Therapeutic and Diagnostic Benefits of Intentional Crosstalk Mediated Ventricular Output Inhibition

Ventricular output inhibition due to crosstalk is generally considered unsafe and something that should be avoided. Special circuits have been incorporated in some dual chamber pacing systems to absolutely prevent this from happening. However, in patients with intact atrioventricular conduction, crosstalk mediated ventricular output inhibition can be beneficial to the evaluation and management of the patient. Utilizing this technique, one can achieve single chamber atrial paced rates which greatly exceed the rates allowed by lower rate limit programming to facilitate an assessment of the integrity of AV nodal conduction and to both convert and suppress some pathological tachyarrhythmias. The methods of achieving crosstalk and its utilization in four patients is discussed in this report.     

Long-Term Performance of Epimyocardial Pacing Leads in Adults: Comparison with Endocardial Leads

The long-term performance of epimyocardiaJ pacing leads in children is well established, but few studies have analyzed the performance in adults. This issue has clinical relevance in view of the increased use of epimyocardial leads with implantable cardioverter defibrillator and antitachycardia pacing systems. We analyzed 93 epimyocardial pacing "systems" (121 leads: 65 unipolar, 28 bipolar) in adult patients (age 57 ± 16 years), implanted since January 1980. Two different models were studied: Medtronic 4951 "Stab–on" (n = 35) and Medtronic 6917/6917A "Screw-in" (n = 58). A control group was created by randomly matching each epimyocardial system with two endocardial leads, according to age and year of implant. Epimyocardial and endocardial leads were followed-up for 44 ± 35 and 43 ± 35 months, respectively (P = NS). Freedom from failure for epimyocardial leads was 0.91 (95% Confidence Interval [95% CI] = 0.82 to 0.96) at 5 years, and 0.91 f95% CI = 0.69 to 0.98) at 10 years. No difference was found between the two analyzed models. Freedom from failure for endocardial leads was 0.97 (95% CI = 0.93 to 0.99) and 0.90 (95% CI = 0.61 to 0.97) at 5 and 10 years, respectively. Epimyocardial Jeads had a significantly poorer short-term survival than endocardiaJ leads, secondarily to earlier "technique related" failures (P = 0.03; relative riskc 3.0; Wilcoxon test). However, overall long-term performance was similar to endocardial leads. Epimyocardial pacing leads, meticulously implanted and tested, have a long-term performance similar to endocardial pacing leads.     

The interrelation between the monophasic action potential duration, cycle length and ischaemia in the human left ventricle.

Steady state monophasic action potentials were recorded from a single site in the left ventricular endocardium during incremental atrial pacing to the point of angina in 25 patients. Ischaemic areas of the left ventricle were documented using a perfusion marker (99mTc-MIBI) simultaneously with the action potential recording procedure. Recordings were obtained from an ischaemic area in 13 patients and from a non-ischaemic area in 12. A linear correlation between action potential duration and cycle length changes was demonstrated for both ischaemic and non-ischaemic zone recordings between cycle length changes of 750 and 428 ms. Ischaemia induced a shortening of the action potential duration significantly greater than that produced by cycle length changes (P less than 0.0001). Mean action potential duration shortening corrected for 100 ms change in cycle length for ischaemic zone recordings was 31.4 +/- 4.2 (SD) compared to 23.3 +/- 3.1 ms for non-ischaemic zone recordings. A range of values of action potential duration shortening in unit time was analysed for sensitivity and specificity for the detection of ischaemia. A value of 26.5 ms per 100 ms change in cycle length provided the optimum compromise with 88% sensitivity and specificity. Our data provide a means of employing the monophasic action potential duration to quantify early localized ischaemia in the presence of an alteration in cycle length.     

Safety and Efficacy of Pacing for Ventricular Tachycardia

This study was undertaken to determine the safety and efficacy of three different pacing modalities on the termination of ventricular tachyarrhythmias. Thirty-two patients were studied in the electrophysiology laboratory. Three randomized pacing modalities were selected for attempted conversion: auto increment, auto burst, and random burst. In all three groups, arrhythmias with cycle lengths shorter than 230 ms required DC shock, with one exception. Those longer than 230 ms were terminated by pacing in 85% of cases. There was a 15% rate of acceleration. Thus, antitachycardia pacing for ventricular tachyarrhythmias should be considered only with defibrillating back-up.     

Diaphragm Pacing in Infants and Children

Since 1976 we have implanted bilateral diaphragm pacers in 34 infants and children: 26 with central hypoventilation syndrome (CHS), three with myelomeningocele, and five with quadriplegia. Compared to adults, several modifications have been necessary to achieve effective ventilation in infants and younger children. In all instances, a tracheostomy has been necessary due to impaired neuromuscular control of upper airway patency during pacing. Bilateral pacing has been necessary to achieve adequate ventilation; in the CHS children with normal awake ventilation, bilateral pacing during sleep eliminates the need for positive pressure ventilation. For the remaining children, adequate awake ventilation is achieved with bilateral pacing, thus permitting substantially greater mobility and limiting use of the ventilator to sleep time. Our longest survivor has now been paced for 10.7 years, and in no instance has phrenic nerve damage occurred secondary to electrical stimulation- Our current pacing regime is characterized by moderate respiratory rates (21 breaths/min), long interpulse intervals (95 ms), and short inspiratory times (0.6 sec), resulting in 50%-75% fewer stimuli/min compared to our previous regime. For all infants and children requiring 24-hour ventilatory assistance, our recent successes in maintaining ventilation using significantly fewer stimuli suggest that long-term continuous pacing is a realistic future goal.     

Fundamental Considerations in Pacing of the Diaphragm for Chronic Ventilatory Insufficiency: A Multi-Center Study

Records were reviewed of 477 patients who had diaphragm pacemakers implanted for treatment of chronic hypoventilation. Three groups were established for comparison. (1) Center group: 165 patients operated on in six medical centers participating in a cooperative study; (2) Noncenter group, sufficient data available: 203 patients operated on by surgeons with experience limited to a few cases; (3) Nonstudy group, minimal data available: 109 patients operated on as in group 2; vital statistics only were contributed. The protocol for data gathering was comprised of 154 major variables. Basic data on age, sex, diagnosis and etiology were analyzed for homogenicity of data among the groups. A comprehensive analysis of the pacing methods, complication and results fom the Center group yielded information on the early experience with diaphragm pacing important to its future application.     

DDDR起搏对心脏功能影响的研究

目的 :探讨DDDR起搏对心脏功能的影响。方法 :选择 12例缓慢性心律失常患者 ,男 7例 ,女 5例 ,年龄平均 6 9.6± 8.4岁。其中病窦综合征 6例 ,完全房室传导阻滞 5例 ,三分支阻滞 1例 ,NHYA心功能Ⅲ级 10例 ,Ⅳ级 2例 ,全部置入DDDR起博器 ,起博后跟踪随访患者 6个月 ,观察NHYA心功级别变化并进行 6分钟步行测试和超声心动图心功能参数测定。结果 :患者置入DDDR起博器后 (NHYA)心功能进步 1级者 3例 ,进步 2级以上者 9例。步行距离术后 3个月提高 2 2 .6 % (P <0 .0 5 ) ,术后 6个月提高 2 9.6 % ;左室射血分数 (LVEF)、每搏量 (SV)、心输出量 (CO)术后 3个月分别提高 33.6 %、2 0 %、2 5 %。术后 6个月分别提高 4 6 .4 %、19.7%、2 4 .9%。结论 :DDDR起博可以显著改善心功状态 ,提高运动耐量 ,是一种理想的起博方式。     

Prehospital Transcutaneous Cardiac Pacing for Symptomatic Bradycardia

We studied patients with symptomatic bradycardia to determine the importance of presenting hemodynamic status and prehospital transcutaneous cardiac pacing (TCP) upon patient survival. Of 51 patients with witnessed cardiovascular decompensation and initial bradycardia, 27 (53%) received TCP. There were no significant differences between the paced patients and those without TCP for mean times from collapse until cardiopulmonary resuscitation, paramedic arrival and a paceable rhythm, or from paramedic arrival until a paceable rhythm. Overall, emergency department arrival with a palpable pulse (26% in paced vs 13% in nonpaced group; P = 0.20) and survival to hospital discharge (15% in paced vs 0% nonpaced group; P = 0.07) tended to be better for the paced group. No patient without a palpable pulse on paramedic arrival survived to leave the hospital. Of patients with a palpable pulse upon paramedic arrival, survival to hospital discharge was greater for the paced group (80% in paced vs 0% in nonpaced group; P = 0.024). TCP appears to be most beneficial in those patients with bradycardia who have a palpable pulse when first seen.     

起搏/除颤螺旋电极植入心肌的急性力学研究

目的对不同构型的螺旋电极旋入及拔出犬心肌的急性力学行为进行测试，为心肌／电极界面的数字建模提供实验依据。方法将实验用犬麻醉后，开胸直视下暴露心腔，将不同头端构型的螺旋电极垂直旋入心肌，通过特殊设计的力学传感器记录电极头端的轴向及扭转受力情况，对比包括心房、心室共11个位点的差异情况；随即将旋入电极以外力强制拔除，记录受力-时间曲线进行分析。结果排除间断施加力量的影响，电极旋入过程的扭矩曲线接近指数曲线，平均扭矩分布范围为0．0003至0．0015，不同构型的电极有明显不同；拔除位点受力以左心室外膜、右心室游离壁、HIS束区域最大，同时可见到明显的不均质性。结论螺旋电极旋入及拔出心肌的受力情况随植入位点、电极头端构型等而不同；心室的受力明显高于心房，其中最牢固位点分别为左心室外膜、右心室游离壁及希氏束。     

Preliminary Evaluation of a Dual Chamber Pacemaker with Bradycardia Diagnostic Functions

LASCAULT, G., et al .: Preliminary Evaluation of a Dual Chamber Pacemaker with Bradycardia Diagnostic Functions . Unexplained syncope is the main indication for the implantation of a diagnostic pacemaker. Studies on those implanted have shown that in patients with unexplained syncope, the diagnosis of paroxysmal bradycardia was feasible and reliable. The present study was designed to evaluate a new bradycardia diagnosis algorithm, loaded in a dual chamber pacemaker, in 24 patients considered as candidates for diagnostic pacemakers. During a mean follow-up of 153 days, at least one bradycardia episode was recorded in 13 patients. The mean number of detected bradycardias was 6 and the median was 3. The mean delay between the algorithm activation and the first bradycardia episode was 67 days. The mechanism of bradycardia was atrioventricular block in 6 patients, sinus node dysfunction in 6 patients, and consecutive blocked atrial premature beats in 1 patient, as indicated by the event markers. In 11 patients bradycardia was recorded during the daytime only or day and night. In two patients the episodes were recorded only at night. Overall, the algorithm was well-tolerated; however, some mild symptoms were observed due to the method of bradycardia determination, allowing bradycardia. Three patients were symptomatic as a direct result of the algorithm operation, and four patients had symptoms related to the single chamber operation of the pacemaker while functioning in the diagnosis mode (VDI). These symptoms were relieved with DDD pacing.