右心室快速临时起搏同时经皮球囊扩张术治疗婴幼儿主动脉瓣狭窄

目的探讨经皮球囊主动脉瓣成形术更加安全地治疗婴幼儿先天性主动脉瓣狭窄的方法和疗效。方法从股动脉途径对婴幼儿先天性主动脉瓣狭窄患者行经皮球囊主动脉瓣成形术。术中扩瓣同时应用右室快速临时起搏使左心室和主动脉收缩压下降,从而使扩张瓣膜的球囊在左室流出道位置稳定,减少球囊的移动和对瓣膜的损伤。结果 1岁2个月和3岁的男性患者2例,体重分别7Kg、16 Kg,球囊/瓣环直径比分别0.83和0.8。术后即刻主动脉收缩峰压跨瓣压差分别从80 mm Hg和90 mm Hg下降至20 mm Hg和18 mm Hg。随访2个月～1年,超声心动图检测主动脉瓣跨瓣压差分别38 mm Hg、43 mm Hg,主动脉瓣返流无明显增加。结论经皮球囊主动脉瓣成形术是治疗婴幼儿先天性主动脉瓣狭窄行之有效的方法。扩瓣同时右室快速临时起搏可保持球囊稳定,减少并发症。     

介入治疗主动脉缩窄的临床探讨

目的主动脉缩窄是一种少见的先天性心血管畸形,患者预后不佳,合并其它先天心血管畸形于婴幼儿期即可死亡,单纯主动脉缩窄患者平均自然寿命仅40岁。既往此类患者的唯一治疗方式是外科手术,然而死亡率和并发症发生率均非常高。本报道探讨球囊成形术和支架植入术治疗主动脉缩窄的有效性和安全性。方法自2005年4月至2010年2月,共对14例患者(男8例)实施主动脉缩窄球囊成形术和支架植入术,年龄(17±9)岁。所有患者入院后常规进行心电图、胸部摄片、超声心动图和必要的化验检查。主动脉弓发育不良型缩窄,合并其它必须外科手术矫治的心血管畸形和严重肺动脉高压存在手术禁忌证者除外。根据患者年龄和主动脉缩窄解剖形态选择介入治疗方式。结果单纯主动脉缩窄9例,合并动脉导管未闭5例;膜状主动脉缩窄12例,管状缩窄2例。合并轻度二尖瓣关闭不全,轻度主动脉瓣关闭不全,先天性二叶主动脉瓣并中度主动脉瓣关闭不全各1例。所有患者均成功实施介入治疗。年龄小于14岁者4例,跨缩窄段压力阶差为(45±9)mm Hg,球囊成形术后2例压力阶差消失,2例存在10 mm Hg以内压力阶差。主动脉缩窄支架植入术10例,跨缩窄段压力阶差为(51±18)mm Hg。8例植入覆膜支架,2例植入非覆膜支架。使用支架大小为8zip×(3.8±0.7)cm,球囊外囊直径(19.7±3.9)mm。5例合并动脉导管未闭患者中,4例行覆膜支架植入术,1例主动脉缩窄段高度迂曲,狭窄远心端主动脉显著扩张,动脉导管未闭直径为9.0mm,实施动脉导管未闭封堵术和裸支架植入术。术后2例患者存在少量压力阶差。1例为外科术后主动脉缩窄患者,采用10 atm压力仍无法将支架彻底扩张,跨缩窄段压力阶差由术前50 mm Hg降至15 mm Hg;另1例为同时实施动脉导管未闭封堵术和裸支架植入术患者,术后压力阶差由49 mmHg降至9 mm Hg。所有患者无?     

经导管人工主动脉瓣植入动物的实验方法及影像分析

目的:建立经导管人工主动脉瓣植入的动物实验方法,确定主动脉窦部造影的最佳投射体位,探讨经腹主动脉植入人工主动脉瓣的可行性、安全性。方法: 选取健康杂种大白猪10只,经右侧股动脉送入猪尾巴导管行左心室造影,确定主动脉窦部造影的最佳投射体位,测量主动脉窦部的直径;经右侧股静脉送入临时起搏电极至右心室,选择合适的起搏频率;经腹主动脉送入22F输送鞘管,观察经输送鞘管推送预载瓣膜支架球囊的可行性、安全性。结果: 左心室造影可在左前斜(30±2)°、头位(10±4)°清楚地显示主动脉窦部及冠脉开口。主动脉窦部的直径为（212±23） mm。实验动物可以耐受连续30 s的快速起搏（240~260次/min）。结论: 经腹主动脉途径植入人工主动脉瓣的方法可行、安全。在左前斜(30±2)°、头位(10±4)°可清楚地显示主动脉窦部。以240~260次/min的频率快速起搏可最大限度地减少血流对球囊的冲击,更好地实现瓣膜植入时的精确定位。     

小主动脉瓣环患者应用小口径生物瓣的临床疗效观察

目的 回顾性分析行小口径（≤21 mm）生物瓣置换和机械瓣置换的小主动脉瓣环患者的临床资料,比较生物瓣置换术后患者血流动力学与机械瓣置换的差异,探讨在小主动脉瓣环的患者中应用小口径生物瓣行主动脉瓣置换术的可行性及安全性。方法 收集2020年11月至2022年8月在武汉亚洲心脏病医院接受治疗的147例小主动脉瓣环患者临床资料和治疗情况,其中机械瓣膜组74例,生物瓣膜组73例。所有患者均符合主动脉瓣置换术手术指征,均行小口径的瓣膜置换。收集患者基线资料、既往病史、术前及术后超声心动图结果、手术相关数据等指标。结果 两组患者体外循环时间、主动脉阻断时间比较无明显统计学差异（P>0.05）。21 mm生物瓣与20 mm机械瓣比较,术后左心房内径[（36.4±7.0）mm比（37.2±10.2）mm,P>0.05],左心室舒张末期内径[（45.7±5.0）mm比（44.4±7.0）mm,P>0.05]未见统计学差异,生物瓣术后射血分数优于机械瓣[（61.1±7.0）%比（57.4±10.4）%,P=0.034],生物瓣术后主动脉跨瓣压峰值差劣于机械瓣[（25.8±7.5）mmH...     

15例拟行经导管主动脉瓣置换术患者主动脉根部影像学与临床应用--单中心早期经验

目的：15例拟行经导管主动脉瓣置换术（TAVI）患者主动脉根部影像学与临床应用的单中心早期临床经验。
　　方法：入选我院2011-03至2013-11拟行TAVI的主动脉瓣重度狭窄患者15例,分别进行计算机断层摄影术（CT）扫描、经胸超声心动图采集主动脉根部解剖数据,并对比主动脉瓣环测量差异。根据CT测量结果选择植入瓣膜型号,通过术后6个月随访,评估术前测量准确性。
　　结果：15例患者术前CT测量主动脉瓣环短径（21.5±2.4）mm,主动脉瓣环长径（27.3±2.7）mm,瓣环平均内径（24.4±2.4）mm,左心室流出道长径（28.3±4.5）mm,左心室流出道平均内经（24.±3.5）mm;升主动脉内径（35.3±4.4） mm。置入A-Venus人工瓣膜26号瓣膜8例,29号瓣膜7例。CT测量主动脉瓣环内径均值大于经胸超声心动图主动脉瓣环内径均值,差异有统计学意义（P<0.001）。经6个月随访,15例患者均未出现主动脉根部破裂、阻挡冠状动脉、主动脉瓣及瓣周中量及以上反流,有4例患者因房室传导阻滞行永久起搏器置入。
　　结论：CT及经胸超声心动图对于主动脉瓣环测量结果存在差异,CT测量可准确有效评估主动脉根部形态及毗邻,为TAVI提供有力支持。     

不同起搏频率对心肌应变的影响

目的 探讨心率对心肌应变的影响。方法 选择20例已植入起搏器的病窦综合征患者。利用常规超声心动图和二维斑点追踪显像技术,测心房起搏频率60,70,80,90和100次/分下每搏输出量和纵向、径向和环状方向上左室18节段收缩期应变峰值并计算心输出量和整体纵向、径向和环状应变峰值。结果 随着起搏频率的增加,每搏输出量和左室各节段、各水平及整体在不同方向上的应变峰值递减,心输出量逐渐递增。起搏频率60,70和80次/分时,整体纵向应变峰值分别为-24. 58% ±10. 19%、-23. 13% ±11. 36%和-20. 20% ±9. 48%（P〉0. 05）;而起搏频率90和100次/分时整体纵向应变峰值分别为-15. 56%±8. 89%（P〈0. 05）和-9. 80% ±6. 01% （P〈0. 001）。起搏频率60,70和80次/分时,整体径向应变峰值分别为33.40%±9. 81%、31. 92% ±10. 69%和28. 84% ±10. 58%（P〉0.05）;而起搏频率90和100次/分时整体径向应变峰值分别为23.34%±8.17%（P〈0.05）和15.77%±7.42%（P〈0.001）。起搏频率60,70和80次/分时,整体环状应变峰值分别为-21. 43% ±8. 48%、-20. 23% ±7. 10%和-17. 65% ±7.25%（P〉0.05）;而起搏频率90和100次/分时整体环状应变峰值分别为-13. 65% ±5. 27% （P〈0. 01）和-8. 23% ±3.72%（P〈0.001）。结论 随起搏频率增加,左室各方向应变下降。心率对应变的影响为负性。     

二叶式主动脉瓣狭窄患者主动脉根部形态学特点对经导管主动脉瓣置换术疗效的影响

目的:探讨二叶式主动脉瓣狭窄患者主动脉根部形态学特点对经导管主动脉瓣置换术(TAVR)疗效的影响。方法:回顾性选取2014年1月至2016年12月在阜外医院、四川大学华西医院及浙江大学附属第二医院行TAVR的二叶式主动脉瓣狭窄患者49例。分析患者主动脉根部形态学特点、手术有效性及安全性,并进行随访。结果:二叶式主动脉瓣无嵴与带嵴类型占比相当(55.1%vs 44.9%),瓣叶钙化程度重[钙化体积HU850=(604.1±318.7) mm~3],平均瓣环周长大于平均瓣环上水平周长[(78.8±7.4) mm vs (67.1±6.7) mm,P0.001],平均左心室流出道(LVOT)周长大于平均瓣环周长[(81.6±10.5) mm vs (78.8±7.4) mm,P=0.003]。置入瓣中瓣患者12例(24.5%),瓣膜置入过深患者14例(34.1%)。置入瓣中瓣患者比无瓣中瓣患者瓣环平均内经[(26.8±2.4) mm vs(23.9±2.0) mm,P0.001]、周长[(85.7±7.0) mm vs (76.6±6.1) mm,P0.001]及LVOT平均内径[(28.4±2.7) mm vs (24.3±3.1) mm,P0.001]、周长[(91.3±9.1) mm vs (78.4±8.9) mm,P0.001]更大,LVOT周长/瓣环上水平周长比值虽差异无统计学意义[(125.5±12.3)%vs (119.4±15.7)%,P=0.067],但趋近阈值。瓣膜置入过深患者比无置入过深患者LVOT周长/瓣环周长比值更大[(108.0±7.4)%vs (101.2±6.7)%,P=0.005]。结论:二叶式主动脉瓣患者的瓣环和LVOT平均内径及LVOT周长/瓣环周长比值对于TAVR中瓣中瓣的置入及瓣膜置入深度具有一定影响。     

经St.Jude Medical双叶瓣的搏动性流体——体外研究

本文报道经 St.Jude Medical 双叶瓣(SJM 瓣)的搏动性流体的体外动力学评价,包括跨瓣压力阶差,模拟主动脉内流体运动的定性显示,应用激光多普勒流速测定仪(LDA)测量流速分布和湍流应力,并与其他人工瓣相比较。实验过程:STM 瓣的组织环直经27mm,按装在模拟循环系统内,以36%甘油为流体,搏动频率72次/分,收缩期270msec,瞬间流量峰值18L/min。按Chandran 法,用发光悬浮树脂微粒显示流体运动。以 LDA 在模拟升主动脉等处进行定量测定。使     

经导管国产化主动脉人工瓣膜支架“瓣中瓣”置入的实验研究

目的使用国产镍钛合金自膨式主动脉瓣膜支架行"瓣中瓣"二次置入,验证使用国产化主动脉瓣膜支架行"瓣中瓣"技术的安全性和有效性,初步探讨国产瓣膜支架经导管"瓣中瓣"治疗衰败生物瓣膜的可行性。方法使用国产瓣膜支架系统进行经导管主动脉瓣膜置入手术,将首次置入的瓣膜支架置于主动脉瓣上,瓣膜支架瓣环与实验羊自身瓣环距离大于10mm,实验羊的主动脉瓣因不同程度受压后出现中～大量的反流。当即运用"瓣中瓣"技术经导管在主动脉瓣区原位置入第二枚瓣膜支架,恢复主动脉瓣功能,对存活山羊在术后即刻和3个月行造影及左心导管评估。结果在所有8只实验羊中,6只山羊成功完成"瓣中瓣"置入,术后3个月随访存活良好。1只山羊在二次置入瓣膜支架定位过低,产生大量瓣周漏导致急性左心衰竭死亡;另1只山羊由于首枚瓣膜支架置入位置过高,造成右冠状动脉开口阻塞,在置入第二枚支架过程中发生室颤死亡。存活实验羊术后复查心电图未出现传导阻滞。"瓣中瓣"手术成功的实验羊造影可见首枚瓣膜支架位置不良,二次置入的瓣膜支架套叠于首枚置入支架内,置入位置理想,瓣膜启闭正常,左右冠状动脉均显影,提示冠状动脉口未见堵塞。左心室造影未见瓣膜明显狭窄,主动脉逆行造影未见瓣膜明显反流,可见支架整体随心脏搏动有明显的收缩和舒张。在"瓣中瓣"置入术后即刻和术后3个月后进行左心导管检查,其收缩期主动脉跨瓣压差分别为(23.5±2.5)mmHg和(24.1±2.6)mmHg,与瓣膜支架置入前收缩期主动脉跨瓣压差比较,差异无统计学意义(P=0.17和P=0.07)。结论经导管置入国产化主动脉瓣膜支架出现定位不良时,运用"瓣中瓣"技术紧急置入另一瓣膜支架,可有效恢复瓣膜功能;国产化主动脉瓣膜支架也可用于治疗生物瓣膜衰败后的"瓣中瓣"二次置入。     

“All in One”技术在“一站式”经导管主动脉瓣置换术联合经皮冠状动脉介入治疗术中的应用

目的 总结“All in One”技术在“一站式”经导管主动脉瓣置换术联合经皮冠状动脉介入治疗（PCI）中应用的初步经验。方法 连续收集2021年7月至2022年9月首都医科大学附属北京安贞医院心脏瓣膜病介入中心在“一站式”经导管主动脉瓣置换术联合PCI中应用“All in One”技术的患者27例进行回顾性分析，总结临床资料、影像学资料、手术操作、住院和出院随访期间主要不良心脑血管事件的发生情况。结果 27例患者平均年龄（74.1±7.8）岁；男15例，女12例；平均美国胸外科医师协会评分（6.02±3.25）%；主动脉瓣重度狭窄22例，单纯主动脉瓣重度反流5例；三叶式主动脉瓣20例，二叶式主动脉瓣7例。术前平均跨主动脉瓣血流速度（4.2±1.2）m/s，跨主动脉瓣平均压差（52.1±13.3）mmHg。所有患者均置入药物洗脱支架，其中左主干病变4例，多支血管病变11例，平均置入支架数量（1.8±0.9）枚，应用冠状动脉斑块旋磨术1例。所有患者在PCI术后均置入自膨胀瓣膜，术中无死亡、心肌梗死、脑卒中、急诊转外科手术、血管并发症发生，1例患者行瓣中瓣手术，无中重度瓣周反流。住院期间无...     

Regional myocardial blood flow in patients with sick sinus syndrome randomized to long-term single chamber atrial or dual chamber pacing--effect of pacing mode and rate

OBJECTIVES: This study aimed to evaluate regional myocardial blood flow (MBF) and global left ventricular ejection fraction (LVEF) during chronic pacing in patients with sick sinus syndrome (SSS) randomized to either single chamber atrial (AAI) or dual chamber (DDD) pacing. BACKGROUND: Experimental studies indicate that chronic pacing in the right ventricular apex changes regional MBF, thereby compromising left ventricular function. METHODS: Thirty patients (age 74 +/- 10 years) were randomized to AAI (n = 15) or DDD (n = 15) pacemakers. After 22 +/- 7 months of pacing, MBF was quantified with 13N-labeled ammonia positron emission tomography scanning at 60 beats per min and 90 beats per min. Patients in the DDD group furthermore underwent MBF measurement at temporary AAI pacing, 60 beats per min. Myocardial blood flow was assessed in the anterior, lateral, inferior and septal regions, and the global mean MBF was calculated. Left ventricular ejection fraction was determined by echocardiography at pacemaker implantation and at the time of MBF measurements. RESULTS: Myocardial blood flow at rates 60 and 90 beats per min did not differ between the AAI and DDD groups. During temporary AAI pacing in the DDD group, MBF was significantly higher than during DDD pacing in both the inferior (p = 0.001) and septal (p = 0.004) regions and also globally (0.61 +/- 0.15 vs. 0.53 +/- 0.13 mL x g(-1) x min(-1), p = 0.005). In the DDD group, LVEF decreased from pacemaker implantation to time of MBF measurements (0.61 +/- 0.09 vs. 0.56 +/- 0.07, p = 0.013). Left ventricular ejection fraction during temporary AAI pacing at time of MBF measurements was not different from LVEF at pacemaker implantation. CONCLUSIONS: In patients with SSS, chronic DDD pacing reduced inferior, septal and global mean MBF as well as LVEF, as compared with temporary AAI pacing. The LVEF reversed to baseline level during temporary AAI pacing despite 22 months of permanent ventricular pacing preceding it. Augmenting pace rate to 90 beats per min increased MBF equally in the two treatment groups.     

Utility of isoproterenol in unmasking latent escape rhythm in pacemaker dependent patients undergoing pacemaker replacement

Pacemaker generator replacement in dependent patients may be managed with a bridging temporary pacing lead or by replacing the generator very expediently. The 2 options involve a small risk, and temporary pacing introduces additional cost. This study was conducted to explore the utility of a graduated rate-decrease protocol with isoproterenol support in unmasking an intrinsic rhythm that would obviate the 2 strategies. The protocol was used in 100 consecutive pacemaker-dependent patients (mean age 74.4 +/- 13.7 years, 56% men) who underwent permanent pacemaker replacement. Device lower rates were decremented in 1-minute intervals to 60, 50, 40, and 30 beats/min. If no intrinsic rhythm of > or =30 beats/min was observed after 1 minute, isoproterenol was infused at 1 microg/min for 2 minutes, followed by 2 microg/min for 2 minutes. Of the 100 patients, 59 demonstrated intrinsic rhythm during pacing step-down alone. Of the remaining 41 patients, 28 (68.3%) demonstrated intrinsic rhythm during isoproterenol infusion. The escape rhythm was junctional in 29%, idioventricular in 23%, conducted atrial fibrillation in 16%, and sinus in 15%. Only 13 of 100 patients (13%) failed to demonstrate adequate intrinsic rhythm after the protocol. In conclusion, this suggests that a standardized protocol to elicit an underlying rhythm in patients previously assessed as pacemaker dependent effectively minimizes the need for temporary pacing during device replacement.     

超声心动图对不同频率AAI及VVI起搏的血流动力学研究

目的本研究的目的在于评价不同频率ＡＡＩ及ＶＶＩ起搏的血流动力学效果，探索最佳起搏频率范围，比较ＡＡＩ及ＶＶＩ起搏的血流动力学效果。方法３７例植入永久心脏起搏器的患者分为两组，ＡＡＩ组１７例，ＶＶＩ组２０例。程控起搏频率从５０～１００次／分，以超声心动图评价其血流动力学效果。结果在ＡＡＩ起搏组，７０次／分起搏的心排血量（ＣＯ）高于５０及６０次／分起搏（Ｐ＜０．０５）。８０～９０次／分起搏的ＣＯ变化无显著性差异。１００次／分起搏的ＣＯ低于９０次／分起搏。在ＶＶＩ起搏组，起搏频率超过８０次／分时，ＣＯ不再增高，１１０次／分起搏的ＣＯ甚至低于７０次／分起搏，左室射血分数（ＬＶＥＦ）则随之下降。但ＡＡＩ起搏的ＣＯ及ＬＶＥＦ在起搏频率相同情况下显著高于ＶＶＩ起搏组。结论在有心脏病的患者，最佳起搏频率范围较窄，为７０～８０次／分。ＡＡＩ起搏的血流动力学效果显著优于ＶＶＩ起搏。     

Effect of increasing heart rate in patients with aortic regurgitation: Effect of incremental atrial pacing on scintigraphic, hemodynamic and thermodilution measurements

This study was performed to assess the effect of pacing-induced tachycardia in patients with aortic regurgitation. In 12 patients (5 men and 7 women with a mean age of 53 years) with aortic regurgitation, left ventricular end-diastolic and end-systolic volume indexes were measured with multigated equilibrium blood pool imaging, and forward cardiac index was determined with thermodilution, both at rest (mean heart rate ± standard deviation 72 ± 8 beats/min) and during atrial pacing at 100 and 120 beats/min. Pacing caused a decremental reduction in left ventricular end-diastolic and end-systolic volume indexes and radionuclide-determined stroke volume index but no change in radionuclide-determined cardiac index or left ventricular ejection fraction. Forward cardiac index increased incrementally from the baseline value at rest to that at 120 beats/min despite a decremental reduction in stroke volume index. There was a stepwise decrease in regurgitant volume/stroke (46 ± 20 ml/m² at baseline, 27 ± 15 at 120 beats/min; p < 0.05) but no change in regurgitant volume/min (3.38 ± 1.80 Iiters/min per m² at baseline, 3.22 ± 1.78 at 120 beats/min; difference not significant [NS]) or regurgitant fraction (0.54 ± 0.13 at baseline, 0.49 ± 0.13 at 120 beats/min; NS). Mean femoral arterial, pulmonary arterial and pulmonary capillary wedge pressures did not change with pacing.     

Effect of heart rate on Doppler indexes of systolic function in humans

Recent investigations have shown Doppler echocardiography to be useful in the noninvasive assessment of left ventricular systolic function. No data exist, however, regarding the influence of heart rate on Doppler measurements of aortic blood flow velocity and acceleration in humans. Thus, 12 normal volunteers underwent continuous wave Doppler ultrasound recording from the suprasternal notch at baseline and during progressive transesophageal atrial pacing at intervals of 10 beats/min between 90 and 140 beats/min while 100% atrial capture and 1:1 atrioventricular conduction were maintained. Subjects were studied both upright (n = 12) and supine (n = 10). With the subject upright at baseline (mean heart rate 77.8 +/- 10.6 beats/min), peak acceleration averaged to 16.8 +/- 3.4 m/s2, and peak modal velocity and flow velocity integral averaged 0.72 +/- 0.14 m/s and 8.4 +/- 2.1 cm, respectively. With pacing at 90 beats/min, peak acceleration decreased to 15.6 +/- 3.6 m/s2, a significant decline from baseline values (p less than 0.005). Similar declines were seen during pacing at 90 beats/min for peak modal velocity and flow velocity integral (0.64 +/- 0.16 m/s and 7.1 +/- 1.9 cm, respectively; both p less than 0.005 versus baseline values). At the peak pacing rate of 140 beats/min, average peak acceleration decreased to 12.8 +/- 3.1 m/s2, and peak modal velocity and flow velocity integral decreased to 0.52 +/- 0.11 m/s and 5.02 +/- 1.25 cm, respectively. A significant linear correlation (r greater than or equal to 0.97, p less than 0.0001) was obtained for the relation between heart rate and peak acceleration, peak modal velocity and flow velocity integral.(ABSTRACT TRUNCATED AT 250 WORDS)     

The feasibility of utilizing the systolic pre-ejection interval as a determinant of pacing rate

Rate-modulated pacing modes adjust the stimulus rate by responding to sensed alterations in physiologic indexes of metabolic demand. This study was designed to determine whether right ventricular pre-ejection interval, measured in patients by a prototype pacemaker system capable of tracking intraventricular volume, changes predictably with exercise and, if so, whether it can be used in an algorithm to vary heart rate appropriately. This system utilizes intraventricular electrical impedance measurements of injected microampere currents to determine intracavitary volume changes. Five pacemaker-dependent patients underwent temporary insertion of a tripolar electrode connected to an external device that sensed cardiac signals, generated an impedance wave form and produced stimuli at rates dependent on pre-ejection interval. Pre-ejection interval did not change as a result of variations in pacing rate itself (347 +/- 41 ms at 70 beats/min versus 321 +/- 19 ms at 130 beats/min), but consistently decreased during graded exercise (by 23% from baseline). During rate-modulated pacing based on pre-ejection interval, heart rate significantly increased during exercise compared with ventricular demand pacing (by 46 +/- 6 versus 7 +/- 6 beats/min, respectively), and increased appropriately during burst exercise. Thus, the pre-ejection interval appears to be a specific, reliable physiologic determinant of pacing rate during exertion, which may be applicable in implantable rate-modulated pacemakers.     

In-vitro and in-vivo electrophysiologic effects of encainide

The intracellular electrophysiologic effects of encainide (E) and its main metabolite, O-desmethyl-encainide (ODE), were studied in guinea-pig papillary muscle preparations and related to the in-vivo electrophysiologic effects observed after intravenous (IV) infusion of E in 11 patients undergoing electrophysiologic study (EPS).At equipotent concentrations of E and ODE, frequency-dependent reductions in V_max studied at pacing rates of 30–180 beats/min ranged from-11.5% to-53%, with maximum reductions of-53% and-47%, respectively at the highest frequency. The kinetics of onset of use-dependent V_max reduction were slower for ODE than for E at each studied pacing rate. The kinetics of total recovery from use-dependent block were still slower (120 seconds for E and 300 seconds for ODE at a 90 beats/min pacing rate).     

Effectiveness of triple-site triggered atrial pacing for prevention of atrial fibrillation after coronary artery bypass graft surgery

BACKGROUND: Recently, several temporary multisite pacing methods have been developed for prevention of postoperative atrial fibrillation (AF). HYPOTHESIS: In this study, we evaluated the effect of triple-site temporary triggered pacing in the AAT mode on the development of AF in patients undergoing coronary artery bypass graft (CABG) at high risk for developing postoperative AF. METHODS: A total of 70 patients undergoing CABG were randomly assigned either to pacing group (study group, n = 35 patients) or to no pacing group (control group, n = 35 patients). The external pacemaker was programmed to pace at the atrial triggered mode at a lower rate of 40 beats/min for 4 days. RESULTS: Atrial fibrillation, defined as lasting > 30 s, occurred in 4 patients (11.4%) in the study group and in 16 patients (45.7%) in the control group (p = 0.003). Sustained AF, defined as AF lasting > 10 min, also was observed less frequently in the study group than in the control group (11.6 vs. 37.1%, p = 0.024). Triple-site triggered atrial pacing was observed to reduce the incidence of AF by 75% and the incidence of sustained AF by 69%. CONCLUSIONS: We believe that multiple-site temporary pacing in the triggered mode is an effective way of preventing postoperative AF. This technique may be used especially in patients at high risk of developing AF.     

Increased sympathetic activity after atrioventricular junction ablation in patients with chronic atrial fibrillation

OBJECTIVES: The aim of this study was to determine the changes in sympathetic nerve activity (SNA) after atrioventricular junction (AVJ) ablation in patients with chronic atrial fibrillation (AF). BACKGROUND: Polymorphic ventricular tachycardia (PMVT) has been reported after AVJ ablation in patients paced at a rate of < or =70 beats/min. We hypothesized that AVJ ablation results in sympathetic neural changes that favor the occurrence of PMVT and that pacing at 90 beats/min attenuates these changes. METHODS: Sympathetic nerve activity, 90% monophasic cardiac action potential duration (APD90), right ventricular effective refractory period (ERP) and blood pressure measurements were obtained in 10 patients undergoing AVJ ablation. Sympathetic nerve activity was analyzed at baseline and during and after successful AVJ ablation for at least 10 min. Data were also collected after ablation at pacing rates of 60 and 90 beats/min. The APD90 and ERP were measured before and after AV block during pacing at 120 beats/min. RESULTS: Sympathetic nerve activity increased to 134 +/- 16% of the pre-ablation baseline value (p < 0.01) after successful AVJ ablation plus pacing at 60 beats/min and decreased to 74 +/- 8% of baseline (p < 0.05) with subsequent pacing at 90 beats/min. Both APD90 and ERP increased significantly. CONCLUSIONS: 1) Ablation of the AVJ followed by pacing at 60 beats/min is associated with an increase in SNA. 2) Pacing at 90 beats/min decreases SNA to or below the pre-ablation baseline value. 3) Cardiac APD and ERP increase after AVJ ablation. The increase in SNA, along with the prolongation in APD, may play a role in the pathogenesis of ventricular arrhythmias that occur after AVJ ablation.     

Abnormalities in myocardial perfusion during tachycardia in dogs with left ventricular hypertrophy: metabolic evidence for myocardial ischemia

This study tested the hypothesis that in the chronically hypertrophied left ventricle pacing stress may cause abnormalities of perfusion that result in myocardial ischemia. Left ventricular hypertrophy (LVH) was produced by banding the ascending aorta of 10 dogs at 6 weeks of age, and studies were carried out after the animals had reached adulthood and when mean left ventricular/body weight ratio was 74% greater than in eight control dogs. Myocardial blood flow was measured with microspheres during pacing at 100, 200, and 250 beats/min, while aortic and coronary sinus blood samples were obtained for determination of concentrations of lactate and the adenosine metabolites inosine and hypoxanthine. In the control dogs, increasing heart rates were associated with an increase in mean myocardial blood flow while subendocardial flow was maintained at a level equal to or greater than subepicardial flow. Myocardial lactate uptake ranged from +60% to -5%, and adenosine metabolites were not detected in coronary sinus blood (less than 0.5 microM/l). In four dogs that underwent aortic banding no production of lactate or adenosine metabolites was observed at any heart rate; in these animals subendocardial flow was maintained at a level equal to or greater than subepicardial flow at all pacing rates. The remaining six dogs with LVH demonstrated net lactate production significantly greater than control during pacing at 250 beats/min; five of these six animals also produced adenosine metabolites.(ABSTRACT TRUNCATED AT 250 WORDS)