Silent myocardial ischemia in diabetics with normal autonomic function

[Silent myocardial ischemia in acute coronary syndrome]

The given review considers the pathogenesis, diagnosis, and clinical significance of silent myocardial ischemia (SMI) in individual patient groups. It discusses the problem of SMI in acute coronary syndrome (ACS), the possible causes of SMI and the specific features of its diagnosis. It also indicates that there is a need for 12-lead ECG telemonitoring in intensive care unit patients with ACS to intraoperatively correct patient management and treatment policy.

Atypical presentation of acute and chronic coronary artery disease in diabetics

In patients with diabetes mellitus, cardiovascular disease is the principal cause of mortality and chest pain is the most frequent symptom in patients with stable and acute coronary artery disease. However, there is little knowledge concerning the pervasiveness of uncommon presentations in diabetics. The symptomatology of acute coronary syndrome, which comprises both pain and non-pain symptoms, may be affected by traditional risk factors such as age, gender, smoking, hypertension, diabetes, and dyslipidemia. Such atypical symptoms may range from silent myocardial ischemia to a wide spectrum of non-chest pain symptoms. Worldwide, few studies have highlighted this under-investigated subject, and this aspect of ischemic heart disease has also been under-evaluated in the major clinical trials. The results of these studies are highly diverse which makes definitive conclusions regarding the spectrum of atypical presentation of acute and even stable chronic coronay artery disease difficult to confirm. This may have a significant impact on the morbidity and mortality of coronary artery disease in diabetics. In this up-to-date review we will try to analyze the most recent studies on the atypical presentations in both acute and chronic ischemic heart disease which may give some emphasis to this under-investigated topic.

Detection of silent myocardial ischaemia in asymptomatic diabetic patients during treadmill exercise testing

BACKGROUND

Diabetic patients have an increased prevalence of atherosclerosis and coronary artery disease. They may also experience higher morbidity and mortality after acute coronary syndrome compared with non-diabetic subjects.

AIM

The objective of this study was to determine the presence of silent myocardial ischaemia by treadmill test in asymptomatic diabetic patients and to compare it with age- and sex-matched subjects without diabetes mellitus.

METHODS

The study design was cross-sectional and the setting was a tertiary care centre. Fifty (42 males, 8 females) asymptomatic patients with diabetes in the age group of 30-70 years were included in the study group and 30 (24 males, 6 females) non-diabetic subjects of comparable age, sex and physical activity were the control group. They were assessed for the presence of silent ischaemia by a standard treadmill test using the Bruce protocol.

RESULTS

Twenty-five of 50 diabetic patients showed a positive response to the exercise stress test, while 7 of 30 controls showed stress test positivity (p < 0.05). The stress test positivity showed a female predilection among diabetic patients (50% in diabetic patients and 16.67% in controls; p < 0.05). Diabetic patients with a positive stress test showed higher prevalence of hypertension (36%) and dyslipidaemia (84%) compared with diabetic patients with a negative stress test (12% and 28%, respectively) [p < 0.001]. The controls showed a better exercise capacity compared with diabetic patients; diabetic patients with a negative stress test had better exercise capacity than those with a positive stress test.

CONCLUSIONS

The treadmill test is a useful, specific, cost-effective, non-invasive tool for detection of silent myocardial ischaemia in asymptomatic diabetic patients.

Characterization of upper thoracic spinal neurons receiving noxious cardiac and/or somatic inputs in diabetic rats

The aim of the present study was to examine spinal processing of cardiac and somatic nociceptive input in rats with STZ-induced diabetes. Type 1 diabetes was induced with streptozotocin (50mg/kg) in 14 male Sprague-Dawley rats and citrate buffer was injected in 14 control rats. After 4-11 weeks, the rats were anesthetized with pentobarbital, ventilated and paralyzed. A laminectomy enabled extracellular recording of T(3) spinal cord neuronal activity. Intrapericardial administration of a mixture of algogenic chemicals (bradykinin, serotonin, prostaglandin E(2) (all at 10(-5)M), and adenosine (10(-3)M)) was applied to activate nociceptors of cardiac afferent nerve endings. Furthermore, somatic receptive properties were examined by applying innocuous (brush and light pressure) and noxious (pinch) cutaneous mechanical stimuli. Diabetes-induced increases in spontaneous activity were observed in subsets of neurons exhibiting long-lasting excitatory responses to administration of the algogenic mixture. Algogenic chemicals altered activity of a larger proportion of neurons from diabetic animals (73/111) than control animals (55/115, P<0.05). Some subtypes of neurons exhibiting long-lasting excitatory responses, elicited prolonged duration and others, had a shortened latency. Some neurons exhibiting short-lasting excitatory responses in diabetic animals elicited a shorter latency and some a decreased excitatory change. The size of the somatic receptive field was increased for cardiosomatic neurons from diabetic animals. Cutaneous somatic mechanical stimulation caused spinal neurons to respond with a mixture of hyper- and hypoexcitability. In conclusion, diabetes induced changes in the spinal processing of cardiac input and these might contribute to cardiovascular autonomic neuropathy in patients with diabetes.

Are diabetic patients less likely to feel angina than nondiabetic controls for a given extent of myocardial ischaemia?

OBJECTIVES

It is widely believed that diabetic patients with coronary artery disease have a reduced ability to feel angina. We investigated whether the diabetic patients referred for myocardial perfusion scintigraphy (MPS) are less likely to experience chest pain in daily life or during treadmill exercise than nondiabetic controls with equivalent extents of inducible hypoperfusion.

METHODS

One hundred and fifteen diabetic patients with ischaemia on single-photon emission computed tomography (SPECT) MPS were matched with 115 nondiabetic controls for age, sex, ethnic origin, method of stress used for MPS, and the extent of reversible hypoperfusion. The prevalence of chest pain from the history and during treadmill exercise (where applicable) was compared between diabetic and nondiabetic patients.

RESULTS

Of the diabetic patients, 18 (16%) were diet-controlled, 56 (49%) were treated with oral hypoglycaemic medication, and 41 (36%) used insulin. Compared with matched controls, diabetic patients were just as likely to give a history of chest pain (79 vs. 76%, P=NS), or to develop chest pain on the treadmill (31 vs. 39%, P=NS).

CONCLUSION

When carefully matched for clinical factors and the extent of ischaemia, diabetic patients referred for MPS are just as likely to experience chest pain as nondiabetic controls, whether in daily life or during treadmill exercise testing.

Non-invasive cardiac imaging techniques and vascular tools for the assessment of cardiovascular disease in type 2 diabetes mellitus

Cardiovascular disease is the major cause of mortality in type 2 diabetes mellitus. The criteria for the selection of those asymptomatic patients with type 2 diabetes who should undergo cardiac screening and the therapeutic consequences of screening remain controversial. Non-invasive techniques as markers of atherosclerosis and myocardial ischaemia may aid risk stratification and the implementation of tailored therapy for the patient with type 2 diabetes. In the present article we review the literature on the implementation of non-invasive vascular tools and cardiac imaging techniques in this patient group. The value of these techniques as endpoints in clinical trials and as risk estimators in asymptomatic diabetic patients is discussed. Carotid intima-media thickness, arterial stiffness and flow-mediated dilation are abnormal long before the onset of type 2 diabetes. These vascular tools are therefore most likely to be useful for the identification of 'at risk' patients during the early stages of atherosclerotic disease. The additional value of these tools in risk stratification and tailored therapy in type 2 diabetes remains to be proven. Cardiac imaging techniques are more justified in individuals with a strong clinical suspicion of advanced coronary heart disease (CHD). Asymptomatic myocardial ischaemia can be detected by stress echocardiography and myocardial perfusion imaging. The more recently developed non-invasive multi-slice computed tomography angiography is recommended for exclusion of CHD, and can therefore be used to screen asymptomatic patients with type 2 diabetes, but has the associated disadvantages of high radiation exposure and costs. Therefore, we propose an algorithm for the screening of asymptomatic diabetic patients, the first step of which consists of coronary artery calcium score assessment and exercise ECG.

Canadian Cardiovascular Society classification of effort angina: an angiographic correlation

BACKGROUND

The Canadian Cardiovascular Society classification (CCSC) remains the standard for grading angina in patients with chronic stable angina. The utility value of this angina grading system in predicting the severity of coronary artery disease is not clear.

AIM

We studied the relationship between the clinical angina grade and the angiographic severity of underlying coronary artery disease.

MATERIALS AND METHODS

The participants in the study were 493 patients with stable angina who had undergone coronary angiography from 1998 to 2001. They were grouped according to their anginal grading and the number of vessels diseased. Significant lesions were defined as 50% narrowing for the left main and 70% for the left and right coronaries and their major branches.

STATISTICAL ANALYSIS

The chi2-test was used for statistical analysis and a P-value <0.05 was taken as significant.

RESULTS

There was no significant difference between the four angina class patients and the incidence of single-, double- and triple-vessel involvement. Class 1 patients had less left main trunk disease than class 4 patients. Class 3 and 4 patients had significantly fewer normal coronary angiograms.

CONCLUSIONS

There is generally little correlation between coronary artery disease and the CCSC of effort angina except for left main disease. Presence or absence of angina rather than the CCSC should indicate the need for coronary angiography.

Assessment of diabetic autonomic neuropathy using twenty-four-hour spectral analysis of heart rate variability: a comparison with the findings of the Ewing battery

A power spectral analysis of heart rate variability has been applied in order to assess diabetic autonomic neuropathy and high frequency spectra are thus considered to possibly reflect vagal nerve integrity in patients with diabetes mellitus. The purpose of this study was to investigate the relationship between the findings of high frequency spectra analysis and the results of the Ewing battery. We performed 24-hour power spectral analysis using an ambulatory ECG monitoring system and standard tests in order to assess diabetic autonomic neuropathy (Ewing battery) in 18 diabetic patients to compare their diagnostic values for diabetic autonomic neuropathy. We used the high frequency amplitude (high frequency spectra; 0.15-0.40 Hz) as a direct measure of vagal nerve integrity from each hourly spectral plot. All hourly high frequency spectra decreased along with the impaired assessment of the battery, especially during the night when the high frequency spectra showed a manifest increase in patients classified as normal according to the battery. High frequency spectra during the night while asleep (22:00-05:00) and during a 24-hour period significantly correlated with the results of the battery. These values markedly decreased even in patients classified as having early vagal damage when compared with those classified as normal. High frequency spectra during night closely reflected the intrinsic vagal nerve integrity in patients with diabetes mellitus. High frequency spectra during night or a 24-hour period is a simple and sensitive measure of diabetic autonomic neuropathy and is considered to be a useful modality for detecting even early changes in autonomic dysfunction.

Silent myocardial ischaemia in patients with proved coronary artery disease: a comparison of diabetic and non-diabetic patients

OBJECTIVE

To determine whether diabetic patients with coronary artery disease are more likely to experience silent myocardial ischaemia than subjects without diabetes.

SUBJECTS

Patients undergoing coronary angiography at a regional cardiothoracic unit, identified as having diabetes from the local district diabetic register/database.

DESIGN

The coronary angiograms and exercise treadmill tests of 100 diabetic and 100 non-diabetic patients who all had significant coronary artery disease and maximal effort exercise tests were reviewed. Patients were individually matched for age group, gender, severity of coronary artery disease, and indication for treadmill test.

OUTCOME MEASURES

Significant coronary artery disease was defined as a stenosis of greater than 50% diameter in at least one of the major coronary artery segments. Exercise tests were graded as positive if the electrocardiographic (ECG) recording showed planar or downsloping ST segment depression of > or = 1 mm in more than two leads at 80 ms post J-point or if there was a blood pressure fall > or = 10 mm Hg after an initial rise. A negative exercise test was defined as one in which the subject experienced no pain, had no ECG changes after maximal effort and had a normal blood pressure response. Subjects who did not experience any form of typical angina-type pain during a positive exercise test were defined as having an episode of silent ischaemia. Patients with symptomatic ischaemia were those who experienced typical angina-type pain with accompanying ST segment changes. Patients with a negative exercise test were defined as having "undetermined ischaemia". This category included all those without ECG evidence of myocardial ischaemia during the exercise test (with or without accompanying chest pain).

RESULTS

In the diabetic patients, 34% had ECG evidence of silent ischaemia on treadmill testing compared with only 19% of the non-diabetic controls (p < 0.02).

CONCLUSIONS

This study shows that diabetic patients with proved coronary artery disease have a higher risk of developing silent myocardial ischaemia during exercise than non-diabetic patients.

Carotid endarterectomy in diabetic patients

OBJECTIVE

The purpose of the current study was to identify the possible short- and long-term effects of diabetes on the outcome of carotid endarterectomy.

METHODS

Medical records were reviewed for 781 carotid endarterectomies (in 734 patients) performed by the same vascular surgeon in a university medical center between January 1994 and December 1998. Patients were divided two groups: those with diabetes (n = 181 patients; 193 operations) and those without diabetes (n = 553; 588 operations). The two groups were similar with respect to mean age, male-female ratio, and contralateral lesions. The only significant differences were a higher prevalence of peripheral vascular disease and dyslipidemia in the diabetic group and a higher prevalence of hemispheric transient ischemic attacks among the nondiabetic patients. Carotid color duplex ultrasound scan had been performed in all patients, and in 56 patients from the diabetic group and 56 patients from the nondiabetic group (matched for age, sex, and contralateral lesions), the distal extension of the lesion from the carotid bifurcation had also been defined. Both of these subgroups were fully representative of their respective groups of origin. Carotid endarterectomy was performed after the induction of general anesthesia; electroencephalographic monitoring was continuous.

RESULTS

Except for the significantly higher prevalence of calcified plaques in the diabetic patients (P <.0001), the characteristics of the carotid disease in the two groups were similar. In the 56-member subgroups, 73.2% of the diabetic and 35.7% of the nondiabetic patients (P <.0001) had lesions extending more than 2 cm beyond the carotid bifurcation. Mean length of plaque beyond the bifurcation was 2.3 +/- 0.09 cm for the diabetic and 1.7 +/- 0.08 cm for the nondiabetic patients (P <.0001). Diabetes was the only factor significantly correlated with plaque length. In the diabetic subgroup, surgery was characterized by significantly longer carotid arteriotomies (P =.03) and clamp times (P <.003). Operative mortality was 1.5% in the diabetic group (2 myocardial infarctions + 1 stroke) and 0.5% in the nondiabetic group (1 myocardial infarction + 2 strokes; P value not significant); stroke rates were 1.5% (3 major strokes) and 0.5% (2 major strokes + 1 minor stroke), respectively (P = not significant). Long-term survival (5 years) was not significantly lower among the diabetic patients.

CONCLUSIONS

Diabetes mellitus does not seem to significantly increase the surgical risk for carotid endarterectomy. The presence of more extensive plaques has no significant effect on the results of surgery.

High incidence of silent myocardial ischemia in elderly patients with non insulin-dependent diabetes mellitus

The present study was designed to reveal the incidence of silent myocardial ischemia in asymptomatic elderly non-insulin-dependent diabetic (NIDDM) patients (aged over 60 years). As a first step screening, maximal treadmill exercise test was performed. Of 140 patients studied, 54 (38.6%) were unable or not expected to achieve diagnostic levels of exercise during treadmill testing. A positive exercise test was noted in 39 of 86 (45.3%) subjects. As a second step examination, dipyridamole thallium scintigraphy was performed for 93 subjects who exhibited a positive exercise test and could not perform a maximal exercise test. Abnormal perfusion pattern was found in 39 of 93 (41.9%), who were finally considered to have a silent myocardial ischemia. Coronary angiography was performed in 18 subjects with diagnosis of silent myocardial ischemia, who gave their consent. Significant coronary artery stenosis was in fact found in 17 of 18 (94.4%) subjects studied, confirming a very high positive predictive value of this diagnostic procedure. In conclusion, elderly NIDDM patients (aged over 60 years) had an extremely high prevalence (estimated 26.3%) of silent myocardial ischemia. This evidence suggests that early and intensive detection may be needed as a part of routine care for this group.

[Significance of silent myocardial ischemia for identification and optimal therapy of patients with latent coronary heart disease. Is there a marker for prognostic indication for PTCA?]

Although percutaneous transluminal coronary angioplasty (PTCA) improves the symptomatic status and exercise capacity of patients with coronary artery disease and stale or unstable angina pectoris, a beneficial effect on long-term prognosis has not been convincingly demonstrated so far. In totally asymptomatic patients with coronary artery disease, however, decision to undertake PTCA is greatly influenced by prognostic considerations. Usually, detection of silent myocardial ischemia in non-invasive examinations (exercise stress testing, ambulatory electrocardiographic monitoring) precedes the angiographic diagnosis of coronary artery disease in these patients.