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For more than a decade, the use of the intraaortic balloon pump (IABP) has been a major tool for providing mechanical support to the patient with failing circulation. Initially, there was considerable hesitation on the part of many clinicians to employ mechanical devices. The utilization of IABP has been traditionally reserved for critically ill patients, and then only as a final desperate measure. This approach to mechanical circulatory support accounts for the substantial lag time between intraaortic balloon pump availability and its widespread use.
The IABP was first conceived and studied by Moulopoulos, Topaz and Kolff (1961-1962),1 and independently by Clauss, Missier, Reed, and Tice in 1962.2 Its further development and testing was sponsored by the Artificial Heart Program of the National Heart Institute beginning in 1966. Clinical studies were begun in 1967, and Kantrowitz reported the first clinical experience in 1968.3 In 1969 large scale clinical investigations of the IABP began with the organization of a cooperative study4 involving ten institutions. With the commercial availability of intraaortic balloons and balloon drive units, the number of institutions investigating the IABP and utilizing it clinically expanded rapidly.
Intra- and postoperative use of the IABP has now gained widespread acceptance in the management of high-risk operative patients with low output states caused by reversible ventricular dysfunction.5–6 Our primary experience with IABP has been with post-cardiotomy patients who, because of a low output state, cannot be weaned from cardiopulmonary bypass despite rigorous pharmacologic intervention.
Patients requiring circulatory assistance in our institutions are placed in a group of adjoining suites in the recovery rooms designated for special procedures. A Circulatory Support Service,7 which was formed around a nucleus of clinical engineers, supervises the unit (Fig. 1). The objective is on-line hemodynamic monitoring of the critically ill post-cardiotomy patient during IABP support. Major components of the system include:
A diagram of the patient monitoring system is shown in Figure 2.
In the operating rooms, after insertion of the intraaortic balloon, an Edwards Laboratories 93A-118-7F Swan-Ganz flow-directed quadruplelumened catheter is inserted through either antecubital, subclavian, or internal jugular vein* with continuous pressure and electrocardiographic monitoring. Selected measurements of right atrial, pulmonary artery and pulmonary capillary wedge pressures, mixed venous oxygen saturation and cardiac output/index determinations are obtained hourly, or more oft-en when indicated, throughout the course of post-cardiotomy IABP support.
Since 1972, 286 patients have been supported by the IABP in our institutions. This number is compared to the total number of adult cardiotomy patients in Figure 3.
In October of 1975, a long-term prospective study of these patients was initiated. A data base consisting of patient characteristics and serial hemodynamic data was established, and all patients supported by IABP were entered into the data base. (Tables I and II present the preliminary data of 247 patients.)
From the analyses of patient population data, several important trends have appeared. Since its clinical introduction in this institution in 1972, the number of patients undergoing IABP has steadily grown from less than 0.5% of the total surgical population to nearly 3.0%o. Earlier utilization of IABP and the accumulation of experience with pre-, intra-, and postoperative patient management techniques have contributed greatly to the significant improvement in patient survival.
In addition, the number of IABP patients discharged from the hospital has shown marked improvement, from 29%to in 1975 to 63% for the first nine months of 1977. The percentage of males and females that required IABP closely paralleled the incidence of males and females with coronary artery disease. Thus far in 1977, males requiring balloon pump assistance outnumber females four to one. Through the years, however, the percent survival for males has remained consistently and significantly higher than females. There has been no significant change in the mean age in the IABP population.
The instances of IABP usage were as follows: Sixty-seven percent of patients required IABP support immediately following cardiopulmonary bypass; 12% required IABP support during the early postoperative period (first three days); acute myocardial infarction cases accounted for 11%; and preoperative elective IABP support occurred in 6% of the patients.
Examination of the duration of IABP support shows that nonsurviving patients usually expire within the first 24 hours of assistance. Survivors require support for variable periods of time, from 12 to 140 hours, with a mean of 61 hours.
Recently, we have begun an in-depth analysis of the actual hemodynamic effectiveness of counterpulsation via IABP. From clinical studies,8–10 we have obtained data that delineates the quantitative changes brought about by actuation of balloon pumping. In addition to the obvious effects on left ventricular parameters, we have studied and documented similar effects on right ventricular dynamics. Serial “on-off” studies were accomplished in representative patients and mean values for heart rate (HR—beats/min), cardiac index (CI—L/min/m2), stroke volume index (SVI—ml/beat/m2), left ventricular minute work ind.ex (LVMWI—kgm/min/m2), right ventricular minute work index (RVMWI—kgm/min/m2), systemic and pulmonary vascular resistance (SVR, PVR—dynes•sec•cm−5), pulmonary arteriolar resistance (PAR-dynes•sec•cm−5), pulmonary artery, pulmonary capillary wedge, right atrial and aortic pressures (PA, PCW, RAP, AoP—mm Hg) were obtained. The results are summarized in Table III.
In addition to effecting immediate decreases in heart rate, left ventricular end-diastolic pressure, mean l.eft atrial pressure and modest increases in cardiac output (left ventricular functions), these results indicate that IABP actuation also produces instantaneous changes in right ventricular performance parameters, i.e., consistent decreases in RAP (right ventricular preload), PAP and PVR (major determinants of right ventricular afterload). All of the above hemodynamic effects were noted without significant changes in mean aortic pressure.
Further studies indicate that the hemodynamic effectiveness of IABP is dependent upon the level of myocardial recovery or deterioration in th.e postcardiotomy/myocardial infarction patient. The observed effects of IABP were inversely r.elated to the level of intrinsic myocardial function (CI) and directly related to the level of peripheral vascular resistance.
The intraaortic balloon pump patient characteristics of 286 patients treated at St. Luke's Episcopal Hospital-Texas Heart Institute are reported. IABP usage has increased sixteen-fold since its inception in 1972. The age distribution of these patients is depicted in Figure 4. Few patients under 30 and-over 70 years of age have been treated. Over half of those from 30 to 69 years of age who were supported by IABP survived. Eighty percent of the patients were male, paralleling the higher incidence of coronary artery disease among males. Surgical patients comprised 90%0 of IABP treated patients, reflecting this institution's emphasis on surgical treatment of acquired cardiovascular lesions. Figure 5 summarizes our experience.
Overall, our survival rate has been 48%o, with 58%o survival rate over the last 24 months, and 63% over the last 12 months.
*French 8 Introduces System, No. 501-608, Cordis Corporation, Miami, Florida 33137.
This article has been reprinted from Cardiovascular Diseases: Bulletin of the Texas Heart Institute 1977;4:428–36.