Inotropic Changes Research Articles

Evidence of Inotropic Improvement in LVAD Patients with High I-CARS Score

<h3>Purpose</h3> A high INTERMACS Cardiac Recovery Score (I-CARS≥7) has greater likelihood of myocardial recovery in bridge-to-recovery patients compared to a low score (<7). This scoring index was limited in predicting echocardiography changes for an unselected left ventricular assist device (LVAD) population. We investigated its use in predicting pressure-volume (PV) loop changes in bridge-to-transplant patients using non-invasively derived PV loops. <h3>Methods</h3> We prospectively recruited 32 HeartWare Assist Device (HVAD) patients (mean 55.9±12.3 years, 81.3% male) and calculated their I-CARS. HVAD controller-derived parameters and oscillometric brachial pressure (SphygmoCor Xcel) were obtained to non-invasively estimate single-cycle ventricular pressure and volume. PV loops (n=77) and contractile indices were derived at pre-defined timepoints post-implant: 1, 3, 6 months (n=26, 29, 22). The trends of contractility indices, dPdtmax (peak contractility in isovolumic phase), dPdtmax/devP (sensitive to inotropic changes) and dPdtmax/LVEDV (independent of preload), were analysed according to high (≥7) vs low (<7) I-CARS. <h3>Results</h3> I-CARS was calculated in all patients (18.5% I-CARS≥7). Patients with low I-CARS were less likely to have <2 years heart failure diagnosis, more likely to have an implanted ICD and a higher pre-implant creatinine level (Table). Other demographic variables were comparable. Using a statistical linear mixed model, high I-CARS patients demonstrated a 0.50±0.15s monthly increase in dPdtmax/devP (p=0.001) and only modest changes in dPdtmax and dPdtmax/LVEDV (p=0.055, p=0.110). dPdtmax, dPdtmax/devP and dPdtmax/LVEDV remained largely unchanged in low I-CARS patients across the 6-month period. <h3>Conclusion</h3> Selective improvement in dPdtmax/devP amongst high I-CARS patients suggests strong associations between determinants of I-CARS and cardiac contractility. Larger scale studies to understand the determinants of I-CARS and its relation to inotropic improvement would inform remodelling.

Hysteretic device characteristics indicate cardiac contractile state for guiding mechanical circulatory support device use

BackgroundAcute heart failure and cardiogenic shock remain highly morbid conditions despite prompt medical therapy in critical care settings. Mechanical circulatory support (MCS) is a promising therapy for these patients, yet remains managed with open-loop control. Continuous measure of cardiac function would support and optimize MCS deployment and weaning. The nature of indwelling MCS provides a platform for attaining this information. This study investigates how hysteresis modeling derived from MCS device signals can be used to assess contractility changes to provide continuous indication of changing cardiac state. Load-dependent MCS devices vary their operation with cardiac state to yield a device–heart hysteretic interaction. Predicting and examining this hysteric relation provides insight into cardiac state and can be separated by cardiac cycle phases. Here, we demonstrate this by predicting hysteresis and using the systolic portion of the hysteresis loop to estimate changes in native contractility. This study quantified this measurement as the enclosed area of the systolic portion of the hysteresis loop and correlated it with other widely accepted contractility metrics in animal studies (n = 4) using acute interventions that alter inotropy, including a heart failure model. Clinical validation was performed in patients (n = 8) undergoing Impella support.ResultsHysteresis is well estimated from device signals alone (r = 0.92, limits of agreement: − 0.18 to 0.18). Quantified systolic area was well correlated in animal studies with end-systolic pressure–volume relationship (r = 0.84), preload recruitable stroke work index (r = 0.77), and maximum slope of left ventricular pressure (dP/dtmax) (r = 0.95) across a range of inotropic conditions. Comparable results were seen in patients with dP/dtmax (r = 0.88). Diagnostic capability from ROC analysis yielded AUC measurements of 0.92 and 0.90 in animal and patients, respectively.ConclusionsMechanical circulatory support hysteretic behavior can be well modeled using device signals and used to estimate contractility changes. Contractility estimate is correlated with other accepted metrics, captures temporal trends that elucidate changing cardiac state, and is able to accurately indicate changes in inotropy. Inherently available during MCS deployment, this measure will guide titration and inform need for further intervention.

Left atrial conduit flow rate at baseline and during exercise: an index of impaired relaxation in patients with heart failure and preserved ejection fraction

Abstract Introduction In healthy subjects, adrenergic stimulation augments left ventricular (LV) long-axis shortening/lengthening, and increases left atrial (LA) to LV intracavitary pressure gradients in early diastole. Lower increments are observed in patients with heart failure with preserved ejection fraction (HFpEF). Purpose We hypothesized that exercise in HFpEF would similarly impair passive LV filling in early-mid diastole, during conduit flow from pulmonary veins. Methods Twenty HFpEF patients (67.8±9.8 years; 11 women), diagnosed according to 2007 ESC recommendations, underwent ramped semi-supine bicycle exercise to submaximal target heart rate (∼100) or symptoms. Seventeen asymptomatic subjects (64.3±8.9 years; 7 women) served as controls. Simultaneous LA and LV volumes were measured from pyramidal 3D echocardiographic full-volume datasets acquired from apical window at baseline and during stress, together with brachial arterial pressure. LA conduit function was computed, from minimum LV volume to ECG P wave, as [LV volume (time) – LV minimum volume] – [LA maximum volume – LA volume (time)] and expressed as average flow rate. The slope of the single-beat preload recruitable stroke work (PRSW) quantified LV inotropic state. Results There were divergent responses in conduit flow rate, which increased by 40% during exercise in control subjects (+17.8±37.3 ml/s) but decreased by 18% in patients with HFpEF (−9.6±42.3 ml/s) (p=0.046); increments during stress correlated with PRSW slope changes (p=0.003). Conclusion In HFpEF conduit flow rate decreases when diastolic dysfunction develops during exercise, in parallel with LV inotropic state changes, thereby contributing to impaired stroke volume reserve. Conduit flow can be measured as a marker of LV relaxation. Funding Acknowledgement Type of funding sources: None.

Measuring the systolic and the diastolic properties of single human pluripotent stem-cell cardiomyocyte for drug testing and disease modeling

Abstract Background The advent of human pluripotent stem cell–derived cardiomyocytes (hPSC-CMs) provided exciting tools for cardiovascular physiological studies, disease modeling and drug testing applications. Current platforms for studying the mechanical properties of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) as single-cells do not measure forces directly, require numerous assumptions, and cannot study cell mechanics at different loading conditions. Objective To establish a novel platform to assess the active and passive mechanical properties of single-cell hPSC-CMs at different loading conditions and to demonstrate the potential of this approach for drug testing and disease modeling applications. Methods and results To allow morphological maturation, hPSC-CMs were treated with Tri-iodo-thyronine hormone, dexamethasone and Insulin-like growth factor-1. The hPSC-CM were then lifted and attached to a highly sensitive optical-force transducer and a piezoelectric length controller and electrically-stimulated. The attached hPSC-CM remained intact and contractile allowing evaluation of their passive and active mechanical properties. Utilizing this technique, single-cell hPSC-CMs exhibited positive length-tension (Frank-Starling) relationships, and appropriate inotropic, klinotropic, and lusitropic changes in response to treatment with isoproterenol. The unique potential of the approach for drug testing and disease modeling was exemplified by treating the cells with doxorubicin (a potential cardiotoxic anti-cancer agent) and omecamtiv mecarbil (a positive ionotropic drug currently in stage 3 clinical trial). The results of these studies recapitulated the drugs' known actions to suppress (doxorubicin) and augment (omecamtiv mecarbil at low dose) cardiomyocyte contractility. Finally, novel insights were gained regarding the cellular effects of these drugs as doxorubicin treatment led to cellular mechanical alternans and high doses of omecamtiv mecarbil suppressed contractility and worsened the cellular diastolic properties. Conclusion A novel method that allows direct active and passive force measurements from single hPSC-CMs at different loading conditions for the first time was established and validated. Our results highlight the potential implications of this novel approach for pharmacological studies and disease modeling studies. Funding Acknowledgement Type of funding source: Public grant(s) – EU funding. Main funding source(s): European Research Council

Video-based assessment of drug-induced effects on contractile motion properties using human induced pluripotent stem cell-derived cardiomyocytes

IntroductionDrug-induced inotropic change is a risk factor in drug development; thus, de-risking is desired in the early stages of drug development. Unlike proarrhythmic risk assessment using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), few in vitro models were validated to predict cardiac contractility. Motion field imaging (MFI), a high-resolution block matching-based optical flow technique, was expected to possess high quantitative predictivity in the detection of contraction speed. We aimed to establish an in vitro model to assess drug-induced contractile changes using hiPSC-CMs and MFI. MethodsMFI was designed to noninvasively characterize cardiomyocyte contractile behavior by analyzing light microscope video images, and maximum contraction speed (MCS) was used as the index of contractility. Using MFI, 9 inactive compounds, 10 negative inotropes, and 10 positive inotropes were tested. Two negative chronotropes, ZD7288 and ivabradine, were also tested. To determine the sensitivity and specificity of the assay, the minimum effective concentration of the MCS was compared with the human effective total therapeutic concentration for 28 compounds in clinical use. ResultsFor 8 negative and 8 positive inotropes, the effects observed in in vivo and clinical studies were detected in MFI assay. MFI assay showed negative chronotropic changes without inotropic changes. MFI assay presented sufficient specificity (83%) and sensitivity (88%), and RNA-sequence analysis provided an insight into the relationship between occurrence of the false compounds and target gene expression. DiscussionWe demonstrated the utility of MFI assay using hiPSC-CMs to assess drug-induced contractile function. These results will facilitate the de-risking of compounds during early drug development.

The cardiac work-loop technique: An in vitro model for identifying and profiling drug-induced changes in inotropy using rat papillary muscles

The cardiac work-loop technique closely mimics the intrinsic in vivo movement and characteristics of cardiac muscle function. In this study, six known inotropes were profiled using the work-loop technique to evaluate the potential of this method to predict inotropy. Papillary muscles from male Sprague-Dawley rats were mounted onto an organ bath perfused with Krebs-Henseleit buffer. Following optimisation, work-loop contractions were performed that included an initial stabilisation period followed by vehicle control or drug administration. Six known inotropes were tested: digoxin, dobutamine, isoprenaline, flecainide, verapamil and atenolol. Muscle performance was evaluated by calculating power output during work-loop contraction. Digoxin, dobutamine and isoprenaline caused a significant increase in power output of muscles when compared to vehicle control. Flecainide, verapamil and atenolol significantly reduced power output of muscles. These changes in power output were reflected in alterations in work loop shapes. This is the first study in which changes in work-loop shape detailing for example the activation, shortening or passive re-lengthening have been linked to the mechanism of action of a compound. This study has demonstrated that the work-loop technique can provide an important novel method with which to assess detailed mechanisms of drug-induced effects on cardiac muscle contractility.

Experimental validation of the prestretch-strain relationship as a non-invasive index of left ventricular myocardial contractility.

BackgroundThe slope of the relationship between segmental PreS and total systolic shortening (S) has been proposed as a non-invasive index of left ventricular contractility. The aim of this study was to correlate this novel parameter to invasive gold standard measurements of contractility and to investigate how it is influenced by afterload.MethodsIn domestic pigs, afterload was increased by either balloon inflation in the aorta or by administration of phenylephrine while contractility was increased by dobutamine infusion. During all interventions, left ventricular pressure-volume measurements and trans-diaphragmatic two-dimensional echocardiographic images were acquired. The PreS-S slope was constructed from 18 segmental strain curves obtained by speckle tracking analysis and compared to the slope of the end systolic PV relationship (Emax) and the pre-load recruitable stroke work (PRSW).ResultsSixteen datasets of increased contractility and afterload were analyzed. During dobutamine infusion, the LV volumes decreased (p<0.05) while ejection fraction increased (p<0.05). Emax, PRSW and the slope of the intra-ventricular PreS-S relation increased significantly during dobutamine infusion. Afterload increase led to increase in systolic blood pressure (105±16mmHg vs. 138±25mmHg; p<0.01) and decrease of LV stroke volume and ejection fraction (p<0.01). The PreS-S slope was not influenced by loading conditions in concordance with the PRSW findings. The absolute values of the PreS-S slope did not correlate with Emax or PRSW. However, the change of the PreS-S slope in relation with different interventions demonstrated good correlation with changes in PRSW or Emax, (r = 0.66, p<0.05 and r = 0.69, p<0.05).ConclusionsThe slope of the PreS-S relationship is sensitive to changes in inotropy and is less load-dependent than conventional non-invasive parameters of left ventricular function. The magnitude of the change of this slope correlates well with changes in invasive contractility measurements making it an attractive parameter to assess contractile reserve or contractile changes during longitudinal follow-up of patients.

Noninvasive system using human iPSC-derived cardiomyocytes to assess drug-induced inotropic changes

Noninvasive system using human iPSC-derived cardiomyocytes to assess drug-induced inotropic changes

Safety and efficacy of levosimendan in a cardiothoracic ICU – 5 year data

Introduction Levosimedan is an intravenous inodilator drug for the treatment of acute heart failure. There is a paucity of real-life physiological data with respect to the efficacy and safety of Levosimendan. We report the 5-year experience of a Tertiary UK Cardio-thoracic Intensive Care Unit (CT ICU). Methods Data was retrospectively analysed from a single centre CT ICU patient information system (Philips ICCA). Data from all patients receiving Levosimendan who survived > 48 hours after Levosimendan infusion were analysed. Results 165 consecutive patients treated with Levosimendan were analysed between Jan 2013 and Jan 2018. Mean age 59.8±16 years, 69.7% male. Indications and associated percentages are as follows: pre cardiac surgery optimisation for patients with left ventricular dysfunction 17.6%, failure to wean off inotropic support post-cardiac surgery 23%, VA-ECMO weaning 19.4%, right ventricular (RV) support post LVAD implantation 2.4%, RV support post cardiac transplant 6% and for acutely decompensated severe chronic heart failure 31.5%. Pre and post inotropic changes with Levosimendan findings are reported in table 1. At 72 hours (a priori specified time point), Levosimendan was associated with a significant reduction in pre- and post-dosage VIS (vasopressor inotropic score) [7(0-571) vs 2(0-428), p Discussion To our knowledge this is the first report and largest review of Levosimendan experience at a tertiary UK CT ICU over a 5-year period. Levosimendan was associated with a significant reduction in Vasopressor/inotropic score at 72 hours and a relative modest increase in inotropy as measured by LVEF and CI. These data suggest measurements specific to the ventriculoarterial coupling response should help phenotype which patients could benefit from this drug.

Nerol Attenuates Ouabain-Induced Arrhythmias.

Nerol (C10H18O) is a monoterpene found in many essential oils, such as lemon balm and hop. In this study, we explored the contractile and electrophysiological properties of nerol and demonstrated its antiarrhythmic effects in guinea pig heart preparation. Nerol effects were evaluated on atrial and ventricular tissue contractility, electrocardiogram (ECG), voltage-dependent L-type Ca2+ current (ICa,L), and ouabain-triggered arrhythmias. Overall our results revealed that by increasing concentrations of nerol (from 0.001 to 30 mM) there was a significant decrease in left atrium contractile force. This effect was completely and rapidly reversible after washing out (~ 2 min). Nerol (at 3 mM concentration) decreased the left atrium positive inotropic response evoked by adding up CaCl2 in the extracellular medium. Interestingly, when using a lower concentration of nerol (30 μM), it was not possible to clearly observe any significant ECG signal alterations but a small reduction of ventricular contractility was observed. In addition, 300 μM nerol promoted a significant decrease on the cardiac rate and contractility. Important to note is the fact that in isolated cardiomyocytes, peak ICa,L was reduced by 58.9 ± 6.31% after perfusing 300 μM nerol (n=7, p<0.05). Nerol, at 30 and 300 μM, delayed the time of onset of ouabain-triggered arrhythmias and provoked a decrease in the diastolic tension induced by the presence of ouabain (50 μM). Furthermore, nerol preincubation significantly attenuated arrhythmia severity index without changes in the positive inotropism elicited by ouabain exposure. Taken all together, we may be able to conclude that nerol primarily by reducing Ca2+ influx through L-type Ca2+ channel blockade lessened the severity of ouabain-triggered arrhythmias in mammalian heart.

Calcium-overloaded sympathetic preganglionic neurons in a case of severe sepsis with anorexia nervosa.

AimWe aimed to show the status of intracellular elements in sympathetic preganglionic neurons in an autopsy case of a 55‐year‐old woman with severe sepsis and cardiac dysfunction with anorexia nervosa.MethodsOur methods include a case report and pathological examinations of autopsied tissues using synchrotron‐generated microbeam X‐ray fluorescence analysis.ResultsA case report of severe sepsis and myocardial dysfunction. The patient had sudden short cardiac arrest without arrhythmia and sequelae, and echocardiogram showed negative inotropic change. The X‐ray fluorescence analysis of autopsied tissues indicated an unusually high concentration of cytosolic calcium in sympathetic preganglionic neurons. However, there were no significant pathological findings of damage in the heart or the cardiovascular autonomic nuclei in the central nervous system.ConclusionThe data indicate that dysfunction of the sympathetic preganglionic neurons exists in a patient of severe sepsis and cardiac dysfunction with anorexia nervosa.

Influence of Vagus Nerve Stimulation parameters on chronotropism and inotropism in heart failure.

Vagus Nerve Stimulation (VNS) has been shown to be useful in heart failure patients, including antiarrhythmic effects, improvement of cardiac function and reduction of the mortality. However, the optimal configuration of VNS can be a difficult task, since there are several adjustable parameters, such as current amplitude (mA), pulse width (ms), burst frequency (Hz), number of pulses and, in the case of cardiac-triggered VNS, the delay (ms) between the R-wave and the beginning of the stimulation. The objective of this paper is to analyse the effect of these parameters, and their interaction, on the chronotropic and inotropic responses to vagal stimulation. 306 VNS sequences were tested on 12 sheep with induced heart failure. Autonomic markers of the chronotropic (changes in RR interval) and inotropic (changes in dP/dtmax) effects were extracted from the observed data. In order to analyse the influence of stimulation parameters on these markers, a sensitivity analysis method was applied. Results illustrate the strong interaction between the delay and the others parameters. The number of pulses, the current and the frequency seem to be particularly influent on chronotropism and inotropism although the effect of the frequency is highly non-linear or it depends on other parameters.

The coronary dilation effect of shen fu injection was mediated through NO.

ObjectivesShen Fu Injection (SF), which consisted of Red ginseng extraction injection (RG) and prepared aconite extraction injection (RA), is a traditional Chinese medicine mainly used for various cardiac diseases. This study is to analyse SF's effects on cardiac performance and coronary circulation. And the coronary dilating effect and mechanism of the above three injections were also explored.MethodsMature male guinea pigs were used as our animal model. We employed two types of perfusion methods (constant pressure and constant flow) in vitro, using Langendorff heart preparations to observe the cardiac function and coronary response to SF (1/200). The coronary dilation effects of the above three injections (1/800, 1/400 and 1/200) were recorded at basal coronary resting tone and when coronary vessels were pre-contracted with a thromboxane A2 analogue (U46619), in the presence or the absence of the inhibitor of nitric oxide synthesis (L-NAME, 10−4 M), the blocker of Ca2+-activated potassium channel(TEA, 10−3 M), or the blocker of adenosine triphosphate (ATP)-sensitive potassium channel (glybenclamide) (10−5 M).ResultsWhen perfused with constant pressure, SF significantly increased coronary flow, left ventricular developed pressure (LVDP) and the rate-pressure product (RPP). When perfused with constant flow, SF produced a significant reduction in the coronary perfusion pressure (CPP), LVDP and RPP. The coronary vasodilatation response of the above three injections can be reduced by L-NAME but was unaffected by TEA or glybenclamide when coronary vessels were pre-contracted with U46619 but not at resting tone. SF, RG and RA can all up-regulate eNOS expression in the human umbilical vein cells (EA.hy926).ConclusionWe demonstrated that SF does not contribute to the inotropic change of myocardium whose improvement is due to alternation of coronary flow. The coronary dilation effect of SF was mediated through RG and RA, via promoting NO release.

Test of the Usefulness of a Paradigm to Identify Potential Cardiovascular Liabilities of Four Test Articles With Varying Pharmacological Properties in Anesthetized Guinea Pigs

The evaluation of proarrhythmic and hemodynamic liabilities for new compounds remains a major concern of preclinical safety assessment paradigms. Contrastingly, albeit functional liabilities can also translate to clinical morbidity and mortality, lesser preclinical efforts are focused on the evaluation of drug-induced changes in inotrope and lusitrope, particularly in the setting of concomitant hemodynamic/arrhythmic liabilities. This study aimed to establish the feasibility of an anesthetized guinea pig preparation to assess functional liabilities in the setting of simultaneous drug-induced electrocardiographic/hemodynamic changes, by evaluating the effects of various compounds with known cardiovascular properties on direct and indirect indices of left ventricular function. In short, twenty nine male guinea pigs were instrumented to measure electrocardiograms, systemic arterial pressure, and left ventricular pressure-volume relationships. After baseline measurement, all animals were given intravenous infusions of vehicle and two escalating concentrations of either chromanol 293B (n = 8), milrinone (n = 6), metoprolol (n = 7), or nicorandil (n = 8) for 10 minutes each. In all cases, these compounds produced the expected changes. The slope of preload-recruitable stroke work (PRSW), a pressure-volume derived load independent index, was the most sensitive marker of drug-induced changes in inotropy. Among the indirect functional indices studied, only the "contractility index" (dP/dtmax normalized by the pressure at its occurrence) and the static myocardial compliance (ratio of end diastolic volume and pressure) appeared to be adequate predictors of drug-induced changes in inotropy/lusitropy. Overall, the data confirms that both electrophysiological and mechanical liabilities can be accurately assessed in an anesthetized guinea pig preparation.

The Myocardium in Mitral Regurgitation

Muscles (from the tensor tympani to the left ventricle [LV]) are in the business of generating force. In cardiac mechanics, the innate ability to generate force independently of preload is called contractility. A central tenet of cardiology is that the prognosis of most cardiac diseases is determined in large part by the health or disarray of the myocardium conferred by this property of contractility. Before the era of molecular biology, a search for the perfect index of contractility had become a Holy Grail of cardiology. Such an index would be independent of preload, afterload, and cardiac volume and mass; sensitive to changes in inotropy; reproducible; and easy to apply. Perhaps the most accurate of these is end-systolic stiffness (the modulus of systolic stress and strain),1 but the tedium of its clinical use is so daunting that it is rarely used. Thus, although dozens of indexes have been proposed, none fulfilled all of the above requisites, and the search was largely abandoned. Thus, the cardiology world has settled on ejection fraction (EF) with all of its foibles as the preferred index of cardiac function. It measures chamber …

Myocardial Inotropic Response to Progressive Exercise in Healthy Subjects

Assessment of myocardial contractile function during exercise is important in gaining an understanding of the normal mechanics of the cardiovascular responses to exercise stress. Such insights are important in identifying determinants of cardiovascular fitness in athletes as well as assessing patients with heart disease. While obtaining such measurements in the past has been challenging, recent echocardiographic developments offer promise of providing new insights into the nature and magnitude of inotropic changes during exercise. This review provides a state-of-the-art overview of these technologies in light of the current understanding of the role of myocardial contractile function in response to a bout of progressive dynamic exercise.

Frequency dependent effect of selective biphasic left vagus nerve stimulation on heart rate and arterial pressure

Activation of the parasympathetic pathway leads to negative chronotropic, dromotropic, and inotropic changes of heart function. The ability to selectively stimulate certain superficial compartments of peripheral nerves has been demonstrated previously. The aim of the present study was to find a clinically acceptable selective biphasic vagus nerve stimulation technique, which could allow gradual regulation of heart rate and systemic arterial pressure. In two patients, the left vagus nerve was stimulated with a combination of quasi-trapezoidal cathodic and rectangular anodic current pulses with different stimulation frequencies (10Hz, 20Hz, 30Hz) and increasing current. The heart rate and systemic arterial pressure decreased with increasing current at all different stimulation frequencies (p<0.05). The heart rate and arterial pressure response was more gradual with 10Hz compared to 20Hz/30Hz vagus nerve stimulation (p<0.05). In conclusion, selective vagus nerve stimulation, with a combination of quasi-trapezoidal cathodic and rectangular anodic current pulses at 10Hz, offers gradual heart rate and systolic arterial pressure control.

Dynamic correction for parallel conductance, GP, and gain factor, α, in invasive murine left ventricular volume measurements

The conductance catheter technique could be improved by determining instantaneous parallel conductance (G(P)), which is known to be time varying, and by including a time-varying calibration factor in Baan's equation [alpha(t)]. We have recently proposed solutions to the problems of both time-varying G(P) and time-varying alpha, which we term "admittance" and "Wei's equation," respectively. We validate both our solutions in mice, compared with the currently accepted methods of hypertonic saline (HS) to determine G(P) and Baan's equation calibrated with both stroke volume (SV) and cuvette. We performed simultaneous echocardiography in closed-chest mice (n = 8) as a reference for left ventricular (LV) volume and demonstrate that an off-center position for the miniaturized pressure-volume (PV) catheter in the LV generates end-systolic and diastolic volumes calculated by admittance with less error (P < 0.03) (-2.49 +/- 15.33 microl error) compared with those same parameters calculated by SV calibrated conductance (35.89 +/- 73.22 microl error) and by cuvette calibrated conductance (-7.53 +/- 16.23 microl ES and -29.10 +/- 31.53 microl ED error). To utilize the admittance approach, myocardial permittivity (epsilon(m)) and conductivity (sigma(m)) were calculated in additional mice (n = 7), and those results are used in this calculation. In aortic banded mice (n = 6), increased myocardial permittivity was measured (11,844 +/- 2,700 control, 21,267 +/- 8,005 banded, P < 0.05), demonstrating that muscle properties vary with disease state. Volume error calculated with respect to echo did not significantly change in aortic banded mice (6.74 +/- 13.06 microl, P = not significant). Increased inotropy in response to intravenous dobutamine was detected with greater sensitivity with the admittance technique compared with traditional conductance [4.9 +/- 1.4 to 12.5 +/- 6.6 mmHg/microl Wei's equation (P < 0.05), 3.3 +/- 1.2 to 8.8 +/- 5.1 mmHg/microl using Baan's equation (P = not significant)]. New theory and method for instantaneous G(P) removal, as well as application of Wei's equation, are presented and validated in vivo in mice. We conclude that, for closed-chest mice, admittance (dynamic G(P)) and Wei's equation (dynamic alpha) provide more accurate volumes than traditional conductance, are more sensitive to inotropic changes, eliminate the need for hypertonic saline, and can be accurately extended to aortic banded mice.

Parameters of ventricular contractility in mice: influence of load and sensitivity to changes in inotropic state

We examined the relative usefulness of parameters to determine left ventricular contractility in mice invasively. The optimal parameter must be sensitive to changes in inotropy and insensitive to changes in loading. Furthermore, it should be able to confirm or reject the hypothesis of altered myocardial contractility after a limited number of experiments. Left ventricular function was assessed in closed-chest mice using a microtip pressure-conductance catheter at baseline and after increases in preload, afterload, or contractility. The parameters are differentially influenced by loading conditions and inotropic state. Only those parameters that could differentiate between basal and increased contractility with a power of 0.85 in ten or less experiments were considered useful. Ejection fraction, preload-recruitable stroke work (PRSW), and dP/dt(max)/V (ed) could demonstrate the smallest changes in contractility. Stroke work, maximal power and dP/dt(max) were most influenced by preload. End-systolic elastance, ejection fraction, and stroke work were afterload-dependent. Dividing the magnitude of the effect of inotropic stimulation to that of load changes gives an index for the usefulness for each parameter. A high ratio indicates that the change in parameter reflects inotropic rather than load change. This ratio was highest for PRSW, which seems to be the best parameter for judging contractility differences in mice.

Biphasic changes in cardiac excitation-contraction coupling early in chronic alcohol exposure

Although the negative inotropic effects of both acute and chronic ethanol (EtOH) exposure are well known, little is known concerning the acute-to-chronic transition of such effects. In this study, our objective was to address this question by detailing the effects that acute EtOH exposure induces on cellular excitation-contraction (EC) coupling and, subsequently, comparing whether and how such changes translate to the early chronic EtOH condition in a rat model known to develop alcohol-induced cardiomyopathy. Acute EtOH exposure, as formerly reported, indeed induced dose-dependent negative inotropic changes in cellular EC coupling, manifest as reductions in cell shortening, Ca2+ transient amplitude, Ca2+ decay rate, and sarcoplasmic reticulum Ca2+ content of isolated rat ventricular cardiac myocytes. Supplementary to this, we found Ca2+ spark character not to be significantly affected by acute EtOH exposure. In contrast, the results obtained from cardiac myocytes isolated from rats fed a diet containing approximately 9% (vol/vol) EtOH for 1 mo revealed changes in these parameters reflecting positive inotropy, whereas at 3 mo, these parameters again reflected negative inotropy similar but not identical to that induced by acute EtOH exposure. No significant changes were evident at either 1- or 3-mo chronic EtOH administration in echocardiographic parameters known to be perturbed in alcoholic cardiomyopathy (ACM), thus indicating that we were examining an asymptomatic stage in chronic EtOH administration consistent with an acute-to-chronic transition phase. Continued study of such transition-phase events should provide important insight into which molecular-cellular components of EC coupling play pivotal roles in EtOH-induced disease processes, such as ACM.