实时三维超声及斑点追踪技术评价非酒精性肝硬化患者左心房功能

目的 应用实时三维超声（RT-3DE）及二维斑点追踪技术（2D-STI）评价非酒精性肝硬化患者左心房结构及功能变化。方法 收集非酒精性肝硬化患者60例,根据肝功能分为Child-Pugh A级、B级、C级3个亚组,并收集16名健康志愿者为对照组。采用RT-3DE测量左心房径线（LAD）、最大容积（LAV_max）、收缩前容积（LAV_pre）、最小容积（LAV_min）,计算左心房整体射血分数（LATEF）、扩张指数（LAEI）、主动射血分数（LAAEF）及被动射血分数（LAPEF）。采用STI测量左心房整体收缩期、舒张早期和舒张晚期平均峰值应变（mSs、mSe、mSa）及应变率（mSRs、mSRe、mSRa）,计算左心房僵硬度（LASt）。结果 与对照组比较,Child-Pugh A级、B级、C级亚组LAD、LAV_max、LAV_pre、LAV_min及LASt增高（P均<0.05）;Child-Pugh B级、C级亚组LAPEF、mSe、mSRe减低（P均<0.05）;Child-Pugh A级、B级亚组LATEF、LAEI、mSs、mSRs、LAAEF、mSa、mSRa增高（P均<0.05）,C级亚组LATEF、LAEI、LAAEF增高（P均<0.05）,mSs、mSRs减低（P均<0.05）。LASt与LAEI、mSs、mSRs、LAPEF、mSe、mSRe呈负相关,与LATEF、LAAEF、LAV_max、LAV_pre、LAV_min、mSa、mSRa无明显相关。结论 非酒精性肝硬化患者左心房随肝功能恶化而出现不同程度功能障碍,RT-3DE和2D-ST技术可早期发现及评估左心房结构和功能异常。     

实时三维超声联合二维斑点追踪成像评价原发性高血压患者左心房功能

目的 采用实时三维超声（RT-3DE）及二维斑点追踪成像（2D-STI）评估原发性高血压患者左心房形态和功能。方法 收集70例原发性高血压患者,根据左心房内径指数将其分为左心房无扩大（NLAE）组（n=35）和左心房扩大（LAE）组（n=35）,并收集35名健康志愿者为对照组。应用RT-3DE检测最大、最小和收缩前左心房容积（LAV_max、LAV_min、LAV_pre）,计算左心房每搏输出量（LASV）、总射血分数（LAEF）、主动射血分数（LAaEF）和被动排空分数（LApEF）。采用2D-STI计算左心房壁的收缩期、舒张早期和晚期平均峰值应变率（mSRs、mSRe、mSRa）。比较3组间上述参数的差异,分析2D-STI与RT-3DE测量参数的相关性。结果 与对照组比较,NLAE组LAaEF、mSRa增高,LApEF、mSRs、mSRe降低（P均<0.05）;与NLAE组比较,LAE组LAV_max、LAV_pre、LAV_min、LASV、LAaEF、mSRa增高,LAEF、LApEF、mSRs、mSRe降低（P均<0.05）。NLAE组和LAE组中,mSRs与LAEF（r=0.70、0.77）、mSRe与LApEF（r=0.80、0.82）、mSRa与LAaEF（r=0.87、0.89）呈明显正相关（P均<0.01）。结论 原发性高血压患者左心房在重构前即已发生功能改变;RT-3DE和2D-STI技术可用于评价原发性高血压患者左心房结构和功能。     

Interatrial septum pacing decreases atrial dyssynchrony on strain rate imaging compared with right atrial appendage pacing

Background: Interatrial septum pacing (IAS‐P) decreases atrial conduction delay compared with right atrial appendage pacing (RAA‐P). We evaluate the atrial contraction with strain rate of tissue Doppler imaging (TDI) during sinus activation or with IAS‐P or RAA‐P. Methods: Fifty‐two patients with permanent pacemaker for sinus node disease were enrolled in the study. Twenty‐three subjects were with IAS‐P and 29 with RAA‐P. The time from end‐diastole to peak end‐diastolic strain rate was measured and corrected with RR interval on electrocardiogram. It was defined as the time from end‐diastole to peak end‐diastolic strain rate (TSRc), and the balance between maximum and minimum TSRc at three sites (ΔTSRc) was compared during sinus activation and with pacing rhythm in each group. Results: There were no significant differences observed in general characteristics and standard echocardiographic parameters except the duration of pacing P wave between the two groups. The duration was significantly shorter in the IAS‐P group compared with the RAA‐P group (95 ± 34 vs 138 ± 41; P = 0.001). TSRc was significantly different between sinus activation and pacing rhythm (36.3 ± 35.7 vs 61.6 ± 36.3; P = 0.003) in the RAA‐P group, whereas no significant differences were observed in the IAS‐P group (25.4 ± 12.1 vs 27.7 ± 14.7; NS). During the follow‐up (mean 2.4 ± 0.7 years), the incidence of paroxysmal atrial fibrillation (AF) conversion to permanent AF was not significantly different between the two groups. Conclusions: IAS‐P decreased the contraction delay on atrial TDI compared to RAA‐P; however, it did not contribute to the reduction of AF incidence in the present study. (PACE 2011; 34:370–376)     

二维斑点追踪成像技术评价阵发性房颤患者射频消融术前后左心房功能

目的 探讨二维斑点追踪成像技术（2D-STI）评价经导管射频消融术（RFCA）前后阵发性房颤（AF）患者左心房功能的变化。方法 对30例因阵发性AF接受RFCA治疗患者（AF组）分别于术前、术后3天、1个月及3个月行超声心动图检查,另选30名健康志愿者为对照组。常规测量左心房前后径（LAD）、二尖瓣舒张早期血流峰值流速（E峰）、二尖瓣环舒张早期速度（Em）,计算E/Em;测量左心房收缩前容积（LAV_P）、最小容积（LAV_min）和最大容积（LAV_max）,计算左心房主动排空率（LAAEF）、左心房被动排空率（LAPEF）;以2D-STI获得左心房各节段应变及应变率曲线,测量并计算左心室收缩期及左心室舒张早、晚期左心房平均峰值应变（mSs、mSe、mSa）、应变率（mSRs、mSRe、mSRa）以及左心房僵硬度（LASt）。比较RFCA前后阵发性AF患者左心房结构和功能的变化。结果 与对照组比较,AF组术前LAD、LAV_p、LAV_min、LAV_max、E/Em、LASt增大,LAPEF、LAAEF、E、Em、mSs、mSe、mSa、mSRs、mSRe、mSRa减低（P均<0.05）。AF患者RFCA术前及术后3天、1个月、3个月左心房应变参数及LASt总体差异均有统计学意义（P均<0.05）,术后3天mSs、mSe、mSa、mSRs、mSRe、mSRa较术前减低,LASt较术前增高（P均<0.05）;术后3个月mSs、mSe、mSa、mSRs、mSRe、mSRa较术前增高,LASt较术前减低（P均<0.05）;术后1个月、3个月mSs、mSe、mSa、mSRs、mSRe、mSRa较术后3天增高,LASt较术后3天减低（P均<0.05）;术后3个月mSRs较术后1个月增高（P<0.05）。结论 阵发性AF患者RFCA术后3天左心房功能下降,术后1个月辅泵功能有所改善,术后3个月左心房储备、辅泵、管道功能均明显改善。     

Impact of Right Ventricular Pacing Sites on Exercise Capacity during Ventricular Rate Regularization in Patients with Permanent Atrial Fibrillation

Background: The deleterious effects of right ventricular apical (RVA) pacing may offset the potential benefit of ventricular rate (VR) regularization and rate adaptation during an exercise in patient's atrial fibrillation (AF). Methods: We studied 30 patients with permanent AF and symptomatic bradycardia who receive pacemaker implantation with RVA (n = 15) or right ventricular septal (RVS, n = 15) pacing. All the patients underwent an acute cardiopulmonary exercise testing using VVI‐mode (VVI‐OFF) and VVI‐mode with VR regularization (VRR) algorithm on (VVI‐ON). Results: There were no significant differences in the baseline characteristics between the two groups, except pacing QRS duration was significantly shorter during RVS pacing than RVA pacing (138.9 ± 5 vs 158.4 ± 6.1 ms, P = 0.035). Overall, VVI‐ON mode increased the peak exercise VR, exercise time, metabolic equivalents (METs), and peak oxygen consumption (VO₂max), and decreased the VR variability compared with VVI‐OFF mode during exercise (P < 0.05), suggesting that VRR pacing improved exercise capacity during exercise. However, further analysis on the impact of VRR pacing with different pacing sites revealed that only patients with RVS pacing but not patients with RVA pacing had significant increased exercise time, METs, and VO₂max during VVI‐ON compared with VVI‐OFF, despite similar changes in peaked exercise VR and VR variability. Conclusion: In patients with permanent AF, VRR pacing at RVS, but not at RVA, improved exercise capacity during exercise.     

左心房容积追踪技术评估缩窄性心包炎患者左心房容积和功能变化

目的 观察左心房容积追踪技术（LAVT）评估手术治疗前后缩窄性心包炎（CP）患者左心房容积和功能变化的临床价值。方法 对20例CP患者及20名健康志愿者（对照组），于心包切除术治疗CP术前（术前组）和术后（术后组）采集心尖四腔及两腔动态超声图像，以LAVT技术获得左心房容积参数，包括最大容积（LAV_max）、预收缩容积（LAV_pre）及最小容积（LAV_min），经体表面积校正得到容积指数（LAVI_max、LAVI_pre、LAVI_min）；以LAVT技术获得左心房容积变化速率参数，包括收缩期峰值充盈速率（dv/dtS）、舒张早期峰值排空速率（dv/dtE）及舒张晚期峰值排空速率（dv/dtA）。根据所得参数计算左心房总射血分数（LATEF）、被动射血分数（LAPEF）和主动射血分数（LAAEF），并进行分析。结果 3组LAV_min差异有统计学意义（P<0.05），术前组和术后组LAV_min均大于对照组（P均<0.05），术前组大于术后组（P<0.05）。3组LATEF、LAPEF、LAAEF、dv/dtS、dv/dtE和dv/dtA差异均有统计学意义（P均<0.05），术前组和术后组均小于对照组（P均<0.05），术前组小于术后组（P均<0.05）。结论 利用LAVT可评估心包切除术前后CP患者左心房容积和功能变化。     

Quantification of left atrial volume and phasic function using cardiovascular magnetic resonance imaging—comparison of biplane area-length method and Simpson's method

Left atrial (LA) enlargement and dysfunction are markers of chronic diastolic dysfunction and an important predictor of adverse cardiovascular and cerebrovascular outcomes. Accordingly, accurate quantification of left atrial volume (LAV) and function is needed. In routine clinical cardiovascular magnetic resonance (CMR) imaging the biplane area-length method (Bi-ALM) is frequently applied due to time-saving image acquisition and analysis. However, given the varying anatomy of the LA we hypothesized that the diagnostic accuracy of the Bi-ALM is not sufficient and that results would be different from a precise volumetric assessment of transversal multi-slice cine images using Simpson's method. Thirty one patients of the FIND-AF_RANDOMISED-study with status post acute cerebral ischemia (mean age 70.5?±?6.2 years) received CMR imaging at 3T. The study protocol included cine SSFP sequences in standard 2- and 4 CV and a stack of contiguous slices in transversal orientation. Total, passive and active LA emptying fractions were calculated from LA maximal volume, minimal volume and volume prior to atrial contraction. Intra- and inter-observer variability was assessed in ten patients. Significant differences were found for LA volume and phasic function. The Bi-ALM significantly underestimated LA volume and overestimated LA function in comparison to Simpson's method (Bi-ALM vs. Simpson's method: LAV_max: 80.18 vs. 98.80 ml; LAV_pre?ac: 61.09 vs. 80.41 ml; LAV_min: 36.85 vs. 52.66 ml; LAEF_Total: 55.17 vs. 47.85%; LAEF_Passive: 23.96 vs. 19.15%; LAEF_Booster: 40.87 vs. 35.64%). LA volumetric and functional parameters were reproducible on an intra- and inter-observer levels for both methods. Intra-observer agreement for LA function was better for Simpson's method (Bi-ALM vs. Simpson's method; ICC LAEF_Total: 0.84 vs. 0.96; ICC LAEF_Passive: 0.74 vs. 0.92; ICC LAEF_Booster: 0.86 vs. 0.89). The Bi-ALM is based on geometric assumptions that do not reflect the complex individual LA geometry. The assessment of transversal slices covering the left atrium with Simpson's method is feasible and might be more suitable for an accurate quantification of LA volume and phasic function.     

Stimulation rate and the optimal interventricular interval during cardiac resynchronization therapy in patients with chronic atrial fibrillation

Background: Optimization of cardiac resynchronization therapy (CRT) with respect to the interventricular (V‐V) interval is mainly limited to pacing at a resting heart rate. We studied the effect of higher stimulation rates with univentricular and biventricular (BiV) pacing modes including the effect of the V‐V interval optimization. Methods: In 36 patients with heart failure and chronic atrial fibrillation (AF), the effects of right ventricular (RV), left ventricular (LV), simultaneous BiV, and optimized sequential BiV (BiVopt) pacing were measured. The effect of the pacing mode and the optimal V‐V interval was determined at stimulation rates of 70, 90, and 110 ppm using invasive measurement of the maximum rate of left ventricular pressure rise (LV dP/dt_max). Results: The average LV dP/dt _max for all pacing modalities at stimulation rates of 70, 90, and 110 ppm was 781 ± 176, 833 ± 197, and 884 ± 223 mmHg/s for RV pacing; 893 ± 178, 942 ± 186, and 981 ± 194 mmHg/s for LV pacing; 904 ± 179, 973 ± 187, and 1052 ± 206 mmHg/s for simultaneous BiV pacing; and 941 ± 186, 1010 ± 198, and 1081 ± 206 mmHg/s for BiVopt pacing, respectively. In BiVopt pacing, the corresponding optimal V‐V interval decreased from 34 ± 29, 28 ± 28, and 21 ± 27 ms at stimulation rates of 70, 90, and 110 ppm, respectively . In two individuals, LV dP/dt_max decreased when the pacing rate was increased from 90 to 110 ppm. Conclusion: In patients with AF and heart failure, LV dP/dt_max increases for all pacing modalities at increasing stimulation rates in most, but not all, patients. The rise in LV dP/dt_max with increasing stimulation rates is higher in biventricular (BiV and BiVopt) than in univentricular (LV and RV) pacing. The optimal V‐V interval at sequential biventricular pacing decreases with increasing stimulation rates.     

Effects of pacing rates on global and regional myocardial blood flow

Background: Information is scarce on the effects of right ventricular apical (RVA) pacing on regional and global myocardial blood flow (MBF). The purpose of this study was to assess the relationship between pacing rate and both regional and global MBF. Methods: Four patients with exclusive atrial pacing and six patients with exclusive RVA pacing underwent three consecutive H₂¹⁵O positron emission tomography scans at 60, 90, and 130 pulses per minute (ppm). For each pacing rate, regional and global MBF was determined. In all patients, the left ventricular (LV) function was normal. Results: By varying the atrial pacing rate from 60 to 130 ppm, the mean global MBF increased from 0.94 to 1.40 mL/g/min, whereas the mean septal to lateral MBF ratio decreased from 1.09 to 0.83. In ventricular‐paced patients at corresponding rates, the mean global MBF also increased from 1.07 to 1.52 mL/g/min but here the mean septal to lateral MBF ratio increased from 0.83 to 1.0. Conclusions: During both acute atrial and RVA pacing, regional and global MBF increases with higher pacing rates. However, the septal to lateral MBF ratio decreases with atrial pacing and increases with RVA pacing in patients with normal LV function. In RVA pacing, these different rate‐dependent effects on regional MBF can be considered as a favorable factor that helps to understand why in some long‐term paced patients, LV function is preserved. (PACE 2011; 34:587–592)     

Altered left ventricular contraction pattern during right ventricular pacing: assessment using real-time three-dimensional echocardiography

Background: Chronic right ventricular apical (RVA) pacing has been associated with increased risk of heart failure and adverse outcome. The acute effects of RVA pacing on three‐dimensional (3D) ventricular function and mechanical dyssynchrony are not well known. We performed a real‐time 3D echocardiographic (RT3DE) study to assess global and regional left ventricular function during RVA pacing. Methods: Twenty‐six patients with implanted cardiac devices and normal intrinsic atrioventricular conduction were included in the study. RT3DE was performed during intrinsic sinus rhythm and during RVA pacing. Quantification of global and regional left ventricular function was performed offline by time‐volume analysis of 16 myocardial segments. Time to reach minimum regional volume was calculated for each segment as a percentage of the cardiac cycle. The systolic dyssynchrony index (SDI) was defined as the standard deviation of these time periods. Longitudinal function was assessed by time‐volume analysis of apical, midventricular, and basal segments. Results: During RVA pacing, a reversed apical‐to‐basal longitudinal contraction sequence was observed in 58% of all patients. RVA pacing was associated with increased left ventricular (LV) dyssynchrony (SDI increase from 4.4 ± 2.2% to 6.3 ± 2.4%, P = 0.001) and reduced LV ejection fraction (decrease from 53 ± 13% to 47 ± 14%, P = 0.05). Conclusion: RT3DE assessment of LV function provides evidence that pacing from the RVA results in acute alterations in LV contraction sequence and increased LV dyssynchrony. Further studies are warranted to assess the potential of RT3DE to identify patients who might be at increased risk of pacing‐induced heart failure or who might benefit from alternate‐site or multisite pacing. (PACE 2011; 76–81)     

左心房容积追踪技术及实时三维超声评价肥厚性心肌病患者左心房功能

目的运用左心房容积追踪(LAVT)技术和实时三维超声心动图(RT-3DE)评价肥厚性心肌病(HCM)患者左心房功能。方法选取HCM患者31例(HCM组)和健康志愿者27名(对照组),运用LAVT技术获取左心房排空率曲线,测量收缩期左心房排空率峰值(dv/dts)、舒张早期左心房排空率峰值(dv/dtE)、舒张晚期左心房排空率峰值(dv/dtA);以RT-3DE测量左心房最大容积(LAVmax)、左心房最小容积(LAVmin)、左心房收缩前容积(LAVp)、左心房被动射血分数(LAPEF)、左心房主动射血分数(LAAEF),并对以上各参数进行对比分析。结果与对照组相比,HCM组dv/dts、dv/dtA增大而dv/dtE减小(P均<0.05),LAVmax、LAAEF增大而LAPEF减小(P均<0.05)。结论联合应用LAVT和RT-3DE可从不同角度综合评价HCM患者左心房功能。     

多层螺旋CT评价不同类型心房颤动患者左心房和左心耳功能

目的 采用多层螺旋CT定量测量心房颤动（AF）患者左心房、左心耳功能,探讨不同类型AF患者之间左心房及左心耳功能的差异。方法 收集71例AF患者,包括阵发性房颤（PAF）40例（PAF组）,持续性房颤（PeAF）31例（PeAF组）。应用心功能后处理软件测量AF患者左心耳最大容积（LAAV_max）、左心耳最小容积（LAAV_min）、左心房最大容积（LAV_max）和左心房最小容积（LAV_min）,并计算左心耳射血分数（LAAEF）、左心耳射血量（LAAEV）、左心房射血分数（LAEF）、左心房射血量（LAEV）。结果 PeAF组LAAEF、LAEF、LAEV均小于PAF组（P均<0.01）,LAAV_max、LAAV_min、LAV_max、LAV_min均大于PAF组（P均<0.05）。2组间LAAEV差异无统计学意义（P=0.23）。AF患者LAAEF与LAEF呈正相关（r_s=0.57,P<0.01）,与AF持续时间呈负相关（r_s=－0.26,P=0.03）。结论 应用多层螺旋CT可以客观评价左心房和左心耳功能,对认识不同分型AF患者左心耳和左心房功能改变有重要临床意义。     

Optimal site for atrial lead implantation in myotonic dystrophy patients: the role of Bachmann's Bundle stimulation

Aim: The aim of this study was to identify the optimal site for atrial lead implantation in myotonic dystrophy type 1 (MD1) patients. Methods: The atrial pacing lead was positioned in the high‐lateral right atrial wall (site A), then in the right atrial appendage (site B), and finally on the interatrial septum (site C) in 22 patients. Pacing and sensing thresholds were obtained for all sites. The lead was repositioned and fixed at the optimal site, defined as the location with the lowest pacing and the highest sensing thresholds. Results: Mean pacing thresholds were 1.46 ± 0.32 V at site A, 1.45 ± 0.33 V at site B, and 0.84 ± 0.24 V at site C. P‐wave amplitude was 1.52 ± 0.45 mV at site A, 1.52 ± 0.49 mV at site B, and 2.60 ± 0.48 mV at site C. Atrial lead was implanted at site C in all patients without complications. Conclusions: Interatrial septum in the region of Bachmann's Bundle seems to be the optimal site for atrial lead implantation in MD1 patients.     

Effect of pacing-induced ventricular dyssynchrony on right ventricular function

Background: Asynchronous electrical activation induced by right ventricular (RV) pacing can cause several abnormalities in left ventricular (LV) function. However, the effect of ventricular pacing on RV function has not been well established. We evaluated RV function in patients undergoing long‐term RV pacing. Methods: Eighty‐five patients and 24 healthy controls were included. After pacemaker implantation, conventional echocardiography and strain imaging were used to analyze RV function. Strain imaging measurements included peak systolic strain and strain rate. LV function and ventricular dyssynchrony by tissue Doppler imaging (TDI) were assessed. Intra‐ and interobserver variabilities of TDI parameters were tested on 15 randomly selected cases. Results: All patients were in New York Heart Association functional class I or II and percentage of ventricular pacing was 96 ± 4%. RV apical induced interventricular dyssynchrony in 49 patients (60%). LV dyssynchrony was found in 51 patients (60%), when the parameter examined was the standard deviation of the time to peak myocardial systolic velocity of all 12 segments greater than 34 ms. Likewise, septal‐to‐lateral delay ≥65 ms was found in 31 patients (36%). All echocardiographic indexes of RV function were similar between patients and controls (strain: ?22.8 ± 5.8% vs ?22.1 ± 5.6%, P = 0.630; strain rate: ?1.47 ± 0.91 s^?1 vs ?1.42 ± 0.39 s^?1, P = 0.702). Intra‐ and interobserver variability for RV strain was 3.1% and 5.3%, and strain rate was 1.3% and 2.1%, respectively. Conclusions: In patients with standard pacing indications, RV apical pacing did not seem to affect RV systolic function, despite induction of electromechanical dyssynchrony. (PACE 2011; 34:155–162)     

Site‐Specific Differences in Latency Intervals during Biventricular Pacing: Impact on Paced QRS Morphology and Echo‐Optimized V‐V Interval

Objective: To investigate differences in latency intervals during right ventricular (RV) pacing and left ventricular (LV) pacing from the (postero‐)lateral cardiac vein in cardiac resynchronization therapy (CRT) patients and their relationship to echo‐optimized interventricular (V‐V) intervals and paced QRS morphology. Methods: We recorded digital 12‐lead electrocardiograms in 40 CRT patients during RV, LV, and biventricular pacing at three output settings. Stimulus‐to‐earliest QRS deflection (latency) intervals were measured in all leads. Echocardiographic atrioventricular (AV) and V‐V optimization was performed using aortic velocity time integrals. Results: Latency intervals were longer during LV (34 ± 17, 29 ± 15, 28 ± 15 ms) versus RV apical pacing (17 ± 8, 15 ± 8, 13 ± 7 ms) for threshold, threshold ×3, and maximal output, respectively (P < 0.001), and shortened with increased stimulus strength (P < 0.05). The echo‐optimized V‐V interval was 58 ± 31 ms in five of 40 (12%) patients with LV latency ≥ 40 ms compared to 29 ± 20 ms in 35 patients with LV latency < 40 ms (P < 0.01). During simultaneous biventricular pacing, four of five (80%) patients with LV latency ≥ 40 ms exhibited a left bundle branch block (LBBB) pattern in lead V₁ compared to three of 35 (9%) patients with LV latency < 40 ms (P < 0.01). After optimization, all five patients with LV latency ≥ 40 ms registered a dominant R wave in lead V₁. Conclusions: LV pacing from the lateral cardiac vein is associated with longer latency intervals than endocardial RV pacing. LV latency causes delayed LV activation and requires V‐V interval adjustment to improve hemodynamic response to CRT. Patients with LV latency ≥ 40 ms most often display an LBBB pattern in lead V₁ during simultaneous biventricular pacing, but a right bundle branch block after V‐V interval optimization. (PACE 2010; 1382–1391)     

Automatic Atrial Threshold Measurement and Adjustment in Pediatric Patients

Background: Automatic threshold measurement and output adjustment are used as default settings in modern pacemakers. The purpose of the study was to assess Atrial Capture Management (ACM) of Medtronic pacemakers in pediatric patients. Methods: Forty children were enrolled in two centers. Median age was 9.8 years (range 0.8–17.5 years). Half had undergone surgery for congenital heart defects; 45% of patients had an epicardial atrial lead. The pacing indication was atrioventricular block in 82% of patients and sinus node disease in 18%. Manually determined atrial thresholds and ACM measurements were compared. Results: ACM measurements were within the expected variation in 37/40 (93%) of the patients. In one patient the threshold was 0.625‐V lower manually than with ACM. One patient had too high an intrinsic atrial rate for ACM to be able to measure threshold. The mean threshold at 0.4 ms was 0.69 ± 0.32 V manually and 0.68 ± 0.35 V with ACM (two‐tailed paired t‐test, P = 0.52) in all patients. The mean difference was 0.012 V (95% confidence interval: ?0.027, 0.053). The mean endocardial threshold was 0.70 ± 0.36 V manually and 0.69 ± 0.38 V with ACM; epicardial threshold was 0.67 ± 0.27 V manually and 0.68 ± 0.32 V with ACM. The difference between the measurements was 0.012 V for endocardial and 0.014 V for epicardial leads. No atrial arrhythmias due to ACM measurements were observed. Conclusions: ACM measures atrial thresholds reliably in pediatric patients with both endocardial and epicardial leads, allowing its use in both. Constant high intrinsic atrial rate may prevent automatic threshold measurement in young children. (PACE 2010; 33:309–313)     

Anatomic and electrophysiological differences between chronic and paroxysmal forms of common atrial flutter and comparison with controls:

Whether chronic typical atrial flutter differs from paroxysmal atrial flutter regarding electrophysiological properties of reentry pathways and cardiac function remains unknown. If so, can remodeling due to long duration of persistently rapid atrial or ventricular rates explain these changes? The aim of the study was to compare RA local conduction velocities and heart function parameters between three groups: (1) chronic atrial flutter, (2) paroxysmal atrial flutter, and (3) controls. The study evaluated 52 patients undergoing radiofrequency ablation for typical atrial flutter. There were 35 patients with chronic atrial flutter (62.7 ± 14 years) and 17 patients with paroxysmal atrial flutter (62.7 ± 10 years). Underlying structural heart disease was present in 20 (57%) of 35 chronic atrial flutter patients and in 7 (41%) of 17 paroxysmal atrial flutter patients (P = 0.1). Chronic atrial flutter duration was 10.9 ± 17 months and paroxysmal atrial flutter duration was 8.5 ± 10 (P = 0.06). RA conduction velocity measurements were carried out before ablation during sinus rhythm under pacing (600‐ms cycle length) with a 12‐pole steerable catheter positioned in the high lateral RA (poles 11‐12 [H6]), mid‐lateral RA (poles 9‐10 [H5]), and along the inferior vena caval tricuspid isthmus (poles 7‐8 [H4]; 5‐6 [H3]; 3‐4 [H2]) with its distal electrode pair at the coronary sinus origin (pole 1‐2 [H1]). Counter‐clockwise RA conduction velocities were assessed from H6 to H1 and clockwise RA conduction velocities from H1 to H6. After successful ablation, RA and LA areas, LV volumes, LVEF, inferior vena caval tricuspid annulus, and coronary sinus tricuspid annulus (septal isthmus) lengths were measured by two‐dimensional echocardiography. The control group included 12 patients without structural heart disease, referred for electrophysiological evaluation of AVN reentry. Counter‐clockwise RA conduction velocities at the inferior vena caval tricuspid isthmus were lower in chronic atrial flutter than in paroxysmal atrial flutter (H4, 1.19 ± 0.4 vs 1.89 ± 1 m/s, P = 0.0051; H3, 1.14 ± 0.4 vs 1.6 ± 0.7 m/s, P = 0.0015; H2, 1.16 ± 0.4 vs 1.53 ± 0.5 m/s, P < 0.0056 and H1, 1.2 ± 0.4 vs 1.5 ± 0.4 m/s, P = 0.03, respectively). Counter‐clockwise RA conduction velocities were identical at the high and mid‐lateral RA. Counter‐clockwise caval isthmus RA conduction velocities from H3 to H1 were significantly different between chronic atrial flutter and controls (H3, 1.14 ± 0.4 vs 1.7 ± 0.3 m/s, P = 0.0014; H2, 1.16 ± 0.4 vs 1.83 ± 0.4 m/s, P < 0.0001 and H1, 1.2 ± 0.4 vs 1.94 ± 0.4 m/s, P < 0.0001, respectively). A difference was found regarding clockwise isthmus RA conduction velocities between the two groups of atrial flutter and controls but not between chronic atrial flutter and paroxysmal atrial flutter. Respectively, chronic atrial flutter had greater RA and LA areas (24.5 ± 5 vs 13 ± 2 cm ² ; P < 0.0001 and 23 ± 5 vs 16 ± 3 cm ² , P < 0.0001), LV end‐systolic and end‐diastolic volumes (50 ± 25 vs 32 ± 13 cm ³ , P = 0.0084 and 112 ± 40 vs 85 ± 25 cm ³ , P = 0.01), septal isthmus length (21 ± 3 vs 13 ± 2 mm, P < 0.0001), and inferior vena caval tricuspid isthmus length (39 ± 6 vs 23 ± 5 mm; P < 0.0001). Chronic common atrial flutter is characterized by more prolonged counter‐clockwise conduction times and larger anatomic conduction pathways than the paroxysmal form, the causal relationship between electrophysiological and anatomic characteristics remains to be demonstrated.     

Performance Evaluation of a Right Atrial Automatic Capture Verification Algorithm using Two Different Sensing Configurations

Background: This acute data collection study evaluated the performance of a right atrial (RA) automatic capture verification (ACV) algorithm based on evoked response sensing from two electrode configurations during independent unipolar pacing. Methods: RA automatic threshold tests were conducted. Evoked response signals were simultaneously recorded between the RA_Ring electrode and an empty pacemaker housing electrode (RA_Ring→Can) and the electrically isolated Indifferent header electrode (RA_Ring→Ind). The atrial evoked response (AER) and the performance of the ACV algorithm were evaluated off‐line using each sensing configuration. An accurate threshold measurement was defined as within 0.2 V of the unipolar threshold measured manually. Threshold tests were designed to fail for small AER (< 0.35 mV) or insufficient signal‐to‐artifact ratio (SAR < 2). Manual threshold measurements were obtained during RA unipolar and bipolar pacing and compared across device indications. Results: Data were collected from 38 patients with RA bipolar leads from four manufacturers. AER signals were analyzed from 34 patients who were indicated for a pacemaker (five), implantable cardioverter‐defibrillator (11), or cardiac resynchronization therapy pacemaker (six) or defibrillator (12). The minimum AER amplitude was larger (P < 0.0001) when recorded from RA_Ring→Can (1.6±0.9 mV) than from RA_Ring→Ind (1.3±0.8 mV). The algorithm successfully measured the pacing threshold in 96.8% and 91.0% of tests for RA_Ring→Can and RA_Ring→Ind, respectively. No statistical difference between the unipolar and bipolar pacing threshold was observed. Conclusions: The RA_Ring→Can AER sensing configuration may provide a means of implementing an independent pacing/sensing method for ACV in the RA. RA bipolar pacing therapy based on measured RA unipolar pacing thresholds may be feasible.     

Insights into the Effects of Contraction Dyssynchrony on Global Left Ventricular Mechano-Energetic Function

Background: The effects of dyssynchrony on global left ventricular (LV) mechanics have been well documented; however, its impact on LV energetics has received less attention. Objective: To assess the effects of LV contraction dyssynchrony on global LV mechano‐energetic function in a pacing‐induced acute model of dyssynchrony. Methods: Using blood‐perfused isolated rabbit heart preparations (n = 11), LV pressure, coronary flow, and arteriovenous oxygen content difference were recorded for isovolumic contractions under right atrial (RA) pacing (control) and simultaneous RA and right ventricular outflow tract (RVOT) pacing (dyssynchrony). LV mechanical function was quantified by the end‐systolic pressure‐volume relationship (ESPVR). Myocardial oxygen consumption‐pressure‐volume area (MVO₂‐PVA) relationship quantified LV energetic function. Internal PVA for MVO_{2 RVOT} was calculated based on the MVO₂‐PVA relationship for RA pacing. Thus, lost PVA (internal PVA–PVA_RVOT) represents the mechanical energy not observable at the global level. Results: Compared to RA pacing, RVOT pacing depressed LV mechanics as indicated by a rightward shift of ESPVR (i.e., increase in V_d from 0.58 ± 0.10 to 0.67 ± 0.10 mL, P < 0.05). Despite depressed mechanics, RVOT pacing was associated with greater MVO₂ such that the MVO₂‐PVA relationship intercept was markedly increased from 0.025 ± 0.003 to 0.029 ± 0.003 mL?O₂/beat/100gLV (P < 0.05). Excess MVO₂ (i.e., MVO_{2 RVOT}– MVO_{2 RA}) significantly correlated with lost PVA (R²= 0.54, P < 0.001). Conclusion: A potential mechanism explaining the observed increase in MVO₂ with dyssynchrony may be that the measured PVA at the global level underestimates the internal PVA at the cellular level, which is likely to be the true determinant of MVO₂.     

Left atrial functional reservoir: predictive value for outcome of catheter ablation in paroxysmal atrial fibrillation

Left arial (LA) function, defined according to conduit, reservoir and booster functions, is closely linked to left ventricular (LV) mechanics, particularly during diastole. Right ventricular pacing (RVP) is thought to impair LA diastolic restoring forces through alteration of ventricular activation. The aim of this study was to determine whether the LA functional reservoir estimated as the change in mean LA ejection fraction (EF) immediately after RVP, and for the second and for the third beats after RVP, predicts clinical outcome in patients with paroxysmal atrial fibrillation (AF) who have undergone catheter ablation (CA). Data from 155 patients with paroxysmal AF (56.0 ± 10.6 years, M:F = 114:41) were analyzed. All patients underwent LA angiography during RVP. LA EFs were measured at the immediate first (LA EF₁), second (LA EF₂) and third beats (LA EF₃) after RVP, using a right anterior oblique 30° view. During follow-up, AF recurred in 35 patients (22.6 %). Mean LA EF₁ was 37.9 ± .8 % in the AF recurrence group and 48.0 ± 8.6 % in the non-recurrence group (P < 0.001). Mean LA EF₂ and LA EF₃ were also lower in the AF recurrence group than in the non-recurrence group (P < 0.001, respectively). Mean percent changes from LA EF₂ to LA EF₃ were ?0.4 ± 3.4 in the AF recurrence group and 5.2 ± 4.9 in the non-recurrence group (P = 0.041). The change in mean EF from LA EF₁ to LA EF₃ in the non-recurrence group was significantly greater than in the recurrence group (P = 0.001). Cox regression analysis showed that predictors of AF recurrence were LA EF₂, LA EF₃ and accompanied obstructive sleep apnea (OSA) (P < 0.001, respectively). Decreased functional LA reservoir (LA EF after RVP) and OSA are significantly related to recurrence of AF following CA in patients with paroxysmal AF.