Ann Thorac Surg 1996;62:1110-1117
© 1996 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Treating Severe Cardiogenic Shock by Large Counterpulsation Volumes
Stamatios F. Stamatelopoulos, MD, PhD,
John N. Nanas, MD, PhD,
Nikolaos S. Saridakis, MD,
Nikolaos A. Zakopoulos, MD,
Stavros Lyropoulos, MD,
George Makrakis, MD,
Andrew Liberidis, MD,
Spyridon D. Moulopoulos, MD, PhD
Department of Clinical Therapeutics, Athens University Medical School, Athens, Greece
Accepted for publication April 26, 1996.
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Abstract
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Background. Intraaortic balloon pumping is known to be ineffective in severe cardiogenic shock. The efficacy of balloon volumes larger than those commonly used is examined.
Methods. In 18 dogs with severe experimental cardiogenic shock (systolic aortic pressure <60 mm Hg, aortic flow <45 mL•min-1•kg-1) the effect of three intraaortic balloon volumes (15, 30, and 45 mL) and a 60-mL paraaortic pump was examined.
Results. The 45-mL balloon covering the full length of the aorta induced the highest (+12.4 ± 2.2 mL•min-1•kg-1; mean ± standard error of the mean) and the 15-mL balloon the lowest increase in aortic flow (F = 14.6, p < 0.0001). Only the 45-mL balloon increased (p < 0.05) urine output and renal artery flow. The 60-mL paraaortic pump induced the highest (F = 10.72, p < 0.002) increase (+36.6 ± 6.5 mL•min-1•kg-1) in aortic flow compared to the three balloons. An 80- to 100-mL paraaortic pump maintained the life of 3 patients in severe cardiogenic shock for 4 hours, 8 days, and 54 days, whereas a 40-mL conventional balloon was completely ineffective.
Conclusions. Experimental and clinical data indicate that the effectiveness of intraaortic balloon pumping in severe cardiogenic shock may be improved by increasing the volume of the balloon (ie, until it fully occupies the aorta).
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Introduction
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Thirty-four years after the initial experimental application of intraaortic balloon pumping [1] the list of its indications continues to get longer [2]. Recent improvements in designing balloon catheters and driving systems have made the application of the method easier, with less vascular complications. However, some of the main limitations of the method have not been overcome. Intraaortic balloon pumping still remains ineffective in supporting patients in severe shock when their systolic aortic pressure cannot be augmented to more than 60 or 70 mm Hg [3].
A theoretic analysis [4] has maintained that balloon volumes larger than the left ventricular stroke volume do not add much to the effectiveness of pumping. However, the use of counterpulsation volumes markedly larger than the one provided by commercially available intraaortic balloons may be more effective [3] in maintaining the life of subjects in severe shock. Experimental evidence has also indicated [3, 5, 6] that the larger the intraaortic balloon the higher the increase in aortic flow during cardiogenic shock. In this article some further data are presented concerning the effect of large counterpulsation volumes, not only on central hemodynamics, but also on other variables of severe cardiogenic shock, such as urine output and renal artery flow.
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Material and Methods
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Animal Study
INTRAAORTIC BALLOON PUMPING OPTIMIZATION.
Acute experiments were performed in 9 adult mongrel dogs weighing from 26 to 32 kg (Table 1
). The animals were anesthetized with nembutal sodium: an initial intravenous administration of 30 mg•kg-1 was followed by 5 to 10 mg•kg-1 at scheduled time intervals. A right femoral vein infusion line was established. After intubation of the trachea and initiation of mechanical ventilation via a positive-pressure Harvard respirator (Harvard Apparatus, South Natick, MA), a left-sided thoracotomy was performed at the fourth intercostal space. In the experimental set-up shown in Figure 1, the following variables were continuously monitored:
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Fig 1. . Experimental set-up for intraaortic balloon volume optimization. By connecting both or either of the balloon catheters to an intraaortic balloon pumping apparatus three counterpulsation volumes could be interchanged: 45 mL (left), 30 mL (middle), and 15 mL (right). (AF = aortic flow; AP = aortic pressure; LIGATIONS = multiple coronary arterial branch ligations around the apex of the heart; LVP = left ventricular pressure.)
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- Pressure in the ascending aorta in all 9 animals. An 8F catheter was inserted via the left carotid artery and connected to an inductance-type transducer.
- Flow in the ascending aorta in all 9 animals. The probe of a two-channel Biotronex Pulsed-Logic flowmeter (Biotronex Laboratory, Inc, Silver Spring, MD) was positioned at the aortic root.
- Pressure in the left ventricle in 4 animals. An 8F catheter was inserted via the right carotid artery and connected to an inductance-type transducer.
- Flow in the anterior descending coronary branch in 3 animals. A 2-mm probe was positioned at the proximal portion of this artery and connected to the flowmeter.
- Flow in the left renal artery in 5 animals. It was measured as described below.
- The urine output from the left kidney in all 9 animals. Left renal artery flow and urine output were measured as follows: A left lateral abdominal incision was made and the peritoneal cavity opened. The intestine was retracted and the posterior peritoneum incised from the left renal hilum to 6 cm caudal across the ureter. A probe connected to a second flowmeter similar to the one mentioned above was placed around the renal artery. The size of the probe was 2 to 4 mm depending on the diameter of the renal artery. A drainage catheter was placed in the left ureter; it was allowed to drain by gravity into a volumetric tube.
- Lead II of the electrocardiogram.
Aortic pressure, aortic flow, and urine output were simultaneously recorded on a multichannel photographic recorder (Electronics for Medicine, White Plains, NY) before laparotomy. They were defined as "baseline values," and they are listed in Table 1
. Three or four variables out of numbers 1 to 5 listed above were simultaneously recorded on the multichannel recorder already mentioned. Recordings were made immediately before and at the end of each pumping session as described below. All values listed in Tables 1 to 6 consist of the mean value of measurements from five subsequent beats recorded with the Harvard respirator kept in the "off" position for 8 seconds. Flow probes were calibrated at the end of each experiment. Mean flows were measured from flow recordings by planimetry.
After heparinization (3 mg•kg-1), catheter-mounted balloons were inserted into the aorta as shown in Figure 1: A catheter bearing two balloons in series was inserted via the left femoral artery, and another catheter bearing a single balloon was inserted via the left subclavian artery. Thus, the aorta was occupied by three balloons in series from the orifice of the left subclavian artery to the aorta's bifurcation; each balloon had a 15-mL capacity when inflated.
Multiple ligations of small coronary arterial branches around the apex of the heart were applied. An intravenous propranolol infusion was established, its rate varying from 0.1 to 1.1 mg•min-1•kg-1, until the continuously recorded systolic aortic pressure was reduced and maintained at less than 60 mm Hg for 5 minutes, despite intravenous plasma expander infusion to maintain left atrial pressure between 14 and 16 cm H2O. The latter was monitored on a calibrated vertical tube attached to a 3-mm polyethylene catheter inserted into the left atrium via its auricle. In 2 of the 9 dogs ventricular fibrillation occurred after ligations. Sinus rhythm was restored by temporarily removing the ligations and applying direct-current shock. No drugs were used during resuscitation.
The simultaneously recorded variables at this stage of the experimental procedure were defined as "postshock values." They are listed in Table 1. Then, intraaortic balloon pumping was applied as follows: By connecting both or either of the balloon catheters (see Fig 1) to an intraaortic pumping apparatus (model 82; Datascope Inc, Paramous, NJ), three subsequent counterpulsation volumes were interchanged in each animal: (1) A 45-mL balloon volume (see Fig 1, left) was obtained when both catheters were connected to the pump via a T tube. (2) A 30 mL balloon volume (see Fig 1, middle) was obtained when only the catheter bearing the double balloon was connected to the pump. To obtain 30-mL balloon pumping under exactly the same conditions with pumping by the 45- or the 15-mL balloon, the catheter bearing the double balloon (inserted via the femoral artery) was pushed until its distal end was close to the orifice of the left subclavian artery; the single balloon catheter (inserted via the subclavian artery) was then pushed until its distal end was close to the bifurcation of the aorta. (3) A 15-mL balloon volume (see Fig 1, right) was obtained when only the catheter bearing the double balloon was connected to the pump. The sequence of pumping using each of the 45-, 30-, and 15-mL counterpulsation volumes in each animal is indicated in Table 1. The pumping sessions lasted for 20 minutes and were separated by control periods, each lasting 5 minutes at least: If the signs of severe cardiogenic shock did not reappear within this 5-minute control period, new coronary arterial ligations, a further increase in propranolol infusion rate, or both were applied.
Balloon position into the aorta and the status of balloon inflation, as shown in Figure 1, was confirmed by palpation at the beginning of pumping sessions because thoracotomy and laparotomy were performed in all dogs. The orifices of the renal arteries sited between the tapering portions of the second and third balloon were not occluded by balloons. Long-bodied animals were selected for the experiments to facilitate balloon manipulations.
All animals received humane care in compliance with the "Guide for the Care and Use of Laboratory Animals" published by the National Institutes of Health (NIH publication 85-23, revised 1985).
PARAAORTIC PUMP.
Severe cardiogenic shock was induced in 9 anaesthetized open-chest dogs weighing 26 to 30 kg, using the same experimental procedure as above. As shown in Figure 2, pumping by means of an intraaortic balloon of 20 mL capacity was interchanged with pumping by means of a paraaortic pump of 60 to 70 mL couterpulsation volume connected to the ascending aorta, as described in detail elsewhere [7, 8]. Each pumping session lasted for 20 minutes. A 5-minute control period, as described above, separated the pumping sessions. All hemodynamic data obtained by either the balloon alone or the paraaortic pump alone or both together were presented in previous reports [7, 8]. In this article only changes in flow induced by the paraaortic and the 20-mL intraaortic balloon pump were included. Flow in this set of experiments was measured by thermodilution.
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Fig 2. . Paraaortic pump and intraaortic balloon as used in the experimental set-up. In humans the stroke volume of the paraaortic pump was 80 to 100 mL and the capacity of the intraaortic balloon was 40 mL.
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STATISTICAL ANALYSIS.
Statistical analysis of data was performed by paired t test to compare values obtained immediately before pumping (control values) with values obtained at the 20th minute of pumping by each of the three intraaortic balloons or by paraaortic pumping. Analysis of variance (one-way analysis) was performed to examine differences in variables among the 15-mL, the 30-mL, and the 45-mL balloon groups, as well as differences in aortic flow among these three balloon groups and the paraaortic pump group. All variables are presented as mean values ± standard error of the mean.
Clinical Application
A paraaortic pump providing a stroke volume of 80 to 100 mL during cardiac diastole was used to support three patients with cardiomyopathy, in severe pump failure. The systolic blood pressure of these 3 patients was less than 60 mm Hg despite conventional intraaortic pumping with a 40-mL balloon and simultaneous dobutamine infusion at a rate of more than 20 µg•min-1•kg-1 for more than 48 hours. The paraaortic pump [7, 8] was placed by cardiac surgeons after midsternotomy and partial clamping of the ascending aorta. Only data concerning patients' survival under paraaortic pumping are included in this report.
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Results
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Animal Study
INTRAAORTIC BALLOON PUMPING OPTIMIZATION.
The severity of the experimental cardiogenic shock is indicated by the marked reduction in systolic (-75.44 ± 4.69 mm Hg; t = 16.08, p < 0.0001) and diastolic (-57.55 ± 1.85 mm Hg; t = 31.10, p < 0.0001) aortic pressure, aortic flow (-61.66 ± 2.85 mL•kg-1•min-1; t = 21.63, p < 0.0001), and urine output (-14.33 ± 1.75; t = 8.18, p < 0.001) as shown in Table 1. The heart rate also decreased (by 24.44 ± 4.03 mL•min-1; t = 6.06, p < 0.01) during shock because propranolol infusion was included in the experimental protocol.
The control values of systolic aortic pressure, aortic flow, and urine output recorded before the initiation of pumping are listed in Tables 2 (for the 15-mL balloon), 3 (for the 30-mL balloon) and 4 (for the 45-mL balloon). No difference could be shown by one-way analysis of variance among the three balloon groups in any of these variables (F = 0.26, p < 0.76, not significant for systolic aortic pressure; F = 1.85, p < 0.15, not significant for aortic flow; and F = 1.25, p < 0.30, not significant for urinary output).
As derived from values listed in Tables 2, 3, and 4 and shown in Figures 3 and 4, the 45-mL balloon increased aortic flow (+12.4 ± 2.2 mL•min-1•kg-1; t =5.6, p < 0.01) and urine output from the left kidney (+2.2 ± 0.7 mL/20 minutes; t = 3.2, p < 0.05). The 30-mL balloon increased aortic flow only (+5.8 ± 1.6 mL•min-1•kg-1; t = 3.6, p < 0.01). The 15-mL balloon did not affect either of these variables. One-way analysis of variance indicated that the three groups differed (F = 26.2, p < 0.0001) in pressure created inside the aorta by balloon expansion ("counterpulsation wave") (see Tables 2–4), the highest value found with the 45-mL and the lowest with the 15-mL balloon (see Figs 3, 4). The same groups did not differ in change induced in systolic aortic pressure (F = 0.104, p < 0.90, not significant). They differed (F = 14,6, p < 0.0001) in change induced in aortic flow; the largest increase was seen with the 45-mL balloon and the smallest one with the 15-mL balloon. They differed (F = 4.12, p < 0.02) in change induced in urine output. Pumping with the 45-mL balloon created a urine output greater than the one induced by either the 30-mL or the 15-mL balloon; the 30-mL balloon group did not differ from the 15-mL balloon group in this variable.
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Fig 3. . Simultaneous coronary blood flow (CBF), aortic flow (AF), and aortic pressure (AP) recordings from an animal in severe experimental cardiogenic shock before (CONTROL) and during 1:1 intraaortic balloon pumping (PUMPING) with a 15-mL (left), a 30-mL (middle), and a 45-mL (right) balloon.
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Fig 4. . Mean change ± standard error of the mean in aortic flow and urine output during pumping with various counterpulsation volumes (either by means of 15-, 30-, and 45-mL balloons or by means of a paraaortic pump of more than 60 mL stroke volume) in severe experimental cardiogenic shock. Statistically significant changes are indicated by asterisks.
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Pumping with the 45-mL balloon reduced left ventricular end-diastolic pressure in all 4 animals in which it was recorded by 2.75 ± 0.47 mm Hg (t = 5.85, p < 0.05). Neither the 30-mL nor the 15-mL balloon induced any change in this variable in the same 4 animals within the 20-minute period of pumping.
Coronary arterial flow increased during pumping in all three groups in the 3 experimental animals in which it was recorded. The 45-mL balloon increased this variable by at least 30% (see Fig 3), whereas no increase greater than 15% was observed when either the 30- or the 15-mL balloon was used in the same animals.
Left renal artery flow (Table 5; Fig 5) increased only with the 45-mL balloon (+0.276 ± 0.070 mL•min-1•kg-1; t = 3.94, p < 0.05) in the 5 animals in which it was measured. The three groups differed (F = 10.43, p < 0.002) in change induced in this variable. The 45-mL balloon created a renal artery flow greater than the one seen with either the 30- or the 15-mL balloon. The 30-mL balloon group did not differ from the 15-mL balloon group in this variable.
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Fig 5. . Simultaneously recorded electrocardiogram (ECG), aortic flow, aortic pressure, and renal artery flow in severe experimental cardiogenic shock before (left) and immediately after (right) the initiation of intraaortic balloon pumping using a 45-mL balloon.
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In 2 experimental animals (numbers 6 and 8) loading of the circulation was performed by means of an intravenous infusion of 0.9% NaCl solution during each of the control periods and at the last minute of each of the corresponding pumping sessions. Aortic flow and left ventricular end-diastolic pressure were continuously recorded during loading. The function curves thus obtained were shifted to the left during pumping only with the 45-mL balloon (Fig 6) in both animals. The function curves under pumping with either the 30-mL or the 15-mL balloons did not differ from the corresponding control curves. This finding indicates that under pumping with the largest of the balloons tested, the left ventricle provided a higher output with a lower end-diastolic pressure.
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Fig 6. . Left ventricular function curves during experimental cardiogenic shock obtained from two experimental animals before (CONTROL) and at the 20th minute of intraaortic balloon pumping (IABP) using the 45-mL balloon. In both experiments (upper and lower diagrams) the function curve was shifted to the left under 45-mL intraaortic balloon pumping. The function curves with either the 30-mL or the 15-mL intraaortic balloons did not differ from the corresponding control curves. (LVEDP = left ventricular end-diastolic pressure.)
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PARAAORTIC PUMP.
The control values of aortic flow prior to the initiation of the two pumping methods (paraaortic versus intraaortic balloon pump) (Table 6) did not differ significantly.
The aortic flow increased (+38.44 ± 5.44 mL•min-1•kg-1; t = 7.02, p < 0.001) under paraaortic pumping only (Table 6). One-way analysis of variance indicated that the four groups (15-mL balloon, 30-mL balloon, 45-mL balloon, and paraaortic pump groups) differed (F = 30.39, p < 0.0001) in changes recorded in aortic flow (see Tables 2–4, 6), the highest value found with the paraaortic pump and the lowest with the 15-mL balloon.
Clinical Data
In 3 patients with dilated cardiomyopathy in severe cardiogenic shock, the systolic blood pressure remained less than 60 mm Hg despite 48 hours of conventional intraaortic balloon pumping by means of a 40-mL balloon. One subject survived for only 4 hours after the application of a paraaortic pump. The addition of intraaortic balloon pumping to paraaortic pumping increased the stroke volume from 80 to 120 mL. It maintained the lives of the remaining 2 patients for 8 and 54 days. The effect of short pumping periods using the 40-mL intraaortic balloon alone, the 80-mL paraaortic pump alone, and combined paraaortic plus intraaortic balloon pumping is shown in Figure 7: The higher the counterpulsation volume, the larger the increase in aortic pressure. This tracing was taken from the patient who survived for 54 days while waiting for a donor heart.
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Fig 7. . Continuously recorded aortic pressure from a patient in severe cardiogenic shock in whom conventional intraaortic balloon pumping with a 40-mL balloon was ineffective. A paraaortic pump was implanted as shown in Figure 2. Without pumping (CONTROL) the systolic aortic pressure of this patient was 50 mm Hg. Observe the effects of intraaortic balloon pumping 1:1 alone (40 ml IABP) and paraaortic pumping 1:1 alone (80 ml PAAP), the combined effect of paraaortic pumping 1:1 plus intraaortic balloon pumping 2:1 [(80 ml PAAP 1:1)+(40 ml IABP 2:1)], and the effect of intraaortic balloon pumping 2:1 alone (40 ml IABP 2:1).
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Comment
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The data presented indicate that, although conventional intraaortic balloon pumping was, as expected [3], ineffective in treating severe experimental or clinical cardiogenic shock, larger counterpulsation volumes provided either by intraaortic balloons occupying the full length of the aorta or by a valveless paraaortic pump were more effective in reversing hemodynamic and other features of this severe syndrome. The hemodynamic data from different-sized balloons were derived from animal experiments alone. We believe that the effect of a large counterpulsation volume on the arterial pressure, as is shown in Figure 7, and the fact that 1 of the 3 patients survived under paraaortic pumping for 54 days, support the efficacy of large counterpulsation volumes in subjects remaining in severe cardiogenic shock despite conventional intraaortic balloon pumping. Undoubtedly, the acute hemodynamic effects of a counterpulsation device as shown mainly in animals are not translated directly into survival, because other parameters may play an important role in the survival of patients with shock. However, as Figure 7 shows, the systolic aortic pressure of this patient without paraaortic pumping was about 50 mm Hg, a pressure level inconsistent with prolonged survival. The acute beneficial effect of a large stroke volume counterpulsation device on this hemodynamic variable was followed by a more than 50-day survival of this patient.
It is possible that two 15-mL balloons may not cause a 30-mL displacement because the total displacement depends on aorta size and capacity. Total displaced blood volume during balloon expansion was not measured. The effect on hemodynamic variables of a larger balloon was taken as evidence of a higher blood volume displacement because no other condition of pumping was altered.
Some possible deleterious effects of pumping using a large intraaortic balloon occupying the full length of the aorta have to be considered. The marked increase in aortic blood volume induced during left ventricular diastole either by the large intraaortic balloon inflation or by the paraaortic pump ejection was followed by an equally large reduction in aortic blood volume in early systole, when the balloon deflated or the air-chamber of the valveless paraaortic pump collapsed. The "empty" space thus created in the aorta, 45 to 70 mL, is substantially larger than the stroke volume of the severely failing left ventricle, which did not exceed 15 mL per beat (as can be calculated from data presented in Table 1). As a result, one might expect that organ perfusion would be reduced, because a significant back-flow from the peripheral arteries to the aorta might be created during balloon deflation in cardiac systole. However, in the experimental model used in this study and for the time length of the experiments both flow in the renal artery and urine output were significantly greater during pumping using the larger (45-mL) balloon rather than any of the smaller ones. This finding is not in agreement with the reports [9] by other authors, who noticed renal artery flow reduction after pumping when the intraaortic balloon was adjacent to the ostia of renal arteries. Also, this finding is not easily explained by established data regarding the physiology of the circulatory system. Some specific effects of counterpulsation by such a large balloon may be involved in this result. First, the faster forward movement of a larger "pump" stroke volume induced by the expansion of the larger balloon increases forward flow. As a result, second, the venous return to the heart increases. Third, the afterload reduction induced by the large balloon deflation in early systole prevents an increase in left ventricular end-diastolic pressure despite increasing venous return. In fact, the present findings indicate that left ventricular end-diastolic pressure is reduced by large balloon counterpulsation. Finally, the impressive increase in coronary flow observed with the large balloon may also improve the performance of the left ventricle. The combined effect of all these mechanisms is probably responsible for shifting the left ventricular function to a "better" Starling's law curve (see Fig 6) noted during 45-mL balloon pumping only.
The fact that renal artery orifices were not occluded during balloon expansion because they were sited between tapered balloon ends may also be responsible for the difference between the findings presented here and previous ones [9].
The efficacy of a counterpulsation technique may be affected by proximity of the implantation site to the aortic valve [10–12]. The closer the implantation site the more effective the device. Thus, the higher efficacy of the paraaortic pump might also be related to the fact that it was implanted in the ascending aorta. However, this was not the case with intraaortic balloon volume optimization, because the experimental protocol used allowed shifting from the larger to the smaller intraaortic balloon pumping and vice versa without altering balloon proximity to the aortic valve.
In conclusion, the data presented indicate that a counterpulsation volume much larger than the one provided by commonly used balloons might be applied as a bridge to implantation of a left ventricular assist device for patients in severe cardiogenic shock not responding to usual intraaortic balloon pumping. Furthermore, the paraaortic pump has been applied in such patients as a bridge to transplantation. Balloons of proper volume (covering the whole length of the aorta) and shape (ie, tapered toward their distal end) might be more effective in severe cardiogenic shock.
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Footnotes
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Address reprint requests to Dr Stamatelopoulos, Alexandra Hospital, 80 Vas Sofias Ave, K. Lourou St, Athens 115 28, Greece.
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References
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- Swartz MT, Sakamoto T, Arai H, et al. Effects of intraaortic balloon position on renal artery balloon flow. Ann Thorac Surg 1992;53:604–10.[Abstract]
- Brown BG, Goldfarb D, Topaz SR, Gott VL. Diastolic augmentation by intraaortic balloon: circulatory hemodynamics and treatment of severe, acute left ventricular failure in dogs. J Thorac Cardiovasc Surg 1967;53:789–804.[Medline]
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Abstract
Introduction
