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J Thorac Cardiovasc Surg 1994;107:569-0575
© 1994 Mosby, Inc.

Cardiopulmonary Bypass, Myocardial Management, and Support Techniques

Evaluation of the pulsatility of a new pulsatile left ventricular assist device—the integrated cardioassist catheter—in dogs

Tokyo and Saitama, Japan

Received for publication Jan. 13, 1993. Accepted for publication May 24, 1993. Address for reprints: Hirofumi Ide, MD, Department of Thoracic and Cardiovascular Surgery, Kyorin Medical School, 6-20-2, Shinkawa, Mitaka-shi, Tokyo, 181, Japan.

Abstract

A new pulsatile left ventricle–femoral artery bypass system (integrated cardioassist catheter system) has been developed for rapid, percutaneous insertion as a left ventricular assist device. Previous experiments revealed its superiority over the intraaortic balloon pump system in maintaining the peripheral circulation and in improving myocardial blood flow and afterload. Our objective was to determine whether the pulsatility of left ventricular bypass of this system would be preferable for maintaining the peripheral circulation and managing the ischemic myocardium as compared with nonpulsatile left ventricular bypass. Ten dogs with profound heart failure were supported by this system. Their hemodynamic status and myocardial blood flow were measured under control, nonpulsatile left ventricular bypass, or synchronous pulsatile left ventricular bypass. Significant differences between the nonpulsatile bypass group and the pulsatile bypass group were observed in the mean increase in aortic pressure (3.5% versus 22.2%, respectively; p < 0.001), total cardiac output (13.0% versus 21.7%; p = 0.004), and myocardial blood flow (9.5% versus 21.8%; p < 0.001). No differences were found between groups in the decrease in left atrial pressure (-20.2% versus -20.2%; p > 0.05). The ratio of diastolic time index/tension time index was shown to be improved significantly in the pulsatile bypass group compared with that of control and nonpulsatile bypass groups (p < 0.001). Thus, the pulsatility of the integrated cardioassist catheter system may support the peripheral circulation and improve the myocardial blood flow and oxygen supply/demand ratio. (J THORACCARDIOVASC SURG 1994;107:569-75)

We developed a new pulsatile left ventricle (LV)–femoral artery (FA) bypass system that used a transaortic valve–LV drainage catheter with an intraaortic balloon situated in the descending aorta (integrated cardioassist catheter [ICAC]), a centrifugal pump and an intraaortic balloon pump (IABP) console (Fig. 1). This new device system can be rapidly placed in an emergency, unlike the conventional LV assist techniques, such as left atrium (LA)–FA bypass ^1-4 or even other LV-aorta bypass techniques, ⁵ which can be difficult to establish. This system would be useful in treating patients with not only profound LV dysfunction after cardiac operations as do other LV assist devices, ^{3, 4, 6-8} but also with an evolving myocardial infarction or with cardiogenic shock, which necessitate the rapid insertion of an LV assist device and coronary intervention.

View larger version (29K): [in this window] [in a new window]   Fig. 1. Clinical application of the ICAC. The perfusion cannula can also be placed from the subclavian artery. AV, Aortic valve; LV left ventricle.

We have already reported ¹³ that the ICAC system as a pulsatile LV bypass is preferable in ameliorating the myocardial blood supply/demand relationship and maintaining peripheral circulation compared with IABP support alone. We designed the present experiment to investigate whether the synchronized diastolic pulsatility of this ICAC system would provide benefits concerning LV unloading and myocardial blood flow, as well as providing hemodynamic stability, as compared with nonpulsatile LV bypass.

MATERIALS AND METHODS

Ten mongrel dogs weighing 18 to 28 kg were anesthetized with intramuscular ketamine hydrochloride (20 mg/kg) and intravenous pentobarbiturate anesthesia (25 mg/kg). After intubation, respiration was controlled with positive-pressure mechanical ventilation with a mixture of room air and low-flow oxygen.

After making a transverse thoracotomy in the fourth intercostal space, a catheter was placed in the LA and in the LV via the LV apex and left carotid artery and connected to a pressure transducer for monitoring pressures. The diastolic pressure time index and the tension time index were calculated from simultaneous measurements of LV and aortic pressure. The subendocardial oxygen supply/demand ratios were estimated by diastolic pressure time index/tension-time index calculations. Electromagnetic flow probes were secured around the main pulmonary artery and the bypass tube, and the total cardiac output (output of LV + bypass flow) and bypass flow were measured. A laser Doppler flow probe was placed on the LV free wall to measure myocardial blood flow with the value expressed in milliliters per minute per 100 gm myocardial weight. ¹⁴

The prototype ICAC used in the canine experiments measured the following: outer diameter 18F, inner diameter 9F, balloon size 20 or 30 ml, and length 60 cm. The catheter tube was made of polyvinyl chloride. After the lower end of the abdominal aorta was exposed by median laparotomy and the right carotid artery was exposed through an incision in the neck, heparin (2.5 mg/kg) was administered intravenously. The ICAC was inserted via an abdominal cutdown to the descending aorta. The guidewire with its soft tip and a pigtail catheter were introduced into the LV through the ICAC cannula with the aid of fluoroscopy. The tip of the ICAC was advanced into the LV cavity, guided by the pigtail catheter. An arterial perfusion cannula (14F) was then introduced into the right carotid artery. Both cannulas were then connected to a tube (³/₈ inch) of the bypass circuit that contained a centrifugal pump (Biopump; Medtronic Bio-Medicus, Eden Prairie, Minn.) primed with heparinized saline solution.

After obtaining baseline measurements, we administered intravenously a ß-blocker (propranolol hydrochloride, 4 to 12 mg) and low-molecular weight dextran to achieve basic biventricular failure and also to control heart rate. In addition, we ligated the branches of left anterior descending coronary artery to induce LV dysfunction of various levels of severity, as determined by hemodynamic monitoring mentioned previously. To control the heart rate, we performed right atrial overdrive pacing after administration of ß-blocker or right ventricular pacing with atrioventricular block formation ¹⁵ to avoid the influence of the heart rate.

In the various states of heart failure under control, nonpulsatile LV bypass, and pulsatile LV bypass measurements were obtained after hemodynamic stability was confirmed. Pulsatile LV bypass was performed by exerting an intraaortic balloon console with the aortic pressure waveforms synchronized to the heart beat on the electrocardiogram, which was adjusted to provide maximal diastolic phase pulsatility, and compared with nonpulsatile LV bypass under the same bypass flow. The bypass flow ranged from 500 to 1700 ml/min. Each group was randomly and sequentially prepared and compared at the same heart rate to avoid the influence of hemodynamic changes over time. All animals were treated humanely in strict accordance with the "Guide for the Care and the Use of Laboratory Animals" published by the National Institute of Health (NIH publication No. 85-23, revised 1985).

Values were expressed as mean ± standard deviation. Paired or nonpaired Student's t tests (double-tailed) were used to compare differences between groups, with the use of the commercially available Stat View software package (Brain Power Inc., Calabasas, Calif.); p values less than 0.05 were considered to be statistically significant.

RESULTS

With the method of pigtail catheter–guided insertion of the ICAC with the aid of fluoroscopy, it took about 3 minutes to place the ICAC into the LV cavity properly. We encountered no complications concerning the LV wall, the aortic valve, or the aortic wall during experiments; this was confirmed at postmortem examination.

The baseline hemodynamic values after full instrumentation are as follows: mean aortic pressure 116.8 ± 8.7 mm Hg, total cardiac output 2.7 ± 0.4 L/min, left atrial pressure 4.0 ± 1.6 mm Hg, mean heart rate 114.6 ± 11.2 beats/min. The mean values of the random and sequential measurements of the hemodynamic parameters in the three groups are summarized in Table I. The mean bypass flow set up in each parameter is shown in Table I, and its mean LV bypass flow was approximately 40% of the normal cardiac output before ß-blocker administration.

View larger version (45K): [in this window] [in a new window]   Fig. 2. Comparison of percentage of changes of hemodynamic parameters pulsatile (P) and non pulsatile (NP) groups. NS, Not significant; AoP aortic pressure; CO, cardiac output; LAP, left atrial pressure.

View larger version (63K): [in this window] [in a new window]   Fig. 3. Comparison of diastolic pressure time index (DPTI) /tension time index (TTI) values among the three groups. Mean bypass flow of the nonpulsatile (NP) and pulsatile (P) groups were1040 ml/min and 1060 ml/min, respectively (statistically not significant). Vertical bars show the standard deviation. Nonpaired t test was used for comparison. NS, Not significant.

Previous reports ^{2, 3, 7-9} have demonstrated that LV bypass, mainly LA-FA bypass, primarily maintains peripheral circulation, irrespective of pulsatile or nonpulsatile flow support and is undoubtedly effective in managing profound LV impairment. To meet the demands of recent advances in interventional cardiology or cardiac surgery, the following issues have precluded widespread clinical application of the various kinds of conventional LV bypass methods.

The ideal LV bypass methods should be implemented rapidly, and preferably, percutaneously, for the treatment of abrupt cardiogenic shock or an evolving myocardial infarction because these conditions can occur not only in the surgical suite after cardiotomy but also in the catheter laboratory and intensive care unit. However, the conventional LV bypass methods, ^{1-5, 7} with their inherent mechanisms that necessitate surgical or complicated procedures for placement, limit their prevalence, unlike IABP. As Axelrod and associates ^{11, 12} pointed out, percutaneous cardiopulmonary bypass (VA bypass) may surpass the LV bypass system in this respect. The new ICAC system for LV bypass offers ease of percutaneous insertion. The present experiments in dogs demonstrated that the draining tube could be placed in the LV through the aortic valve in about 3 minutes with the aid of fluoroscopy and an internal guidewire catheter, as previously mentioned, without complications. In theory, in the clinical setting, this device could be installed promptly at the bedside with the aid of echocardiography and initiated quickly. Thus, this new system, unlike conventional LV bypass, overcomes the difficulty of insertion that is associated with the transatrial septal puncture required with LA-FA bypass, ^{1, 2, 10} which precludes its widespread application. The ICAC system can be implemented with a centrifugal pump and an IABP console, in contrast to other methods. ^{2, 5, 8, 9, 11, 12, 16} Another clinical advantage of the ICAC for LV-FA bypass is that it does not induce stagnation of the blood in the LV, as seen with traditional LA-FA bypass, which presents the risk of LV thrombus formation and subsequent systemic embolism. However, the recently developed intraarterial axial-flow blood pump, the Hemopump (Nimbus Medical, Inc., Rancho Cordova, Calif.) may have some superiority over the ICAC ⁸ because it necessitates minimal surgical procedure without thoracotomy like the ICAC system and also supplies LV bypass flow support of up to 4 L/min; once it is introduced, its drive shaft is only 9F, preventing lower limb ischemia of the inserted site, unlike the ICAC, although it requires its specific power console and provides nonpulsatile flow.

Thus, theoretically the ICAC system has some potential superiority over the conventional LV assist device ^{1-3, 5, 7-10, 16} for practical use. The other pulsatile bypass systems ^{2, 5, 7, 9-12, 16} have adopted an intrinsic way of using the pulsatile pump to achieve pulsatility for perfusion as a possible alternative to the conventional intraaortic balloon counterpulsation method we used. However, with regard to simplicity and effectiveness, the following disadvantages exist for an intrinsic method in comparison with conventional intraaortic balloon pulsatility ^{2, 7, 9-12, 16}: (1) intrinsic method necessitates a pulsatile pump system unlike the widely used IABP console, (2) effective pulsatility would be obtained only with a large perfusion catheter, (3) synchronized pulsation would not be possible in the presence of severe tachycardia, and (4) perfusion from the FA would not produce intense pulsation at the aortic coronary ostium, where maximal pulsatility is required. Therefore, we consider our extrinsic approach to be preferable. In addition, the ICAC bypass allows easy weaning to IABP counterpulsation. The integration of the balloon portion and the draining cannula is indispensable, in that the independent insertion of the cannula and IABP creates two problems. First, the bilateral FAs are occupied by perfusion and draining cannulation, and the IABP would not be inserted percutaneously. Second, the balloon would not be implemented effectively in the descending aorta, where a drainage tube is placed as an obstacle in the event of independent use.

As for myocardial salvage after the revascularization of the ischemic myocardium, the efficacy of cardiac assist devices has been evaluated mainly according to whether they have the ability of limiting the size of myocardial infarct. ^{9, 12, 17-20} Instead, this experimental study was designed to evaluate the pulsatility of ICAC system as an LV-aorta (FA) bypass in view of myocardial oxygen supply and unloading status especially for salvaging ischemic myocardium and hemodynamic stability.

In this canine model, two points should be taken into consideration. First, we adopted the insertion site of the left carotid artery instead of the site distal to the intraaortic balloon, simulating the insertion site of the perfusion catheter via the subclavian artery, not the FA. The main reason was to avoid the technical difficulty of returning the blood from the FA without causing lower limb ischemia. The preliminary experiments comparing these two insertion sites showed no significant difference in the aortic root waveforms and actual pressure, indicating that the one–aortic chamber model exerts minimal effect on its perfusion site, although there might be some difference in clinical situations. Second, we administered ß-blocker and ligated the coronary arteries in the LV regions to achieve various degrees of biventricular failure to simulate the clinical condition of LV-dominated heart failure. Its extent of cardiac failure compared with that of normal canine hearts after full instrumentation for this experiment has been previously described and is shown in Table I. The hemodynamic findings estimated from mean aortic pressure and total cardiac output demonstrated the significant benefit of adding electrocardiogram-gated pulsatility on the maintenance of the peripheral circulation, provided that the ICAC system is used under certain LV dysfunction protocols, such as ours; the results in other settings might not agree with other experimental results of normal cardiac function ^{10, 21} or even the LAD ligation model. ¹⁹ Those studies have shown no significant hemodynamic improvement. In their models, LV bypass flow and LV output itself are considered to have the relationship of mutual compensation, and pulsatile LV bypass itself brings about no significant hemodynamic improvements. In our model of cardiac failure, pulsatile LV bypass increased the aortic pressure by 22.2% and the cardiac output by 21.7%, with a flow support of 990 ± 390 ml/min and 1090 ± 420 ml/min, respectively. In the clinical setting, these values would theoretically be obtained under a flow support of approximately 2 to 2.5 L/min (about 40% of the normal cardiac output) and preclude the ICAC size and length for clinical application. Although those maximal flows might be sufficient for a clinical report, ⁷ the potential disadvantage of the restricted maximal flow determined by the long draining tube of a limited size is shown to be compensated by its pulsatility from our experiment. In the clinical setting, as is expected, this catheter should be long, inserted from the FA to the LV, and preferably smaller in its outer diameter to prevent lower limb ischemia of the inserted site, thus limiting its maximum bypass flow. Our experimental data show also that a maximal flow of more than 2 L/min is necessary to achieve the same hemodynamic effect as was discussed previously. With these requirements in mind, we created a clinical model of the ICAC. In brief, its length is 90 cm, outer diameter 20F, and inner diameter 15F. It is made of heparin-coated polyurethane. In vivo and in vitro flow characteristics in dogs showed that its maximal flow is of more than 2 L/min without cavitation in a centrifugal pump head and hemolysis (unpublished data). We are now ready to use it clinically.

No significant difference in left atrial pressure was observed between the pulsatile and nonpulsatile groups, indicating that the reduction in the LV preload could be attributed to the flow support itself, which is in agreement with previous study. ¹⁰ Pulsatility is considered to have little contribution. This phenomenon and its explanation are supported by the results of other investigators ^{7, 21} and by the results of our previous study, ¹³ which examined and compared the IABP and ICAC and showed the superiority of the ICAC as a pulsatile LV-aorta bypass over the IABP alone and in which pulsatility itself did not reduce left atrial pressure values.

With regard to the salvage of the ischemic myocardium, we did not evaluate the actual infarct size or infarct size/area at risk ratios during the reperfusion of ischemic myocardium, as is used by other investigators to validate various assist devices. ^{9, 12, 17-20} Instead, we measured the myocardial blood flow and calculated the LV afterload (pressure load), which is the theoretic basis of myocardial salvage. Calculation of tension-time index and myocardial oxygen consumption has been used exclusively* to assess and quantitate the unloading status of the heart. Some articles have shown that a nonpulsatile VA bypass is ineffective for decreasing the tension-time index values ^{11, 12} and myocardial oxygen consumption, ^{11, 22} indicating the potential inability of VA bypass to unload the LV, whereas even a nonpulsatile LA-aorta bypass can reduce tension-time index values ^{9, 17, 18} and myocardial oxygen consumption ^{17, 22-24} and LV stroke work. ²¹ Thus, Spencer and colleagues ⁶ have applied the LA-FA bypass in the treatment of postcardiotomy LV impairment with good clinical results. Their more recent reports have shown, however, that the pulsatility of the VA bypass is a highly useful adjunct for salvaging the ischemic myocardium. ^{11, 12} Subsequent studies that compared the LV-aorta bypass and LA-aorta bypass revealed an advantage of the former in reducing tension-time index values, ¹⁹ myocardial oxygen consumption, ²⁵ and myocardial infarct size. ^{19, 26} This advantage may be a result of a difference in the efficacy of inducing LV decompression, which supports the preferable effect of our bypass method. It should be noted that nonpulsatile flow delivers its unloading condition secondary to a complete LV decompression. ^{17, 19, 21, 22, 23} In contrast from our findings, adding pulsatility to the LV bypass appears to be an important means of improving the myocardial oxygen supply/demand ratios and the actual myocardial blood flow under incomplete decompression. This outcome is generally consistent with the results of other investigations of pulsatile LV bypass. ^{2, 5} Grossi and associates ^{10, 20} showed a preferable effect of the pulsatile LA-FA bypass in reducing tension time index values, epicardial/endocardial flow ratio, and myocardial infarction size, whereas Rose and associates ²¹ suggested the inability of pulsatility of a partial, as compared with a total, LV bypass. Others ⁹ showed no significant difference of LV afterload estimated by tension-time index measurement between pulsatile and nonpulsatile flow in LA-aorta bypass. The present study showed a significant improvement of myocardial blood supply/demand ratio, as reflected by diastolic pressure time index/tension-time index measurements with its pulsatility even under incomplete LV decompression. Also, our previous study with a similar protocol ¹³ showed a significant increase of diastolic pressure time index/tension-time index ratios as compared with the use of counterpulsation alone, indicating that constant LV flow support may augment the effect of counterpulsation. Furthermore, as mentioned previously, LV output estimated by total cardiac output and bypass flow was shown to decease under LV bypass, indicating that LV bypass, whether pulsatile or nonpulsatile, reduces LV volume loads.

In conclusion, the ICAC systems for conducting partial LV-FA bypass ameliorated the myocardial oxygen supply/demand relationship, in addition to maintaining the peripheral circulation in LV-dominated profound heart failure in dogs.

Acknowledgments

We acknowledge the assistance of Muneyasu Saitoh, MD, Professor of the Department of Cardiology, Omiya Medical Center, Jichi Medical School, in statistical analysis.

Footnotes

From the Department of Thoracic and Cardiovascular Surgery, Kyorin Medical School, Tokyo,^a the Department of Cardiovascular Surgery, Omiya Medical Center, Jichi Medical School, Saitama,^b and the Research Center for Advanced Sciences and Technology, University of Tokyo, Tokyo,^c Japan.

* References ^{9-12, 17-20, 22-24.}

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Takashi Ino Hideo Adachi Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ide, H. Articles by Fujimasa, I. Search for Related Content PubMed PubMed Citation Articles by Ide, H. Articles by Fujimasa, I.