有良好的应用价值。     

Dual Atrio-ventricular Nodal Pathways and Atrial Fibrillation

The determinants of the ventricular rate during atrial fibrillation were studied in a group of eleven patients demonstrating dual A-V nodal pathways during atrial stimulation. The shortest R-R interval and the mean ventricular cycle length during at least 1 min of pacing-induced atrial fibrillation were compared: a) to the effective and functional refractory period of the fast pathway; b) to the effective refractory period of the slow pathway determined during atrial stimulation, at two or more different basic cycle lengths of pacing; and c) to the shortest cycle length during atrial stimulation followed by 1:1 A-V conduction. A group of 8 patients not demonstrating dual A-V nodal pathway-curves during atrial stimulation was used as a control. In both groups the shortest R-R interval during atrial fibrillation was best predicted by the shortest cycle length followed by 1:1 A-V conduction during atrial stimulation. The mean ventricular cycle length during atrial fibrillation was not accurately predicted by any of the variables studied. The similar results in patients with and without dual A-V nodal pathways suggest that concealed conduction from one to another A-V nodal pathway does not play a role in determining the ventricular response during atrial fibrillation in patients with dual A-V nodal pathways.     

The Importance of the Left Atrioventricular Interval during Atrioventricular Sequential Pacing

During atrioventricular (AV) sequential pacing from the right heart, the interval between the left atrium and ventricle may vary from the programmed AV interval depending on the position of the atrial and ventricular electrodes and interatrial and interventricular conduction. The aim of this study was to determine the hemodynamic effects of altering the left AV interval while keeping the programmed AV interval constant. Four male and 17 female patients, aged 49 ± 15 years were studied. The left AV interval was measured by a catheter in the coronary sinus. Stroke volume and mitral flow were measured by simultaneous echo Doppler during AV sequential pacing from the right atrial appendage and right ventricular apex at programmed AV intervals of 100. 60, and 6 ms. The atrial catheter was then positioned on the atrial septum and the measurements repeated. With the atrial catheter in the right atrial appendage, interatrial activation time (118 ± 20 ms) was similar to interventricular activation time (125 ± 21 ms) and the left AV interval was almost identical to the programmed right AV interval. There was a significant correlation between interatrial and interventricular activation times (r = 0.8; P < 0.001). Positioning the atrial electrode on the septum decreased interatrial activation time by 39 ± 12 ms and increased the left AV interval by a similar amount. At a programmed AV interval of 60 ms, the left AV interval increased from 67 ± 15 ms to 105 ± 17 ms after the atrial catheter was repositioned from the appendage to the septum (P < 0.001). Compared to pacing from the right atrial appendage, atrial septal pacing increased mitral A wave velocity integral (2.8 ± 1.4 vs 4.4 ±1.7 cm at a programmed AV interval of 60 ms, P < 0.01), decreased E wave velocity integral (8.1 ± 2.2 vs 6.1 ± 2.4 cm, P < 0.001) but did not alter stroke volume (44.8 ± 10.6 vs 44.9 ± 10.1 mL). In contrast, a 40 ms decrease in the programmed right AV interval from 100 to 60 ms decreased stroke volume from 48.0 ± 10.0 to 44.9 ± 10.2 mL (P < 0.001). There was a strong relationship between interatrial and interventricular conduction so that patients with prolonged interatrial conduction still had equivalent left and right AV intervals during atrioventricular sequential pacing from the right atrial appendage and right ventricular apex. Positioning the atrial electrode on the septum decreases interatrial activation time and increases the left AV interval by about 40 ms but has minimal hemodynamic effect in patients without heart failure.     

Postpausal Ventricular Fibrillation Analyzed by Holter-ECG: A Case Report

A 70-year-old male patient with a myocardial infarction, 3 months previously, happened to be wearing a Holter monitor at cardiac arrest during micturition. The patient had ventricular fibrillation (VF) and was successfully resuscitated by means of defibrillation. Analysis of the Holter tape revealed atrial fibrillation and secondary ventricular premature beats (VPB), i.e., VPBs dependent upon a relatively long interval between the two preceding heartbeats. The VF was preceded by an especially long R-R interval (1.45 sec) following a run of especially short R-R intervals implying the sharpest deceleration of the ventricular rate during 1 hour Holter recording preceding the cardiac arrest. A peculiar large alteration of the T wave configuration was also found to precede the VF.