End-diastolic flow reversal limits the efficacy of pediatric intra-aortic balloon pump counterpulsation

BACKGROUND

Counterpulsation with an intra-aortic balloon pump (IABP) has not achieved the same success or clinical use in pediatric patients as in adults. In a pediatric animal model, IABP efficacy was investigated to determine whether IABP timing with a high-fidelity blood pressure signal may improve counterpulsation therapy versus a low-fidelity signal.

METHODS

In Yorkshire piglets (n = 19; weight, 13.0 ± 0.5 kg) with coronary ligation-induced acute ischemic left ventricular failure, pediatric IABPs (5 or 7 mL) were placed in the descending thoracic aorta. Inflation and deflation were timed with traditional criteria from low-fidelity (fluid-filled) and high-fidelity (micromanometer) blood pressure signals during 1:1 support. Aortic, carotid, and coronary hemodynamics were measured with pressure and flow transducers. Myocardial oxygen consumption was calculated from coronary sinus and arterial blood samples. Left ventricular myocardial blood flow and end-organ blood flow were measured with microspheres.

RESULTS

Despite significant suprasystolic diastolic augmentation and afterload reduction at heart rates of 105 ± 3 beats per minute, left ventricular myocardial blood flow, myocardial oxygen consumption, the myocardial oxygen supply/demand relationship, cardiac output, and end-organ blood flow did not change. Statistically significant end-diastolic coronary, carotid, and aortic flow reversal occurred with IABP deflation. Inflation and deflation timed with a high-fidelity versus low-fidelity signal did not attenuate systemic flow reversal or improve the myocardial oxygen supply/demand relationship.

CONCLUSIONS

Systemic end-diastolic flow reversal limited counterpulsation efficacy in a pediatric model of acute left ventricular failure. Adjustment of IABP inflation and deflation timing with traditional criteria and a high-fidelity blood pressure waveform did not improve IABP efficacy or attenuate flow reversal. End-diastolic flow reversal may limit the efficacy of IABP counterpulsation therapy in pediatric patients with traditional timing criteria. Investigation of alternative deflation timing strategies is warranted.

Controlling methods of a newly developed extra aortic counter-pulsation device using shape memory alloy fibers

Diastolic counter-pulsation has been used to provide circulatory augmentation for short term cardiac support. The success of intra-aortic balloon pump (IABP) therapy has generated interest in long term counter-pulsation strategies to treat heart failure patients. The authors have been developing a totally implantable extra aortic pulsation device for the circulatory support of heart failure patients, using 150 µm Ni-Ti anisotropic shape memory alloy (SMA) fibers. These fibers contract by Joule heating with an electric current supply. The special features of our design are as follow: non blood contacting, extra aortic pulsation function synchronizing with the native heart, a wrapping mechanical structure for the aorta in order to achieve its assistance as the aortomyoplsty and the extra aortic balloon pump. The device consisted of rubber silicone wall plates, serially connected for radial contraction. We examined the contractile function of the device, as well as it controlling methods; the phase delay parameter and the pulse width modulation, in a systemic mock circulatory system, with a pneumatically driven silicone left ventricle model, arterial rubber tubing, a peripheral resistance unit, and a venous reservoir. The device was secured around the aortic tubing with a counter-pulsation mode of 1:4 against the heartbeat. Pressure and flow waveforms were measured at the aortic outflow, as well as its driving condition of the contraction phase width and the phase delay. The device achieved its variable phase control for co-pulsation or counter-pulsation modes by changing the phase delay of the SMA fibers. Peak diastolic pressure significantly augmented, mean flow increased (p<0.05) according to the pulse width modulation. Therefore the newly developed extra aortic counter-pulsation device using SMA fibers, through it controlling methods indicated its promising alternative extra aortic approach for non-blood contacting cardiovascular circulatory support.

Counterpulsation with symphony prevents retrograde carotid, aortic, and coronary flows observed with intra-aortic balloon pump support

A counterpulsation device (Symphony) is being developed to provide long-term circulatory support for advanced heart failure (HF) patients. In acute animal experiments, flow waveform patterns in the aortic, carotid, and coronary arteries were compared during Symphony and intra-aortic balloon pump (IABP) support. Human data were examined for similarities. The 30-mL Symphony was compared to a 40-mL IABP in calves with cardiac dysfunction (80-100 kg, n = 8). Aortic pressures and aortic, carotid, and coronary artery flows were simultaneously recorded at baseline (devices off) and during 1:1 and 1:2 support. Forward, retrograde, and mean flows were calculated and compared for each test condition. Findings were also compared to aortic flow measurements recorded in HF patients (n = 21) supported by 40-mL IABP. IABP caused significant retrograde flows in the aorta, coronary (IABP: -24 ± 8 mL/min, Symphony: -6 ± 2 mL/min, baseline: -2 ± 1 mL/min, P < 0.05), and carotid arteries (IABP: -30 ± 5 mL/min, Symphony: -0 ± 0 mL/min, baseline: -0 ± 0 L/min, P < 0.05) during ventricular systole compared to the Symphony. IABP support produced higher diastolic pressure and flow augmentation compared to Symphony. Due to retrograde flows during IABP support, Symphony provided higher overall coronary, carotid, and aortic flows. Similar reduction in total aortic flows due to retrograde flow was observed in HF patients during IABP support. Counterpulsation with an IABP via aortic volume displacement produces retrograde flows during rapid balloon deflation that reduces total flow. Counterpulsation with Symphony via volume removal eliminates retrograde flow and improves total flow more than that achieved with IABP. The Symphony may provide long-term hemodynamic benefits in HF patients.

Comparison of pulsatile with nonpulsatile mechanical support in a porcine model of profound cardiogenic shock

The aim of this study was to examine whether pulsatility by intraaortic balloon counterpulsation (IABP) is an important adjunct to the treatment of profound cardiogenic shock (CS) with a widely used, nonpulsatile centrifugal pump (CP). In each of 18 anesthetized, open chest pigs, the outflow cannula of the CP was inserted in the aortic arch through the right external carotid artery, and the inflow cannula of the CP was placed in the left atrium. A 40 cc IABP was subsequently placed in the descending aorta through the left external carotid artery. CS was induced by occlusion of coronary arteries and the infusion of propranolol and crystalloid fluid. Mean aortic pressure, pulse pressure, aortic end diastolic pressure, left ventricular end diastolic pressure, right atrial pressure, and heart rate were monitored. Cardiac output and left anterior descending artery flow were measured with a transit time ultrasound flowmeter. During profound CS, life sustaining hemodynamics were maintained only with the support of the assist devices. Hemodynamic support with the CP was associated with a nearly nonpulsatile flow and a pulse pressure of 7 +/- 4 mm Hg, which increased to 33 +/- 10 mm Hg (p = 0.000) after combining the CP with the IABP. Compared with the hemodynamic support offered by the CP alone, addition of the IABP increased mean aortic pressure from 40 +/- 15 to 50 +/- 16 mm Hg (p = 0.000), cardiac output from 810 +/- 194 to 1,200 +/- 234 ml/min (p = 0.003), and left anterior descending artery flow from 26 +/- 10 to 39 +/- 14 ml/min (p = 0.001). In profound CS, mechanical support provided by a continuous flow CP is enhanced by the added pulsatility of the IABP.

Basic Principles of the Intraaortic Balloon Pump and Mechanisms Affecting Its Performance

The intraaortic balloon pump (IABP) is the single most effective and widely used device for temporary mechanical assistance of the failing heart. Although the principles underlying IABP function are simple, various biologic factors often determine its performance in a particularly complicated way. We briefly describe the basic disciplines of counterpulsation by IABP and the induced hemodynamic changes while clarifying the biologic mechanisms that play a crucial role in the modification of IABP acute hemodynamic performance.

New Aspects on the Role of Blood Pressure and Arterial Stiffness in Mechanical Assistance by Intra-aortic Balloon Pump: In-vitro Data and Their Application in Clinical Practice

Despite the well-known beneficial effects of the intra-aortic balloon pump (IABP) generally, there are still some clinical conditions accompanied by IABP ineffectiveness. The aim of this study was the investigation of the independent effects of arterial stiffness and blood pressure on acute IABP effectiveness. For this purpose, a mock circulatory system and 20 patients with cardiogenic shock due to acute myocardial infarction, were employed. It was shown that IABP acute efficiency was determined primarily by arterial compliance (AC) rather than blood pressure alone. IABP induced low hemodynamic effects in patients with systolic blood pressure > 80 mm Hg but with increased AC, whereas IABP resulted in greater hemodynamic effectiveness in cases with systolic pressure < 70 mm Hg but lower AC. The present study provides evidence concerning the hemodynamic conditions, which might lead to optimization of IABP or to the prediction of its acute hemodynamic performance, based on both measurements of AC and blood pressure.

Heart rate effect on hemodynamics during mechanical assistance by the intra-aortic balloon pump

Heart rate (HR) has been characterized as an important cardiovascular parameter that affects acute hemodynamic performance of intra-aortic balloon counterpulsation (IABC). However, the effect of HR on hemodynamics during mechanical assistance by the IABC has neither been clarified nor quantified. We sought to evaluate the relationship between IABC and HR and also to examine whether there is a range of HR with optimum hemodynamic response to IABC.

METHODS

20 patients (14 males--6 females, mean age 64.4 +/- 11.4 years) with post-infarction cardiogenic shock undergoing IABC treatment were evaluated. Hemodynamics were recorded for each patient once per day during the assistance period; 131 measurements were taken and thus a wide range of heart rates was obtained (64-141 bpm). The following changes in aortic pressures were used to evaluate acute IABC performance on: a) the maximal increase of diastolic aortic pressure induced by IABC and b) the reduction in systolic and end-diastolic aortic pressure.

RESULTS

Non-linear regression analysis and analysis of variance revealed that a significant correlation exists between IABC performance indices and heart rate. At HR<80 bpm, IABC performance tended to be reduced, whereas the increase in HR above 110 bpm resulted in a significant reduction of all IABC performance indices. In contrast, IABC operating at 80-110 bpm resulted in optimum hemodynamic performance. In conclusion, the effect of heart rate on IABC performance is non-linear indicating that IABC may be more effective when operating within 80-110 bpm.

Arterial compliance is a main variable determining the effectiveness of intra-aortic balloon counterpulsation: quantitative data from an in vitro study

Quantitative data concerning the effect of arterial compliance (AC) on the effectiveness of intra-aortic balloon counterpulsation (IABC) are lacking. The main objective of this study was to investigate the relationship between AC and IABC performance. For this purpose we constructed a Windkessel, lumped-element, hydraulic model of the systemic circulation. The model consisted of a left ventricular assist device (LVAD), a compliance chamber, a peripheral resistor and two open reservoirs. Two Datascope Driving systems were used to operate the LVAD and intra-aortic balloon. We studied the effect of arterial compliance on the effectiveness of IABC at different levels of mean pressure (55, 75 and 95 mmHg) and heart rates (80, 100, 120 bpm). Three indices were used to evaluate IABC performance: the reduction of systolic and end-diastolic "arterial" pressure and the augmentation of diastolic pressure, induced by the IABC. A 22% decrease in AC (1.8-1.4 ml/mmHg) lead to a 30-40% increase in the indices of IABC performance, independently from pressure. In conclusion, arterial compliance significantly affects IABC efficacy and it could be considered as a further clinical criterion to decide IABC application.

Treating severe cardiogenic shock by large counterpulsation volumes

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 (i.e., until it fully occupies the aorta).