Microvascular spasm in the cardiomyopathic Syrian hamster: a preventable cause of focal myocardial necrosis

Apical hypertrophic cardiomyopathy: evaluation by noninvasive and invasive techniques in 23 patients

Over a 3 year period we evaluated 23 patients (16 men, seven women) with apical hypertrophic cardiomyopathy by noninvasive and invasive methods. Sixteen patients had chest pain. In 17, results of cardiovascular examination were normal. The electrocardiogram showed precordial inverted T waves in all patients and these were of mild-to-moderate amplitude (less than 10 mm) in 18 and giant (greater than 10 mm) in five. M mode echocardiography revealed a typical pattern of contraction and relaxation in the apical region of the left ventricle that was associated with significant hypertrophy. These findings were confirmed by two-dimensional echocardiography. Systolic anterior motion of the mitral valve was not observed nor was there any evidence of obstruction of the left ventricular outflow tract. Results of Doppler echocardiographic study of the mitral and aortic flow were normal in all patients but one who had mild mitral insufficiency. Radionuclide studies of 14 patients revealed a mean left ventricular ejection fraction of 66 +/- 6% (range 55% to 79%), with normal left ventricular contraction in all patients but two with apical hypokinesis. In all six patients who underwent catheterization a characteristic appearance of the left ventricle at end-systole as well as abnormal end-diastolic contour were noted on the left ventricular angiogram, but the "ace of spades" configuration was seen in only one. We conclude that the 23 patients studied form a homogeneous group of individuals with nonobstructive apical hypertrophic cardiomyopathy, which differs in many respects from cardiomyopathies reported by other investigators.

Defective trophic response of brown adipose tissue of myopathic hamsters

Hamsters with muscular dystrophy (BIO 14.6) have a smaller than normal amount of brown adipose tissue. Two stimuli that promote growth of brown adipose tissue in normal hamsters, short photoperiod and eating a high-fat diet, are here shown to be without effect on brown adipose tissue of myopathic hamsters. Cold-induced growth of brown adipose tissue occurs normally [Am. J. Physiol. 239 (Cell Physiol. 8): C18-C22, 1980]. There is a normal rate of turnover of norepinephrine in brown adipose tissue of the myopathic hamster but a failure of the tissue to hypertrophy in response to norepinephrine is unlikely since norepinephrine does not appear to mediate the trophic response [Am. J. Physiol. 247 (Endocrinol. Metab. 10): E793-E799, 1984]. Denervation results in a marked reduction in size (protein content) of brown adipose tissue of normal hamsters but has very little effect on the size of brown adipose tissue of myopathic hamsters. A central, possibly hypothalamic, defect in the myopathic hamster is postulated to underlie its abnormal control of brown adipose tissue hypertrophy.

Sir Thomas Lewis redivivus: from pebbles in a quiet pond to autonomic storms

Images

Beneficial hemodynamic effects of intravenous and oral diltiazem in severe congestive heart failure

Concern persists about the potential negative inotropic effects of calcium channel blockers in patients with severely depressed myocardial function. Therefore, intravenous diltiazem (100 to 200 micrograms/kg per min infusion) was administered for 40 minutes followed by oral diltiazem (90 to 120 mg/8 hours) for 24 hours to patients with advanced congestive heart failure (New York Heart Association class III to IV, mean ejection fraction 26 +/- 4 [SD]). Intravenous diltiazem (eight patients) increased cardiac index 20% (2.05 +/- 0.8 to 2.47 +/- 0.8 liters/min per m2, p less than 0.01), stroke volume index 50% (22 +/- 9 to 33 +/- 12 ml/m2, p less than 0.001) and stroke work index 27% (19 +/- 10 to 24 +/- 10 g-m/m2, p less than 0.05); while reducing heart rate 23% (97 +/- 18 to 75 +/- 11 beats/min, p less than 0.01), mean arterial pressure 18% (95 +/- 13 to 78 +/- 7 mm Hg) and pulmonary wedge pressure 34% (29 +/- 9 to 19 +/- 7 mm Hg), without altering maximal first derivative of left ventricular pressure (dP/dtmax). Oral diltiazem (seven patients) produced equivalent hemodynamic effects. Transient junctional arrhythmias were observed in three of eight patients with intravenous diltiazem and one of seven patients with oral diltiazem. It is concluded that intravenous and short-term oral diltiazem improve left ventricular performance and reduce myocardial oxygen demand by heart rate and afterload reduction without significantly depressing contractile function in severe congestive heart failure. Caution should be exercised to avoid potential adverse, drug-induced electrophysiologic effects in such patients.

Histologic and ultrastructural studies on the myocardium in spontaneously diabetic KK mice: a new animal model of cardiomyopathy

The hearts from spontaneously diabetic KK mice and control mice were examined by light and electron microscopy. Myocardial degeneration, myocardial fibrosis and calcium deposits in the myocardium were extensive in KK mice aged 8 weeks. In myocytes of newborn KK mice, an irregular arrangement of myofibrils and poorly formed Z bands were found. Ultrastructural changes in myocytes of KK mice aged 4 weeks consisted of destruction of mitochondria, degenerated myofibrils and abnormalities of Z bands. However, increased mucopolysaccharides in interstitium and thickened basement membranes of capillaries were not found in KK mice, in contrast to the previous reports of myocardial changes in diabetic C57BL/KsJ mice, alloxan-diabetic dogs and hypertensive-diabetic rats. These observations suggest that the cardiomyopathy found in KK mice is not secondary to diabetes mellitus but is caused by other factors. In conclusion, myocardial ultrastructural abnormalities are present in newborn KK mice. Thus, this animal can be used as a model of cardiomyopathy.

Myocardial micronecrosis produced by microsphere embolization. Role of an alpha-adrenergic tonic influence on the coronary microcirculation

Microspheres approximately 25 or 50 micrometers in diameter were systemically embolized from the left ventricular cavity. The number of microspheres given was empirically chosen to minimize the possibility of more than one microsphere lodging in an arteriole (3 mg/kg), yet was sufficient to allow for adequate histological assessment. The dogs were sacrificed after 24 hours, and focal areas of myocytolytic necrosis were noted in the myocardium. Groups of dogs were given pretreatment with drugs 10 minutes before embolization. Dogs pretreated with phentolamine (n = 8) and prazosin (n = 2) did not reveal any areas of myocardial necrosis after embolization with 25-micrometers microspheres. Cardiac lesions were also prevented in four of five dogs pretreated with verapamil. In contrast, cardiac lesions were not prevented by pretreatment with yohimbine (n = 2), dipyridamole (n = 3), propranolol (n = 2), or atropine (n = 2). Drug pretreatment with phentolamine or verapamil was not able to prevent cardiac lesions after embolization with 50-micrometers microspheres. Furthermore, despite a greater number of microspheres physically present in the subendocardial layer, the necrotic lesions were more frequent in the mid-wall and epicardial layers. Lesions produced by 25- or 50-micrometers emboli were also significantly smaller in the endocardium. Systemic embolization with microspheres excluding the coronary circulation did not produce cardiac lesions. We conclude that mechanical interruption of the coronary circulation with a 25-micrometers microsphere may be a necessary but not sufficient condition to produce cardiac necrosis. An alpha 1-adrenergic mechanism is also involved in the production of these lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Hypothesis: is congestive cardiomyopathy caused by a hyperreactive myocardial microcirculation (microvascular spasm)?

In most congested, dilated cardiomyopathies, pathologic analysis reveals focal myocardial necrosis, microscopic scarring, interstitial fibrosis, and myocellular hypertrophy. The focal nature of these processes indicates that the cardiomyopathies may not be due to diffuse abnormalities of cardiac muscle cells, at least in the early stages, but that the changes may represent focal events affecting discrete, small volumes of tissue. Experimental evidence of microvascular hyperreactivity (spasm), both in the hereditary cardiomyopathy of the Syrian hamster and in the acquired cardiomyopathy of the hypertensive-diabetic rat, suggests that transient spasm of the myocardial microcirculation may lead to focal myocellular necrosis and scarring, which then causes the unaffected myocardial cells to undergo compensatory hypertrophy in order to normalize the increased load per unit of myocardium. When enough myocardium is lost and the compensatory hypertrophy results in decreased contractility, congestive heart failure ensues as a systemic response to altered ventricular function. The efficacy of verapamil therapy in the Syrian hamster in preventing microvascular spasm, cell necrosis, and the subsequent development of a cardiomyopathy has provided hope that similar preventive treatment can be applied to patients with early stages of cardiomyopathy.