Myron W. Wheat

Hydrodynamic Forces in Dissecting Aneurysms IN-VITRO STUDIES IN A TYGON MODEL AND IN DOG AORTAS

It has been argued that pulse wave characteristics are important factors in extension and rupture of acute dissecting aneurysms. To test this, a standard model of an aorta was constructed, consisting of an outer layer of Tygon tubing and an inner layer of rubber cement. An “intimal tear” was produced and the “aorta” was subjected to nonpulsatile and pulsatile flow with increasing increments of pressure. With nonpulsatile flow alone (97 experiments) no dissection occurred at pressures up to 400 mm Hg. Pulsatile flow produced rapid and usually complete dissection with a maximum systolic pressure of 120 mm Hg. The extent of dissection per pulse was related to dp/dtmax in the fluid. No dissection occurred until a critical value of dp/dtmax (790 mm Hg/sec) was reached. Dog aortas were then used in place of the Tygon tube “aorta” with similar results; i.e., dissection did not occur with nonpulsatile flow, but did occur with pulsatile flow (3800 mm Hg/sec). The dissecting dog aorta ruptured to the outside or reentered the vessel lumen. It was concluded that pulse wave characteristics, particularly dp/dtmax, are important in the propagation of dissection.

Reversible pulmonary hypertension in a child with respiratory obstruction and cor pulmonale

Laryngotracheomalacia usually is a self-limited disease causing only noisy respiration. This report describes an infant born with a severe form of this anomaly who manifested cor pulmonale and congestive heart failure by 29 months of age. Suprasystemic pulmonary artery pressures were noted at the time of the initial cardiac catheterization. The child improved clinically after tracheostomy, and a repeat cardiac catheterization at 4 years of age showed a marked decrease in pulmonary artery pressure. Though a frequent cause of stridor in infancy, to our knowledge laryngotracheomalacia has not been reported as associated with cor pulmonale.

Dissecting aneurysms of the aorta: Present status of drug versus surgical therapy

Abstract Dissecting aneurysm is the most common acute catastrophe involving the aorta, occurring at the rate of about 5 per year per one million population and representing about one in each 500 autopsies. Fewer than 5 per cent of patients with acute dissecting aneurysms of the aorta die immediately and in most patients there is adequate time to make the definitive diagnosis and institute treatment. Intensive drug therapy is the initial treatment of choice in most dissecting aneurysms of the aorta, and particularly so in the acute cases, where the success rate approaches 90 per cent. Surgical therapy should be used in acute dissecting aneurysms only in cases of failure of drug therapy to control hypertension and/or progression of dissection, impending rupture, uncontrollable aortic valve insufficiency, or occlusion of major branches of the aorta. Surgical therapy is indicated electively in the chronic dissection with severe aortic valve insufficiency or enlargement of a localized aneurysm.

Surgical Treatment of Aneurysms of the Aortic Root

Abstract A standardized technique for the definitive treatment of chronic aneurysm of the aortic root complicated by aortic valve insufficiency is reviewed. This technique includes (1) excision and graft replacement of the aneurysm from the aortic annulus to the distal ascending aorta or arch, (2) replacement of the insufficient aortic valve with a Starr-Edwards prosthesis, and (3) implantation of the coronary artery orifices into the sides of the prosthetic graft. Angiocardiographic and pathological studies in long-term survivors have shown no instances of further aneurysmal enlargement or dissection, good function of the graft, no aortic valve insufficiency, and patent coronary artery orifices. Thirteen patients have been treated in this fashion with 2 hospital deaths.

The Mechanism of the Generation of the Third and Fourth Heart Sounds

A simple unitarian concept of the mechanism of third and fourth sounds is presented. This study demonstrates that the third sound occurs during early rapid diastolic ventricular filling at a time when atrial pressure exceeds ventricular pressure. It is recorded within the ventricle and on the ventricular wall. It coincides with ventricular muscle vibrations. The fourth sound is demonstrated to consist of two components, both occurring when atrial pressure exceeds ventricular. The first component coincides with the peak of atrial contraction, is recorded within the atria, and is inaudible. The second component, which is audible (25 to 70 cycles per second) and follows the first by 0.01 to 0.02 second, is recordable within the ventricle coinciding with the impact of blood from atrial systole against the ventricular wall. These observations demonstrate that the audible third and fourth heart sounds have a common origin in the ventricles and have the same temporal and hemodynamic relationships regardless of etiology.

Myocardial Lysosomes in Experimental Atrial Septal Defects

Preliminary observations in patients undergoing open-heart surgery have suggested that the lysosomes in the right atrium are increased in patients with atrial septal defects. This increase in lysosomes per myocardial cell appears to be directly related to the size of the left to right shunt. The following experiments were performed to see if similar findings could be produced in an experimental model. Atrial septal defects were produced in seven dogs. The biopsy specimens were prepared for ultrastructural examination and viewed with an electron microscope. Lysosomes were counted in representative sections and an estimate of the lysosomes per square micron of heart tissue obtained. The number of lysosomes per square micron of myocardium increased significantly following the creation of atrial septal defects in dogs, with the most marked increase occurring in the right ventricle. Several small atrial septal defects closed spontaneously, as proved by cardiac catheterization, and in these animals the elevated lysosome counts present initially returned toward normal after obliteration of the left to right shunt at the atrial level. Control dogs showed no significant increase in myocardial lysosomes over the 18-month period despite repeated thoracotomies and myocardial biopsy. These studies add further evidence to support the role of the lysosome as an important intracellular organelle which is related to cellular stress.

Localization of Tritiated Digoxin in Dog Myocardium by Electron Microscopic Autoradiography

Five mongrel dogs were given 0.08 mg/kg of tritiated digoxin over a 24-hour period. Left ventricular myocardium was excised and subsequently fixed, dehydrated, and embedded in Epon 812 epoxy resin. Tissue was sectioned and coated with a monolayer of photographic nuclear emulsion and exposed for varying time intervals up to three months. After development these autoradiographs were viewed with the electron microscope. It was found that of the total number of nuclear tracks counted, 75% were found to overlie the sarcomere of the myofibril, 27% to overlie the mitochondria, and 8% to overlie other structures. Of those tracks associated with the sarcomere, 72% were found to overlie the A band. Evaluation of the data obtained and the techniques used are presented.

Cineangiographic Studies in Patients with Starr-Edwards Aortic Valves

Aortic root cineangiography has been carried out in 21 consecutive survivors of replacement of the aortic valve with a Starr-Edwards ball-valve prosthesis. In nine of 21 patients, a significant leak around the rim of the prosthesis was demonstrated. In four reoperated patients, this leak was confirmed to be secondary to disruption of the suture material, usually in patients with heavily calcified annuli. Cineangiographic studies are necessary for complete postoperative evaluation of prosthetic values.

Correction of Ventricular Septal Defect in Childhood

Abstract One hundred and two consecutive patients underwent operative repair of ventricular septal defect with 9 operative deaths. Preoperative cardiac catheterization was performed in 100 patients. Severe pulmonary hypertension was present preoperatively in 8 of the 9 patients who died. Two patients had permanent heart block. Postoperative cardiac catheterization was performed in three-quarters of the surviving patients. Two patients had significant residual ventricular septal defect. The 92 surviving patients have been followed up to eleven years postoperatively and are asymptomatic.

Poll on Thoracic Surgical Training

Abstract In 1969, an ad hoc committee was appointed by The Society of Thoracic Surgeons to investigate attitudes concerning the past, present, and future of thoracic and cardiovascular surgery. A poll consisting of 34 questions regarding thoracic surgical training background, professional relations with the community, the future of thoracic surgery, and the Board of Thoracic Surgery was circulated in 1970 to the members of The Society of Thoracic Surgeons. From a total membership of 806 at that time, there were 533 respondents (66%). Later in the year, the questionnaire was sent to 64 directors of thoracic surgery training programs, 41 of whom responded (64%). Following this, a letter was sent to a number of men eminent in the field of thoracic and cardiovascular surgery, requesting them to comment on the results of the poll and to express their ideas on all aspects of thoracic surgical training. Hereafter these surgeons are referred to as the consultant group. The following material constitutes the final report of the ad hoc committee and is published in The Annals for the information of the members of The Society of Thoracic Surgeons and other interested individuals.