心室颤动的时-频分析和胺碘酮的作用

研究心室颤动时主导频率的动态性空间时间变化。在19只犬中建立正交心电图和心脏电除颤系统;诱发心室颤动持续10~30 s;使用时-频分析法分析心室颤动时频率的时频变化。另有4只犬在诱发心室颤动后静注胺碘酮100 mg以观察主导频率的改变。结果显示:在427个10 s VF和335个30 s VF的试验中,主导频率的变化与平均频率相差12%~18%;79个使用胺碘酮的试验中,主导频率的均值和变异性均降低。表明:在10~30 s心室颤动时心电图主导频率有明显和持续性的变异,胺碘酮可减小心室颤动时的频率和变异。     

信号平均心电图频谱时间标测检测冠心病及持续性室性心动过速／心室颤动患者结果的分析

目的：本研究观察了频谱时间标测检测心室晚电位心室对冠状动脉粥样硬化性心脏病（冠心病）患者持续性室性心动过速（室速）／心室颤动（室颤）发生的预测价值，并观察了心肌梗死、缺血及心肌梗死部位对心室晚电位的影响。方法：用频谱时间标测法，对２１０例健康人（Ⅰ组）、２０２例冠心病心绞痛患者（Ⅱ组）、１００例陈旧性心肌梗死患者（Ⅲ组）及３９例心肌梗死并持续性室速／室颤患者（Ⅳ组）的信号平均心电图进行分析，根据健康人的正常因子值确定心室晚电位诊断标准，并用Ｘ２检验对各组患者心室晚电位阳性率进行比较。结果：心室晚电位阳性率Ⅰ组与Ⅱ组无显著差异（Ｐ＞０．０５）；Ⅲ组与Ⅳ组显著高于Ⅰ组（Ｐ均＜０．００５）及Ⅱ组（Ｐ均＜０．００５）；Ⅳ组显著高于Ⅲ组（Ｐ＜０．００５）。不同心肌梗死部位无显著差异（Ｐ＞０．０５）；多部位与单部位心肌梗死无显著差异（Ｐ＞０．０５）。预测的敏感性为５１．３％、特异性为９１．０％、阳性预告值为３５．１％、阴性预告值为９５．２％。结论：频谱时间标测检测心室晚电位对预测持续性室速／室颤的发生有重要价值，心肌梗死部位、心肌缺血对心室晚电位的发生无影响。     

Ventricular fibrillation frequency

BACKGROUND: Ventricular-fibrillation (VF) wave frequency is known to decrease with prolonged, untreated VF. VF wave frequency is used as an algorithm to identify VF in AEDs and ICDs; yet the nature of the frequency change is not appreciated. METHODS: In this study, anesthetized pigs were used and VF was induced electrically. VF wave frequency was measured each second during VF for periods up to 200 sec. Defibrillation was achieved with transchest electrodes. VF wave frequency was plotted for each second during VF. In 2 animals, CPR was applied and VF wave frequency was measured. RESULTS: In all cases VF wave frequency decreased with increasing duration of VF. At the onset of VF, the VF wave frequency ranged from 5 to 12/sec. A plot of the normalized ratio of VF wave frequency during fibrillation to the VF frequency at induction decreased to between 0.1 and 0.8 of the initial frequency. In one of the animals, VF was initiated, CPR was provided and the VF wave frequency was measured over a 200-second period. Then, the procedure was repeated without CPR. Beyond 130 seconds, the VF frequency with CPR was higher than that without CPR, indicating myocardial oxygenation. CONCLUSION: Those who use VF wave frequency to identify the presence of VF should be aware of the nature of the VF wave frequency decrease with the passage of time.     

Visceral Adiposity and the Risk of Metabolic Syndrome Across Body Mass Index: The MESA Study

ObjectivesThis study sought to evaluate differential effects of visceral fat (VF) and subcutaneous fat and their effects on metabolic syndrome (MetS) risk across body mass index (BMI) categories.BackgroundThe regional distribution of adipose tissue is an emerging risk factor for cardiometabolic disease, although serial changes in fat distribution have not been extensively investigated. VF and its alterations over time may be a better marker for risk than BMI in normal weight and overweight or obese individuals.MethodsWe studied 1,511 individuals in the MESA (Multi-Ethnic Study of Atherosclerosis) with adiposity assessment by computed tomography (CT). A total of 253 participants without MetS at initial scan underwent repeat CT (median interval 3.3 years). We used discrete Cox regression with net reclassification to investigate whether baseline and changes in VF area are associated with MetS.ResultsHigher VF was associated with cardiometabolic risk and coronary artery calcification, regardless of BMI. After adjustment, VF was more strongly associated with incident MetS than subcutaneous fat regardless of weight, with a 28% greater MetS hazard per 100 cm²/m VF area and significant net reclassification (net reclassification index: 0.44, 95% confidence interval [CI]: 0.29 to 0.60) over clinical risk. In individuals with serial imaging, initial VF (hazard ratio: 1.24 per 100 cm²/m, 95% CI: 1.08 to 1.44 per 100 cm²/m, p = 0.003) and change in VF (hazard ratio: 1.05 per 5% change, 95% CI: 1.01 to 1.08 per 5% change, p = 0.02) were associated with MetS after adjustment. Changes in subcutaneous fat were not associated with incident MetS after adjustment for clinical risk and VF area.ConclusionsVF is modestly associated with BMI. However, across BMI, a single measure of and longitudinal change in VF predict MetS, even accounting for weight changes. Visceral adiposity is essential to assessing cardiometabolic risk, regardless of age, race, or BMI, and may serve as a marker and target of therapy in cardiometabolic disease.     

Sudden Cardiac Death From the Perspective of Coronary Artery Disease

Sudden cardiac death accounts for approximately 50% of all deaths attributed to cardiovascular disease in the United States. It is most commonly associated with coronary artery disease and can be its initial manifestation or may occur in the period after an acute myocardial infarction. Decreasing the rate of sudden cardiac death requires the identification and treatment of at-risk patients through evidence-based pharmacotherapy and interventional strategies aimed at primary and secondary prevention. For this review, we searched PubMed for potentially relevant articles published from January 1, 1970, through March 1, 2014, using the following key search terms: sudden cardiac death, ischemic heart disease, coronary artery disease, myocardial infarction, and cardiac arrest. Searches were enhanced by scanning bibliographies of identified articles, and those deemed relevant were selected for full-text review. This review outlines various mechanisms for sudden cardiac death in the setting of coronary artery disease, describes risk factors for sudden cardiac death, explores the management of cardiac arrest, and outlines optimal practice for the monitoring and treatment of patients after an acute ST-segment elevation myocardial infarction to decrease the risk of sudden death.