Evidence for cardiomyopathy in familial diabetes mellitus

Diabetic cardiomyopathy

Diabetes mellitus is associated with a specific cardiomyopathy. This is evident from the clinical-pathological work and the epidemiologic data from the Framingham study. Noninvasive studies of diabetics have shown alterations in systolic and diastolic function that may ultimately lead to clinical heart failure. The relationship of these cardiac changes to the type of diabetes, its duration, and its severity is not settled. However, a correlation between changes in heart function and other complications of diabetes has been demonstrated. Insufficient prospective data is available from noninvasive studies to establish the frequency of progression from subclinical cardiac dysfunction to overt congestive failure. The pathogenesis of this disorder is still uncertain. Pathological studies have shown changes in the intramural arteries, arterioles, and capillaries but their functional significance is uncertain. Experimental studies have shown interstitial changes leading to an apparently less compliant left ventricle in the diabetic dog and monkey. In the diabetic rat reversible changes were found in myocardial function, related to changes in contractile proteins and intracellular calcium metabolism. In both species, the response to anoxia or ischemia was altered in the presence of diabetes. However, irreversible depression of the contractile element was not found in most animal studies of isolated diabetes. In contrast, the combination of hypertension and diabetes leads to substantial cardiac damage and circulatory congestion, both in clinical and experimental investigations. Clearly much more work must be carried out to understand the pathogenesis, treatment, and ultimately the prevention of diabetic cardiomyopathy.

Pathomorphologic aspects of muscular tissue in diabetes mellitus

Biopsy specimens from the myocardium were examined in a series of 145 patients who had elected coronary arterial bypass grafting. The patients were divided into three groups; 1) overtly diabetic (OD) patients; 2) chemically diabetic (CD) patients, who demonstrated impaired glucose tolerance only when stressed with a sugar load; and 3) normoglycemic, nondiabetic (ND) patients, who served as a control group. Tissue plugs from the left anterior apical segment of the heart and from the quadriceps femoris in 71 patients, for comparative evaluation, were prepared for ultrastructural examination. Findings were as follows: 1) Myocardial hypertrophy and interstitial fibrosis were twin characteristic abnormalities, seen in all but two of the biopsy specimens; capillary endothelial changes, the third most common abnormality, were present in approximately half of these specimens, regardless of the patients' metabolic status. 2) In patients matched by sex, age, weight, blood pressure, preoperative myocardial ventricular function, and coronary arterial integrity, capillary basal laminar thickening represented a pathomorphologic hallmark, distinguishing structural alterations in the diabetic from those in the normoglycemic patient. 3) Although clear-cut and statistically significant thickening of basal laminae was noticeable in OD patients, a) in the quadriceps markedly increased laminar thickening was present in a number of ND patients, rendering interpretation of this change in skeletal muscle as pathognomonic for diabetes doubtful; and b) within cardiac muscle this increase in laminar width was less than that seen in skeletal muscle, leaving the functional implications of this alteration in doubt. 4) Early but statistically significant increases in capillary basal laminar thickening were observed in the myocardium of CD patients; these patients demonstrated impaired glucose tolerance only when stressed with a sugar load, without exhibiting overt diabetic manifestations. 5) In this group of highly selected patients with epicardial coronary arterial disease, the histopathologic profile of the diabetic myocardium did not include distinctive abnormalities sufficient to warrant the designation of "diabetic cardiomyopathy," indicating that coronary arterial bypass grafting can be recommended for the diabetic patient who requires this procedure.

Effects of acute ketotic and non-ketotic diabetes on the myocardial muscarinic receptors

Myocardial membranes from rats rendered diabetic with streptozotocin were used to determine muscarinic receptors with 3H-quinuclidinyl benzilate. In the acute state of diabetes, four days after induction, the density of receptors were equal in controls, insulin (glucosuria) and non insulin-treated (glucosuria and ketonuria) diabetic animals. In myocardial membranes from diabetic rats agonist binding to the muscarinic receptor was shifted to higher affinity than in controls. Computer modeling revealed that guanine nucleotides transformed agonist binding from two sites to a site of low affinity in controls. In membranes from insulin-treated diabetic animals the shift to lower affinity occurred but two receptor sites remained. In non insulin-treated membranes the nucleotides failed to exert any effect. Inhibition of adenylate cyclase by the muscarinic agonist oxotremorine was amplified in diabetic membranes. This indicates that the function of the inhibitory nucleotide binding protein (NI), as reflected by agonist binding to the receptor and adenylate cyclase inhibition, is sensitive to the hormonal status.

Diabetic myocardial alterations in ultrastructure and function

Myocardial samples taken from six healthy and six alloxan-diabetic dogs by means of percutaneous needle-biopsy were investigated electronmicroscopically. Specific increase in the number of collagen fibers and that of mitochondria were demonstrated beside the widening of Z bands. In the same experimental animals, a close, inverse correlation was detected (y = 0.0068x + 0.1680; r = 0.8648; F = 29.6705; n = 12) between the values of the left ventricular passive elastic modulus and those of the plasma glucose disappearance rate determined immediately before the haemodynamic investigation. On the basis of the ultrastructural findings, the proliferation of collagen fibers can be made also responsible for functional disorder of the diabetic myocardium.

Exercise-induced left ventricular dysfunction in young men with asymptomatic diabetes mellitus (diabetic cardiomyopathy)

Radionuclide ventriculographic studies were performed at rest and during exercise on 30 consecutive men, aged 21 to 35 years with diabetes mellitus without evidence of coronary artery or any other cardiovascular disease, and in 20 normal age-matched subjects. Sixteen (53%) were treated with insulin and 14 (47%) were treated with either diet (6 patients) or oral antidiabetic therapy (8 patients). All patients from both groups had normal left ventricular (LV) ejection fraction (EF) at rest. In 5 of the 30 diabetic patients (17%), LVEF decreased after exercise, in 8 (27%) it remained unchanged and in 17 it increased normally. Mean LVEF at rest and after exercise in this group was 66 +/- 7% and 72 +/- 7% (+/- standard deviation), respectively. In all normal subjects, LVEF increased after exercise. Mean LVEF at rest and after exercise in the normal group was 66 +/- 7% and 76 +/- 9%, respectively. No patient had evidence of regional dysfunction at rest or after exercise. LV function was not related to serum glucose levels during the test, modality of treatment, insulin dependency or duration of the disease. Three of 4 patients with diabetic microvascular complications showed LV dysfunction. In 4 of 5 patients in whom LVEF decreased after exercise, thallium studies showed normal perfusion. Thus, diabetes mellitus may cause exercise-induced global LV dysfunction in young men with no evidence of cardiovascular disease. This phenomenon apparently does not seem to follow the known course of diabetic microvascular complications.

Clinically unrecognized ventricular dysfunction in young diabetic patients

Left ventricular function at rest and during supine bicycle exercise was assessed by gated radionuclide angiography in 20 diabetic patients and 18 normal control subjects without clinical evidence of heart disease. The diabetic patients were aged 21 to 44 years and all except one used insulin. No subject developed chest pain or electrocardiographic changes during exercise. Both groups had a similar rest and exercise heart rate and blood pressure, and both achieved similar work loads. The control group had an ejection fraction at rest of 65.4 +/- 6.2% (mean +/- SD) and only 1 of 18 showed a decrease with exercise; peak exercise ejection fraction averaged 77.1 +/- 7.8%. The diabetic group had a mean ejection fraction at rest of 63.7 +/- 6.5%, similar to that of the control group, but 7 of 20 showed a decrease during exercise; the exercise ejection fraction averaged 67.7 +/- 9.7%, significantly lower than that of the control group (p less than 0.01). The diabetic patients varied widely in ejection fraction response to exercise, ranging from an increase of 25% to a decrease of 21%. This response did not correlate with age, sex, duration of diabetes, smoking, retinopathy, exercise heart rate, blood pressure or rate-pressure product, work load attained or ejection fraction at rest. These data suggest that approximately one-third of patients with diabetes have subclinical left ventricular dysfunction without correlation to risk factors for atherosclerosis or other diabetic complications. Whether this is due to unrecognized coronary artery disease or primary myocardial disease remains unknown.

Combined renovascular hypertension and diabetes in rats: a new preparation of congestive cardiomyopathy

Myocardial function, electrophysiologic characteristics, and structure were studied in rats with both renovascular hypertension and streptozotocin-induced diabetes (HD). Ventricular papillary muscles from untreated rats with HD showed a marked slowing of isometric and isotonic contractions. Peak developed tension and peak shortening were preserved, except in one animal with findings of congestive heart failure. Transmembrane action potentials increased fivefold in duration. Myocardial interstitial fibrosis was frequently observed. Physiologic parameters of rats with HD treated by left nephrectomy, captopril, and insulin were very similar to those of age-matched controls. The mortality rate of rats with HD was 43% over 5 to 6 months in the first study. In a second study, spontaneously dying rats with HD were compared with those deliberately killed. A 55% mortality was observed over 7 months. Myocardial structural damage and histologic evidence of congestive heart failure were more frequent in spontaneously dying rats with HD. Combined renovascular hypertension and diabetes in rats appears to be a new preparation of congestive cardiomyopathy.

Increased congestive heart failure after myocardial infarction of modest extent in patients with diabetes mellitus

To elucidate the factors involved in the reduced survival rate of diabetic patients after acute myocardial infarction (AMI), we prospectively evaluated 100 patients with well-documented diabetes and 426 control patients. We characterized infarct size and analyzed the incidence and severity of congestive heart failure (CHF) and subsequent death with respect to infarct size. The extent of the index infarct was less in diabetic compared to nondiabetic patients, 16.2 +/- 2.2 CK-gm-eq/m2 compared with 19.2 +/- 0.9 (p less than 0.02). However, CHF was more prevalent in diabetic patients (31.2% of the diabetic patients compared to 15.7%). The difference was most prominent in diabetic patients who had sustained prior infarction (50% compared to 16%), but was evident also in diabetic patients with initial infarction (26% compared to 16%). The mortality rate was greater in diabetic patients (p less than 0.04). When diabetic and nondiabetic patients were stratified with respect to the presence or absence of CHF, survival curves were comparable. The increased incidence of CHF despite a smaller infarct size suggests that additional factors must contribute to myocardial dysfunction and the resultant excess in mortality.

Decrease in ventricular beta-adrenergic receptors in trained diabetic rats

The effects of physical training on beta-adrenergic receptors were evaluated in heart ventricular tissue of diabetic rats. Mild diabetes mellitus was induced in rats with streptozotocin (45 mg/kg, iv). They were then submitted to a progressive 10-week running programme on a treadmill. Binding studies were done at six different concentrations of (-) [3H]dihydroalprenolol (0.5 to 14.4 nM) with ventricular membrane preparations from control (n = 13), sedentary diabetic (n = 9) and trained diabetic rats (n = 10). Direct linear plot analysis of the data revealed that the total number of beta-adrenoceptors was reduced in sedentary diabetic rats as compared to control (2231 +/- 207 vs 2922 +/- 211 fmol/ventricles; P less than 0.05); however, there was no significant change in the receptor density expressed as fmol/mg of membrane protein (40 +/- 3 vs 43 +/- 3; P greater than 0.05). On the other hand, the beta-adrenergic binding sites were decreased in training diabetic rats, either expressed as the total number of receptors (1920 +/- 179 vs 2922 +/- 211; P less than 0.01), or as fmol/mg of membrane protein (30 +/- 3 vs 43 +/- 3; P less than 0.01). There was no significant change in the dissociation constant (KD) of these receptors between groups (KD = 4.08 +/- 0.51, 4.69 +/- 0.93 and 2.88 +/- 0.39 nM respectively for control, sedentary diabetic and diabetic trained animals). The basal epinephrine concentration was significantly increased in trained diabetic rats (102 +/- 21 pg/ml vs 47 +/- 7 for control (P less than 0.05) and vs 49 +/- 9 for sedentary diabetic (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intravenous insulin infusion on mortality among diabetic patients after myocardial infarction

A review of the records of 353 diabetic patients after a myocardial infarction confirmed the high mortality associated with the condition. The influence of improved diabetic control achieved by intravenous insulin was assessed in 64 patients and compared with earlier experience in a diabetic control group. The frequency of the major complications of myocardial infarction was unchanged and the death rate in both groups was identical (33%); even the patients with blood glucose concentrations greater than 20 mmol/l on admission failed to benefit. Thus careful control of blood glucose concentrations after myocardial infarction in diabetic patients fails to improve the outcome of this high risk group.

The heart in diabetes

Since the introduction of insulin, heart disease has become a major impediment to survival in persons with diabetes mellitus. Coronary disease has increased severity and accelerated development in diabetic persons compared with an age- and sex-matched nondiabetic population. A peculiar vulnerability of women to the influence of diabetes with loss of premenopausal coronary disease protection has been found. The symptomatology of coronary events may differ and coronary care data show a higher incidence of sudden death in diabetic patients who have a myocardial infarction than in their non-diabetic counterparts. Insulin may play a role in the myocardial adjustment to an ischemic insult by enhancing glucose intake and suppressing lipolysis and ketogenesis. Carbohydrate intolerance in dogs, rhesus monkeys and humans appears associated with similar histologic and compositional changes in the myocardium. Abnormalities in diastolic ventricular function not attributable to large- or small-vessel coronary disease have been found in the diabetic subjects of each species. Studies in humans who have diabetes have assessed single pressure-volume relationships and more exacting measures of ventricular compliance are needed. Abnormalities of myocardial function in patients with diabetes have been found using echo and radionuclide techniques. Many of these findings need to be correlated with invasive data or confirmed in larger populations. Autonomic dysfunction is common in diabetic persons and may imply an associated poor prognosis. Reflex abnormalities in parasympathetic function are most prevalent and occur before sympathetic dysfunction.

Improvement of myocardial function in diabetic rats after treatment with L-carnitine

The effects of L-carnitine administration on the severity of diabetes were investigated. Serum glucose, free fatty acids (FFA), triglycerides, and ketones from diabetic and normal rats injected for 2 weeks with 3 g/kg/d of either L-carnitine or saline were assayed. Hearts were analyzed for carnitine and long-chain acyl coenzyme A. L-carnitine treatment to diabetic rats significantly reduced serum glucose, FFA, triglycerides, and ketones. In nondiabetic rats, carnitine increased serum ketones while FFA and triglycerides were decreased. L-carnitine treatment to diabetic rats prevented a decrease in myocardial total carnitine content. Long-chain acyl carnitine increased while long-chain acyl coenzyme A decreased. In another experiment, L-carnitine administration (750 mg/kg/d for 14 days) significantly improved the recovery of cardiac output after 60, 90, and 120 minutes of ischemia in diabetic perfused hearts. These results suggest that L-carnitine therapy may reduce the severity of diabetes mellitus and improve myocardial performance.

Hormonal influences on cardiac myosin ATPase activity and myosin isoenzyme distribution

It has been recognized for a long time that changes in hormone secretion can influence cardiac function; however, the biochemical basis for these changes has only recently been clarified. In this review the influences of hormonal status on the contractile protein myosin is discussed. Myosin has a rod-like portion and a globular head and consists of two myosin heavy chains (MHC) and four light chains (LC), two of which are identical. The globular head is the site of an ATP-splitting enzyme, the myosin ATPase, and increases in myosin ATPase activity are closely related to an increased velocity of contraction of the heart. Myosin ATPase activity shows marked response to alterations in thyroid hormone, insulin, glucocorticoid, testosterone and catecholamine levels, but marked animal species differences in this response occur. Thyroid hormone administration to normal rabbits, for example, increases myosin ATPase activity markedly, but the myosin ATPase activity of hyperthyroid rats remains unchanged. In contrast, in hypothyroid rats myosin ATPase activity is markedly decreased but the hypothyroid rabbit shows no such response. These species-related differences in the hormonal response of myosin ATPase activity result from the predominance pattern of specific myosin isoenzymes. In the normal rat heart three myosin isoenzymes, V1, V2 and V3, can be separated electrophoretically. Myosin V1 predominates (70% of total myosin), and has the highest myosin ATPase activity, whereas in rabbits myosin V3, which has a lower myosin ATPase activity, is the predominant isomyosin. Thyroid hormone administration to rabbits induces myosin V1 predominance and therefore increases myosin ATPase activity, whereas in hyperthyroid rats only a small further increase in V1 predominance can occur. The alterations in myosin isoenzyme predominance and myosin ATPase activity are closely correlated to changes in cardiac contractility. Hormone-induced alterations in myosin isoenzyme predominance are mediated through changes in the formation of two isoforms of myosin heavy chain. Changes in the expression of different myosin heavy chain genes are most likely responsible for the thyroid hormone and insulin-induced alterations in myosin isoenzyme predominance. Investigation of the control of myosin heavy chain formation can provide further insights into the hormonal control of a multigene family as well as broaden our understanding of the molecular events which result in altered cardiac contractility.(ABSTRACT TRUNCATED AT 400 WORDS)

Altered myocardial response to ouabain in diabetic rats: mechanics and electrophysiology

Diabetes induced by streptozotocin in rats is associated with changes in the mechanical function of isolated ventricular papillary muscle. Relaxation is slowed and shortening velocity is depressed. The effects of ouabain (10(-7) to 2 x 10(-4)M) and changes in extracellular calcium ([Ca2+]0 = 0.6 to 12 mM) on the mechanical and electrical properties of normal and diabetic papillary muscles were studied. High doses of ouabain caused a rise in resting tension and a fall in developed tension in both diabetic and control muscles. However, these changes were strikingly greater in diabetic muscles which developed partial contractures at 10(-4)M. The altered response to ouabain was observed in chronically (5 to 7 weeks or 3 months) but not acutely (less than 1 week) diabetic animals. Similarly, the response to ouabain was restored to normal after chronic (5 weeks) therapy with insulin but not after acute (4 days) therapy. In both normal and diabetic muscles, the mechanical effects of increasing [Ca2+]0 from 2.4 to 12.0 mM were qualitatively similar to those seen with ouabain at 10(-5) to 10(-4)M. Electrophysiologic studies showed that under control conditions action potentials of diabetic muscles were significantly longer than those of normal muscles. Treatment with progressively higher concentrations of ouabain (10(-7) to 10(-4)M) and [Ca2+]0 (2.4 to 12.0 mM) caused shortening of both normal and diabetic action potentials, but the effects of these interventions were much greater in the diabetics. These results suggest that the response of diabetic muscles to ouabain is markedly different from normal and that this altered response may be due to impaired regulation of intracellular Ca2+ levels in diabetic myocardium.

Preclinical abnormality of left ventricular performance in patients with insulin-dependent diabetes mellitus

The left ventricular systolic function of 32 patients with insulin-dependent diabetes mellitus was investigated by measurement of systolic time intervals. Patients with clinical signs of sclerosis in the coronary arteries were excluded. Twenty-nine sex- and age-matched healthy people served as controls. Resting values of PEP/LVET ratio and of the corrected pre-ejection period were significantly higher in diabetics than in controls. The alterations of systolic time intervals during volume-loading induced by passive leg-raising as well as by isometric handgrip test indicated an increase in left ventricular performance in healthy people. The unchanged systolic time intervals observed in diabetics during the same loadings indicated a decrease in the functional reserve of the diabetic left ventricle. The systolic time intervals observed in patients with type-1 diabetes could be evaluated as a preclinical abnormality of left ventricular performance and as early signs of diabetic cardiomyopathy.

Systolic time intervals in diabetes

The systolic time intervals at rest of 16 Type 1 (insulin-dependent) and 30 Type 2 (non-insulin-dependent) otherwise healthy adult diabetic patients selected from primary health care clinics were compared with those of age- and sex-matched normal subjects by paired analysis. There was no significant difference in prevalence of smoking, body mass index, fasting serum cholesterol or mean blood pressure between the diabetic and control groups. Mean rate-corrected pre-ejection period (diabetic patients: 132.7 +/- 2.1 ms, normal subjects: 134.6 +/- 3.5 ms (+/- SEM), left ventricular ejection time (diabetic patients: 413.9 +/- 3.0 ms, normal subjects: 421.5 +/- 4.7 ms) electromechanical systole (diabetic patients: 544.9 +/- 2.5 ms, normal subjects: 548.0 +/- 3.5 ms) and pre-ejection period/left ventricular ejection time ratio (diabetic patients: 0.36 +/- 0.01, normal subjects: 0.34 +/- 0.01) were not significantly different between the two groups (p greater than 0.05) and systolic time intervals did not correlate with duration of diabetes or type of treatment. Thus, we did not detect subclinical cardiomyopathy in healthy diabetic patients by this technique. However, a statistically significant skew in the distribution of systolic time intervals in the diabetic group (p less than 0.025) suggests the possibility of an 'at risk' population in which a more sensitive technique might demonstrate impaired ventricular performance.

Beta blockade in asymptomatic diabetics with abnormal rest electrocardiograms

Diabetic patients without evidence of vascular disease often reveal non-specific ST-T changes and prolonged QTc intervals in their ECGs. In an attempt to elucidate the role of autonomic dysfunction in the etiology of these changes, we compared the ECGs and beat to beat variations in 22 patients with changes in repolarization before and one hour after beta blockade. None had clinical evidence of ischaemic heart disease or peripheral vascular disease. In 19 patients (86%) the ST-T changes persisted after beta blockade. Heart rate was 75.6 +/- 15.3/min before and 64.3 +/- 9.6/min after beta blockade, while the QTc interval was 0.43 +/- 0.02 sec before and 0.41 +/- 0.02 sec after propranolol. Beat to beat variation during deep breathing is diminished in diabetic patients. Beta blockade reversed this phenomena. We conclude that while beat to beat variations and prolongation of QTc are likely to be consequent to autonomic neuropathy, the ST-T changes do not appear to be due to increased sympathetic tone and their etiology is yet to be determined.

Hypertensive diabetic cardiomyopathy in the rat: ultrastructural features

We previously described a cohort of diabetic patients with typical congestive cardiomyopathy, in whom myocardial lesions were related to concomitant high blood pressure. To evaluate the association of diabetes mellitus and hypertension in more detail, we studied 4 groups of rats with either no disease, streptozotocin-induced diabetes mellitus, renovascular hypertension, or a combination of hypertension and diabetes. Analysis revealed significant myocardial fibrosis and degeneration in the hypertensive-diabetic group when compared to controls, without an obvious relationship to small vessel lesions. The myocardial alterations appeared similar to those observed in patients with hypertension and diabetes mellitus. Of note, although hypertensive animals had focal moderate lesions, diabetic animals had no pathological changes. To further characterize these histological changes, we performed electron microscopy on the 4 animal groups, which we are reporting in this study. Our analysis of the ultrastructural alterations confirms the previous histological observations. Diabetic animals only had increased cellular lipid, and mild, focal areas of myofibrillolysis, with no significant increases in perivascular and perisarcolemmal basal lamina. Consistent with our light microscopic finding that PAS positive material was associated with interstitial or replacement fibrosis, we noted basal lamina proliferation in the hypertensive and hypertensive-diabetic groups, particularly in areas of scarring. Pericapillary basal lamina was increased to the greatest extent in the hypertensive-diabetics. Qualitative alterations of myocardial cells and muscular blood vessels were similar in both the hypertensive and hypertensive-diabetic animals; however, there were more extensive changes in the latter group. This study provides further evidence that the combination of diabetes mellitus and hypertension produces significantly greater myocardial lesions than with either disease alone, not only at the light microscopic level, but ultrastructurally as well. Although the pathogenesis of this cardiomyopathy is unknown it may be related to abnormalities of the cardiac microcirculation. The prevalence of hypertension in the diabetic population suggests that greater attention should be paid to the combination of these 2 conditions and their effects on the heart.

Echocardiographic evidence for impaired myocardial performance in children with type I diabetes mellitus

Thirty-three children with type I diabetes mellitus and 51 normal children underwent M-mode echocardiography. Abnormalities of myocardial performance were present in many of the diabetic children. The mean end-systolic volume of the left ventricle was greater in diabetics compared to control subjects. Mean ejection fraction, minor axis shortening, and velocity of circumferential fiber shortening were decreased in the diabetics. There was no evidence of increased myocardial mass in these diabetic children. There was no correlation between myocardial dysfunction, clinical assessment of control, or glycohemoglobin in the diabetic children.

Vectocardiographic "bites" as possible early findings of cardiac involvement in diabetic patients without clinical evidence of heart disease

We performed a standard vectorcardiogram (VCG) in 87 diabetics, aged 20-77 years, orally- or insulin-treated, and in 41 normal subjects. None had cardiac history or symptoms. Among diabetics, 31 had no vectocardiographic abnormalities, 23 had various VCG changes, 33 showed electrical "bites" of various length (6-22 msec) and voltage (0.05-0.3 mV). In 8 normal subjects (19.4%) we found "bites" of similar voltage and length as in diabetic patients. A significantly positive linear relation was found between "bites" length and diabetes duration, in insulin-dependent diabetics only. By step-wise regression analysis we detected, in all diabetic patients with "bites," at a fixed value of diabetes duration, a significantly negative relation between "bites" length and patients' age. Moreover, the insulin treated patients showed a metabolic regulation index significantly worse than orally-treated diabetics; also diabetes duration was significantly higher in insulin-treated subjects. If "bites" may reflect an early heart involvement in diabetes, insulin-dependent patients seem to have a more severe cardiac damage in dependence of the diabetes duration. Finally, in the younger diabetics the heart diseases seems to be earlier and more advanced.

Increased incidence and clinical correlation of persistently abnormal technetium pyrophosphate myocardial scintigrams following acute myocardial infarction in patients with diabetes mellitus

"Persistently abnormal" technetium-99m stannous pyrophosphate myocardial scintigrams (PPi+) appear to be associated with a relatively poor prognosis after acute myocardial infarction (AMI). To assess the incidence and implications of PPi+, we performed a retrospective analysis in 29 patients with and 25 patients without diabetes mellitus who had abnormal myocardial scintigrams within 4 days of AMI and who had follow-up scintigrams at least 3 months after hospital discharge. There were no significant differences between patients with and without diabetes as regards age, incidence of transmural or nontransmural AMI, or degree of left ventricular dysfunction after AMI. Persistently abnormal PPi+ occurred more commonly in patients with diabetes than in nondiabetic patients (18 of 29, 62%, compared to 3 of 25, 12%; p less than 0.001). Patients with chronic PPi+ had more frequent cardiac complications following hospital discharge (p less than 0.005) including death, recurrent AMI, unstable angina, and intractable congestive heart failure. Postmortem analysis in two patients with diabetes and chronic PPi+ revealed marked myocytolysis. Thus, patients with diabetes mellitus have an increased incidence of post-AMI "persistently abnormal" technetium (PPi+) scintigrams and relatively poor prognosis following myocardial infarction.

The meaning of bites on the vectorcardiogram: study in adriamycin cardiomyopathy

We examined 106 VCGs of cancer patients receiving Adriamycin (ADM) to investigate the nature and meaning of bites. It is known that ADM causes patchy areas of myocardial degeneration and necrosis, the appearance of which is dose dependent. Thirty-eight cancer patients not yet receiving ADM were examined to provide controls. Patients were divided into six groups, according to total cumulative ADM dose received. The incidence of bites in the different groups was shown to be as follows: group 1 (controls, 38 patients) 13.1%; group 2 (1-100 mg/m2 of body surface ADM, 23 patients) 39.1%; group 3 (101-200 mg/m2, 33 patients) 42.2%; group 4 (201-300 mg/m2, 25 patients) 56%; group 5 (301-400 mg/m2, 15 patients) 66.6%; group 6 (greater than 400 mg/m2, 10 patients) 90%; groups 2-6 52.8%. These percentages show a trend which is highly correlated with the total cumulative dose of ADM (p=0.00005). The influence of age on the appearance of bites has been excluded by analyses of trends in patients below and over 50 years (p=0.08). In 80.35% of cases, bites appear on more than one plane and mostly close to the maximum vector (Vmax). We therefore think that these results favor the hypothesis that bites are the electrophysiologic expression of lesions, such as small fibrotic and necrotic areas, which interfere with the normal spread of the ventricular depolarization wavefront.

Non-invasive assessment of left ventricular function in diabetics without clinical heart disease

Left ventrical performance was assessed by systolic and diastolic time intervals measured echocardiographically in 24 diabetic patients without clinical heart disease and in 18 healthy subjects. It was found that diabetics had longer PEP, higher PEP/LVET ratio and longer IVRT (p less than 0.01). The possible pathogenetic explanations of these abnormalities are discussed and it is concluded that the measurement of time intervals is a useful method for detecting this myocardial dysfunction on the preclinical stage.

The effect of streptozotocin-induced diabetes in rats on cardiac contractile proteins

In order to determine whether diabetic cardiomyopathy in rats is associated with altered contractile proteins, male and female rats were made diabetic with intravenous streptozotocin (STZ). Calcium ATPase activity of cardiac actomyosin was significantly decreased after 1 week of diabetes and was depressed by 60% by 2 weeks. Rats pretreated with 3-O-methyl glucose to prevent the hyperglycemia caused by STZ had normal Ca2+-actomyosin ATPase activities, and non-diabetic rats whose food was restricted to keep their body and heart weights similar to those found in diabetic animals had only a slight fall in actomyosin ATPase activity. Ca2+-ATPase and actin-activated ATPase activities of pure myosin were similarly depressed in preparations from hearts of diabetic animals. Sodium dodecylsulfate gel electrophoresis and isoelectric focusing failed to reveal differences in the patterns of contractile proteins or light subunits between diabetics and controls, but pyrophosphate gels showed a shift in the myosin pattern. Because of depressed circulating thyroid hormone levels in diabetic animals, cardiac contractile proteins were also studied in preparations from thyroidectomized rats. Calcium activities of actomyosin and myosin ATPase were lower than values found in hearts of diabetic rats. When diabetic animals were kept euthyroid with thyroid replacement, actomyosin ATPase activity was still depressed. Thus STZ diabetes causes a significant decrease in cardiac contractile protein ATPase activity. This may be related to altered proportions of myosin isoenzymes.

Myocardial composition and function in diabetes. The effects of chronic insulin use

This study was undertaken in an animal model of mild diabetes to determine if provision of chronic insulin replacement during postprandial hyperglycemia may modify the abnormalities of myocardium. Group 1 served as controls with normal glucose tolerance by intravenous testing. Two additional groups were made diabetic with low doses of alloxan. Diabetic animals of Group 2 were untreated (n = 6). Group 3 animals (n = 6) received regular insulin daily to reduce postprandial hyperglycemia. After one year with maintained body weight, the animals were studied in the intact anesthetized state using the indicator dilution technique for left ventricular volume determinations. Basal left ventricular function and contractility were similar to normals in both diabetic groups. During intraventricular infusion of saline, end-diastolic pressure rose to higher levels in untreated diabetes (14.8 +/- 2 mm Hg) than normals (8.8 +/- 0.84), despite similar basal levels. Insulin treatment was associated with higher filling pressures than in group 1 as well as reduced end-diastolic volume response. Collagen concentrations were enhanced an average of 50% in layers from the inner to outer myocardium in both untreated and treated diabetics, associated with sodium and water accumulation. Since hypertrophy was not present, the diminished compliance appeared related to increased collagen levels. On electron microscopy, the subcellular organelles of the cardiac cell appeared normal in both diabetic groups. Thus, collagen accumulation and abnormal myocardial function in this model of diabetes is not affected by control of postprandial hyperglycemia, but a potential role for sustained hormone replacement is not excluded.

Reversibility of diabetic cardiomyopathy with insulin in rats

Diabetes appears to cause a cardiomyopathy independent of atherosclerotic coronary artery disease and hypertension. Left ventricular papillary muscle function studies in rats made severely diabetic with streptozotocin have shown a slowing of relaxation and a depression of shortening velocity. However, the effects of insulin therapy on the myocardial mechanics of diabetic rats have not been studied. Therefore, rats diabetic for 6-10 weeks were treated with PZI insulin for 2, 6, 10, or 28 days and the mechanical performance of their left ventricular papillary muscles was compared to that of untreated diabetics and age-matched controls; cardiac contractile protein enzymatic activity was also measured. Neither 2 nor 6 days of therapy had any effects on the depressed cardiac muscle performance of diabetic animals, although plasma glucose concentration was restored to normal. By 10 days of therapy, recovery of mechanical performance was nearly complete, and by 28 days of therapy, complete reversal of the altered myocardial mechanics was observed. Crystalline insulin added to the bath (9 mU/ml) had no effect on myocardial mechanics in either diabetics or controls. A gradual recovery of actomyosin and myosin ATPase activity in the hearts of insulin-treated diabetic animals was also found, complementing the mechanical studies. In addition to demonstrating a gradual but complete reversibility of the abnormalities in papillary muscle function in diabetic rats (although control of hyperglycemia was less than ideal), this study confirms that this model of a cardiomyopathy is not a result of streptozotocin-induced cardiac toxicity. Additional data are provided indicating that depressed thyroid hormone levels in diabetic rats are not responsible for the mechanical changes observed.

Left ventricular function in diabetes mellitus. I: Methodology, and prevalence and spectrum of abnormalities

Frequent abnormalities of left ventricular function were detected in 212 established diabetic patients using non-invasive techniques. Diabetics without angina or heart failure (n = 185) were significantly different from normal subjects (n = 50) in beat-to-beat variation, ratio of pre-ejection period to left ventricular ejection time, pre-ejection period index, isovolumic relaxation time, and interval from minimal dimension to mitral valve opening. Diabetics with angina (n = 18) were similar to control subjects with angina (n = 25); they showed a significant dimension change during the isovolumic period as compared with other diabetics and normals. Sixteen diabetics without angina also showed outward motion during the isovolumic period (incoordinate relaxation) and 13 had abnormal systolic time intervals. Four diabetics suffered a myocardial infarction during the study period; all had previously shown incoordination. Comparison of diabetics with a diastolic blood pressure below 100 mmHg and between 100 and 125 mmHg showed that the latter had a thicker posterior wall; the enlarged systolic dimension and reduced fractional shortening were the result of the inclusion of five of the 11 diabetic subjects with heart failure in the hypertensive group. Insulin-dependent diabetics tend to have more pronounced abnormalities of left ventricular function than those not requiring insulin. Patients selected from a diabetic clinic frequently have impaired left ventricular function, and ventricular hypertrophy, when present, in primarily caused by hypertension.

Left ventricular function in diabetes mellitus. II: Relation between clinical features and left ventricular function

We have shown a close relation between clinical microvascular complications and abnormalities of left ventricular function in 185 established diabetics without clinical heart disease. In 50 insulin-dependent diabetics who presented at under 20 years of age there was a correlation between the duration of diabetes and the isovolumic relaxation time, minimal dimension to mitral valve opening, and ratio of pre-ejection period to left ventricular ejection time. Diabetics with mild microvascular complications were similar to diabetics with no complications except for minor prolongation of the diastolic time intervals. Those with severe complications were significantly different from diabetes with milder complications and normal controls in all variables of left ventricular function. A close relation between left ventricular function and the microvascular complications index (code 0 when no complications to code 7 when all present and severe) was found for the following variables: isovolumic relaxation time, the interval from minimal dimension to mitral valve opening, ratio of pre-ejection period to left ventricular ejection time, and pre-ejection period index. It is concluded that in diabetes abnormalities of left ventricular function are related to duration of disease and complications; and that a diabetic specific heart muscle disorder occurs frequently in patients with severe microvascular complications.

Hypertensive-diabetic cardiomyopathy in the rat: an experimental model of human disease

The authors recently described a group of diabetic patients with severe congestive heart failure, hypertension, and minimal coronary artery disease, who had significant myocardial degeneration apparently secondary to the combined effects of high blood pressure and diabetes on the heart. To evaluate the effects of hypertension and diabetes mellitus more fully, the authors studied four groups of rats with either no disease, streptozotocin-induced diabetes mellitus, renovascular hypertension, or a combination of hypertension and diabetes. They employed semiquantitative light microscopy, which revealed significantly greater replacement fibrosis in the hypertensive-diabetic rats when compared with the other three groups. Interstitial fibrosis was increased in the hypertensive-diabetic animals, though it was just below the 5% level of significance when compared with the hypertensives. Further analysis, however, revealed that those hypertensive-diabetic animals with the greatest relative cardiac hypertrophy, as measured by the heart weight/body weight ratio, had significantly increased interstitial fibrosis. Surprisingly, diabetes mellitus alone produced no morphologic light-microscopic alterations; yet 8 weeks of combined hypertension and diabetes mellitus led to myocardial degeneration similar to the human disease. These changes do not appear to be secondary to abnormalities of intramyocardial muscular vessels. Measurement of 3 parameters of vascular disease revealed that hypertensive animals with less myocardial damage had greater vascular changes than the more severely affected hypertensive-diabetics. This study provides evidence that the combination of diabetes mellitus and hypertension produces significantly greater myocardial lesions than either disease alone. The similarity of the lesions with those observed in human patients suggests that the hypertensive-diabetic rat is a useful model for elucidating the pathogenesis of clinical myocardial disease in patients with hypertension and diabetes mellitus.

The effect of diabetes on performance and metabolism of rat hearts

To explore the effects of diabetes on myocardial function and metabolism we injected male rats with streptozotocin and studied their hearts 8 weeks later. Blood sugar levels in the treated rats were about 600 mg/100 ml. Body and heart growth rates were diminished. When studied in an isolated working rat heart apparatus using 5.5 mM glucose, hearts of diabetic animals showed diminished cardiac output and stroke work at high filling pressures. There also were significant depressions in peak left ventricular systolic pressure, peak aortic flow rate, maximum negative dP/dt, myocardial oxygen extraction, myocardial lactate production, and effluent lactate:pyruvate ratios. Myocardial glycogen stores, calculated glycogen utilization, and pyruvate production were increased in hearts of diabetics, and myocardial oxygen consumption was the same as in control hearts. The end-diastolic pressure-volume relationship was shifted to the right in hearts of diabetics. Most of the abnormalities observed in hearts of diabetic rats persisted when insulin and 15 mM glucose were included in the perfusion medium. Hearts from young rats or from age-matched food-restricted rats with heart weights similar to those of diabetics did not show depressed function or a pressure-volume shift. Our findings indicate that streptozotocin diabetes in rats results in abnormal myocardial performance. This is not due to restrictions in coronary flow or myocardial oxygenation and is not correctable by the provision of high glucose plus insulin in the perfusion medium.

Altered myocardial mechanics in diabetic rats

Diabetes mellitus is associated frequently with congestive heart failure in humans, even in the absence of associated coronary disease or hypertension. Nevertheless, the effects of the diabetic state on myocardial mechanics have not been studied. Accordingly, diabetes was induced in female Wistar rats by injection of streptozotocin (60 mg/kg). Left ventricular papillary muscles were studied 5, 10, and 30 weeks later and compared with controls. Relaxation was delayed significantly and velocity of shortening was depressed at all loads. However, the passive and active force-length curves, as well as the series elastic properties, were not altered. The changes in cardiac performance were found over a range of muscle lengths, stimulus frequencies, and bath concentrations of calcium, glucose, and norepinephrine. The duration of diabetes had no major effect on the mechanical changes observed. The possible influences of drug-induced cardiac toxicity, malnutrition, and altered thyroid hormone levels have been considered; the latter two factors could not be excluded completely from having some influence on the mechanical properties of diabetic cardiac muscle. Evidence is cited showing abnormalities in calcium uptake by sarcoplasmic reticulum and depressed actomyosin ATPase activity. Thus a cardiomyopathic state has been produced in the rat consequent to the induction of experimental diabetes mellitus. Various mechanisms for this entity have been suggested.

Intramyocardial microarteriopathy

1. Two basic types of arterial vessels can be distinguished in the myocardium. a) Compacta or Ventricular Wall Type. Intramyocardial microarteries with ring musculature of the media. b) Papillary Muscle Type. Arteries with longitudinal musculature arranged as bundles in the broad media. 2. The manifestation of intramyocardial microarteriopathy differs in these vessel types. PAS-positive and elastica-rich cushion-like thickening of the intima mainly occurs in the compacta type. Arterial vessels of the trabecular portion additionally show hyperelastosis of intima and media. The degenerative lesions of the papillary muscle type are characterized by early degeneration of the smooth muscle cells and hyperfibroelastosis of intima and media. 3. Pathological vascular lesions in the compacta and papillary muscle type occur more frequently in the left ventricle, and increase with age. 4. Slight and medium lesions are in the majority. Severe vascular changes are seen in the 7th to 9th decade in about 5-10% (compacta type) and in 30-35% (papillary muscle type) respectively. 5. Hypertension seemed to raise the frequency of slight and medium lesions in the compacta type vessels. In the papillary muscle type the degenerative lesions frequently extend from the top to the bottom of the papillary muscles. 6. No significant difference between frequency and severity of vascular lesions in diabetics and in the control group could be demonstrated. 7. It appears that pathological vascular lesions occur less frequently in compacta type vessels in cases of high-grade stenosis due to extramural coronary artery sclerosis. 8. Impairment of the quality of myocardial circulation is only encountered in the presence of severe pathological vascular lesions.

Absence of correlation between coronary arterial atherosclerosis and severity or duration of diabetes mellitus of adult onset

The relation between the severity and duration of diabetes mellitus and the severity of ischemic heart disease is uncertain. The clinical findings and the findings at autopsy were studied in 185 patients with diabetes mellitus of adult onset who ranged in age from 37 to 91 years and had a clinical diagnosis of diabetes established for a few days to 50 years before death. No statistically significant association was demonstrated either by simple correlation or by multivariate regression analysis between the clinically diagnosed severity or duration of diabetes and either the overall coronary disease, the number of diseased vessels or the number of myocardial infarctions. The presence of other expected correlations in the multivariate analysis suggested that the results of this study were not spurious. However, comparison with 185 age- and sex-matched control patients revealed that on the average, diabetic patients have more overall coronary disease (p < 0.002), more diffuseness of coronary disease (p < 0.005), more coronary collateralization (p < 0.001), more vessels involved by atherosclerosis (p < 0.001) and more myocardial infarcts (p < 0.001). The results suggest that although diabetes mellitus of adult onset is a condition in which the larger coronary arteries are subject to more atherosclerosis than are those in nondiabetic subjects, the progression of the atherosclerotic disease is unrelated to the duration or severity of the diabetes mellitus.

Systolic and diastolic time intervals in young diabetics

Systolic and diastolic time intervals were used to examine left ventricular performance in 22 young diabetic men (mean age 25 years) with no apparent clinical heart disease. Pre-ejection period index (PEPI), left ventricular ejection time index (LVETI), electromechanical systole index (QS2I), PEP to LVET ratio, the a wave percentage amplitude of the apexcardiogram (a/H5 ratio), the rapid filling wave (RFW), and the A2O interval were obtained in the conventional manner in 22 diabetics and 22 healthy men. The heart rate, diastolic pressure, PEP/LVET ratio, a/H per cent ratio, and A2O interval were significantly increased and LVET decreased in the diabetic group. QS2I, PEPI, and RFW did not differ from that in the normal group. Twenty-three per cent of patients had an abnormal systolic time interval, 54 percent an abnormal diastolic time interval, and 23 per cent had both abnormal intervals. Though these studies provide no difinite evidence of a cause, the abnormalities found may reflect a subclinical diabetic cardiopathy.

Hereditary and acquired cardiomyopathies in experimental animals: mechanical, biochemical, and structural features

Evidence has been presented regarding alterations of contractile behavior muscle biochemistry, and ulstrastructure during the course of the hereditary hamster cardiomyopathy. Also, preliminary structural and mechanical data were presented on the acquired cardiomyopathy of diabetes mellitus in experimental animals. In the hamster model, contractile performance, measured as isometric tension and rate of tension development, was shown to be depressed throughout the course of the disease, whereas normalized force-velocity relationships returned to normal only during the compensated stages of hypertrophy. Force-frequency relationships were depressed in myopathic muscles, indicating the presence of alterations in the muscle activation system, namely, the biochemical and functional integrity of the sarcoplasmic reticulum. Analysis of the contractile proteins in myopathic muscle has revealed depressions of Ca2+ activity in purified myosin in addition to an independently increased neutral protease activity that results in the specific degradation of LC2 of myosin. Sympathetic time and norepinephrine turnover increase progressively during the course of the disease. These changes are accompanied by decreasing tissue levels of neorepinephrine and increasing levels of dopamine, indicating a shift in the rate-limiting step for norepinephrine synthesis. Alterations were also noted in nuclear protein composition and serotonin levels. Microscopically, the myolytic and calcification changes that characterize the hamster cardiomyopathy have been confirmed. In addition, contraction bands and lysosomal changes have been observed that may relate to cateholamine hypersensitivity. In the experimental model of diabetic cardiomyopathy, a significant alteration in relaxation process was demonstrated despite the fact that peak tension development and its rate of development were unaltered. Also, the length dependence of contractile behavior was altered when compared to that of age-matched controls, indicating a potential loss of contractility reserve. When animals with combined hypertension and diabetes were studied, bothe contraction and relaxation processes were affected to a greater degree.