Ann Thorac Surg 2000;70:1264-1269
© 2000 The Society of Thoracic Surgeons
Original articles: cardiovascular
Ascending versus descending aortic balloon
Pumping: organ and myocardial perfusion during ischemia
Bart P. Meyns, MD, PhDa,
Yousuke Nishimura, MD, PhDa,
Ramadan Jashari, MDa,
Rozalia Racz, MD, PhDa,
Veerle H. Leunensa,
Willem J. Flameng, MD, PhDa
a Department of Cardiac Surgery, Catholic University Leuven, Leuven, Belgium
Address reprint requests to Dr Meyns, C.E.H.A., Provisorium 1, Minderbroedersstraat 17, B-3000 Leuven, Belgium
e-mail: bart.meyns{at}uz.kuleuven.ac.be
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Abstract
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Background. The ICS-Supracor (Abiomed, Danvers, MA) is a preshaped ascending aorta balloon pump. We compared the effects of this catheter with the classical descending intraaortic balloon pump (IABP). The study focused on hemodynamic effects, myocardial blood flow in normal and ischemic regions, cerebral perfusion, and peripheral organ perfusion.
Methods. We placed a stenosis on the lateral branch of the coronary artery to reduce flow 50% (sheep). Measurements included hemodynamic changes, myocardial blood flow, and organ flow (colored microspheres) at baseline, after stenosis, during IABP support, and during ICS support.
Results. Counterpulsation with the ICS led to a significantly higher peak diastolic aortic augmentation than with the IABP (IABP, 99 ± 14 mm Hg; ICS, 140 ± 29 mm Hg; p = 0.003). There was no significant change in cerebral perfusion or peripheral organ perfusion. Myocardial blood perfusion was significantly increased by the IABP as well as the ICS. This effect was seen in ischemic and nonischemic regions (subendocardial and subepicardial). The ICS improved myocardial blood flow significantly more than the IABP (IABP, 0.65 ± 0.1 mL/min/g; ICS, 0.94 ± 0.06 mL/min/g; p = 0.0005).
Conclusions. The ICS increases myocardial blood flow in ischemic regions significantly more than the IABP, without impairment of cerebral flow. Assessment of vascular complications, peripherally and in the ascending aorta, has to await results of clinical trials.
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Introduction
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The beneficial effect of balloon counterpulsation is well known. Diastolic inflation of a balloon, positioned in the descending aorta, increases diastolic blood pressure and myocardial perfusion and reduces left ventricular work [1–3]. The technical evolution of the balloon catheters, now available at an 8-French size, has led to a liberal use of the intraaortic balloon pump (IABP) in heart failure as well as prophylactically in high-risk patients.
The placement of the balloon in the ascending aorta augments these beneficial effects of counterpulsation [4–7]. In patients with severe peripheral vascular disease, requiring support in the postoperative period, the balloon pump is often inserted in the ascending aorta [8]. However, the insertion of the balloon upside down via the ascending aorta has its drawbacks. For one, it requires a resternotomy to remove the device. Second, the manipulation of the ascending aorta contains the risk of plaque dislodgment. Third, there is basic concern about the blood flow going to the neck vessels.
The ICS-Supracor (ABIOMED, Danvers, MA) is a specifically designed ascending aorta balloon catheter suitable for introduction via the groin. We evaluate the basic hemodynamic effect of this new device in comparison with a standard descending aorta balloon pump. We test for brain perfusion, peripheral organ perfusion, and myocardial perfusion in ischemic areas. To analyze the effect in ischemic areas, we use a model of critical coronary stenosis avoiding circulatory shock [9].
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Material and methods
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Balloon catheters
The intraarterial cardiac support system (ICS) is a balloon catheter located in the ascending aorta. The balloon has a volume of 45 mL and a maximum diameter of 35 mm (Fig 1). Its shape and size are chosen to occlude the ascending aorta during diastole and to augment aortic root pressure. The balloon is mounted on a 12.5-French catheter, which is preshaped to the curvature of the aortic arch and allows femoral introduction.
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Fig 1. The ascending aortic balloon pump (ICS-Supracor). Its oval-shaped balloon has a volume of 45 cc and is designed to occlude the ascending aorta distally to maximize aortic root pressure.
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The standard IABP placed in the descending aorta was a 40-mL balloon mounted on a 9-French catheter (St. Jude Medical, Chelmsford, MA). Both catheters were driven by the same console with a driving helium volume of 40 mL.
Animal instrumentation
Seven sheep (mean weight 56 ± 7 kg) were anesthetized with intravenous pentobarbital (3 mg/kg), intubated, and mechanically ventilated with 60% oxygen. Anesthesia was maintained with 0.5% to 2% halothane, and 0.2 mg/kg piritramide was administered every 40 minutes. All animals received humane care in compliance with the "Guide for the Care of and Use of Laboratory Animals" prepared by the Institute of Laboratory Animal Resources and published by the National Institutes of Health (NIH publication 85-23, revised 1985).
Via a cut-down in the left neck, a triple lumen central venous line (jugular vein) and a fluid-filled arterial pressure line (carotid artery) were inserted. Left thoracotomy was performed in the fifth intercostal space. On opening of the pericardium, 100 mg lidocaine was administered to avoid arrhythmias during manipulation. The left groin was incised, the femoral artery mobilized, and the balloon pump introduced. A fluid-filled pressure line was inserted in the left atrium and a micro-tip catheter transducer (Millar Instruments, Inc, Houston, TX) was placed in the left ventricle, through the apex. All pressure transducers were connected to a Triton pressure module (Triton, San Diego, CA). The lateral branch of the left coronary artery was visualized in the atrioventricular groove near its origin. An electromagnetic flow probe was positioned around it and connected to a flow meter (Nyhon Kohden, Tokyo, Japan). A second electromagnetic flow probe (Skalar, Delft, The Netherlands) was placed around the pulmonary artery for continuous measurement of cardiac output. A set of ultrasonic transit-time crystals, consisting of one endocardial and one epicardial crystal, was sutured to the posterolateral region of the heart. These crystals were connected to a sonomicrometer module (Triton) for measurement of wall thickening.
Experimental protocol
Myocardial wall thickening, left ventricular pressure, first derivative of the left ventricular pressure, arterial blood pressure, coronary flow, cardiac output, and left atrial pressure were continuously recorded on an eight-channel chart recorder (Nyhon Kohden). After stabilization, a first set of colored microspheres was injected into the left atrium (Fig 2). A stenosis was applied to the lateral branch of the left coronary artery. This stenosis was tightened until a drop of 50% in the baseline coronary flow in that vessel occurred and was then left untouched for 10 minutes. After 5 minutes of stenosis, a second set of colored microspheres was injected via the left atrial catheter and the balloon pump (ICS or IABP) was started. Five minutes later, a third injection of microspheres was given. The stenosis was relieved, the balloon pump stopped, and time was allowed for all parameters to stabilize. Then, the same stenosis was applied again and a fourth set of microspheres was given after 5 minutes. This time, the alternative counterpulsation (ICS or IABP) was started, and after 5 minutes, the last set of microspheres was injected. The type of counterpulsation (ICS or IABP) was alternated in sequence of use.
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Fig 2. Experimental protocol. Two periods of coronary stenosis are applied (each 10 minutes). The balloon pump support (ICS or IABP) is applied during the last 5 minutes. Colored microspheres (MS) are injected at baseline, during the first ischemia, during the first balloon pump support, during the second ischemia, and during the second balloon pump support. The type of balloon pump used (IABP or ICS) alternated between experiments.
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Myocardial and organ flow measurement
Nine million 15-mm-diameter polystyrene microspheres of five different colors (white, red, yellow, blue, and violet) were injected on five different occasions during the protocol. The microspheres were injected in a volume of 3 mL over 30 seconds. Arterial reference blood was withdrawn during 90 seconds from the aorta at a flow rate of 10 mL/min. On termination of the experiment, 1-g tissue samples were isolated from lungs, cerebrum, cerebellum, spleen, liver, pancreas, stomach, small bowel, large bowel, renal cortex, renal medulla, skin, and muscles. The hearts were removed, trimmed of excess fat, and cut in five slices along the short axis. Three right ventricular and nine left ventricular regions were identified and biopsy samples were taken from each region from the subepicardium as well as from the subendocardium. The second slice (counting from the base of the heart) from each animal was processed for quantification of the colored microspheres content. The microspheres content was determined by the methods described by Kowallik and associates [10], Rudolph and Heyman [11], and Wieland and associates [12].
Data analysis
Data were analyzed with the Statistica statistical software package (Statsoft Inc, Tulsa, OK). Organ flows and hemodynamic data are presented as means ± standard deviation. Hemodynamic data were analyzed with a one-way multivariate analysis of variance for differences between types of counterpulsation. Paired comparisons with control values were performed with the two-tailed paired Student’s t test.
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Results
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Hemodynamic changes
The influence of the coronary stenosis on overall hemodynamics was mild. Systolic and diastolic perfusion pressure, cardiac output, and left atrial pressure are shown in Table 1. During the initial 5 minutes of coronary stenosis, the cardiac output is reduced (from 4.9 ± 1 to 4.2 ± 1 L/min; p = 0.03) and the left atrial pressure slightly increased (from 9 ± 5 to 12 ± 7 mm Hg; P = NS). The major hemodynamic effect of balloon counterpulsation is the significant increase in diastolic perfusion pressure, measured in the carotid artery. The ICS provides higher peak diastolic aortic augmentation than the IABP (IABP, 99 ± 14 mm Hg; ICS, 140 ± 29 mm Hg; p = 0.003). The end diastolic aortic pressure without mechanical assistance was 69 ± 20 mm Hg. In case of the ICS, with its occlusive working mode, this recorded diastolic blood pressure is an underestimation of the aortic root pressure. Cardiac output and left atrial pressure remain practically unchanged during the balloon pump support. Figure 3 illustrates the effect of the ICS balloon pump. The significant higher aortic root pressure results in an immediate increase in coronary flow.
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Fig 3. Chart recording of the left ventricular pressure (LVP), aortic root pressure (ABP), and coronary flow (CF) during ICS counterpulsation and in control situation. The first five heartbeats were assisted with the ICS, the following were not. The increase in aortic blood pressure during diastole has an immediate effect on coronary flow (arrows).
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The coronary stenosis, allowing 50% of baseline myocardial flow, had a limited effect on myocardial wall thickening (Table 1). The changes during stenosis and consequent counterpulsation are not significant. The first derivative of the left ventricular pressure (dP/dt) shows, however, a significant drop as soon as the stenosis is applied (Table 1). Neither the initiation of counterpulsation nor the type of balloon used results in an important effect.
Peripheral organ perfusion
The perfusion in the different organs is shown in Table 2. As the overall hemodynamic changes were very mild, there is no significant influence of the coronary stenosis on peripheral organ perfusion. The best perfused area of the body is the renal cortex. The flow changes in that region are extremely sensible. This is shown by the drop in perfusion on initiation of coronary stenosis. The counterpulsation did not alter organ perfusion. There was no difference in organ perfusion during ICS and IABP support. There was no reduction of the brain perfusion by the ascending aortic pump (ICS). There was no significant reduction of renal perfusion by the descending aortic balloon pump (IABP).
Myocardial perfusion
Subendocardial and subepicardial myocardial flow in the different regions of the heart are shown in Figure 4. Application of the coronary stenosis leads to a significant reduction of myocardial blood flow in the subendocardium (from 1.02 ± 0.1 to 0.55 ± 0.1 mL/min/g; p < 0.000001) as well as the subepicardium (from 0.86 ± 0.1 to 0.52 ± 0.05 mL/min/g; p < 0.000001). The lateral wall of the heart, supplied by the stenosed vessel, was identified and these areas were labeled as the ischemic regions. In these regions, the ischemia was most explicit in the subendocardial area (Fig 4B). Initiation of balloon pump support with the descending aorta IABP leads to a significant increase in blood flow in these ischemic regions. The increase was present in both subepicardial (0.62 ± 0.09 mL/min/g; p = 0.000006) and subendocardial (0.65 ± 0.1 mL/min/g; p = 0.0002) zones. The initiation of the ascending aorta ICS leads to an even greater increase in blood flow in all regions. This improvement in myocardial flow is significantly better with the ICS than with the IABP (p = 0.0005). The ICS brings the myocardial blood flow in the ischemic areas close to control values.
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Fig 4. Subepicardial (white bars) and subendocardial (black bars) myocardial blood flow at baseline, during ischemia, IABP support, and ICS support. (A) Mean myocardial blood flow in all regions. (B) Myocardial blood flow in the ischemic regions (supplied by the stenosed vessel: lateral wall). (C) Myocardial blood flow in the nonischemic regions. *A significant difference as compared with the flow during unsupported ischemia.  A significant difference between ICS and IABP values.
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Comment
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Reestablishment of myocardial blood flow is the most important hemodynamic measure in ischemic heart disease. Intraaortic balloon pumping has been in widespread clinical use for postcardiotomy low output syndrome, prophylactically in high-risk patients, after thrombolysis after acute myocardial infarction, and after angioplasty. The benefits of positioning the catheter in the ascending aorta instead of in the descending aorta has been studied for many years. Earlier studies showed that the closer a counterpulsation device is placed to the aortic valve, the higher the peak diastolic aortic augmentation and the greater the coronary blood flow [4, 5]. Lazar and colleagues showed, in a pig model, that myocardial recovery is superior with a balloon placed in the ascending aorta than in the descending aorta [6]. They showed a reduced area of necrosis and better myocardial wall motion after 90 minutes during coronary occlusion. The ascending aortic balloon was shown to be successful in a resuscitation model for cardiac arrest in pigs [13]. Gitter and colleagues tested the ICS-SupraCor device and studied coronary bypass flow during ascending and descending aortic counterpulsation in a pig model. They found that the ascending aorta counterpulsation increases graft flow in both internal mammary artery and venous conduits [7].
This ICS ascending aortic balloon pump is well designed and offers the advantage of ascending aortic balloon pumping from a standard peripheral access via the groin. Unlike the classical balloon pump positioned upside down in the ascending aorta, this ICS catheter is designed to occlude the ascending aorta distally to make a squeezing movement as it comes to its full expansion reaching the highest possible aortic root pressure.
In the design of this animal study, we wanted to assess the effect of this device on myocardial perfusion and address the possible influence on brain perfusion. To clarify these items, we needed an animal model that did not lead to circulatory shock. The physiology during and after circulatory shock differs and does not allow an accurate measurement of organ flow. Second, the effect of counterpulsation in cardiogenic shock models leads to an improvement of the general hemodynamic situation. This obscures the possible measurement of the effect of counterpulsation on myocardial flow in situ. We have chosen a model that provides us with an ischemic as well as a nonischemic region of the heart and with stable hemodynamics. This model of creating a coronary stenosis of 50% of the baseline flow in one coronary artery permits us to differentiate the effects of both types of balloon pumps.
We showed that this ascending aortic balloon significantly increases myocardial perfusion in ischemic regions beyond the level of the classical descending aortic balloon pump. This increase in myocardial blood flow was evenly spread in all ischemic regions of the heart (subepicardial and subendocardial). In addition, there was no sign of reduced brain perfusion, nor of any other organ perfusion. We did not illustrate the possible unloading capacities of this device. The effect of the applied ischemia on overall hemodynamics was, as intended, very limited, and the assistance of the nonfailing heart did not lead to significant reduction in left atrial pressure or derivative of the left ventricular pressure.
We still have unresolved questions concerning this new ICS device in its clinical use. We did not address the question whether this device could dislodge atherosclerotic plaques in the ascending aorta or cause hemolysis. Clearly, our sheep had no atherosclerotic disease. Clinical practice teaches that the degree of atherosclerosis of the ascending aorta is often underestimated. A perfect positioning of this balloon pump with fluoroscopy is mandatory. The ease with which a descending aortic catheter is placed blindly can make the placement of the ascending catheter in urgent situations more cumbersome.
Second, there is a considerable danger of vascular complications with a 12.5-French groin catheter. Arafa and colleagues reported in a recent study of 590 patients treated with IABP that major vascular complications occurred in 8% of the patients [14]. They identified, like other authors, vascular disease, myocardial shock, small body surface area, and large catheter size as the independent risk factors [14, 15]. The recent reduction in vascular complications with the use of balloon catheters is due to the smaller diameters used in recent years. It is logical to assume that the 12.5-French catheter of the ICS device will lead to a significant increase in vascular complications as compared with the current balloon pumps.
There are clinical settings in which these issues are of minor importance. Several patients receive an IABP during or after angioplasty. In this setting, with the patient on the catheterization table, the problem of exact positioning with fluoroscopic help disappears. Second, patients with postcardiotomy heart failure can have a surgical introduction of the device in the ascending aorta. The appropriate design of this ICS catheter with its short balloon and occlusive mode of working provides benefits over the use of a descending aortic catheter placed in the ascending aorta. Definitely, in patients with severe cardiac failure, the IABP is insufficient to improve the chances of survival [16]. As many of those patients are not transplant candidates, the step from the IABP to the initiation of a ventricular assist device is difficult. The Hemopump was an ideal solution for this class of patients but has been withdrawn [17]. This more powerful balloon pump might save lives in those patients who present with the risk factors of nonsurvivors with the classical IABP [16].
Our results demonstrate a superior increase in myocardial blood flow with the ICS ascending aortic balloon pump as compared with the descending aortic catheter. There is no detrimental effect on cerebral perfusion. The degree of complications caused by vascular access and dislodged plaques in the ascending aorta has to await the results of clinical trials.
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Acknowledgments
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This study was funded by a grant from the "Fonds voor Wetenschappelijk Onderzoek, Vlaanderen," Credit no. 3.0233.95.
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Accepted for publication April 5, 2000.
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Abstract
Introduction
