快速心室起搏制备扩张型心肌病心力衰竭犬模型的方法学探讨

目的　应用快速心室起搏的方法制备扩张型心肌病心力衰竭犬模型 ,并对其方法学进行改进。方法　 6只成年健康杂种犬麻醉后先通过射频消融希氏束致Ⅲ度房室传导阻滞 ,再经静脉植入心内膜起搏电极 ,脉冲发射器为技术处理后的人用永久起搏器。起搏频率为 2 5 0次 min ,起搏时间持续 (2 3 6± 2 5 7)d。结果　除有相应症状、体征外 ,所有动物均成功制备为扩张型心肌病心力衰竭模型 ;B超和病理解剖检查证实有心脏扩大、心室壁变薄以及肝瘀血、肺瘀血 ;病理切片显示心肌细胞空泡变性、肝窦扩张充血、肺泡内含铁血黄素沉积。结论　改进后的快速心室起搏制备充血性心力衰竭动物模型的方法更为安全、可靠、实用。     

胃多导电刺激及胃液体排空犬动物模型的建立

目的建立胃浆膜多导联电刺激和胃排空动物模型。方法在12条英国比格犬的胃大弯浆膜层包埋四对心内起搏电极,距幽门40cm空肠近端行一造瘘口。结果①造瘘管收集食糜的方法简单易行,通过其排空量,能了解不同的电刺激和不同的电刺激参数对胃动力的作用。②胃浆膜多导联电极记录的胃体、胃窦慢波电信号清晰、稳定,能准确地记录不同时间和不同实验的胃慢波变化。③单导联和多导长脉冲电刺激均能控制胃慢波。结论胃浆膜多导联电极是研究胃电生理、胃电起搏及胃电起搏对胃排空的影响较理想的方法。英国比格犬是此模型的理想材料。     

犬腋下小切口制作慢性心房颤动模型

目的探讨应用腋下小切口开胸术建立犬慢性心房颤动模型的可行性。方法取健康比格犬14只,随机分为实验组(7只)与对照组(7只)。应用左侧腋下小切口微创技术开胸植入起搏器,实验组犬以400次/分连续起搏8周诱导心房颤动,对照组不起搏。术后观察犬的一般情况,定期监测心电图,记录犬的肢体导联心电图变化,观察心房颤动的发生情况。结果14只犬均顺利完成实验。应用左侧腋下小切口微创技术开胸,手术时间缩短,术后并发症减少。实验组7只犬经连续起搏8周,均出现典型的心房颤动心电图改变。结论应用腋下小切口微创技术开胸制作犬慢性房颤模型是安全可行的,犬术后无手术死亡及严重并发症,恢复快。说明与常规切口开胸手术相比创伤明显减小,值得在犬慢性房颤模型建立中推广应用。     

远东刺猬正常心电图的描记

本文采用标准双极导联(Ⅰ、Ⅱ、Ⅲ)和加压单极肢导联(aVR、aVL、aVF)对12只成体远东刺猬Erinaceus amurensis进行心电图测定。结果表明,远东刺猬的平均心率为294±46次/min,均为窦性心律。各导联的波形均较规则而稳定,所有导联都有QRS波群和T波,P波只在导联Ⅰ、Ⅱ、aVF中较明显,R′波明显存在于导联Ⅲ中。     

心室不同部位起搏对正常犬和扩张型心肌病心力衰竭犬模型在体心肌跨室壁复极离散的影响

实验以正常犬和扩张型心肌病心力衰竭犬(dilated cardiomyopathy congestive heart failure,DCM-CHF)模型为对象、以心肌跨室壁复极离散的相关参数为指标,研究左心室心外膜起搏、双心室起搏(模拟临床上心室再同步治疗的方法)后的心肌电生理特性变化。实验以快速右心室起搏的方法制备DCM-CHF犬模型;正常犬和DCM-CHF犬均经射频消融希氏束制备三度房室传导阻滞模型;采用同步记录犬体表心电图和内膜下、中层、外膜下三层心肌单相动作电位(monophasic action potentials,MAP)的方法,测定不同部位起搏时的QT间期、Tpeak-Tend(Tp-Te)间期和三层心肌的单相动作电位时程(MAP duration,MAPD)、跨室壁复极离散度(transmural dispersion of repolaization,TDR)。结果显示:在正常犬,左室心外膜与双心室起搏后三层心肌的MAPD均延长,同时TDR增大(左室心外膜起搏47.16 ms、双心室起搏37.54 ms、右室心内膜起搏26.75 ms,P<0.001),体表心电图Tp-Te间期的变化与之平行;在DCM-CHF犬较正常犬已表现出中层心肌MAPD延长(276.30 ms vs 257.35 ms,P<0.0001)和TDR(33.8 ms vs 27.58 ms,P=0.002)增大的基础上,左室心外膜参与起搏后仍进一步使三层心肌的MAPD延长和TDR增大。研究结果提示,左室心外膜起搏和双心室起搏后使内膜下、中层     

一种快速起搏右心室诱导犬慢性心衰模型的新方法

目的探讨快速起搏右心室高效建立大动物慢性心衰模型的方法。方法随机选择雄性健康杂种犬5只,采用心室非同步起搏模式,起搏频率(260±10)次/分持续4周,通过观察起搏前、后犬的体征,以及超声心动图心功能参数、心脏形态学变化来评价快速起搏右心室建立犬慢性心衰模型的高效性和安全性。结果 5只犬经快速右心室起搏均出现呼吸困难、活动减少、体质量减轻、浆膜腔积液等慢性心衰的症状和体征,超声心动图证实左心室射血分数由61.50%±3.36%降至38.60%±2.88%。结论快速起搏右心室建立犬慢性心衰模型能更好地模拟人类慢性心衰的病理生理变化,造模所需时间短,动物死亡率低,是一种高效、安全的大动物慢性心衰模型建立方法,为研究慢性心衰的发病机制打下基础。     

犬双心室多点组合同步起搏的心肌力学效应研究

目的 :探讨多点组合同步心室起搏对犬心肌收缩 /舒张力学效应和心脏作功的影响。方法 :12只犬 ,随机进行 5种组合模式的双心室同步起搏 ,并以自身窦性心律状态 (SNR )作为对照。记录各起搏状态下 :左室内压上升和下降最大数率 (±dp/dtmax)、左室松弛时间常数 (τ)、左 /右室游离壁室壁肌张力 (L/RV tensileforce ,L/RV TF)、每搏量 (SV )、左室每搏功 (LVSW )和右室每搏功 (RVSW )等心肌收缩 /舒张力学和心脏作功参数。结果 :双室cHisB LVPL起搏和RVA LVPL起搏的心肌收缩力学参数 +dp/dtmax和L/RV TF较右室双点cHisB RVA起搏增加 ,前两组的心肌舒张力学参数 dp/dtmax也较cHisB RVA起搏增加 ,而τ值较后者缩短。双室三点cHisB RVA LVPL起搏和cHisB RVA LVA起搏的上述各参数均优于双室cHisB LVPL起搏和RVA LVPL起搏。而cHisB RVA LVPL起搏的 +dp/dtmax和L/RV TF均较cHisB RVA LVA起搏增加。cHisB RVA LVPL起搏 dp/dtmax较cHisB RVA LVA起搏提高 6.0 % ,τ值缩短 3 .7%。cHisB LVPL起搏和RVA LVPL起搏的SV、LVSW和RVSW等心室作功参数均较cHisB RVA起搏增加 ,而HisB RVA LVPL起搏的上述心脏作功各参数 ,亦分别较cHisB RVA LVA起搏和cHisB LVPL起搏有不同程度的增加。结论 :双室三点cHisB RVA LVPL组合同     

不同部位起搏对正常和心力衰竭犬心室跨壁复极梯度的影响（英文）

跨壁复极梯度的改变可能导致跨壁复极离散度的增加和室速的增多,跨壁复极离散可能在左室心外膜起搏相关猝死中发生重要作用。本研究对心力衰竭(心衰)犬进行心室不同部位起搏,观察左心室跨壁复极梯度的变化。选用8条健康杂种犬,随机分成健康对照组和心衰组(n=4),心衰组4条健康犬经快速右心室心内膜心尖部(right ventricular apical endocardium,RV_(Endo))起搏4～5周建立慢性充血性心衰模型。健康对照组和心衰组分别在右心房(right atrium, RA)起搏、RV_(Endo)起搏、左心室心外膜(left ventricular lateral epicardium, LV_(Epi))起搏及双心室(biventricular, Biv)同步起搏的条件下,应用自制的跨室壁单相动作电位(monophasic action potential, MAP)记录电极,于左心室同步记录和测量三层心肌(内层、中层、外层)的MAP时程(MAP duration, MAPD)。结果显示,健康对照组窦性心律时左心室三层心肌MAPD比较:中层内层外层,各层之间比较均有统计学差异(均P 0.05);RV_(Endo)、LV_(Epi)、Biv起搏时MAPD仍为中层内层外层,心外膜层与心内膜层MAPD比较无统计学差异(P 0.05);每种起搏时中层与心外膜层及心内膜层的MAPD比较均有统计学差异(均P 0.05)。与健康对照组比较,心衰组不同起搏模式(RA起搏、RV_(Endo)起搏、LV_(Epi)起搏、Biv起搏)时左心室心肌各层的MAPD均延长(均P 0.05)。心衰组RA、RV_(Endo)、LV_(Epi)及Biv起搏时左心室三层心肌MAPD均表现为中层内层外层,但各层心肌MAPD均无统计学差异(均P 0.05)。通过应用改良标测导管记录MAP的方法,我们发现健康犬RA起搏时左心室心内膜层、中层及心外膜层存在明显的跨壁梯度,RV_(Endo)、LV_(Epi)、Biv起搏时左心室心内膜与心外膜间跨壁梯度消失;然而心衰犬左心室的三层心肌在RA、RV_(Endo)、LV_(Epi)、Biv起搏时均不存在跨壁梯度,这些结果有助于加深对心衰患者室性心律失常发生机制的理解。     

β3肾上腺素受体减轻持续房颤心房结构重构及收缩功能降低

为了研究β3肾上腺素受体在持续房颤心房重构中的作用,本研究选择实验犬21只,随机分为假手术组(n=7)、房颤组(n=7)和抑制剂组(n=7)。无菌条件下开胸后在犬右心耳缝植螺旋型起搏电极,连接实验用埋藏式高频起搏器(起搏模式AOO,600次/min),同时抑制剂组犬埋置持续给药泵,假手术组犬仅缝植起搏电极但不起搏,另2组犬心房快速起搏4周。分别于起搏前、起博4周后,检测记录各组犬房颤诱发情况;测量各组犬LAVmax、LAVmin和LAEF;测定左心耳LAAVmax,LAAVmin和LAAEF。我们发现起搏4周后,与假手术组相比,房颤组犬LAVmax、LAVmin、LAAVmax和LAAVmin均显著增加(p0.01),LAEF和LAAEF均明显下降(p0.01)。抑制剂组犬LAVmax、LAVmin、LAAVmax和LAAVmin均较房颤组有所降低(p0.01),而LAEF(p0.01)和LAAEF增加(p0.05)。假手术组和抑制剂组两组间比较可见显著差异。结果表明β3受体抑制剂能够减轻心房快速起搏犬心房结构重构和收缩功能降低,有益于防治房颤的心房结构重构。     

N-乙酰半胱氨酸对犬心房快速起搏电重构的影响

目的:探讨N-乙酰半胱氨酸(NAC)对犬心房快速起搏电重构的影响。方法:取16只犬,随机分为对照组和NAC干预组。NAC组按照15mg/kg/d剂量给予NAC口服6周时间。在犬右房置入电极,快速起搏右心房,诱发房颤并维持2小时。在起搏前后分别测定有效不应期(AERP)。结果:房颤后对照组AERP显著缩短,AERP频率适应性下降(P<0.05);而NAC组房颤前后AERP和AERP频率适应性均无明显变化。结论:在心房快速起搏致房颤2h的模型中,NAC对心房电重构具有明显的保护作用。     

Atrial Pacing to Control Heart Rate and Rhythm in Acute Cardiac Conditions

Increasing the heart rate by a bedside atrial pacing technique was successfully utilized to treat serious cardiac arrhythmia or failure in 13 patients. Nine of these had ventricular arrhythmia refractory to drugs. Seven had evidence of sinus node depression or disease since their sinus pacemaker was below 70 beats per minute under decompensated conditions. In five, coronary artery disease was associated with the bradycardia and in two, digitalis toxicity was related to depression of the intrinsic pacemaker rate. Two patients in the coronary group required implantation of a permanent demand ventricular pacemaker. Hemodynamic studies were performed in seven patients. Only one patient had no increase in cardiac output with pacing rates above his resting rate. The other six patients showed an increase in cardiac output from 22 to 81% at paced rates between 70 and 125/minute. The duration of pacing ranged from one hour to 14 days and averaged five days.     

Coupled pacing improves cardiac efficiency during acute atrial fibrillation with or without cardiac dysfunction

Coupled pacing (CP), a method for controlling ventricular rate during atrial fibrillation (AF), consists of a single electrical stimulation applied to the ventricles after each spontaneous activation. CP results in a mechanical contraction rate approximately one-half the rate during AF. Paired stimulation in which two electrical stimuli are delivered to the ventricles has also been proposed as a therapy for heart failure. Although paired stimulation enhances contractility, it greatly increases energy consumption. The primary hypothesis of the present study is that CP improves cardiac function during acute AF without a similar increase in energy consumption because of the reduced rate of ventricular contractions. In a canine model, CP was applied during four stages: sinus rhythm (SR), acute AF, cardiac dysfunction (CD), and AF in the presence of cardiac dysfunction. The rate of ventricular contraction decreased in all four stages as the result of CP. In addition, we determined the changes in external cardiac work, myocardial oxygen consumption, and myocardial efficiency in the each of four stages. CP partially reversed the effects of AF and CD on external cardiac work, whereas myocardial oxygen consumption increased only moderately. In all stages but SR, CP increased myocardial efficiency because of the marked increases in cardiac work compared with the moderate increases in total energy consumed. Thus this pacing therapy may be a viable therapy for patients with concurrent atrial fibrillation and heart failure.     

Leadless pacemaker implantation for pediatric patients through internal jugular vein approach: A case series of under 30 kg

BackgroundWe demonstrate a case series of 8 pediatric patients, all under 30 kg, who had leadless pacemaker implants via the internal jugular vein.MethodsA retrospective review of pediatric leadless pacing placement via the internal jugular vein at the University of Minnesota Masonic Children's Hospital and UC Davis Medical Center from 2018 through 2021 was performed. Rationales for pacing, demographics of patients, pacing thresholds, and longevity of devices were recorded.ResultsEight internal jugular pacemaker insertions were performed successfully in patients weighing between 10.9 kg and 29 kg. Five patients had Micra implantation via the right internal jugular vein, whereas 3 patients had insertion via the left internal jugular vein. No surgical cut-downs were performed. No venous complications occurred. Up to 3 years of follow-up were noted.ConclusionLeadless pacemaker implantation, via left or right internal jugular veins, is feasible without surgical cutdown in patients <30 kg     

Hemodynamic effects of pacing-induced tachycardia in valvular aortic stenosis.

The hemodynamic effects of tachycardia were studied in 13 patients with valvular aortic stenosis. Observations were made during sinus rhythm (average heart rate 80 beats/min) and two periods (P1 and P2) when atrial pacing increased the heart rate to 109 and 131 beats/min respectively. The cardiac index did not change, but the left ventricular stroke work index fell from 61.8 to 39.5 g X m/m2 (p less than 0.001) as the heart rate increased. The left ventricular end-diastolic pressure averaged 18 mm Hg during sinus rhythm and fell to about 11.5 mm Hg at P1 and P2 (p less than 0.001). The brachial arterial systolic pressure did not change during pacing, but the left ventricular systolic pressure fell from 208 mm Hg to 201 mm Hg during P1 (p less than 0.05) and 193 mm Hg during P2 (p less than 0.001). The mean systolic aortic valve gradient averaged 64 mm Hg during sinus rhythm and fell to 51 mm Hg during P2 (p less than 0.001), and the peak aortic valve gradient fell from 82 to 69 mm Hg during P2 (p less than 0.001). The left ventricular ejection time fraction increased from 26.9% during sinus rhythm to 31.9% during P1 (p less than 0.05) and 34.7% during P2 (p less than 0.005). Because of the prolonged left ventricular ejection time fraction and smaller stroke volume, a smaller pressure gradient developed across the stenosed valve at higher heart rates. The pacing test was of little value in assessing left ventricular function and thus is not useful during invasive investigations of valvular aortic stenosis.     

Marshall to the rescue in cardiac resynchronization therapy: Left ventricular lead placement in coronary sinus ostial atresia

This case highlights the importance of proper identification of congenital anomalies of the coronary sinus for the successful placement of left ventricular lead during cardiac resynchronization therapy device implantation. We discuss an alternate route for left ventricular lead placement via the vein of Marshall when the coronary sinus ostium in the right atrium was atretic and was facing difficulty initially in detecting the anomaly.     

Heart rate as a determinant of the decay rate of the cardiac inotropic response to sympathetic nervous activity

The cardiac responses to sympathetic nerve stimulation were measured in a series of open-chest, anesthetized dogs. In half the animals, the hearts were in a sinus rhythm; in the remaining animals, the hearts were in an atrioventricular (AV) junctional rhythm. Cocaine markedly prolonged the decay times of the chronotropic responses after cessation of sympathetic stimulation, regardless of the type of rhythm. The decay times of the inotropic responses were only slightly prolonged by cocaine in animals with a sinus rhythm, but the prolongations were pronounced in animals with an AV junctional rhythm. The lower basal heart rate appeared to be more responsible for the greater decay times of the inotropic responses in the animals with an AV junctional rhythm than in those with a sinus rhythm. In a second series of dogs, complete heart block was produced, cocaine was given, AND the hearts were paced at four different frequencies. The mean decay time of the inotropic response to sympathetic stimulation varied inversely AND substantially with the pacing frequency. The change in contraction frequency probably affects the rate of neurotransmitter dissipation from the ventricular myocardium, by altering either the coronary blood flow or the massaging action of the cardiac contractions.     

Transvenous implantation of a ventricular pacing lead in a patient with an artificial tricuspid valve prosthesis

The preference for treatment of symptomatic bradycardia is transvenous right ventricular pacing combined with atrial synchronisation if applicable. In the case of congenital anomalies where no conduit is present between the peripheral veins and the right ventricle, it is not possible to place the ventricular pacing lead in the right ventricle. Also the presence of an artificial valve in the tricuspid position excludes placement of an endocardial right ventricular pacing lead. Since the introduction of biventricular pacing, new guiding catheters and leads used as a transvenous route for left ventricular pacing are available. We report implantation of a ventricular pacing lead in the great cardiac vein for permanent ventricular pacing in a patient with a tricuspid valve prosthesis.     

Ventricular pump function under ectopic excitation of the frog heart

The ventricular pump function under ectopic excitation of the heart was studied in decapitated and pithed adult frogs Rana temporaria (n = 21) at 18-19 degrees C. The intraventricular pressure was recorded with a catheter via ventricular wall. During pacing of the ventricular base and apex, the systolic pressure decreased (6.1 +/- 4.5 mm Hg and 8.9 +/- 5.0 mm Hg, respectively) as compared to the supraventricular rhythm (8.9 +/- 5.0 mm Hg, p < 0.05). The end-diastolic pressure decreased insignificantly both under basal and apical pacing. The systolic rate of pressure rise during dP/dtmax decreased under ventricular pacing, especially during pacing of the ventricular apex, as compared to the supraventricular rhythm (14.4 +/- 6/9 mm Hg/s and 22.1 +/- 11.2 mm Hg/s, respectively, p < 0.003). The isovolumetric relaxation (dP/dtmin) slowed during apical pacing as compared to the supraventricular rhythm (-25.1 +/- 13.6 and -35.6 +/- 18.3 mm Hg/s, respectively, p < 0.03). Ectopic excitation of the ventricular base and apex resulted in increase of the QRS duration (93 +/- 33 ms and 81 +/- 30 ms, respectively) as compared to the supraventricular rhythm (63 +/- 13 ms, p < 0.05). Thus, pacing of different ventricular areas ventricular myocardium with the ventricular pump function being reduced more obviously during the apical pacing compared to the pacing of ventricular base.     

Video-Assisted Implantation of a Left Ventricular Lead and Intrathoracic Tunneling to a Right-Sided CRT-D Device

We describe two cases in which a biventricular implantable cardioverter defibrillator for cardiac resynchronization therapy had to be placed on the right side due to unsuitability of the left subclavian vein. Endocardial implantation of a left ventricular lead through the coronary sinus was previously attempted but was unsuccessful. Implantation of the epicardial left ventricular pacing lead was performed through video-assisted thoracic surgery on the left side. The connector end of the left ventricular pacing lead was tunnelized through the anterior mediastinum into the right pleural space. The right-sided pocket was then opened. A tunnel was created from the pocket to the thoracic wall, and the pleural space was entered over the second rib. The lead was retrieved from the right pleural space and connected with the Cardiac resynchronization therapy-device (CRT-D). Both procedures and postoperative periods were uneventful. Intrathoracic left-to-right tunneling of an epicardial left ventricular lead by video-assisted thoracic surgery is feasible and safe. It provides an alternative to subcutaneous tunneling.     

Atrial electrogram quality in single-pass defibrillator leads with floating atrial bipole in patients with permanent atrial fibrillation and cardiac resynchronization therapy

Many patients receiving cardiac resynchronization therapy (CRT) suffer from permanent atrial fibrillation (AF). Knowledge of the atrial rhythm is important to direct pharmacological or interventional treatment as well as maintaining AV-synchronous biventricular pacing if sinus rhythm can be restored. A single pass single-coil defibrillator lead with a floating atrial bipole has been shown to obtain reliable information about the atrial rhythm but has never been employed in a CRT-system. The purpose of this study was to assess the feasibility of implanting a single coil right ventricular ICD lead with a floating atrial bipole and the signal quality of atrial electrograms (AEGM) in CRT-defibrillator recipients with permanent AF.