Intraaortic balloon pump counterpulsation and cerebral autoregulation : an observational study

The use of Intra-aortic counterpulsation is a well established supportive therapy for patients in cardiac failure or after cardiac surgery. Blood pressure variations induced by counterpulsation are transmitted to the cerebral arteries, challenging cerebral autoregulatory mechanisms in order to maintain a stable cerebral blood flow. This study aims to assess the effects on cerebral autoregulation and variability of cerebral blood flow due to intra-aortic balloon pump and inflation ratio weaning.

A prospective pilot study evaluating the ‘cardiac decompensation score’ in the setting of intraaortic balloon counterpulsation

The study objective was to determine whether the ‘cardiac decompensation score’ could identify cardiac decompensation in a patient with existing cardiac compromise managed with intraaortic balloon counterpulsation (IABP). A one-group, posttest-only design was utilised to collect observations in 2003 from IABP recipients treated in the intensive care unit of a 450 bed Australian, government funded, public, cardiothoracic, tertiary referral hospital. Twenty-three consecutive IABP recipients were enrolled, four of whom died in ICU (17.4%). All non-survivors exhibited primarily rising scores over the observation period (p < 0.001) and had final scores of 25 or higher. In contrast, the maximum score obtained by a survivor at any time was 15. Regardless of survival, scores for the 23 participants were generally decreasing immediately following therapy escalation (p = 0.016). Further reflecting these changes in patient support, there was also a trend for scores to move from rising to falling at such treatment escalations (p = 0.024). This pilot study indicates the ‘cardiac decompensation score’ to accurately represent changes in heart function specific to an individual patient. Use of the score in conjunction with IABP may lead to earlier identification of changes occurring in a patient's cardiac function and thus facilitate improved IABP outcomes.

Coronary collateral growth by external counterpulsation: a randomised controlled trial

The efficacy of external counterpulsation (ECP) on coronary collateral growth has not been investigated in a randomised controlled study. Objective To test the hypothesis that ECP augments collateral function during a 1 min coronary balloon occlusion.

Cause or effect of arteriogenesis: compositional alterations of microparticles from CAD patients undergoing external counterpulsation therapy

Recently, a clinical study on patients with stable coronary artery disease (CAD) showed that external counterpulsation therapy (ECP) at high (300 mmHg) but not at low inflation pressure (80 mmHg) promoted coronary collateral growth, most likely due to shear stress-induced arteriogenesis. The exact molecular mechanisms behind shear stress-induced arteriogenesis are still obscure. We therefore characterized plasma levels of circulating microparticles (MPs) from these CAD patients because of their ambivalent nature as a known cardiovascular risk factor and as a promoter of neovascularization in the case of platelet-derived MPs. MPs positive for Annexin V and CD31CD41 were increased, albeit statistically significant (P<0.05, vs. baseline) only in patients receiving high inflation pressure ECP as determined by flow cytometry. MPs positive for CD62E, CD146, and CD14 were unaffected. In high, but not in low, inflation pressure treatment, change of CD31CD41 was inversely correlated to the change in collateral flow index (CFI), a measure for collateral growth. MPs from the high inflation pressure group had a more sustained pro-angiogenic effect than the ones from the low inflation pressure group, with the exception of one patient showing also an increased CFI after treatment. A total of 1005 proteins were identified by a label-free proteomics approach from MPs of three patients of each group applying stringent acceptance criteria. Based on semi-quantitative protein abundance measurements, MPs after ECP therapy contained more cellular proteins and increased CD31, corroborating the increase in MPs. Furthermore, we show that MP-associated factors of the innate immune system were decreased, many membrane-associated signaling proteins, and the known arteriogenesis stimulating protein transforming growth factor beta-1 were increased after ECP therapy. In conclusion, our data show that ECP therapy increases platelet-derived MPs in patients with CAD and that the change in protein cargo of MPs is likely in favor of a pro angiogenic/arteriogenic property.

ECG-triggered muscular counterpulsation for treatment of low cardiac output

BACKGROUND: Skeletal muscular counterpulsation (MCP) has been used as a new noninvasive technique for treatment of low cardiac output. The MCP method is based on ECG-triggered skeletal muscle stimulation. The purpose of the present study was to evaluate acute hemodynamic changes induced by MCP in the experimental animal. METHODS: Eight anaesthetized pigs (43+/-4 kg) were studied at rest and after IV â-blockade (10 mg propranolol) before and after MCP. Muscular counterpulsation was performed on both thighs using trains (75 ms duration) of multiple biphasic electrical impulses with a width of 1 ms and a frequency of 200 Hz at low (10 V) and high (30 V) amplitude. ECG-triggering was used to synchronize stimulation to a given time point. LV pressure-volume relations were determined using the conductance catheter. After baseline measurements, MCP was carried out for 10 minutes at low and high stimulation amplitude. The optimal time point for MCP was determined from LV pressure-volume loops using different stimulation time points during systole and diastole. Best results were observed during end-systole and, therefore, this time point was used for stimulation. RESULTS: Under control conditions, MCP was associated with a significant decrease in pulmonary vascular resistance (-18%), a decrease in systemic vascular resistance (-11%) and stroke work index (-4%), whereas cardiac index (+2%) and ejection fraction (+6%) increased slightly. Pressure-volume loops showed a leftward shift with a decrease in end-systolic volume. After â-blockade, cardiac function decreased (HR, MAP, EF, dP/dt max), but it improved with skeletal muscle stimulation (HR +10% and CI +17%, EF +5%). There was a significant decrease in pulmonary (-19%) and systemic vascular resistance (-29%). CONCLUSIONS: In the animal model, ECG-triggered skeletal muscular counterpulsation is associated with a significant improvement in cardiac function at baseline and after IV â-blockade. Thus, MCP represents a new, non-invasive technique which improves cardiac function by diastolic compression of the peripheral arteries and veins, with a decrease in systemic vascular resistance and increase in cardiac output.

The effect of innate compliance on the performance of a counterpulsation device

Cardiovascular disease (CVD) continues to be one of the top causes of mortality in the world. World Heart Organization (WHO) reported that in 2004, CVD contributed to almost 30% of death from estimated worldwide death figures of 58 million[1]. Heart failure treatment varies from lifestyle adjustment to heart transplantation; its aims are to reduce HF symptoms, prolong patient survival and minimize risk [2]. One alternative available in the market for HF treatment is Left Ventricular Assist Device (LVAD). Chronic Intermittent Mechanical Support (CIMS) device is a novel (LVAD) heart failure treatment using counterpulsation similar to Intra Aortic Balloon Pumps (IABP). However, the implantation site of the CIMS balloon is in the ascending aorta just distal to aortic valve contrasted with IABP in the descending aorta. Counterpulsation coupled with implantation close to the aortic valve enables comparable flow augmentation with reduced balloon volume. Two prototypes of the CIMS balloon were constructed using rapid prototyping: the straight-body model is a cylindrical tube with a silicone membrane lining with zero expansive compliance. The compliant-body model had a bulging structure that allowed the membrane to expand under native systolic pressure increasing the device’s static compliance to 1.5 mL/mmHg. This study examined the effect of device compliance and vascular compliance on counterpulsating flow augmentation. Both prototypes were tested on a two-element Windkessel model human mock circulatory loop (MCL). The devices were placed just distal to aortic valve and left coronary artery. The MCL mimicked HF with cardiac output of 3 L/min, left ventricular pressure of 85/15 mmHg, aortic pressure of 70/50 mmHg and left coronary artery flow rate of 66 mL/min. The mean arterial pressure (MAP) was calculated to be 57 mmHg. Arterial compliance was set to be1.25 mL/mmHg and 2.5 mL/mmHg. Inflation of the balloon was triggered at the dicrotic notch while deflation was at minimum aortic pressure prior to systole. Important haemodynamics parameters such as left ventricular pressure (LVP), aortic pressure (AoP), cardiac output (CO), left coronary artery flowrate (QcorMean), and dP (Peak aortic diastolic augmentation pressure – AoPmax ) were simultaneously recorded for both non-assisted mode and assisted mode. ANOVA was used to analyse the effect of both factors (balloon and arterial compliance) to flow augmentation. The results showed that for cardiac output and left coronary artery flowrate, there were significant difference between balloon and arterial compliance at p < 0.001. Cardiac output recorded maximum output at 18% for compliant body and stiff arterial compliance. Left coronary artery flowrate also recorded around 20% increase due to compliant body and stiffer arterial compliance. Resistance to blood ejection recorded highest difference for combination of straight body and stiffer arterial compliance. From these results it is clear that both balloon and arterial compliance are statistically significant factors for flow augmentation on peripheral artery and reduction of resistance. Although the result for resistance reduction was different from flow augmentation, these results serves as an important aspect which will influence the future design of the CIMS balloon and its control strategy. References: 1. Mathers C, Boerma T, Fat DM. The Global Burden of disease:2004 update. Geneva: World Heatlh Organization; 2008. 2. Jessup M, Brozena S. Heart Failure. N Engl J Med 2003;348:2007-18.

The intra-aortic balloon pump in heart failure management : implications for nursing practice

Management of acute heart failure is an important consideration in critical care. Mechanical support of the failing heart is crucial for improving health outcomes. The most common Australasian application of intraaortic balloon counterpulsation (IABP) is in the setting of cardiogenic shock. High end users of IABP (>37/annum) demonstrate significantly lower mortality for cardiogenic shock managed with IABP (p <0.001) in contrast to hospitals which employ limited IABP (<4/annum). This underscores the importance of proficiency in managing patient receiving IABP support. Nurses play a crucial role in carding for patients with acute heart failure. This paper summarises care considerations for management of the IABP.

Physical coronary arteriogenesis: a human "model" of collateral growth promotion

In patients with coronary artery disease, the size of myocardial infarction mainly determines the subsequent clinical outcome. Accordingly, it is the primary strategy to decrease cardiovascular mortality by minimizing infarct size. Promotion of collateral artery growth (arteriogenesis) is an appealing option of reducing infarct size. It has been demonstrated in experimental models that tangential fluid shear stress is the major trigger of arterial remodeling and, thus, of collateral growth. Lower-leg, high-pressure external counterpulsation triggered to occur during diastole induces a flow velocity signal and thus tangential endothelial shear stress in addition to the flow signal caused by cardiac stroke volume. We here present two cases of cardiac transplant recipients as human "models" of physical coronary arteriogenesis, providing an example of progressing and regressing clinical arteriogenesis, and review available evidence from clinical studies on other feasible forms of physical arteriogenesis.

Control of ventricular unloading using an electrocardiogram-synchronized Thoratec paracorporeal ventricular assist device

OBJECTIVE: Current pulsatile ventricular assist devices operate asynchronous with the left ventricle in fixed-rate or fill-to-empty modes because electrocardiogram-triggered modes have been abandoned. We hypothesize that varying the ejection delay in the synchronized mode yields more precise control of hemodynamics and left ventricular loading. This allows for a refined management that may be clinically beneficial. METHODS: Eight sheep received a Thoratec paracorporeal ventricular assist device (Thoratec Corp, Pleasanton, Calif) via ventriculo-aortic cannulation. Left ventricular pressure and volume, aortic pressure, pulmonary flow, pump chamber pressure, and pump inflow and outflow were recorded. The pump was driven by a clinical pneumatic drive unit (Medos Medizintechnik AG, Stolberg, Germany) synchronously with the native R-wave. The start of pump ejection was delayed between 0% and 100% of the cardiac period in 10% increments. For each of these delays, hemodynamic variables were compared with baseline data using paired t tests. RESULTS: The location of the minimum of stroke work was observed at a delay of 10% (soon after aortic valve opening), resulting in a median of 43% reduction in stroke work compared with baseline. Maximum stroke work occurred at a median delay of 70% with a median stroke work increase of 11% above baseline. Left ventricular volume unloading expressed by end-diastolic volume was most pronounced for copulsation (delay 0%). CONCLUSIONS: The timing of pump ejection in synchronized mode yields control over left ventricular energetics and can be a method to achieve gradual reloading of a recoverable left ventricle. The traditionally suggested counterpulsation is not optimal in ventriculo-aortic cannulation when maximum unloading is desired.

ECG-triggered skeletal muscle stimulation improves hemodynamics and physical performance of heart failure patients

BACKGROUND: Muscular counterpulsation (MCP) was developed for circulatory assistance by stimulation of peripheral skeletal muscles. We report on a clinical MCP study in patients with and without chronic heart failure (CHF). METHODS AND RESULTS: MCP treatment was applied (30 patients treated, 25 controls, all under optimal therapy) for 30 minutes during eight days by an ECG-triggered, battery-powered, portable pulse generator with skin electrodes inducing light contractions of calf and thigh muscles, sequentially stimulated at early diastole. Hemodynamic parameters (ECG, blood pressure and echocardiography) were measured one day before and one day after the treatment period in two groups: Group 1 (9 MCP, 11 no MCP) with ejection fraction (EF) above 40% and Group 2 (21 MCP, 14 no MCP) below 40%. In Group 2 (all patients suffering from CHF) mean EF increased by 21% (p<0.001) and stroke volume by 13% (p<0.001), while end systolic volume decreased by 23% (p<0.001). In Group 1, the increase in EF (6%) and stroke volume (8%) was also significant (p<0.05) but less pronounced than in Group 2. Physical exercise duration and walking distance increased in Group 2 by 56% and 72%, respectively. CONCLUSIONS: Noninvasive MCP treatment for eight days substantially improves cardiac function and physical performance in patients with CHF.

Microvascular response to metabolic and pressure challenge in the human coronary circulation

In vivo observations of microcirculatory behavior during autoregulation and adaptation to varying myocardial oxygen demand are scarce in the human coronary system. This study assessed microvascular reactions to controlled metabolic and pressure provocation [bicycle exercise and external counterpulsation (ECP)]. In 20 healthy subjects, quantitative myocardial contrast echocardiography and arterial applanation tonometry were performed during increasing ECP levels, as well as before and during bicycle exercise. Myocardial blood flow (MBF; ml·min(-1)·g(-1)), the relative blood volume (rBV; ml/ml), the coronary vascular resistance index (CVRI; dyn·s·cm(-5)/g), the pressure-work index (PWI), and the pressure-rate product (mmHg/min) were assessed. MBF remained unchanged during ECP (1.08 ± 0.44 at baseline to 0.92 ± 0.38 at high-level ECP). Bicycle exercise led to an increase in MBF from 1.03 ± 0.39 to 3.42 ± 1.11 (P < 0.001). The rBV remained unchanged during ECP, whereas it increased under exercise from 0.13 ± 0.033 to 0.22 ± 0.07 (P < 0.001). The CVRI showed a marked increase under ECP from 7.40 ± 3.38 to 11.05 ± 5.43 and significantly dropped under exercise from 7.40 ± 2.78 to 2.21 ± 0.87 (both P < 0.001). There was a significant correlation between PWI and MBF in the pooled exercise data (slope: +0.162). During ECP, the relationship remained similar (slope: +0.153). Whereas physical exercise decreases coronary vascular resistance and induces considerable functional capillary recruitment, diastolic pressure transients up to 140 mmHg trigger arteriolar vasoconstriction, keeping MBF and functional capillary density constant. Demand-supply matching was maintained over the entire ECP pressure range.

The development and investigation of a novel pulsatile heart assist device

Cardiovascular diseases (CVD) contributed to almost 30% of worldwide mortality; with heart failure being one class of CVD. One popular and widely available treatment for heart failure is the intra-aortic balloon pump (IABP). This heart assist device is used in counterpulsation to improve myocardial function by increasing coronary perfusion, and decreasing aortic end-diastolic pressure (i.e. the resistance to blood ejection from the heart). However, this device can only be used acutely, and patients are bedridden. The subject of this research is a novel heart assist treatment called the Chronic Intermittent Mechanical Support (CIMS) which was conceived to offer advantages of the IABP device chronically, whilst overcoming its disadvantages. The CIMS device comprises an implantable balloon pump, a percutaneous drive line, and a wearable driver console. The research here aims to determine the haemodynamic effect of balloon pump activation under in vitro conditions. A human mock circulatory loop (MCL) with systemic and coronary perfusion was constructed, capable of simulating various degrees of heart failure. Two prototypes of the CIMS balloon pump were made with varying stiffness. Several experimental factors (balloon inflation/deflation timing, Helium gas volume, arterial compliance, balloon pump stiffness and heart valve type) form the factorial design experiments. A simple modification to the MCL allowed flow visualisation experiments using video recording. Suitable statistical tests were used to analyse the data obtained from all experiments. Balloon inflation and deflation in the ascending aorta of the MCL yielded favourable results. The sudden balloon deflation caused the heart valve to open earlier, thus causing longer valve opening duration in a cardiac cycle. It was also found that pressure augmentation in diastole was significantly correlated with increased cardiac output and coronary flowrate. With an optimum combination (low arterial compliance and low balloon pump stiffness), systemic and coronary perfusions were increased by 18% and 21% respectively, while the aortic end-diastolic pressure (forward flow resistance) decreased by 17%. Consequently, the ratio of oxygen supply and demand to myocardium (endocardial viability ratio, EVR) increased between 33% and 75%. The increase was mostly attributed to diastolic augmentation rather than systolic unloading.

Modello matematico per lo studio della risposta cardiovascolare alla contropulsazione esterna

In questo lavoro di tesi si è realizzato un modello matematico con l’intento di fornire uno strumento per lo studio della risposta cardiovascolare alla contropulsazione esterna. L’ EECP (Enhanced External Counterpulsation) è un metodo non invasivo di assistenza cardiaca basato sull’applicazione di pressioni sincronizzate col ritmo cardiaco su determinate superfici corporee. I benefici della terapia su pazienti con sofferenze cardiache sono confermati dalle tabelle cliniche; rimane tuttavia non chiaro il legame diretto tra questi e la EECP. La base del lavoro è un modello della circolazione sanguigna adattato allo studio della situazione in esame e riprodotto mediante il software di calcolo Matlab. Il modello proposto e la relativa simulazione numerica permettono la visualizzazione istantanea delle modifiche che l’azione di contropulsazione apporta al flusso e alla pressione sanguigna, al fine di offrire un aiuto nella ricerca di un legame diretto tra la EECP e i benefici che questa terapia ha sul paziente.