WEDNESDAY MORNING, APRIL 2, 1969

8:30 A.M. Scientific Session: THORACIC SURGERY FORUM

Grand Ballroom

37. A Permanent Transvenous Atrial Electrode Catheter

Nicholaus P. D. Smyth, Laszlo Vasarhelyi,* and

William McNamara,* Washington, D.C.

Synchronous pacing in patients with complete heart block offers several advantages over asynchronous (fixed rate) and demand pacing. These include: response to increased physiological demand by an increase in rate as well as stroke volume, and preservation of the hemodynamic advantage of the "atrial kick." The lack of a suitable transvenous electrode for permanent "P" wave pick-up has restricted the application of synchronous pacing, since thoracotomy is still required for reliable detection of the "P" wave. Patients with symptomatic bradycardia without heart block are currently treated by demand ventricular pacing. A more logical treatment for many of these patients would be demand or fixed rate, atrial pacing. The lack of a suitable transvenous electrode for permanent atrial pacing has slowed the development of this approach. We have developed a unipolar catheter electrode which can be inserted transvenously and securely positioned in the right atrium. Studies in the dog show stable location of the catheter, with satisfactory "P" wave pick-up and atrial capture on stimulation for up to 30 days. Atrial stimulating thresholds are consistently higher than ventricular thresholds measured in the same animal at the same time. A modification of the catheter suitable for use in patients has been developed and clinical trial is in progress. Satisfactory short-term results have been obtained in two patients.

38. Long-Term Follow-Up of a New Method of Pacer Lead Implantation

James R. Jude, Kazi Mobin-Uddin,* Carlos R. Lombardo,* and

George M. Callard,* Miami, Fla.

Cardiac pacemaker leads were implanted under local anesthesia on the out-flow tract of the right ventricle in 25 patients over a period of three years. The parasternal approach used did not enter the pleural space. It retained the simplicity of the transvenous method with the reliability of the epicardial suture technique The pacer power pack was placed in the epigastrium or sub-pectoral area. Both fixed rate and demand pacemakers were employed. In three patients the incision was extended to the left and the electrodes placed on the left ventricle due to the absence of a bare area on the right ventricle. One patient died post-operatively of renal failure. There have been no late deaths. The battery pack has been replaced in six patients giving an opportunity to study the threshold for stimulation of the electrodes on the right ventricle. The thresholds varied from 1.5 to 4.0 milliamperes with the longest measured at 24 months of 2.5 milliamperes. No lead difficulties have been seen with follow-up up to 36 months, n view of changing opinions, an employment of a transvenous electrode with problems of repositioning or perforation, this method provides an alternative simple method of placement without general anesthesia.

39. Water and Solute Excretion Following Cardio-Pulmonary Bypass with Hemodilution: The Effects of the Osmolarity of the Perfusion-Prime

J. B. Das,* A. J. Eraklis,* and J. E. Jones,* Boston, Mass.

Sponsored by Robert E. Gross

Renal water and solute excretion was studied following open-heart surgery with hemodiluted primes of varying osmolarity (290 mOsm/L-377 mOsm/L). The water and electrolyte content of skeletal muscle and red cells before and following bypass was also measured. With hyperosmolar primes, a hypertonicity of the plasma and a sharp osmotic diuresis was noted within the first six hours after cardio-puhnonary bypass. In the next 18 hours the urinary output for the hyperosmolar groups dropped well below (22.5.ml/hour/1.73m²) that for the iso-osmolar group (37.3 ml/hour/ 1.73m²). However, the total solute excretion in the hyperosmolar group was only slightly higher (729 mOsm/day/1.73m²) than the solute excretion in the iso-osmojar group (672 mOsm/day/1 73m²). The obligatory water loss is greater in the hyperosmolar groups leading to a relative dehydration, persistent hyperosmolarity of the serum, hypernatremia and high BUN levels. The water and solute excretion was correlated with changes in water and electrolyte content of red cells and skeletal muscle. An increase in sodium and water content of the cells accompanied by a potassium washout was noted during cardio-pulmonary bypass at lie highest prime-osmolarities studied. The data collected suggests that monitoring the osmolarity of the prime prior to cardio-pulmonary bypass and the patient's serum post-operatively will offer a guide to fluid therapy and avoid sudden shifts of water and electrolytes between fluid compartments.

40. Development of a Membrane Oxygenator: Overcoming Blood Diffusion Limitation

Robert H. Bartlett,* Diane Kittredge,* Bertram S. Noyes, Jr ,*

Ralph Willard,* and Philip A. Drinker,* Boston, Mass.

Sponsored by Dwight E. Harken

Current membrane oxygenators are limited by diffusion _of oxygen through the laminar blood film at the membrane surface, achieving only 10-30% of the gas transfer capacity of the membrane. We have previously described the cpnvective mixing produced in a fluid flowing through a torsionally oscillating helix. This principle, applied to membrane oxygenator design, has been shown to eliminate the blood film limitation. A helix of 5-mil silicone rubber membrane was made by wrapping 10 feet of .25 in. diameter tubing around a 12 inch cylinder. Oxygen transfer to blood in vitro increased from 45 cc/m²/min. to 203 cc/m²/min. as the frequency of oscillation was increased Maximum possible oxygen transfer through 5-mil silicone rubber tubing is 205 cc/m²/min.(670 mmHg gradient). These observations were repeated in veno-venous and arterio-venous bypass in dogs. The oxygenator has performed at maximum transfer rates in vivo periods up to 7 hours. In this system there is no blood-gas interface, hemolysis is negligible, and bubbling cannot occur. Rapid flow through the oscillating large-bore tubing prevents stagnation and decreases the tendency to thrombosis. Studies are underway to evaluate prolonged extracorporeal oxygenation in the dog.

41. An Appraisal of Blood Trauma and the Blood-Material Interface Following Prolonged Assisted Circulation

W. F. Bernhard, L. Button,* T. Robinson,* S. Kitrilakis,* and

C. G. Lafarge, Boston, Mass.

Assisted circulation (flows of 1500-3000 ml/minute) was carried out (continuously) in 30 calves (7-120 days), employing a totally implantable, Left Ventricular-Aortic assist pump. The pneumatically actuated, double-valved device was completely lined with flocked Dacron fibrils to encourage deposition of a smooth, cellular interface. In some experiments, the pump matrix was seeded with bovine fetal fibroblasts to accelerate pseudoendothelial development. These primitive cells, maintained in tissue culture (37°C), were obtained from fetuses (two to five months gestation) by trypsinization of muscle and connective tissue. In 20 animals, sacrified after 30 days of bypass, histologic study of the lining revealed masses of viable fibroblasts and collagen attached to the Dacron matrix. Identification of fetal cells was accomplished with liquid scintillation using C¹⁴-Thymidine Blood trauma was minimal and consisted of: a 15 percent hematocrit reduction; temporary (14 day) increase in incubated osmotic fragility; and a 24 hour increase in mechanical fragility. Erythrocyte survival (D.F.P.³²) was reduced approximately ten percent (24 day half-life). Red cell mass (Cr⁵¹) was also less, with a reciprocal rise in plasma volume. Plasma hemoglobin, haptoglobins, reticulocyte count, platelets, and intracellular cations were unchanged.

42. Closed Chest Left Heart Bypass Without Anticoagulation

Akio Wakabayashi,* William Dibtrick,* and John E. Connolly,

Irvine, Calif.

Need for heparinization has been a major handicap preventing prolonged assisted circulation. Experiments were undertaken to devise a non-thrombogenic transseptal left heart bypass unit. A Dennis transseptal cannula, an arterial cannula, and polyvinyl tubings were coated with Graphite-Poly-urethane-Polyvinyl. The pump consisted of a silicone rubber bag with Dacron velour linings energized with compressed oxygen via an adjustable automatic switch and solenoid valve. Two homograft aortic valves were used as inlet and outlet valves of the pump. The following circuit was established in six dogs and tested for 10 to 30 hours without anticoagulation The circuit consisted of a Dennis transseptal cannula placed through the right jugular vein into the left atrium. The blood was then pumped from die left atrium back to a carotid artery. Blood pressure and primary output were maintained within normal range throughout all bypasses. No transfusions were required. All dogs survived and none showed blood diarrhea which is common when an extracorporeal circulation with heparinization is used for a prolonged period. No clotting was found in the pump unit and no animal showed neurologic damage at later sacrifice. This is the first successful use of left heart bypass for a prolonged period without thoracotomy and heparinization.

43. On-Line Digital Analysis of Respiratory Mechanics and the Automation of Respirator Control

Mark Hilberman,* John Schill,* and Richard M. Peters,

Chapel Hill, N.C.

The construction of an automatic system of respirator control depends on detailed studies of respiratory mechanics in the postoperative period. At first a digital control system will be essential. We have used a medium-sized digital computer to perform breath-by-breath analysis of pressure and flow, measurements which are then used to calculate compliance, resistance, total work, resistive work, tidal volume, and rate. A 40% reduction in compliance and a 40% increase in resistance is quite usual on the first day after cardiac surgery, however in individual cases large changes predict deterioration of function and may be used for alarm purposes. Previous work has demonstrated the deterioration of respirator efficiency following such pulmonary changes and detection of these acute changes form essential input for a respirator control system. We have a number of measurements which show that the pressure the respirator "sees" is not necessarily the same one "seen" by the lungs (because of nasotracheal tubes, etc.). This discrepancy must be taken into account if a successful system is to be developed which will warn the physician and control a respirator. Both the needed information and the possible network will be demonstrated.

44. Protracted Survival After Homotransplantation of the Lung and Simultaneous Contralateral Pulmonary Artery Ligation

Frank J. Veith,* Kenneth Richards,* and Parvez Lalezari,*

New York, N.Y.

Sponsored by Allan E. Bloomberg

Previous attempts to demonstrate the absolute functional adequacy of homografted lungs by ablation of contralateral pulmonary function have failed. Twenty dogs underwent left lung homotransplantation. When the pulmonary artery anastomosis was made distensible by spatulation of host and donor artery or by insertion of a vein patch, the vascular resistance of the transplant decreased 14-52% following ligation of the right pulmonary artery which was performed immediately after completion of the transplant. Recipients were treated with low dose azathioprine and rabbit anti-dog lymphocyte serum. All dogs lived at least 5 days after operation showing that transplanted lungs with a distensible arterial anastomosis can provide total pulmonary function and can vasodilate to accept the entire cardiac output without damage to the pulmonary microvasculature Eleven dogs survived 4-20 weeks without pulmonary hypertension or decreased exercise tolerance. Eight still live. Thus, with distensible arterial anastomoses and heterologous anti-lymphocyte serum, lung homotransplantation can dependably produce recipient survival even when the transplant is responsible for total respiratory and pulmonary vascular function. These observations indicate the absolute functional adequacy of lung homografts and provide an experimental basis for lung homotransplantation in patients with pulmonary hypertension.

45. Intermittent Inflatable Endotracheal Cuffs

James F. Arens,* and John L. Ochsner, New Orleans, La.

Long-term controlled and assisted ventilation has resulted in complication secondary to the cuffs on either endotracheal or tracheostomy tubes. Constant cuff pressure causes ischemia of the tracheal wall with subsequent stenosis. A cuff that inflates only during the inspiratory phase of the respirator and deflates during the expiratory phase will allow better blood flow to the trachea. A device has been designed to produce a constant volume of air delivered only during inspiration to the cuffs when either a pressure cycle or volume cycle respirator is employed Series of anesthetized dogs which were ventilated mechanically for 72 hours have been compared. Ten dogs had constantly inflated cuffs and another 10 had cuffs intermittently inflated by the designed device. At completion of the experiment the animals were sacrificed. In a similar series, the animals were allowed to recover and were sacrificed two weeks later. In each series the tracheae were compared grossly and microscopically. Results of this study revealed a marked difference. The advantages of the intermittently inflated cuff will be reviewed and the mechanical device used to inflate and deflate the cuff will be demonstrated Use of this device should prevent tracheal ischemia associated with long-term ventilation.

46. Oxygen Consumption After Oxygen Therapy for Hypoxemia

A. G. Groves,* J. H. Duff,* A. P. H. McLean,* R. LaPointe,*

and L. D. Maclean, Montreal, Quebec

Although increased oxygen concentration of inspired air will often correct hypoxemia, it has not been shown that oxygen therapy improves oxygen consumption (VO₂). This study attempts to determine the relationship between arterial pO₂ and VO₂ after administration of 50% O₂ to hypoxemic patients in septic shock, hypoxemic post-operative patients with atelectasis, and the dog with atelectasis produced by balloon occlusion of the right mainstem bronchus. In 5 hypoxemic patients with septic shock, average pO₂ while breathing 20% O₂was 47 mmHg and average VO₂ was 272 ml/min. Administration of 50% O₂ increased average pOa to 87 mmHg but average VO₂ was unchanged (265 ml/min). Two of these patients had hyperlacticacidemia (98 mg%, 74 mg%). Similarly, in 5 patients with atelectasis, 50% O₂ raised the pO₂ but VO₂ did not increase.

	CONTROL		ATELECTASIS
	20% O2	50% O2	20% O2	50% O2
pO2mmHg	98.7	236.5	51.7	74.5
VO2 ml/min	147.8	147.4	170.	167.
M.V. 1/min	5.84	4.82	9.65	6.29
TEMP.	100.5°	100.13°	102.2°	101.97°

The table summarizes data obtained from 10 dogs before and after bronchial occlusion. Although 50% O₂ increased average pO₂ in dogs with atelectasis, VO₂ was not increased pO₂ does not reflect VO₂. In ranges of pO₂ seen clinically, administration of 50% O₂ increased arterial pO₂ but failed to improve VO₂.

47. Mitral and Aortic Valve Replacement with Autogenous Fascia Lata on a Stent

W. Sterling Edwards, Robert B. Karp,* and David Robillard,*

Birmingham, Ala.

Autogenous tissue has not received extensive clinical trial in cardiac valve replacement because of difficulty in constructing functioning valves at the operating table. Senning reports occasional incompetence from tailoring errors in constructing aortic valves of fascia lata, but in those with competent valves, he reports a five year follow-up without degeneration or calcification of the fascia, which is quite impressive. A technique has been developed to construct tricuspid semilunar valves of autogenous fascia lata. Fascia is cut to a pattern, folded over a mold designed from the sinuses of valsalva and sutured to a rigid metal stent. The stent is not cloth covered, but is completely covered by fascia so that no foreign material is exposed to blood and so that autogenous tissue is sutured directly to the valve ring for secure healing. The valve is constructed and tested for competence with water pressure while the chest incision is made and cannulations performed Human aortic and mitral valves have been successfully replaced using this technique. Valves of this design can be inserted as quickly as a prosthesis. They can be made any size; procurement, sterilization and storage are not a problem, and there should be no rejection.

48. A New Technique for Replacement of the Mitral Valve by a Homograft Semilunar Valve

Magdi H. Yacoub,* and C. Frederick Kittle, Chicago, Ill.

In 13 patients the mitral valve was replaced with either an aortic or pulmonary homograft; in 7 of these the aortic valve was also replaced with a homograft. A new technique of implanting the aortic valve in the mitral position has been devised to maintain function of the aortic sinuses, to allow mobility of the mitral orifice, and to avoid any protrusion into the left ventricular cavity. These have been mentioned as criticisms of previous techniques. The aortic valve and its adjacent aorta are sutured at both ends to a Dacron tube slightly longer than the sinuses are deep. A collar of pericardial-covered Dacron is attached to the atrial side of the graft. The ventricular side of this prosthesis is sutured first to the mitral annulus; on the atrial side the collar is sutured to the atrium constituting a new atrial floor. Of 13 patients (34 to 68 years old) 10 are living and well; 5 are double and 5 single valve replacements. Valves were generally prepared by radiation and freezing. Postoperative results from 2-12 months indicate a very good correction of the hemodynamic lesion. In no instance has anticoagulant therapy been used or thrombo-embolic phenomena observed.

49. Hemodynamic State Following Open Mitral Valve Replacement and Reconstruction

Claude A. Rouleau,* Robert L. Frye,* and F. Henry Ellis, Jr.,

Rochester, Minn.

Hemodynamic studies were carried out preoperatively, at operation, for 3 days after operation, and prior to dismissal in 36 patients undergoing open operations on the mitral valve. In 27 patients the valve was resected and replaced, a Kay-Shiley disc valve being used in 9, a Smeloff-Cutter full orifice ball valve in 9, and a Starr-Edwards valve in 9. Nine patients had mitral valve reconstruction. The cardiac index was lowest on the afternoon of operation, (1.9 (L/min/M²) after prosthetic replacement and 1 5 (L/min./M²) after valve reconstruction) but increased from a preoperative mean of 2.1 to 3.1 at dismissal after valve replacement and from 2.2 to 2.9 after reconstruction. LA and PA pressures decreased immediately after operation. Pulmonary arteriolar resistance showed an early increase but was below preoperative values at dismissal. Left ventricular enddiastolic pressure was above normal in the immediate postoperative period. There was no statistically significant difference in hemodynamics between the four operative procedures. It is concluded that the low cardiac output seen after open operations on the mitral valve is not related to the presence of a prosthesis within the heart, to valve design or to the disruption of normal chordal papillary attachments.

*By Invitation