Experimental hemodynamic studies with a permanent ventricular assist device The dynamic aortic patch Steven J. Phillips, M.D., George Zorzi, M.D.,+ Dov Jaron, Ph.D., Paul Freed, M.S., Leon Zoireff, M.D., Alejandro Aris, M.D., and Adrian Kantrowitz, M.D., Detroit, Mich. Mechanicat circulatory assistance by means of diastolic pressure augmentation has proved beneficial in the management of left ventricular failure.'-* Intra-aortic phase- shift balloon pumping, a temporary form of this mode of assistance, has proved success- ful in the treatment of acute left ventricular failure’? secondary to myocardial infarc- tion. A permanently implanted assist device, the dynamic aortic patch (DAP), which is similar to the balloon pump in function, was developed. This study describes the hemo- dynamic effects of the DAP in dogs. Materials The DAP consists of an ellipsoidal sili- cone rubber pumping chamber encased in Dacron velour (Fig. 1). A silicone rubber, pneumatic conduit encased in Dacron velour connects the pumping chamber through a transcutaneous connector to an external driv- ing unit. Conductive polyurethane, having a permanent negative surface charge which From the Department of Surgery, Sinai Hospital of De- troit, Detroit, Mich. 48235. Supported by U. S. Public Health Service Grant HE-13737. Received for publication April 27, 1972. +Dr. Zorzi is deceased. enhances the growth of a pseudointima, backs the Dacron velour that lines the blood interface? 1° (Fig. 2). The DAP has an approximate stroke volume of 15 c.c.? Nineteen experiments were performed in 10 anesthetized dogs ventilated with the chest open. Through an incision in the sixth or seventh left intercostal space, the chest was opened and snares were passed around the proximal and distal descending thoracic aorta. The intercostal vessels were tied off at their origin. By means of a roller pump, left heart bypass from the left atrium to the femoral artery was instituted. A longitudinal incision equal to the length of the DAP was made in the thoracic aorta. The DAP was sewn into the aorta with a double row of continuous everting sutures, and the suture line was reinforced with Dacron felt. Sutures were placed so that the addition of the patch did not appreciably increase the diameter of the aorta (Fig. 3). Large-bore polyethylene catheters were placed in the central aorta via the carotid artery and in the right atrium and left ven- tricle by direct puncture. Biotronex flow probes were placed around the aortic root and left circumflex coronary artery. The 471 472 Phillips et al. Fig. 1. Extravascular surface of dynamic aortic patch booster. Fig. 2, Vascular interface of dynamic aortic patch booster. electrocardiogram was recorded via needle electrodes applied subcutaneously to the limbs. Flow probes were connected to a Biotronex 610 electromagnetic flowmeter system, and pressure catheters were con- nected to Statham strain gauges. Electro- cardiogram, right atrial pressure, left ven- The Journal of Thoracic and Cardiovascular Surgery Fig. 3. Dynamic aortic patch booster sewn into the thoracic aorta. tricular pressure, central aortic pressure, central aortic flow, and left circumflex coro- nary artery flow were simultaneously dis- played and recorded on a direct-writing San- born recorder. Hemodynamic parameters were measured with the patch off (control) and compared with the patch on (pumping). Cardiac output was determined from the aortic flow curve. Stroke volume was taken as cardiac output divided by heart rate per minute. The tension time index was derived from the integrated area under the left ven- tricular pressure curve. Left ventricular stroke pressure work (SPWLV) in gram- meters per beat was calculated from the formula: (SV) (MAP) (1.35) 1,000 , SPWLV = where SV is stroke volume and MAP is mean arterial pressure. Mean systolic ejection rate (MSER) in milliliters per second was calculated from the formula: SV Volume 65 Number 3 March, 1973 Left Ventricular Pressure mm Hg Central Aortic Pressure mm Kg Central Aortic Flow eo/sec Left Circumflex Coronary Artery Flow cc/sec Dynamic aortic patch 473 OFF eaten ON [epics 1 BCG. ain Siin| Fig. 4. Sequential hemodynamic changes with the dynamic aortic patch booster static (off) and dynamic (on). where DS is the duration of systole in seconds. Systemic vascular resistance (SVR), ex- pressed in resistance units, was calculated from the formula: MAP SVR = —_-, co where CO is cardiac output. All data were subjected to statistical anal- ysis. The significance of the differences be- tween the control (static patch) and the experimental (dynamic patch) was deter- mined by a paired t test. Results Fig. 4 represents the sequential flow and pressure tracings with the patch static (con- 474 Phillips et al. Table I. Hemodynamic changes with the dynamic aortic patch active Per cent change | Probability Parameter from control value TTI -23.3 < 0.01 SPWLV -17.5 < 0.01 LVPP -23.2 < 0.01 SVR -32.1 < 0.01 co +16.2 < 0.01 MDP +18.7 < 0.01 CBF +4] < 0.01 MSER +36.1 < 0.01 Legend: TTI, Tension time index. SPWLV, Left ventricular stroke pressure work. LVPP, Left ventricular peak pressure. SVR, Systemic vascular resistance. CO, Cardiac output, MDP, Mean diastolic pressure. CBF, Circumflex blood flow. MSER, Mean systolic ejection rate. trol) and dynamic (pumping) in a normo- tensive animal. Table I summarizes the hemodynamic changes that occurred when the DAP group was compared to the control group. The ten- sion time index decreased 23.3 per cent (S.D. 11), systemic vascular resistance de- creased 32.1 per cent (S.D. 12), left ven- tricular peak pressure decreased 23.2 per cent (S.D. 14), and the stroke pressure work of the left ventricle decreased 17.5 per cent (S.D. 10). Increases in the mean aortic diastolic pressure and cardiac output were 18.7 per cent (S.D. 14) and 16.2 per cent (S.D. 8), respectively. Left circumflex coronary blood flow increased 41.0 per cent (S.D. 27), and the mean systolic ejection rate increased 36.1 per cent (S.D. 11). All data were statistically significant at values of p < 0.01. Discussion A device that works on the principle of diastolic augmentation, in order to be hemo- dynamically effective, must fulfill the follow- ing criteria: It must consistently be ac- curately timed"! and driven so that it will effectively (1) reduce the left ventricular afterload and hence the myocardial oxy- gen consumption, and (2) increase the total coronary blood flow. In addition to a fa- vorable hemodynamic response, a perma- nently implanted left ventricular support device should be nonthrombogenic and pro- The Journal of Thoracic and Cardiovascular Surgery mote the development of a pseudointima at the blood interface.* 12 It should be non- traumatic to the blood elements and be dur- able. The DAP, a permanent left ventricular assist device, fulfills the above-mentioned criteria. The driving unit is portable and simple to operate as previously reported.® 1 Other studies in this laboratory indicate that the DAP creates negligible blood trauma, has minimal thromboembolic potential, and enhances the growth of a pseudointimal layer at the blood interface.*: 12 This study indicates that the DAP is hemodynamically effective as a permanent left ventricular assist device. The decreases in stroke pressure work of the left ventricle, tension time index, left ventricular peak pres- sure, and systemic vascular resistance indi- cate that the DAP can improve myocardial function by reducing myocardial tension and hence oxygen demands. The simultaneous increases in the mean systolic ejection rate, coronary blood flow, mean diastolic pressure, and cardiac output point out a generalized metabolic and hemodynamic improvement. Summary The hemodynamic effects of a DAP for permanent ventricular assistance by diastolic augmentation were studied in dogs. 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