Ventricular Epicardial Surface Research Articles

A computer model of the left ventricular epicardial surface for quantification of jeopardized myocardium

A computer program has been developed that can be used to quantify the extent of probable myocardial damage which will result from occlusion of a jeopardized coronary vessel. The program, used as an adjunct to coronary arteriography, permits calculation of an area of an arbitrary segment of the left ventricular epicardial surface. This segmental area, when expressed as a fraction of the total LV epicardial area, is a measure of the myocardial mass supplied by a specific coronary arterial vessel. The computer program has been extended to include graphic, three-dimensional simulation of different views of the left ventricular epicardium.

Responses to activation of cardiac sympathetic afferents with epicardial bradykinin.

The cardiovascular reflex responses mediated by cardiac sympathetic afferent fibers (CSA) appear to differ depending on the nature of the activating stimulus. Although electrical stimulation of CSA may result in either excitatory of inhibitory reflex responses in both cats and dogs, topical application of bradykinin to these sensory endings elicits only excitatory reflex responses in cats. The present experiments were performed to determine whether CSA activated by epicardial bradykinin also mediate solely excitatory reflex responses in the dog. The changes in efferent cardiac or renal sympathetic nerve activity, mean arterial pressure, and heart rate resulting from application of bradykinin to the left ventricular epicardial surface were determined in 15 chloralose-anesthetized, sinoaortic-denervated vagotomized dogs. Activation of CSA with bradykinin (0.1--120 g/ml) elicited inhibitory responses in eight dogs, excitatory responses in four dogs, and biphasic responses in three dogs. Both excitatory and inhibitory reflexes were eliminated by cardiac sympathetic afferent denervation. The results show that, in the dog, cardiac receptors with sympathetic afferent fibers activated by epicardial bradykinin mediate nonuniform reflex responses that tend to be predominantly inhibitory.

Quantitative measurement of left ventricular volumes in man from radiopaque epicardial markers.

The distances between three or four radiopaque markers located on the left ventricular epicardial surface at the apex and in the region of the minor axes in 22 subjects showed close correlations with left ventricular chamber radii, length, volume and wall thickness determined from biplane angiograms over the range of stroke volume. The markers were previously placed during heart surgery. Regression equations relating the distances between epicardial markers and chamber volumes were used to predict volumes for other beats. There was close agreement of end-diastolic, end-systolic, and stroke volumes as determined by the angiographic and epicardial marker methods for premature atrial contraction beats and post premature contraction beats, and in studies performed during rest and exercise. Time-volume curves determined by the epicardial marker and angiographic methods were similar. It is concluded that epicardial marker measurements can be used to quantitate beat-to-beat left ventricular chamber volume and dimension changes.

The shape and movements of the human left ventricle during systole: A study by cineangiography and by cineradiography of epicardial markers

The shape of the left ventricular cavity and the movements of the mitral valve, aorta and coronary arteries were studied in cineangiograms obtained from normal subjects and patients with coronary arterial disease, mitral stenosis or atrial septal defect. Movements of the left ventricular epicardial surface were studied by postoperative cineradiography of radiopaque markers previously attached during closed mitral valvotomy. The pre-ejection and ejection phases of systole were identified from the simultaneously recorded phonocardiogram, apex cardiogram, indirect carotid pulse pressure tracing and electrocardiogram. The left ventricular epicardial surface contracted in an approximately symmetrical fashion with slight rotational movements about the long axis most marked at the beginning and end of systole, but contraction of the left ventricular cavity appeared less symmetrical because of the systolic increase in wall thickness, approximation of trabeculae and movements of the mitral valve. During pre-ejection, the left ventricular cavity narrowed anteroposteriorly, the descent of the base began and a slight anticlockwise rotation of the epicardial surface was accompanied by a slight thrust of the apex toward the chest wall. During ejection, narrowing of the left ventricular cavity and the descent of the base continued, and a slight clockwise rotation and retraction of the apex occurred in late systole. The symmetry of left ventricular contraction may be due to the similarity of contractility and afterload of individual myocardial fibers, and the slight rotational movements may be a result of sequential activation of the left ventricular myocardium from endocardial to epicardial surface.

Experimental studies of ST-T changes in electrocardiogram: effect of local or total hypoxemia of the canine heart on the unipolar lead electrogram and on the trans-membrane potential recorded from the ventricular epicardial surface

To clarify the mechanism of ST-T changes in electrocardiogram, these changes that appear on the direct unipolar electrogram recorded from the ventricular surface were compared with the changes of transmembrane potentials simultaneously recorded from the vicinity of direct unipolar electrogram. This study was conducted on the in situ canine heart under conditions of total and local hypoxemia. Method Seventy-seven mongrel dogs weighing about 15 kg were used, and each animal was anesthetized intravenously by pentobarbital sodium 25 mg per kg of body weight. Then the heart was exposed after performing thoracotomy under artificial positive pressure respiration. In order to prevent the undue movement of recording site on ventricular surface, the inner and outer rings attached to the supporting frame were placed over the pericardial surface, and then the portion of the pericardium within the inner ring was dissected away. Ringer's solution with the temperature of approximately 33°C was constantly dripped upon the epicardial surface, in order to prevent dryness. Using the central terminal system of Wilson, a unipolar surface electrogram was taken simultaneously with transmembrane potentials from the epicardium within the inner ring. The surface electrode consisted of tungsten wire 100 micron in diameter, and was gently placed on the ventricular surface by micromanipulator. The transmembrane potential of the individual cell was recorded from a flexibly mounted ultramicroelectrode such as described by WOODBURY and BRADY (1956). The indifferent electrode consisted of tungsten wire with a diameter of about 100 micron, placed 2 to 4 mm away from the site of penetration by microelectrode. Total hypoxemia of the ventricles was induced by letting a dog inhale the mixture-gas of oxygen 4% and of nitrogen gas 96% for from 6 to 8 minutes. For producing the local hypoxemia of the ventricle, approximately 120 ml of venous blood was taken from the femoral vein by syringe. At this time special care was paid to venous blood, that is, venous blood was kept from exposure to room-air by a layer of floating liquid paraffin in the syringe. This venous blood was kept at approximately 36°C. This venous blood was perfused at a pressure of 100 mmHg into the artificial coronary circuit made between the left carotid artery and the anterior descending branch of the canine left coronary artery (heparinized 500 units per kg/body weight). The room temperature was kept between 24 to 25°C through-out the experiment.

Measurement of left ventricular diameter in the dog by cardiac catheterization. Validation and physiologic meaningfulness of an ultrasonic technique.

A cylindrical ultrasonic transducer on a catheter tip lodged in the cleft between the free wall of the right ventricle and the interventricular septum provides an easily measured echo from the posteroinferior left ventricular epicardial surface. The sonic path represents a diameter of the left ventricle at approximately its largest cross-sectional area. Experiments in six dogs demonstrated that measurements by ultrasound agree within ±6% with simultaneous radiographic measurements of left ventricular diameter. Procedures designed to alter left ventricular volume were employed in 14 dogs to clarify the physiologic meaningfulness of the left ventricular diameter measured by ultrasound. Both end-diastolic and end-systolic diameter increased with anoxia, with sudden injections of saline into the left ventricle, after propranolol, and after inflation of a balloon in the thoracic aorta. These diameters decreased with isoproterenol, with increased heart rate, and after inflation of a balloon in the inferior vena cava. The present technique provides accurate and physiologically meaningful estimates of left ventricular diameter. Ventricular diameter measurements obtained during cardiac catheterization should permit assessment of ventricular distensibility and of ventricular function.

Epicardial electrocardiograms recorded in the course of seven cases of heart surgery.

Thirty-eight direct electrocardiographic records have been obtained by applying an exploring electrode directly to the epicardium after incision of the pericardium in the case of seven patients subjected to thoracotomy for various forms of heart surgery. These cases include three individuals with the tetralogy of Fallot, one with mitral stenosis, one with coarctation of the aorta, one with probable pulmonary atresia and one with a patent ductus arteriosus. This exploration has permitted us to study the patterns obtained in different regions of the right and left ventricular epicardial surfaces in four patients with right ventricular hypertrophy, two patients with left ventricular hypertrophy, and one patient with a heart whose left ventricle-right ventricle ratio was probably little disturbed.