Increased protein synthesis during right ventricular hypertrophy following pulmonary stenosis in the dog

The synthesis rates of mixed protein in the left and right ventricles were the same in normal dogs, averaging 7.8% per day. After five days, pulmonary stenosis protein synthesis rate in the right ventricle increased rapidly to 13.6% per day and subsequently decreased to near normal by 12 days, during which time the right ventricle protein mass increased by 48% after five days and by 73% after 12 days. Similarly the synthesis rate of the myofibrillar and sarcoplasmic proteins was almost doubled after five days of stenosis. The protein synthesis rate in the left ventricle did not change significantly during the 24 days of pulmonary stenosis.

Familial hypertrophic cariomyopathy and lentiginosis

Members of three generations of a family studied, manifest profuse lentiginosis and hypertrophic cardiomyopathy. The autosomal dominant inheritance of this syndrome is established. Lentiginosis should alert the physician to possible underlying heart disease.

Series elasticity in the intact heart. Evidence for the application of the Hill model for muscle to the intact left ventricle

Several recent studies have shown that the contractile state of the intact heart may be described by the instantaneous relationships between contractile element velocity, length and stress. However, there is little direct evidence that the intact heart can be described by a model containing at least a contractile element and a series elastic component (SEC). In isolated muscle the series elastic component can be analyzed by determining the length changes following quick releases to known loads during contraction. The characteristics of the effective SEC of the intact left ventricle (LV) were determined by a quick release method in 8 dogs in which the left ventricle contracted isovolumically against a balloon inserted via the mitral annulus. During active contraction, sequential withdrawals of 0.5 to 7.0 ml of fluid were performed rapidly (5-18 msec) by an electrically-timed, springloaded syringe. From these releases the calculated maximum extension of the SEC averaged 4.03 +/- 0.27% of LV circumference at LV pressures averaging 79/6 mmHg (systolic/end-diastolic; range 66-107/0-15 mmHg.) The reductions of the left ventricular midwall circumference were plotted against the corresponding changes in mean wall stress. The load extension curve determined in this manner was unchanged by varying the time of release and by norepinephrine infusion. These data support a model for the intact LV that contains an undamped SEC, the characteristics of which resemble those of isolated cardiac muscle.

Augmentation of myocardial digoxin concentration in hemorrhagic shock

The effect of the shock state on myocardial digoxin uptake and plasma digoxin levels was examined in unanesthetized dogs following hemorrhage. Five minutes after intravenous administration of tritiated digoxin the myocardial digoxin content in animals with shock was greater than in normal animals in both left ventricle (LV) (165 plus or minus 15 (SD) ng/g vs 130 plus or minus 26 ng/g, P smaller than 0.02 and right ventricle (RV) (142 plus or minus 13 ng/g vs 111 plus or minus 22 ng/g. P smaller than 0.02) as was the plasma digoxin concentration (61.6 plus or minus 11.8 ng/ml vs 44.3 plus or minus 4.6 ng/ml, P smaller than 0.02). After one hour, in another group of dogs, the difference in myocardial concentration of digoxin between test and normal groups was even greater (LV: 213 plus or minus 26 ng/g vs 133 plus or minus 13 ng/g, P smaller than 0.001; RV: 171 plus or minus 9 ng/g vs 111 plus or minus 8 ng/g. P smaller than 0.001) despite lower plasma digoxin concentration in the test group (12.9 plus or minus 2.9 ng/ml vs 17.3 plus or minus 2.5 ng/ml, P smaller than 0.05). Diminished peripheral blood flow, peripheral digoxin delivery and uptake were probably responsible for the early difference in plasma digoxin levels. Resultant greater plasma concentrations of digoxin presented to the myocardium in the early phase, coupled with relative preservation of myocardial blood flow, may explain the greater myocardial uptake in animals with shock although myocardial mechanical factors may also be implicated. Augmented uptake of digoxin by the myocardium in canine hemorrhagic shock may be relevant to the altered susceptibility to glycoside action in clinical shock syndromes.

The effect of chronic cardiac volume overload on regional myocardial blood flow in the dog

1. Regional myocardial blood flow was studied in the anaesthetized, open-chest dog with a large chronic aorto-caval fistula, using carbonized microspheres of 7-10 mum diameter. The results from fourteen dogs with fistulae of 4-84 days duration were compared to those from nine normal animals. 2. Myocardial blood flow to all areas of both ventricles was increased to between 180 and 250% of the normal despite lower aortic diastolic (coronary diastolic) pressure. Myocardial blood flow in the right ventricle was lower than in the left in both groups of dogs although the increase above normal in dogs with fistulae was relatively greater in the right ventricle. Increased myocardial blood flow is attributed to coronary autoregulation resulting from increased myocardial oxygen consumption due to increase in myocardial tension development. 3. Although absolute blood flow to the inner left ventricular wall was markedly increased in all dogs with fistulae, in those with aortic diastolic pressure below 55 mmHg the ratio of flow in the inner to that in the outer free left ventricular wall was significantly less than in those with aortic diastolic pressure above 55 mmHg (P less than 0 with 02). Low aortic diastolic pressurere and diastolic coronary perfusion pressure probably resulted in relative ischaemia of the inner left ventricular wall.

Regression of left ventricular dilation and hypertrophy after removal of volume overload. Morphological and ultrastructural study

Gross and ultrastructural changes occurring in the left ventricle in response to chronic volume overload were studied in dogs. One group of dogs was examined 28-43 days after an aortocaval fistula had been created; congestive heart failure had developed at the time of the examination. Two other groups of dogs were investigated 78 ± 17 ( SD ) days and 178 ± 4 days after similar fistulas had been closed. A group of control dogs was also studied. Aortocaval fistulas produced significant left ventricular dilation and hypertrophy. Ultrastructural changes included enlargement and distortion of intercalated disks, increase in number but decrease in size and relative volume of mitochondria, and loss of lateral alignment of sarcomeres. Left ventricles, 78 days after the fistulas had been closed, were not different ultrastructurally or grossly from those in dogs with patent fistulas. After 178 days of closure, ventricular mass and volume had decreased; mass was still significantly greater than that in normal dogs, but cavity volume was not. Ultrastructural abnormalities in dogs after 178 days of closure were much less marked than those in dogs with patent fistulas, and ultrastructure was hardly distinguishable from normal. The findings in these experiments indicate that gross and ultrastructural abnormalities produced in the left ventricle by chronic volume overload are largely, if not completely, reversible.

Digitalis-induced increase in aortic regurgitation and the contrasting effect of glucagon in the sedated dog

The hemodynamic and phasic ascending aortic flow changes induced by acetylstrophanthidin and glucagon were studied in closed-chest sedated dogs with aortic regurgitation. While the positive inotropic effect of both agents was reflected in an increase in peak rate of rise of left ventricular pressure, acetylstrophanthidin increased aortic regurgitation, while glucagon decreased it. With the former, left ventricular end-diastolic pressure rose from 20+/-6 to 27+/-6 mm Hg (P < 0.005), but fell from 18+/-4 to 11+/-3 mm Hg (P < 0.001) with glucagon. Acetylstrophanthidin increased systemic vascular resistance, aortic diastolic pressure, and diastolic regurgitant flow rate, and, heart rate and the duration of regurgitation per beat and per minute being unchanged, regurgitant flow per beat increased 32+/-15% (P < 0.001). Glucagon decreased regurgitant flow per beat 27+/-14% (P < 0.001) because of abbreviation of diastole associated with tachycardia, and because of reduction in regurgitant flow rate. Despite tachycardia, the duration of regurgitation per minute was unchanged, and the small fall in regurgitant blood flow per minute was not significant, but this pertained in the face of 47% increase in effective cardiac output (P < 0.001). In contrast, acetylstrophanthidin increased regurgitant flow per minute 28+/-14% (P < 0.001) without change in effective cardiac output. The increase in cardiac contractility, tachycardia, and systemic vasodilatation induced by glucagon preferentially enhanced forward blood flow, which led to reduction in left ventricular volume overload, while it increased cardiac output. Contrarily, acetylstrophanthidin increased aortic regurgitation and, despite its inotropic effect, increased left ventricular volume overload without an increase in cardiac output.

Diastolic geometry and sarcomere lengths in the chronically dilated canine left ventricle

In 10 dogs left ventricular geometry and ultrastructure were examined 3 to 12 weeks after chronic ventricular dilatation was induced by means of a large arteriovenous shunt. Following cardiac catheterization, the hearts were arrested and fixed in diastole at the left ventricular end-diastolic pressures (LVEDP) which existed in the beating heart. Transmural LVEDP were increased in all animals (avg. 27 mm Hg). The diastolic pressure-volume relationship was shifted to the right, the average end-diastolic volume of the chronically dilated ventricles (avg. 103 ml) being larger than that of previously studied acutely dilated ventricles (avg. 72 ml, P <.01), but calculated diastolic wall stress values were not different. Sarcomere lengths in the chronically dilated hearts averaged 2.19±.02 µ ( SE ) (range 2.11 to 2.27), a value near the apex of the sarcomere length-tension curve, but not significantly different from sarcomere lengths in acutely dilated ventricles. Slippage between myofibrils, reflected by a loss of normal alignment of the Z lines, appeared to be one mechanism underlying this adaptation. The findings indicate that sarcomeres in the canine left ventricular wall are remarkably resistant to chronic as well as to acute overstretch. They further imply that little or no Frank-Starling reserve mechanism was available in these ventricles and raise the possibility that a descending limb of the heart's performance as a pump need not reflect a descending limb at the sarcomere level.

Contractile properties of cardiac muscle in hyperthyroidism. Analysis of behavior of hyperthyroid cat papillary muscle in vitro relevant to thyrotoxic heart disease

Right ventricular papillary muscles from hyperthyroid and normal cats were studied in vitro at 30°C, at contraction frequencies of 12, 30 and 60/min. At 12/min the contractility of hyperthyroid muscles was significantly greater than normal, as indicated by greater velocity of isotonic shortening, isometric tension development, and rate of tension development. Isotonically contracted muscle lengths were smaller and time to peak isometric tension less. At 60/min, velocity of shortening was still greater and time to peak tension less in hyperthyroid muscles, but isometric developed tension, rate of tension development, and isotonically contracted muscle lengths and shortening were not different. Increasing frequency from 12/min to 60/min resulted in immediate positive inotropic responses in both groups, but a smaller response in hyperthyroid than normal muscles. Over subsequent minutes, a slight decrease in contractility occurred in normal muscles but the decrease was significantly greater in hyperthyroid muscles. The difference in response to increasing frequency is attributed to more profound hypoxia in hyperthyroid muscles at high contraction frequencies. Predisposition of the muscle to hypoxia induced by hyperthyroidism then becomes an important determinant of the net effect of hyperthyroidism on myocardial contractility. The experimental situation is analogous to the coexistence, in vivo, of thyrotoxicosis and other conditions predisposing to coronary insufficiency, such as coronary artery disease or ventricular hypertrophy; that hyperthyroidism does not then augment contractile state in respect to tension development or muscle shortening helps explain the occurrence of thyrotoxic heart failure in response to the body's increased requirements for blood flow.

Active length-tension relations compared in isometric, afterloaded and isotonic contractions of cat papillary muscle. Their dependence on inotropic state

Isometric, afterloaded and isotonic contractions of cat right ventricular papillary muscle were studied in vitro at 30°C or 37°C. The length to which muscle contracted under a given total load varied directly with initial muscle length. The discrepancies between contracted muscle lengths depended upon load and the inotropic state of the muscle. In control contractions at 12/min, the maximum discrepancy occurred at a load of 0.5 g or 1 g and averaged 0.47 ± 0.04 ( SD ) mm while after acetylstrophanthidin (0.75 µg/ml) the maximum discrepancy occurred between 3- and 5-g load and averaged 0.62 ± 0.07 mm ( P < 0.001). At low loads acetylstrophanthidin decreased the discrepancy at 0.5-g load from 0.41 ± 0.08 mm to 0.22 ± 0.05 mm ( P < 0.001). Acetylstrophanthidin increased developed tension at optimum muscle length by 71 ± 23% ( P < 0.001). Increasing frequency of contraction from 12/min to 60/min induced greater decrease in time to peak tension than occurred with acetylstrophanthidin (30% vs. 15%) but produced little change in either isotonic or isometric contracted length-tension relations. Since the differences between contracted length-tension relations were not influenced by abbreviation of active state induced by frequency changes, it is unlikely that the lesser abbreviation with acetylstrophanthidin was responsible for the changes it produced. Rather, they may be related to the intensity and duration of active state reflecting increased energy release in the contractile process.

Autonomic blockade by propranolol and atropine to study intrinsic myocardial function in man

Blockade of cardiac autonomic nervous activity by an intravenous injection of 0.2 mg/kg propranolol and 0.04 mg/kg atropine was used with cardiac catheterization to study intrinsic cardiac function in 47 patients with normal hearts and known graded myocardial disease. After blockade, significant hemodynamic abnormalities became apparent at rest in the majority of patients with known disease, many of whom had normal control findings. This occurred partly through a reduction in the normal range of cardiac function at rest, and partly through changes in the abnormalities associated with disease: after blockade, diseased hearts had normal stroke volumes, but beat more slowly, and had higher left ventricular filling pressures. The heart rate after blockade was fixed; this was defined as the intrinsic heart rate (IHR); it ranged from 57 to 126 beats/min in different patients. Both the IHR and left ventricular end-diastolic pressure after blockade were sensitively and quantitatively related to the severity of myocardial disease. When, after blockade, arterial pressure was raised by angiotensin, the IHR was unchanged; normal hearts maintained their stroke volume and increased stroke work; diseased hearts maintained stroke volume less well and stroke work was unchanged or fell. Abnormal ventricular responses corresponded well with abnormal ventricular function at rest. In different patients the IHR was significantly related to each available index of left ventricular function. Other studies in animals have shown that the IHR is closely related to intrinsic myocardial contractility in certain forms of experimental heart failure. An analogous relationship existing between the IHR and myocardial function in patients with heart disease is suggested as the explanation for the IHR/ventricular function relationship in this study. If so, the IHR may prove valuable as an index of myocardial function in man, since it can be measured simply and safely in clinical practice.