Ischaemia induced alternans of action potential duration in the intact-heart: dependence on coronary flow, preload and cycle length

Clinical and experimental evidence relate action potential duration(APD) alternans to ischaemic heart disease and ventricular arrhythmias.The present investigation was performed to study the quantitativerelationship between APD alternans and the degree ofischaemia,loading conditions and cycle length (CL) in an intact heart. Monophasic action potentials (MAP) were simultaneously recordedby contact electrodes from two left (LV) undone right ventricular(RV) sites in 20 Langendorff-perfused rabbit hearts. The preparationswere subjected to global ischaemia at flow rates ranging from40% of normal flow to complete cessation of flow. Pacing wasperformed at either constant or regularly changing CL. The magnitudeof APD alternans was expressed as beat-to-beat differences inaction potential duration of two consecutive MAPs. During normalper fusion, neither very fast pacing at a CL of 200 ms nor periodicalrate switches resulted in persistent APD alternans. Pacing ata constant CL of 800 ms did not induce A PD alternans at completecessation of flow for 6 min. However, alternans developed progressivelyat a constant CL of 400 ms after 2.8±0.3 min of completeischaemia at the pre-loaded LV, andafter 4.6±0.4 minat the unloaded RV (P<0.01). The reduction of preload atthe LV from 15 to 5 mmftg end-diastolic pressure delayed developmentof APD alternans from 2.8±0.3 min to 4.3±0.4 min(P < 0.05) at 400 ms CL. Following graded under per fusionof 40%, 20% and 10% of initial flow, persistent APD alternansdeveloped in relation to the degree of flow reduction and increasedprogressively with duration ofischaemia. APD alternans at theLV always preceded the onset of APD alternans at the RV. Inexperiments with identical flow rates the shortest CL of 200ms resulted in the greatest and earliest initiation of APD alternanscompared to the longer CL (P<0.01, P<0.001). An increasein CL from 400 to 800 ms immediately abolished APD alternans,generated by the shorter CL, at any time during the 6 min periodof complete ischaemia. Similarly, increasing the cycle lengthfrom 200 or 400 to 600 ms eliminated APD alternans up to 6 minof ischaemia and significantly reduced its magnitude between7 and 10 min within a few beats. We conclude that persistent APD alternans is a characteristicfinding in the rabbit heart during global ischaemia. It is asensitive parameter of the severity of ischaemia and dependson the degree and duration of ischaemia as well as on the preload.The CL appears to have an independent effect on the generationof APD alternans, which is functionally separate from the effectof CL on the ischaemic burden. An eventual impact of these observationscould be the application of APD alternans as a diagnostic toolin electrophysiological examinations of myocardial ischaemiain experimental and clinical settings.     

Effects of the enantiomers of disopyramide and its major metabolite on the electrophysiological characteristics of the guinea-pig papillary muscle

Summary Disopyramide, a Class la antiarrhythmic drug, is clinically used as a racemic mixture; R(–)disopyramide and S(+)disopyramide. The major metabolite in man is desisopropyldisopyramide: R(–)desisopropyl-disopyramide and S(+)desisopropyldisopyramide. The effects of the four compounds were compared on the electrophysiological characteristics of the guinea-pig papillary muscle using the standard microelectrode technique. At an external K⁺ concentration of 5.4 mmol/l and a stimulation frequency of 1 Hz, S(+)disopyramide (20 mol/l) increased action potential duration (APD) by more than 18%, while it was diminished by 6% in the presence of R(–)disopyramide. Resting membrane potential amounted to –87.1 ± 0.5 mV (n = 14) and –85.6 ± 1.2 mV (n = 10), respectively. Also a small but significant difference in effect on the maximal rate of depolarization was observed, R(–)disopyramide being more potent, related with a slower recovery of the maximal rate of depolarization.The enantiomers of the metabolite appeared to be three times less potent than those of the parent drug in their effect on the maximal rate of depolarization. The characteristics of the enantiomers of the metabolite correlated with those of the parent drug: also the R(–)-enantiomer was more potent in decreasing the maximal rate of depolarization and caused more shortening of the action potential than the S(+)enantiomer.Time constants for onset and recovery of/from rate dependent block of the maximal rate of depolarization were dependent upon the external K⁺ concentration, both for the enantiomers of the parent drug and those of the metabolite. Onset slowed down while recovery accelerated when external K⁺ was increased. Time constants were lower for the metabolite.When stimulation interval was shortened, the effect on the maximal rate of depolarisation increased. Only for the metabolite statistical significant stereoselective differences were observed at all stimulation intervals. The effects on the action potential duration were dependent upon stimulation interval; for all enantiomers the action potential duration tended to be relatively (% of control) higher at short stimulation intervals than at large stimulation intervals. The effect on the maximal rate of depolarization was also voltage dependent, but no significant differences were observed between the enantiomers, for the parent drug as well as for the metabolite. Send offprint requests to N. Verbeke at the above address     

腰硬联合麻醉用于分娩镇痛的临床研究

目的：探讨腰硬联合麻醉(CSEA)减轻或消除产痛以及对产程、胎儿、分娩方式的影响。方法：选择305例无产科及麻醉禁忌症的初产妇，在产程进入活跃早期宫口开大3—4cm时，给予腰硬联合麻醉(观察组)，并与同期条件相似、未给予任何镇痛方法的305例初产妇进行对比(对照组)。比较两组产妇产痛程度、产程进展速度、分娩方式及对胎儿的影响。结果：观察组镇痛有效率较对照组明显升高(P＜0．01)，又活跃期较对照组明显缩短，宫颈口扩张速度加快，经阴道分娩助产率增高(P＜0．05)。胎儿窘迫及新生儿窒息、产后出血发生率两组则无显的统计学意义(P＞0．05)。结论：CSEA可有效用于分娩镇痛、加速产程，且对胎儿及产妇无不良影响，值得推广应用。     

A training program on exclusive breastfeeding in maternity wards.

OBJECTIVES: To estimate whether a 3-day training program for health professionals was followed by changes in maternity ward practices and in the rate of exclusive breastfeeding. METHODS: A retrospective study in the maternity ward of a French university hospital involved two cross-sectional samples of 323 mother-infant pairs in 1997 and 324 in 2000. RESULTS: The rate of exclusive breastfeeding at discharge increased from 15.8% (12.0-20.2) in the before sample to 35.2% (30.0-40.6) in the after sample (P<0.01). This result persisted in the multivariable analysis [adjusted odds ratio, 2.74 (1.72-4.37)]. Infants in the before sample were less likely to be breastfed within 1 h of birth (9.2% vs. 16.9%, P=0.01), to room-in 24 h/day (56.6% vs. 72.6%, P<0.01), and were more likely to receive formula supplementation (77.6% vs. 54.0%, P<0.01). CONCLUSIONS: A training program for health professionals can be effective in improving maternity ward practices and increasing exclusive breastfeeding rate at discharge.     

规范化Ⅰ、Ⅱ类切口手术预防性抗菌药物使用的实施效果分析

目的 探讨实施院内规范化围手术期预防用药方案的可行性和效果。方法 选择外科Ⅰ、Ⅱ类切口择期手术病例，以2003年10月～2004年3月出院者210例作为实验组，按规范方案用药，以2002年10月～2003年3月出院者212例作为对照组，按习惯方法用药，考察预防手术部位感染的效果及费用指标。结果 实验组与对照组手术部位感染的发生率没有显著性差异，抗菌药物费用、药品费用、住院费用显著降低。结论 在院内制定和实施规范化的围手术期预防用药方案的做法切实可行，可以促进合理用药，降低医疗费用，节约卫生资源，值得推广。     

室性早搏的快速检测方法

提出一种利用相关性和RR间期比相结合的快速室性早搏的检测算法.该算法具有一定的病人自适应性.通过MIT-BIH心律失常数据库的验证,该方法对Normal和PVC有很高的识别率.     

急性心肌梗死患者Q-T离散度分析

目的分析急性心肌梗死(AMI)患者Q-T离散度(Q-Td)的动态变化,及其与恶性室性心律失常的关系。方法测量50例急性心肌梗死病人住院期间Q-Td及校正Q-T离散度(Q-Tcd),分析其与恶性室性心律失常的关系。结果50例AMI患者住院期间Q-Td动态变化揭示了Q-Td与恶性室性心律失常的密切关系,38例急性心肌梗死Q-Td及Q-Tcd入院时较出院有非常明显延长(P<0.05)。结论Q-Td可作为预测急性心肌梗死发生恶性室性心律失常的一项敏感指标。     

Association of sleep duration with socio‐economic status and behavioural problems among schoolchildren

Aim: In this population‐based study, we aimed to determine the total sleep duration (TSD), its association with socio‐economic status (SES) and behavioural symptoms among schoolchildren. Methods: A cross‐sectional study was performed among schoolchildren in Istanbul. A structured questionnaire evaluating the sleep schedule variables was filled out by their parents. SES was determined according to the Turkish SES scale. Results:  The mean age of 2669 children was 8.2 ± 2.4 years, and 51% of the students were girls. The mean TSD was 10.20 ± 1.04, and the mean bedtime was 21.57 ± 0.56 (both in hours, minutes ± SD). Boys tended to go bed later (p = 0.004) and slept less than girls (p = 0.02). The duration of sleep disruptions increased (p < 0.001), whereas TSD decreased with age (p < 0.001). Multiple linear regression revealed that waking time and TSD decreased significantly (p < 0.05) with higher SES among both girls and boys. Sleep fragmentation was associated with habitual snoring, parasomnias, daytime sleepiness and conduct symptoms. Conclusion: Decreased total sleep duration is more prominent in boys, older children and children among higher socio‐economic status. Insufficient sleep attributed to shortened total sleep duration by age and higher socio‐economic status might have a negative effect on both sleep hygiene and psychological well‐being in schoolchildren.