无症状心肌缺血阈的临床意义

目的评价无症状心肌缺血阈。方法62例冠心病患者，通过24小时心电监测，检测冠心病患者的心肌缺血阈值(MIT)、MIT的变异度(IV)，以及每阵缺血发作持续时间(TMI)和ST段最大位移(STm)，以及昼夜缺血阵数(IN)。结果共检出506阵心肌缺血，93．5％在ST段压低时心率加快，夜间心肌缺血阈值较低，但缺血时间及ST段压低程度明显重于昼间。结论高心肌缺血阈、低心肌变异率与心肌耗氧增加有关，低心肌缺血阈、高心肌变异率与冠脉痉挛有关。     

冠心病患者无症状心肌缺血阈的分析

目的：探讨冠心病患者无症状心肌缺血阈的临床意义。方法：应用24h动态心电监测，检测62例冠心病患者心肌缺血阈值、MIT的变异度、每次缺血发作持续时间和ST段最大位移，以及昼夜缺血次数。结果：共检出506次心肌缺血，93．5％在ST段压低时心率加快，夜间心肌缺血阈值较低，但缺血时间及ST段压低程度明显重于昼间。结论：心肌缺血有不同的机制，应根据情况给予不同的治疗。     

124例冠心病心肌缺血的动态心电图分析

目的 探讨动态心电图(DCG）对检测无症状心肌缺血(SMI)的临床应用价值。方法记录心肌缺血发作的初始心率(IT)、最高心率(HMIT)、最低心率(LMIT)、持续时间(TMI)和ST段最大位移(STM)以及24h总缺血阵数(TIN)、时间(TIT)和ST段压低幅度,并计算心肌缺血阈变异度(IV),并对检测结果进行分类、分析及统计学处理。结果124例中ST-T改变960阵次,其中768阵次属SMI,192阵次为有症状心肌缺血(SYMI);SMI发作86．98％与活动有关;SMI日间发作多于夜间,以上午(6：00～12：00)为发作高峰期．占全天发作的41．93％,夜间心肌缺血阈值(IT)较低,但缺血时间及ST段压低程度明显重于昼间：混合型心肌缺血的IT显著低于单纯型心肌缺血。结论DCG是临床上监测SMI的重要方法之一,对临床评估SMI的预后有重要的临床意义。     

老年冠心病者无症状心肌缺血阈的分析

目的 探讨老年冠心痛者无症状心肌缺血(SMI)时心肌缺血阈(MIT)的发生规律及临床意义.方法 对128例患者进行24h动态心电图(DCG)检测,观察其MIT值、MIT变异度、每次缺血发作持续时间和ST段最大位移,以及昼夜缺血次数.结果 共检测984阵心肌缺血,其中932阵为SMI,93.6%在ST段压低时心率加快,心率增快的高低与缺血的程度呈正相关,夜间MIT较低,缺血时间及ST压低程度明显重于昼间(P<0.05).结论 DCG是临床上检测SMI的重要方法之一,对临床评估SMI的预后及给药有重要临床意义.     

动态心电图对无症状心肌缺血的评价

目的：探讨动态心电图（Holter）一过性ST段压低对无症状心肌缺血的诊断价值。方法：应用Holter监测152例冠心病患者心肌缺血发生阵次、每次缺血发作时间和ST段最大下移，并行冠状动脉造影检查。结果：Holter监测的152例无症状心肌缺血患者中，冠脉造影检查示冠状动脉有意义狭窄者149例（98％）；单纯无痛性心肌缺血（SMI）123例（81％）；伴其他时段典型心绞痛29例（19％）；心肌缺血发作时，快频率依赖者107例（70％）；昼夜发作规律为6：00～12：00发生最高，这期间检出523阵次，占78％。结论：Holter检出的无症状心肌缺血绝大部分为冠脉病变引起．对于冠心病的诊断和疗效评定有重大价值。     

冠心病无症状性心肌缺血的动态心电图表现及其诊断价值

目的：应用动态心电图（DCG）检测冠心病（CAD）的无症状性心肌缺血（SMI）,以探讨其发生率、发病规律、病情和预后关系。并由此评价DCG诊断SMI及指导临床治疗的应用价值。方法：采用12导联DCG记录系统,对224例CAD患者连续监测24h,回放分析观察ST段移位值;心肌缺血阈等指标。结果：224例CAD患者中发生心肌缺血204例（91．07％）,共检出694次心肌缺血发作,而其中589次为SMI（84．87％）;心肌缺血性ST段下移发作以6：00～12：00时最为频繁。而0：00～6：00时出现最少;夜间缺血ST段下移持续时间延长,心肌缺血阈变异性值增高;心率越快,诱发的心肌缺血越严重,ST段下移越明显。结论：DCG是较理想的诊断SMI的非创伤性辅助检查方法。     

心肌缺血阈值及其变异度动态心电图检测研究

本文对５２例冠心病（ＣＡＤ）患者进行２４小时动态心电图检测。共检出４７４阵缺血发作，以慢频率缺血（７７．６％）居多。夜间心肌缺血阈值较低，且缺血持续时间及ＳＴ段压低程度明显长和重于昼间。受检者心肌缺血阈值的变异度（Ｖ）为２２．６±１。７％，与缺血总阵数呈密切正相关。单纯快、慢频率缺血者与混合型缺血者比较，后组总缺血阵数，总缺血时间、Ｖ均较前组为劣。本研究提示。日常生活中的缺血发作多为血管张力变化引起的心肌供氧减少所致；ＣＡＤ患者间冠脉张力存在较大的个体差异，冠脉张力的高低同心肌缺血程度有一定的联系。此外．推测混合型缺血患者的冠际病变较重；应予足够重视。     

12导同步动态心电图对冠心病无症状心肌缺血的分析

目的探讨12导同步动态心电图（DCG）对冠心痛无症状心肌缺血（SMI）的诊断意义。方法对临床确诊的88例冠心痛者的24h DCG所记录的缺血型ST段进行分析。结果88例中,缺血型ST段下移514阵次,其中SMI365阵次,占发作盛数70％;伴胸痛、胸闷不适的心肌缺血105阵次,占发作总数的20．4％。结论DCG是检测SMI的重要方法。     

冠心病心率变异与心肌缺血的关系

本文３５例冠心病人均做２４ｈ动态心电图检查，逐段记录２４ｈ缺血心电图ＳＴ段下移时间，观察收肌缺血与心率变异之间的关系。心率变异采用统计方法计算２４ｈＲ－Ｒ间期标准差，１３例病人标准差小于５０ｍｓ为心率变异低组，２２例病人标准差大于５０ｍｓ为心率变异高组。心率变异低与心率变异高两组病人比较，心肌缺血发作阵数和总缺血时间有显著性差异，总缺血时间与心率变异呈低度负相关（ｒ＝－０．２９，Ｐ〈０．０５）；两     

冠心病心肌缺血动态心电图的临床分析

目的探讨冠心病者心肌缺血与心律失常的关系。方法应用动态心电图（DCG）进行临床分析，监测135例冠心病者心肌缺血发生阵次、每次缺血发作时间和ST段最大压低，以及昼夜缺血次数。结果无痛性心肌缺血（SMI）92例，占68．1％；伴典型心绞痛12例，占8．8％；心肌缺血发作时，快频率依赖者86例，占63．7％。昼夜发作规律为6：00—12：00发生最高，检出694阵次占57.9％。结论DCG对心肌缺血和心律失常的种类、时间、数量与日常活动的关系、变化规律以及药效可进行详细的观察，是监测心肌缺血和心律失常有效方法之一。     

心绞痛患者528次缺血性ST段下移分析

83例心绞痛患者经24小时动态心电图监测到528次缺血性ST段下移,分析结果表明:1.在心绞痛患者缺血性ST段下移中,无症状性心肌缺血占75％,发生次数是有症状的3倍;2.缺血性ST段下移,85％与活动有关;3.缺血性ST段下移有明显的昼夜分布规律,上午6—10时为发作高峰,占全天总次数32％。提示在冠心病治疗中应重视包括无症状性心肌缺血在内的总缺血负荷,并结合缺血的昼夜分布规律调整给药时间。     

Role of increases in heart rate in determining the occurrence and frequency of myocardial ischemia during daily life in patients with stable coronary artery disease.

OBJECTIVES. The goal of this study was to investigate the role of increases in heart rate in the development of ischemic episodes recorded during ambulatory electrocardiographic (ECG) monitoring in patients with stable coronary artery disease and to establish the importance of such increases in determining the frequency of ambulatory myocardial ischemia. BACKGROUND. The factors that determine the occurrence and frequency of episodes of myocardial ischemia that patients with stable coronary artery disease experience during daily life have not been clearly defined. In particular, the role of increases in heart rate in the development of myocardial ischemia is controversial. METHODS. To address these issues, 54 patients (42 men and 12 women, mean age 60.5 +/- 8 years) with proved coronary artery disease who had > or = 1 mm ST segment depression during exercise testing underwent an exercise treadmill test with use of the National Institutes of Health combined protocol and a 48-h period of ambulatory ECG monitoring. The exercise ischemic threshold was determined as the heart rate at the onset of ST segment depression during exercise testing. RESULTS. During monitoring, 48 (89%) of the 54 patients had at least one episode of ST segment depression (mean +/- SD 6.6 +/- 5 episodes, range 0 to 22). The majority (320 of 359 or 89%) of ischemic episodes were preceded by an increase in heart rate > or = 10 beats/min; the most significant increase (22.3 +/- 10 beats/min) occurred during the 5-min period before the onset of the episode. An ischemic episode occurred 80% of the times the heart rate reached the exercise ischemic threshold. A strong correlation was observed between the number of times the exercise ischemic threshold was reached during monitoring and both the number and the duration of ischemic episodes (r = 0.90 and 0.71, respectively, p < 0.0001). CONCLUSIONS. Increases in heart rate that exceed the exercise ischemic threshold are commonly observed before the onset of episodes of ambulatory myocardial ischemia in patients with stable coronary artery disease. Moreover, such increases constitute an important determinant of the frequency of myocardial ischemia during daily life. These findings may explain the variability observed in the number of ischemic episodes and may have important implications for the mechanisms that contribute to myocardial ischemia in daily life and for the clinical evaluation of patients with coronary artery disease.     

Quantitation of transient myocardial ischemia by digital, ambulatory electrocardiography

Transient myocardial ischemia is more frequently silent than accompanied by angina. The frequency of ischemia varies markedly from day to day, so that in order to accurately define the total ischemic burden, it may be necessary to quantitate ischemic episodes for periods longer than 24 hours. Therefore, a programmable, digital device was developed for long-term, interactive, ambulatory monitoring of the electrocardiogram, which uses variations in a time-averaged ST level as an indicator of myocardial ischemia. The electrocardiographic signal is digitized at 256 Hz and analyzed by an algorithm. If ST depression is planar or downsloping and persists for more than 40 seconds, and if the ST depression is equal to or more than a user-programmed threshold, the device marks the onset of an ischemic event and times it. The algorithm has been validated by comparison of its analysis of the ST segment to human and computerized analyses of frequency-modulated Holter recordings and stress tests. To assess the feasibility and utility of long-term monitoring, patients with documented coronary artery disease were monitored continuously for 14-day periods. Of 26 patients enrolled, 8 completed a protocol for individualization of anti-ischemic therapy using transdermal nitroglycerin. Over 90% of ischemic episodes in this group of patients, all of whom had had a previous myocardial infarction, were silent. Treatment with 10 mg of transdermal nitroglycerin reduced the number of ischemic episodes by 59% and the duration of ischemia by 60% (p less than 0.001); there was no diminution in the effectiveness of treatment from week 1 to week 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long-term variation in myocardial ischemia during daily life in patients with stable coronary artery disease: its relation to changes in the ischemic threshold.

Long-term variation in the frequency of myocardial ischemia during daily activity in patients with coronary artery disease who do not experience symptomatic changes has not been documented. Because at one point in time, the magnitude of such ischemia is strongly related to the ischemic threshold measured during exercise testing, this study was undertaken to determine whether patients with stable coronary artery disease show long-term variations in the frequency and duration of myocardial ischemia and to establish whether such variability is related to parallel changes in the ischemic threshold during exercise testing. Forty consecutive patients (mean age 61 +/- 8 years) who showed a stable clinical course over greater than or equal to 12 months were studied with a repeat exercise treadmill test and ambulatory electrocardiographic (ECG) monitoring after withdrawal of antianginal medications. The ischemic threshold was determined as the exercise time at 1 mm of ST segment depression. The mean interval to both follow-up evaluations was 15 +/- 3 months. Among the 23 patients with myocardial ischemia on ambulatory ECG monitoring at initial evaluation, the number and duration of ischemic episodes at follow-up were increased in 5 patients (mean increase 3.6 +/- 2 episodes and 123 +/- 98 min), unchanged in 1 patient and decreased in 17 patients (mean decrease 2.6 +/- 2 episodes and 98 +/- 72 min). Of the 17 patients without ischemic episodes at initial evaluation, 3 had evidence of ischemia on follow-up ambulatory ECG monitoring.(ABSTRACT TRUNCATED AT 250 WORDS)     

State of the art in stress testing and ischaemia monitoring

Electrocardiography remains the most widely used method for detecting myocardial ischemia. ST segmentabnormalities in the resting 12-lead electrocardiogram in subjects with angina and coronary risk factors seem todefinitely indicate ischemic heart disease and an adverse prognosis. ST depression during exercise testing is thefirst line provocative test for ischemic heart disease although it has a mean sensitivity of only 68% anda slightly higher specificity (77%). The presence or absence of chest pain in patients with anischemic ST response to exercise testing does not change the risk of future ischemic events. However, STdepression during the recovery period is associated with increased risk both for acute coronary events andcoronary death, whereas silent ischemia during recovery is an even stronger predictor than during exercise. Theamplitude of ST depression has not been documented to reflect the magnitude of ischemia. Therefore, new methodsare under investigation such as adding R and Q wave amplitude criteria, maximal ST/heart rate slope, linearregression analysis of the heart rate related change in ST depression and a score integrating ST segment amplitudeand slope changes. The demonstration of episodic ST segment depressions in the ambulatory setting, even withoutaccompanying chest pain, are an expression of transient ischemia and such episodes seem to represent a poorprognosis. In the hospital setting, ST depression detected by continuous monitoring is related to the clinicaloutcome. ST segment monitoring during the first 6–9 hours after coronary care unit admission providesimportant prognostic information on-line and considerably improves early risk stratification. Such continuous STmonitoring overcomes some of the limitations of static monitoring, as it improves the likelihood of capturing themaximal point of ST deviation, as well as early episodes of reocclusion that are manifest as recurrent STelevation.     

Variability of episodic ST segment depression in chronic stable angina: Implications for individual and group trials of therapeutic efficacy

Objectives. This study was conducted to quantify the variability of episodic ST segment depression in chronic stable angina and enable assessment of the impact of interventions in individual patients and clinical trials.Background. Episodic myoeardial ischemia can be detected by ST segment depression on ambulatory electrocardiographic (ECG) monitoring and may be important for the assessment of outcome. Variability of the number and duration of episodes has important unplications for monitoring and therapeutic strategies.Methods. We studied 36 patients, aged 37 to 77 years (median 60), with stable angina and coronary artery disease by serial ambulatory ECG monitoring for a total of 415 days. A nested analysis of variance was carried out to assess the sources of spontaneous variation, and power function analyses were performed.Results. During 415 days of monitoring, 1,882 episodes of ST segment depression were detected (mean frequency ± SD, 4.5 ±4.1/day, duration 67 ± 87 min/day, 25% in association with pain). Considerable variability was found within and between patients for both the number and the duration of ischemic episodes. For a patient monitored for 24 h before and after treatment, an 81% reduction in the number of episodes would be required to show a significant benefit; if monitoring were performed for 4 days four times before and after therapy, a 46% decrease would be significant. In clinical trials, a true reduction of ≥15% in ischemic episodes is required to have sufficient power to obtain statistical significance.Conclusions. The natural variability of transient myocardial ischemia in patients with chronic stable angina can be quantified and this information used to study the effectiveness of interventions in both individual patients and clinical trials.     

Evaluation of exercise test reproducibility in patients with ischemic cardiopathy

We evaluated the repeatability of some measurements taken during the bicycle ergometer exercise test (exercise duration, heart rate and pressure rate product at angina and ST segment depression times) in 166 consecutive non-selected ambulatory patients with proven ischemic heart disease. One hundred and sixty-six patients with history of angina and/or myocardial infarction performed three exercise tests within seven days of wash-out. Eighty-six (58.1%) of these experienced angina and ischemic ST segment depression during all three tests (group 1), and 80 (48.2%) finished at least one test without angina or ST segment depression (group 2). The degree of angina (according to Canadian Cardiovascular Society classification) was higher in the first group than in the second one; on the contrary, exercise duration as well as pressure rate product at ischemic threshold, heart rate and pressure rate product at the onset of angina were significantly lower (0.001 less than p less than 0.05) in the former group. In group 1, we analyzed ergometric parameter measurement "repeatability" during the three consecutive exercise tests. The analysis of variance for repeated measurements showed that exercise duration and pressure rate product values at ischemic threshold did not vary significantly in the three tests, while other ergometric parameters showed a greater variability (0.001 less than p less than 0.05). Age, previous myocardial infarction or rest angina, the number of critically stenotic coronary vessels and the ejection fraction did not condition the repeatability of the test. In conclusion, in our population of non-selected ischemic patients only 52% developed angina and ischemic ST segment depression during all three exercise tests performed.(ABSTRACT TRUNCATED AT 250 WORDS)