Pacemaker Mediated Tachycardias In Single Chamber Rate Responsive Pacing

LAU, C.-P., ET AL.: Pacemaker Mediated Tachycardias In Single Chamber Rate Responsive Pacing. Although pacemaker mediated tachycardias are classically associated with dual chamber pacemakers, single chamber rate responsive pacemakers are also susceptible to such tachycardias under special circumstances. A unipolar activity sensing rate responsive pacemaker (Activitrax 8403) was implanted in an 83-year-old man with complete atrioventricular block. The pacemaker was programmed at an output of 5 V, activity threshold medium, rate response 5, and lower and upper rates of 70 and 125 beats/min, respectively. He presented with palpitations at rest and muscle twitching of the pacemaker pocket 4 months after implantation. Examination confirmed that the pacemaker had flipped over, resulting in pocket pacing which in turn activated the activity sensor, resulting in a rate response. The increase in pacing rate lead to a higher frequency of pocket pacing, thus leading to positive feedback increase in rate. With the patient at rest, pacemaker mediated rates were 106, 91, and 74 beats/min at low, medium and high thresholds, respectively. Decreasing the output to 2.5 V eliminated pocket pacing and the tachycardia. As a result of the reversal of the pacemaker, a similar rate response during exercise could only be achieved at a more sensitive rate responsive setting. Thus, pacemaker mediated tachycardia can complicate pacemaker "flipping" in single chamber activity sensing rate responsive pacemakers. Methods for the avoidance and treatment of pacemaker flipping are discussed. A review of other sensor mediated tachycardias is also presented.     

丙戊酸对致死性失血性休克犬器官功能和预后的影响

目的 探讨组蛋白去乙酰化酶抑制剂丙戊酸(VPA)对致死性失血性休克犬器官功能和预后的影响.方法 20只成年雄性Beagle犬,采用颈总动脉放血(按全身血容量的42%计算)制备失血性休克模型.将模型犬按随机数字表法分为休克对照组和VPA治疗组,每组10只.VPA治疗组于失血后1.5 h静脉注射(静注)VPA 100 mg/kg(溶于20 ml生理盐水),休克对照组在失血后24 h内静注20 ml生理盐水;失血后24 h起两组犬均实施延迟静脉补液.在非麻醉状态下测定犬失血前(0 h)和失血后不同时间点平均动脉压(MAP)及血浆丙氨酸转氨酶(ALT)、肌酐(Cr)和肌酸激酶同工酶(CK-MB),记录尿量及72 h生存率.结果 两组失血后2 h MAP均显著降低;随后VPA治疗组MAP(mm Hg,1 mm Hg=0.133 kPa)迅速回升,于失血后4、8和24 h显著高于相应休克对照组(58.4±7.6比40.3±5.0,84.4±8.0比56.4±4.4,92.6±10.3比72.6±8.9,P＜0.05或P＜0.01).VPA治疗组0～8、8～24、24～48和48～72 h尿量均显著多于休克对照组,但仍显著少于失血前(0 h).两组失血后血浆ALT、Cr和CK-MB均较0 h显著升高;VPA治疗组失血后4 h起器官功能指标显著低于休克对照组[ALT(U/L):80.1±9.8比112.2±10.1;Cr(μmol/L):74.5±8.3比88.0±7.6;CK-MB(kU/L):10.39±1.10比13.67±1.46,P＜0.05或P＜0.01],但失血后72 h仍显著高于0 h(ALT:79.5±7.1比40.5±4.4;Cr:85.6±7.1比46.6±4.8;CK-MB:7.63±0.86比1.66±0.21,均P＜0.01).VPA治疗组失血后72 h生存率显著高于休克对照组[70%(7/10)比20%(2/10),P＜0.05].结论 犬42%血容量失血后静注VPA能有效提高MAP,增加尿量,减轻器官功能损害,提高72 h早期生存率,有潜力成为战争或突发事故及灾害时低血容量休克现场救治的有效药物.     

应用彩色M型多普勒测量舒张早期左室流入道血流传播速度评价冠心病患者左室舒张期功能

目的 :用彩色M型多普勒测量舒张早期左室流入道血流传播速度评价冠心病患者左室舒张功能并鉴别二尖瓣“假性正常”的充盈类型。方法 :选择 5 9例冠心病患者及 3 0例正常人 ,根据二尖瓣血流频谱形态和临床资料分为四组。第1组频谱形态正常型 ( 2 >E/A >1) ;第 2组松弛受损型 (E/A <1) ;第 3组假性正常型 ( 2 >E/A >1) ;第 4组限制型 (E/A≥ 2 )。均与正常组对照。应用彩色M型多普勒测定舒张早期血流传播速度 ,同时用脉冲Doppler测二尖瓣口的血流速度频谱。结果 :血流传播速度在冠心病各组内呈进行性减低 ( P <0 .0 1) ,截断点为 45cm/s。结论 :彩色M型多普勒测量血流传播速度能无创、简便、准确地评价左室舒张功能 ,无假阴性。对二尖瓣血流频谱“假性正常”者具有鉴别价值     

彩色多普勒血流图及能量图对甲状腺良恶性肿瘤的诊断价值

目的 探讨彩色多普勒血流成像（CDFI）及彩色多普勒能量图（CDE）对甲状腺良恶性肿瘤鉴别的价值。 方法 对60例甲状腺肿瘤患者（良性46例，恶性14例）行CDFI和CDE检查，了解肿瘤周边及内部血流分布情况。 结果 血流显示率在CDFI及CDE中分别为65．0％和90．0％，CDE较CDFI提高25．0％（P〈0．05）。甲状腺恶性肿瘤CDFI及CDE大多数表现为血流丰富，且肿瘤内部血流多于肿瘤周边血流，显示率分别为69．2％和76．9％；良性肿瘤大多数表现为血流稀疏，且肿瘤周边血流多于肿瘤内部血流，显示率分别为69．2％和76．9％，二者无显著差异（P〉0．05）。 结论 CDE在甲状腺肿瘤血流的敏感性和准确性上优于CDFI，但二者对肿瘤良恶性的鉴别意义无明显差别。     

彩色多普勒超声观测动脉滤器对猪颈动脉血流的影响

目的应用彩色多普勒超声观察动脉滤器对活体猪颈动脉血流的影响。方法选择7只中华小型猪，在猪右侧颈动脉内置入滤器，应用彩色多普勒超声在置入滤器前后分别测量颈动脉血流频谱并进行分析。结果动脉滤器置入前后颈动脉频谱形态相似，RI、PI升高，差异没有统计学意义（P值分别为0．334，0．425），平均血流速度降低40．3％（P=0．034）。1例滤器置入后远端血流频谱呈静脉样，造影可见血管完全阻塞，取出的动脉滤器内可见大量血栓。结论动脉滤器置入可引起颈动脉平均血流速度降低，彩色多普勒超声可以量化评价由滤器引起的颈动脉血流参数的变化，是目前监测实验动脉血流参数最佳方法。     

重庆市某区2001～2004年恶性肿瘤发病率分析

目的为评价重庆市某区开展社区恶性肿瘤健康教育和早发现、早诊断、早治疗的干预效果提供基线资料.方法通过已经建立的肿瘤发病登记制度,从医院病案、基层报病和死亡统计收集肿瘤病例.结果某区2001～2004年恶性肿瘤粗发病率128.02/10万(男性158.68/10万,女性96.48/10万),发病率随年龄的增长而上升;其中,肺癌发病率居首位,其次为肝癌、食道癌及直肠癌.结论肿瘤发病资料是疾病防治和病因学等研究的基础,应进一步加强这方面的工作.     

Temporal Relationship Between Exercise and QT Shortening in Patients with QT Pacemakers

The present study was undertaken to examine the temporal relationship between exercise and QT interval shortening as one of the principal determinants for the functioning of QT pacemakers. Ten patients (mean age of 72.6 years) with implanted QT pacemakers were subjected to supine bicycle exercise with two different slopes, 90% and 80%. The QT interval as seen by the pacemaker was monitored by telemetry and stored on magnetic tape. After the beginning of exercise QT prolongation of a few msec occurred up to 40 sec in most patients. The earliest QT shortening of 4 msec was noted after 63.4 sec with 90% slope and 75.7 sec with 80% slope. The difference was not significant. The further time course was dependent on slope and pacemaker algorithm. Maximal QT shortening was 65.9 msec with 90% and 69.8 msec with 80% slope. It was seen 29.2 sec after termination of exercise with 90% slope and 69.5 sec with 80% slope (P < 0.05). There was no correlation of the measured delays with age. Earliest rate response in QT driven pacemakers is determined by earliest QT shortening on one hand and by the slope setting of the pacemaker on the other, where the limiting parameter appears to be QT shortening, which occurs after the first minute of exercise.     

Initial Experience with a New Single Chamber, Dual Sensor Rate Responsive Pacemaker

In August 1991, a new single chamber pacemaker became available that utilizes information from two sensors, activity and stimulus-to-T wave (QT) interval. We are reporting on the first 90 implants in 21 centers. T wave sensing was adequate at implantation in 88/90 patients, with a safety margin of > 100% in 86/90, Activity sensing was adequate in all patients. The contribution of each sensor fsensor blending) is programmable for each patient. Of 75 patients assessed at 1 month after implant, three have been programmed to "Activity-Only" mode, and 72 to dual sensor mode. Of these, 18 have been programmed to "QT < Activity," 48 to "QT = Activity," and 6 to "QT > Activity." Forty-five patients underwent exercise testing in dual sensor mode and a subgroup of 15 also underwent exercise testing in Activity-Only mode. The dual sensor mode produced a more gradual increase in pacing rate. Sensor Cross Checking^tmsatisfactorily prevented a sustained high pacing rate in tests of false-positive activity sensing (tapping, vibrating pacemaker, or static pressure). The maximum pacing rate on walking downstairs (94.2 ± 7.2 ppm) was similar to that produced by walking upstairs (91.6 ± 5.9 ppm). We conclude that initial assessment of this dual sensor, single chamber, rate responsive pacemaker confirms that the algorithm for combining data from two sensors functions satisfactorily. Dual sensor rate responsive pacing may offer significant advantages over single sensor devices, and further studies of this novel device are indicated.     

Automatic Sensor Adjustment in a Rate Modulated Pacemaker

A new feature (AutoSlope) has been introduced that can automatically adjust the sensor slope based on the chronic activity level of the patient. The algorithm adjusts the slope once per week so that 99% of the sensor response is maintained between the base rate and 23% of the difference between the programmed Base Rate and the Max Sensor Rate. Offsets are available for fine titration of sensor response in individual patients. The AutoSlope feature was evaluated in 93 patients with DDDR pacemakers (Trilogy DR+, Pacesetter). Patients were seen at 1, 3, and 6 months for a total of 178 evaluations. At each evaluation, the AutoSlope value was recorded. Patients then performed a brisk walk at sensor values equivalent to the AutoSlope value. Desired sensor rate was compared to the rate achieved by AutoSlope for the exercise period. Long-term sensor performance was evaluated by analyzing the sensor histogram. AutoSlope provided the desired sensor rate in most patients. Use of AutoSlope offsets allows fine titration of rate modulation in individual patients. Ongoing changes in sensor performance provided by AutoSlope allow patients to achieve a desired sensor rate from one evaluation to another without changes in permanent programmed settings. Programming a low maximum sensor rate may limit sensor response in some patients.     

High Physical Activity is Associated with an Improved Lipid Profile and Resting Heart Rate among Healthy Middle-aged Chinese People

Objective To investigate the effects of physical activity (PA) on dyslipidemia and elevated resting heart rate (RHR) in a large-scale cross-sectional study in China. Methods We recruited community-based individuals who were 40-60 years old using a cluster sampling method. The PA levels of the participants were classified as low, moderate, or high, using the International Physical Activity Questionnaire. Dyslipidemia was defined as the detection of abnormalities in lipid indicators, and 4 lipid parameters were evaluated using fasting blood samples. Multivariate logistic regression analyses were used to evaluate the associations of PA with dyslipidemia and RHR. Results A total of 10,321 participants (38.88% men) were included in this study. The percentages of individuals with high, moderate, and low PA levels were 46.5%, 43.9%, and 9.6%, respectively. In both men and women, high PA provided odds ratios of 0.88 [95% confidence interval (CI): 0.83, 0.94] for dyslipidemia and 0.82 (95% CI: 0.73, 0.92) for elevated RHR, compared to participants with low PA. Conclusion Our data suggested that substantial health benefits (related to dyslipidemia and elevated RHR) occurred at higher intensity PA, with greater energy consumption, in middle-aged Chinese people, and particularly in men.