Effect of spinal cord stimulation on heart rate variability and myocardial ischemia in patients with chronic intractable angina pectoris—A prospective ambulatory electrocardiographic study

Background and hypothesis: Spinal cord stimulation is an effective treatment for chronic refractory angina pectoris. Its efficacy is related to an anti-ischemic action, possibly as a result of modulation of the autonomic nervous system. Therefore, the influence of spinal cord stimulation on the autonomic nervous system and myocardial ischemia was prospectively studied in 19 consecutive patients with intractable angina pectoris. Methods: Patients were included when demonstrating > 0.1 m V STsegment depression on the exercise electrocardiogram (ECG) during two separate treadmill tests. After enrollment, heart rate variability together with ischemic indices were studied with 48 h ambulatory ECG monitoring. Assessments were made at baseline and after 6 weeks of spinal cord stimulation therapy. Results: After 6 weeks, no significant changes in heart rate variability were detected. However, ischemic indices on the ambulatory ECG, as well as anginal attacks and consumption of sublingual nitrate tablets, were significantly decreased. Conclusion: Autonomic modulation assessable with heart rate variability analysis may not be the explanatory mechanism of action for the decrease of anginal attacks and ischemia, exerted by spinal cord stimulation used as an adjuvant therapy in patients with chronic intractable angina pectoris.     

Influence of perfusion pressure and heart rate on local myocardial flow in the collateralized heart with chronic coronary occlusion

We studied the influence of controlled changes in perfusion pressure and heart rate on the regional distribution of myocardial flow in normal dogs and in dogs with multiple chronic coronary artery occlusions but without infarctions.Local myocardial blood flow was determined with the tracer microsphere technique. By step-wise altering of systemic blood pressure during maximal vasodilation classical pressure flow relations were obtained. One week after complete chronic occlusion a functionally and anatomically well-defined compartmentation of blood flow was found. The dilatory reserve is clearly compromised not only in the collateral-dependent myocardium but also in the apparently normal myocardium which delivers collateral flow. An “arterio-arterial shunting” mechanism is shown to exist. Several months after coronary occlusion, regional myocardial flow is still non-homogeneous. Although the coronary dilatory capacity of the collateralized myocardium is nearly normal, that of the normal myocardium is found to be higher than normal. Vessel growth in both areas is discussed as being responsible for this phenomenon.Right ventricular pacing during maximal vasodilation produces a flow decrease to the endocardial muscle layers in normal dogs, while the epicardial flow is unchanged. One week after complete chronic coronary occlusion pacing during maximal vasodilation reduces the dilatory capacity in the collateralized areas to such an extent that the supplementary increase in myocardial oxygen demand will induce ischemia because of the compromised oxygen supply.     

Diagnosis of silent myocardial ischemia using ambulatory electrocardiographic monitoring with pedometer,analysis of heart rate,and ST loop in ambulatory electrocardiogram

Background: It has been suggested that episodes of silent myocardial ischemia (SMI) might influence the prognosis of patients with ischemic heart disease, as its consequences are similar to those of myocardial ischemia accompanied by pain. Ambulatory electrocardiogram (ECG) is generally employed in diagnosis as well as in evaluation of clinical efficacy in patients with SMI, but problems related to its application remain because of the difficulty in differentiating between nonischemic and ischemic ST-segment depressions and because of the absence of data concerning body movement. Methods and results: We developed a method for simultaneously recording onto magnetic tape both the ECG chart and pedometer count, as well as a program which enables semi-automatic analysis of the heart rate (HR)-ST relationship. This new method was employed to record ambulatory ECG along with pedometer count for a total of 70 patients, consisting of 53 with coronary heart disease who were shown to have ischemic heart disease, and 17 with various heart diseases in whom coronary angiography revealed no coronary stenosis. The HR-ST relationship was assessed for periods during which steps were recorded by the pedometer, that is, when patients were confirmed to have been under exertion effort. Patients demonstrating the following findings were diagnosed as true positive for SMI: the ST segment level did not decline until HR increased to a certain threshold, and the rate of change in the ST-segment level noted thereafter was ?0.025 mm/beats/min or lower; or the ST-segment depression induced by effort continued even after discontinuation of exercise, after which time HR began to decrease, and the HR-ST loop consequently described a counterclockwise rotation. Evaluation of the HR-ST relationship based on these criteria revealed excellent results, as demonstrated by values of 79.2% for sensitivity and 94% for specificity. Conclusion: Our newly developed method of assessment of the HR-ST relationship via analysis of simultaneous data from an ambulatory ECG and a pedometer appears to be time saving, highly objective, and useful with regard to the diagnosis of SMI and evaluation of the therapeutic effect of drugs in patients with ischemic heart disease.     

A metaanalysis of predischarge risk stratification after acute myocardial infarction with stress electrocardiographic, myocardial perfusion, and ventricular function imaging

We assessed the relation of abnormal predischarge noninvasive test results to outcomes in postmyocardial infarction patients. We included series published from 1980 to 1995 containing only myocardial infarction patients, enrolling most patients after 1980, testing within 6 weeks of infarction, having follow-up rates > 80%, and having 2 × 2 frequency outcome rates for test results, that were the latest of multiple reports. Sensitivity, specificity, and predictive values were calculated for test results for 1-year outcomes (cardiac death, cardiac death or reinfarction). Univariable and summary odds were calculated for test results. Reports (n = 54) included a total of 19,874 patients and were primarily retrospective (76%) and small series (35% of reports included < 5 deaths). One-year mortality ranged from 2.5% for pharmacologic stress echocardiography to 9.3% for exercise radionuclide angiography. Positive predictive values for most noninvasive risk markers were < 0.10 for cardiac death and 0.20 for death or reinfarction. Electrocardiographic, symptomatic, and scintigraphic risk markers of ischemia (ST-segment depression, angina, a reversible defect) were less sensitive (≤44%) for identifying morbid and fatal outcomes than markers of left ventricular dysfunction or heart failure (exercise duration, impaired systolic blood pressure response, and peak left ventricular ejection fraction). The positive predictive value of predischarge noninvasive testing is low. Markers of left ventricular dysfunction appear to be better predictors than markers of ischemia. Limitations of the literature—small samples and widely varying event rates—impede our ability to discern the accuracy of predischarge noninvasive testing. More rigorous, controlled trials are required to elucidate the relative value of these tests for risk stratification.     

冠心病患者无症状性心肌缺血与心率变异性的临床研究

目的探讨冠心病患者无症状性心肌缺血(SMI)的发生规律及与心率变异性的关系。方法应用24 h动态心电图分析206例冠心病患者发作心肌缺血情况并根据其是否伴有心绞痛,分为有症状性心肌缺血(Ⅰ组)和SMI(Ⅱ组),并与对照组进行心率变异性(HRV)对比。结果检出单纯SMI例数占冠心病心肌缺血例数的71%,SMI发作次数占心肌缺血次数的81.2%,SMI持续时间及ST段压低程度均显著高于有症状性心肌缺血,心肌缺血发作时间差异无统计学意义,高峰在06∶00~12∶00,00∶00~06∶00最少;各组HRV的特点:SMI时各时域指标依次减少,Ⅰ组、Ⅱ组与对照组比较,Ⅱ组与Ⅰ组比较,各参数差异均有统计学意义(均P<0.05)。结论SMI是冠心病患者心肌缺血最常见表现形式,心肌缺血改变了心脏自主神经调节的均衡性,而SMI的发生可能与心脏自主神经病变加重有关,SMI缺血程度、持续时间是引起急性心脏事件的重要因素。     

健康人心率震荡的昼夜节律及其与心率变异性的相关性分析

心率震荡（heart rate turbulence，HRT）的病理生理机制至今仍未完全阐明，一些资料表明其与压力反射敏感性高度相关，且与心率变异性（heart rate variability，HRV）之间也存在显著的相关关系。本组资料观察健康人HRT的昼夜变化并通过与HRV的相关性分析，进一步探讨HRT与自主神经的关系。     

Coronary vascular K+ATP channels contribute to the maintenance of myocardial perfusion in dogs with pacing-induced heart failure

The functional role of coronary vascular ATP-sensitive potassium (K+ATP) channels in the regulation of coronary blood flow (CBF) has not been determined in chronic heart failure (CHF). To test the hypothesis that K+ATP channels contribute to myocardial perfusion in HF, we examined the effects of intracoronary infusion of glibenclamide, an inhibitor of K+ATP channels, on basal CBF in control and CHF dogs. CHF was produced in mongrel dogs by pacing the right ventricle for 4 weeks. Under anesthesia, CBF in the left anterior descending coronary artery, other hemodynamic and metabolic parameters, or regional myocardial blood flow were measured. Basal CBF was less in CHF dogs than in controls. Glibenclamide at the graded doses (5, 15 and 50 microg x kg(-1) x min(-1) decreased CBF in both control and CHF dogs. The percentage decrease in CBF with glibenclamide at 50 microg x kg(-1) x min(-1) was greater (p<0.01) in CHF dogs than in controls. The greater decrease in CBF with glibenclamide at 50microg x kg(-1) x min(-1) was associated with myocardial ischemia. Glibenclamide decreased myocardial blood flow in each sublayer of the myocardium in the 2 groups. These results suggest that the basal activity of coronary vascular K+ATP channels is increased in CHF dogs but not in controls. This may contribute to the maintenance of myocardial perfusion in CHF.     

单纯收缩期高血压患者的心率震荡与心率变异

目的:观察单纯收缩期高血压(ISH)患者的心率震荡(HRT)和心率变异(HRV)的变化。方法:记录24h动态心电图,计算窦性HRT的初始值(TO)和震荡斜率值(TS)以及HRV的SDNN、pNN50和LF/HF,比较ISH组(85例)、普通高血压组(80例),正常对照组(58例)3组之间的差别,分析HRT和HRV之间的相关性。结果:ISH组、普通高血压组的HRT和HRV与正常对照组的HRT和HRV比较差异均有统计学意义(P<0.05),ISH组的TS和LF/HF较普通高血压组明显降低(P<0.05);HRV的各项指标和HRT均有良好的相关性,其中pNN50与HRT相关系数最高。结论:原发性高血压患者有显著的HRT减弱及HRV的异常,其中ISH患者较普通高血压患者更加明显,且HRT与HRV的密切相关,表明心脏自主神经功能紊乱可能对于高血压的发生及预后均有重要影响。     

Association of heart rate response with scan and left ventricular function on adenosine myocardial perfusion imaging.

To evaluate the association of heart rate (HR) response with abnormal scan and/or left ventricular (LV) function in patients undergoing adenosine myocardial perfusion imaging, we retrospectively studied 188 consecutive patients who underwent a standard adenosine stress test (without exercise) and myocardial perfusion imaging (MPI) using technetium-99m sestamibi radioisotope. Change in HR was calculated by subtracting HR at rest from peak HR. The percentage change in HR was calculated. All patients underwent stress and resting single-photon emission computed tomography (SPECT) imaging. LV ejection fraction (EF) was calculated using gated SPECT. Mean age was 60 +/- 12 years and 135 of the patients (72%) were women. We divided the patients into 2 groups: group 1 (142 patients, 75%) had normal scans and group 2 (46 patients, 25%) had abnormal scans; abnormal scans were defined as presence of either fixed defects, reversible defects, or both. Average HR increased by 29 beats/min in the normal scan group compared with 19 beats/min in the abnormal scan group (p = 0.0004). Forty-seven patients (25%) had reduced EF (<45%). This group had an average HR and percentage HR increase of 20 beats/min (29%) compared with an increase of 29 beats/min (44%) in patients with normal EF (p = 0.002 and p = 0.002, respectively). Thus, a diminished HR response had a significant association with both an abnormal scan and reduced EF on adenosine MPI.     

Assessing myocardial perfusion with the transthoracic Doppler technique in patients with reperfused anterior myocardial infarction: comparison with angiographic, enzymatic and electrocardiographic indices.

AIMS: Doppler guidewire studies demonstrated that the no-reflow phenomenon in acute myocardial infarction is associated with characteristic coronary blood flow pattern. We investigated the potential of coronary flow measurement with transthoracic Doppler technique to detect the no-flow in the patients with reperfused infarction, and compared it to that of other modalities. METHODS AND RESULTS: We performed intracoronary myocardial contrast echocardiography after successful primary coronary intervention in the 94 patients with first, anterior wall infarction. Coronary blood flow in the left anterior descending artery was detected with transthoracic Doppler echocardiography within 24 h after reperfusion in 83 patients (88.3%). Twenty-two patients with the no-reflow had significantly lower systolic peak velocity (5.1 +/- 4.2 vs. 8.1 +/- 6.2 cm/s, p = 0.04), higher diastolic peak velocity (38.2 +/- 10.3 vs. 30.8 +/- 15.7 cm/s; p = 0.04), and shorter diastolic deceleration time (134 +/- 41 vs. 424 +/- 202 ms; p < 0.0001) than those with good-reflow. Systolic flow reversal was more frequently observed in those with no-reflow (18.2% vs. 3.3%, p = 0 .02). Diastolic deceleration time < 185 ms detected the no-reflow with far higher sensitivity/specificity (95.5%/95.1%) than TIMI frame count (45.5%/91.8%), ST resolution (54.5%/73.8%) and creatinine kinase-MB (54.5%/88.5%). CONCLUSION: Analysing coronary blood flow pattern can detect the no-reflow after anterior infarction better than other angiographic, electrocardiographic and enzymatic modalities.     

Mechanisms of angina pectoris in syndrome X assessed by myocardial perfusion dynamics and heart rate variability

The fundamental abnormality in syndrome X (angina pectoris,ischaemia-like stress ECG despite angiographically normal coronaryarteries) might be patchily distributed increased tone in pre-arteriolarcoronary vessels with compensatory release of adenosine. Theaim of this study was to confirm this hypothesis and to exploreits relationships with autonomic system functioning. Using parametric positron emission tomography, myocardial perfusionwas examined in 480 segments in 16 syndrome X patients and 16age- and sex-matched healthy volunteers. Autonomic functionwas explored by Holier monitoring of time domain parametersof heart rate variability. Compared to volunteers, both meanperfusion (123 ± 55 vs 87±16mg. min^–1. 100g^–1;P<0.01) and its coefficient of variation (17.0±3.2vs 13.6±2.2%; P<0.01) as a measure of perfusion heterogeneity,were higher in patients with syndrome X. In contrast to thefindings in the control subjects, patients showed an inverserelationship between perfusion heterogeneity (coefficient ofvariation of segmental perfusion) and autonomic tone (heartrate variability parameters). Since marked perfusion heterogeneity (inversely related to autonomictone) and higher overall perfusion were found, the study supportsthe data that in syndrome X hyperreactivity of small coronaryvessels with compensatory release of adenosine may be patchilydistributed.     

Transmyocardial laser revascularization with the Holmium:YAG laser does not improve myocardial perfusion in the acutely ischemic heart: an experimental study measuring myocardial perfusion by a thermal imaging camera

BACKGROUND: Transmyocardial laser revascularization (TMLR) is a new surgical therapy for patients with end-stage coronary artery disease refractory to conventional therapy. TMLR should act by improvement of perfusion of the lasered myocardium. Blood should be delivered from the cavity of the heart to the surface of the myocardium. The aim of this study was to measure perfusion of normal, ischemic, and ischemic myocardium after TMLR. METHOD: We used a new method of perfusion measurement by an infrared thermal imaging system in an open-chested adult sheep model with temporary and permanent occlusion of the dominant diagonal branch. RESULTS: A significant fall from normal perfusion of the myocardium to reduced after inducing ischemia (p<0.01) and a significant rise again after reperfusion (p<0.001) could be shown. Perfusion measurements after TMLR did not significantly differ from perfusion measurements after inducing ischemia (p=0.2). CONCLUSION: In the presented sheep model, laser revascularization could not improve myocardial perfusion after acute ischemia as seen by the infrared thermal imaging system.     

24-hour electrocardiographic study of heart rate and rhythm patterns in population of healthy children.

Twenty-four hour electrocardiographic recordings were made on 104 randomly selected, healthy 7 to 11-year-old children. Ninety-two were technically adequate and suitable for analysis. The mean highest heart rate measured by direct electrocardiographic analysis over nine beats was 164 +/- 17. The mean lowest heart rates were 49 +/- 6 over three beats', and 56 +/- 6 over nine beats' duration. The maximum duration of heart rates less than 55/minute was 40 minutes. At their lowest heart rates 41 children (45 per cent) had junctional escape rhythms, the maximum duration of which was 25 minutes. Nine children showed PR intervals greater than or equal to 0.20 s and included three with Mobitz type I second degree atrioventricular block. Nineteen (21%) had isolated supraventricular or ventricular premature beats (less than 1/hour). Sixty subjects (65%) had sinus pauses that could not be distinguished on the surface electrocardiogram from those previously described as sinuatrial exit block or sinus arrest. The maximum duration of sinus pause measured over 24 hours on each child was 1.36 +/- 0.23 seconds. Thus apparently healthy children show variations in heart rate and rhythm over 24 hours hitherto considered to be abnormal.     

A study of the variations in myocardial perfusion induced by systemic thrombolysis in acute myocardial infarct using sequential scintigraphy with 201-thallium

To assess scintigraphic changes induced by intravenous streptokinase therapy, serial rest redistribution thallium-201 perfusion imaging was performed in 62 patients with acute myocardial infarction lasting less than 6 hours. Twenty-seven patients randomized to treatment with intravenous streptokinase (group A) and 35 to conventional therapy (group B) underwent thallium-201 scintigraphy as soon as possible after admission to the coronary care unit (early study). Regional myocardial perfusion was assessed using thallium-201 scintigraphy 7-9 days later in each patient (late study). The size of the perfusion defect was evaluated using a semi-quantitative score. The size of the perfusion defect decreased in serial scans in both group A (preintervention score: 12.1 +/- 6.8; redistribution score: 11.4 +/- 6.8; late study: 8.8 +/- 7.0) and group B (12.8 +/- 6.5; 12.3 +/- 6.7; 10.6 +/- 7.5, respectively). No statistical difference in myocardial perfusion was found between the two groups, on late study. Peak serum creatine kinase MB (CKMB) was earlier in group A than in group B (1030.8 +/- 326.6 vs 1361.0 +/- 271.1: p less than 0.001). The fast CKMB release group (onset of symptoms-peak of CKBM less than or equal to 900 minutes) exhibited higher thallium-201 uptake when compared to the slow CKMB release group, at the time of late study (perfusion defect score: 6.1 +/- 5.7 vs 10.7 +/- 7.3: p = 0.03). Reversibility was observed in 21/62 patients (34%). Reversibility corresponded to unchanged or improved perfusion defect score on late study in 18/21 patients (86%). Nevertheless 20/41 (49%) patients not showing redistribution of thallium-201 within pre-treatment defect had an improvement in regional perfusion on late study. Reversibility was observed in 9/14 (64%) patients with fast CKMB release and in 12/47 (26%) patients with slow CKMB release. We conclude that the early peak of CKMB is associated with a higher uptake of thallium-201 on late study. Furthermore, the reversibility of perfusion defect on redistribution imaging forecasts evolution of scintigraphic perfusion, but, when this is not present, it doesn't rule out late improvement of thallium-201 myocardial uptake. The low sensitivity and specificity of redistribution imaging and the procedure related delay in instituting therapy make thallium-201 scintigraphy unreliable in the evaluation of myocardial reperfusion following thrombolysis.