Use of a conductance (volume) catheter and transient inferior vena caval occlusion for rapid determination of pressure-volume relationships in man

Measurement of cardiac function using pressure-volume conductance catheter technique in mice and rats

Ventricular pressure-volume relationships have become well established as the most rigorous and comprehensive ways to assess intact heart function. Thanks to advances in miniature sensor technology, this approach has been successfully translated to small rodents, allowing for detailed characterization of cardiovascular function in genetically engineered mice, testing effects of pharmacotherapies and studying disease conditions. This method is unique for providing measures of left ventricular (LV) performance that are more specific to the heart and less affected by vascular loading conditions. Here we present descriptions and movies for procedures employing this method (anesthesia, intubation and surgical techniques, calibrations). We also provide examples of hemodynamics measurements obtained from normal mice/rats, and from animals with cardiac hypertrophy/heart failure, and describe values for various useful load-dependent and load-independent indexes of LV function obtained using different types of anesthesia. The completion of the protocol takes 1-4 h (depending on the experimental design/end points).

Multimodal evaluation of in vivo magnetic resonance imaging of myocardial restoration by mouse embryonic stem cells

OBJECTIVE

Mouse embryonic stem cells have demonstrated potential to restore infarcted myocardium after acute myocardial infarction. Although the underlying mechanism remains controversial, magnetic resonance imaging has provided reliable in vivo assessment of functional recovery after cellular transplants. Multimodal comparison of the restorative effects of mouse embryonic stem cells and mouse embryonic fibroblasts was performed to validate magnetic resonance imaging data and provide mechanistic insight.

METHODS

SCID-beige mice (n = 55) underwent coronary artery ligation followed by injection of 2.5 x 10(5) mouse embryonic stem cells, 2.5 x 10(5) mouse embryonic fibroblasts, or normal saline solution. In vivo magnetic resonance imaging of myocardial restoration by mouse embryonic stem cells was evaluated by (1) in vivo pressure-volume loops, (2) in vivo bioluminescence imaging, and (3) ex vivo TaqMan (Roche Molecular Diagnostics, Pleasanton, Calif) polymerase chain reaction and immunohistologic examination.

RESULTS

In vivo magnetic resonance imaging demonstrated significant improvement in left ventricular ejection fraction at 1 week in the mouse embryonic stem cell group. This finding was validated with (1) pressure-volume loop analysis demonstrating significantly improved systolic and diastolic functions, (2) bioluminescence imaging and polymerase chain reaction showing superior posttransplant survival of mouse embryonic stem cells, (3) immunohistologic identification of cardiac phenotype within engrafted mouse embryonic stem cells, and (4) polymerase chain reaction measuring increased expressions of angiogenic and antiapoptotic genes and decreased expressions of antifibrotic genes.

CONCLUSION

This study validates in vivo magnetic resonance imaging as an effective means of evaluating the restorative potential of mouse embryonic stem cells.

Investigation of mouse conductance catheter position deviation effects on volume measurements by finite element models

The conductance catheter system is used to measure the instantaneous ventricular conductance, and real-time ventricular volumes is then determined by converting the measured conductance to volume. In fact, two different conductance-to-volume conversion equations for conductance catheters have been proposed, the Baan's classic equation and Wei's nonlinear equation. The accuracy of this volume estimation method is limited by several factors, such as the deviation of the catheter position inside the ventricle. The effects of the mouse catheter radial and longitudinal position deviations on the measured conductance are investigated with finite element models. Moreover, the capacities of the two conversion equations to calibrate the error induced by the catheter position variation are evaluated and compared. According to the simulation results, the error-calibrated capacity of the nonlinear conversion equation is better.

Volume catheter parallel conductance varies between end-systole and end-diastole

In order for the conductance catheter system to accurately measure instantaneous cardiac blood volume, it is necessary to determine and remove the contribution from parallel myocardial tissue. In previous studies, the myocardium has been treated as either purely resistive or purely capacitive when developing methods to estimate the myocardial contribution. We propose that both the capacitive and the resistive properties of the myocardium are substantial, and neither should be ignored. Hence, the measured result should be labeled admittance rather than conductance. We have measured the admittance (magnitude and phase angle) of the left ventricle in the mouse, and have shown that it is measurable and increases with frequency. Further, this more accurate technique suggests that the myocardial contribution to measured admittance varies between end-systole and end-diastole, contrary to previous literature. We have tested these hypotheses both with numerical finite-element models for a mouse left ventricle constructed from magnetic resonance imaging images, and with in vivo admittance measurements in the murine left ventricle. Finally, we propose a new method to determine the instantaneous myocardial contribution to the measured left ventricular admittance that does not require saline injection or other intervention to calibrate.

Impact of heart rate on mechanical dyssynchrony and left ventricular contractility in patients with heart failure and normal QRS duration

AIMS

The quantification of mechanical dyssynchrony has important diagnostic value and may help to determine optimal therapy in heart failure (HF). We hypothesized that mechanical dyssynchrony may be augmented at increased heart rates in patients with HF and normal QRS duration.

METHODS AND RESULTS

From online segmental conductance catheter signals, we derived indices to quantify temporal and spatial aspects of mechanical dyssynchrony during systole in 20 control subjects, 20 HF patients with normal QRS duration, and 12 HF patients with complete left bundle branch block (CLBBB). Data were collected at baseline, and then following a 40 bpm increase in heart rate induced by right atrial pacing. Mechanical dyssynchrony in HF patients with normal QRS duration or CLBBB was higher than that found in control subjects. In HF patients with normal QRS duration, mechanical dyssynchrony increased from 37.4+/-4.8% at baseline to 43.2+/-4.4% with increased heart rate (p<0.01), the resultant degree of mechanical dyssynchrony was similar to that at baseline in the HF patients with CLBBB. Increased heart rate did not affect dyssynchrony in the control patients.

CONCLUSION

Mechanical dyssynchrony was augmented as heart rate increased by right atrial pacing in patients with HF and normal QRS duration.

Evidence of time-varying myocardial contribution by in vivo magnitude and phase measurement in mice

Cardiac volume can be estimated by a conductance catheter system. Both blood and myocardium are conductive, but only the blood conductance is desired. Therefore, the parallel myocardium contribution should be removed from the total measured conductance. Several methods have been developed to estimate the contribution from myocardium, and they only determine a single steady state value for the parallel contribution. Besides, myocardium was treated as purely resistive or mainly capacitive when estimating the myocardial contribution. We question these assumptions and propose that the myocardium is both resistive and capacitive, and its contribution changes during a single cardiac cycle. In vivo magnitude and phase experiments were performed in mice to confirm this hypothesis.

Continuous ejection fraction estimation by model-based analysis of an aortic pressure waveform: comparison to echocardiography

Left ventricular ejection fraction (EF) is perhaps the most clinically significant index of global ventricular function. EF is measured in clinical practice using imaging methods such as non-invasive echocardiography. However, imaging methods generally require a skilled operator and expensive equipment. Thus, EF is not sufficiently monitored. To this end, we have recently developed a novel technique to continuously (i.e., automatically) estimate EF by model-based analysis of an aortic pressure waveform. Here, we review the technique and present its evaluation with respect to reference echocardiography measurements from three dogs during diverse interventions. We report an overall EF error of only 8.3%. With further successful testing, the technique may ultimately be utilized for continuous EF monitoring in research and clinical settings in which an aortic catheter is employed.

The effect of lung inflation on absolute ventricular volume measurement by conductance

BACKGROUND

Conductance catheter in vivo ventricular volume measurements during lung ventilation may provide important information on left ventricular (LV) function. Breathing potentially may alter parallel conductance (V(c)), complicating interpretation of the conductance-derived volume signals. The effects of controlled positive pressure lung inflation (PPLI) on measured parallel conductance with dual-field conductance volumetry were investigated.

METHODS

Eight anaesthetized pigs were instrumented with an LV dual-field conductance volumetry catheter. V(c) was measured repeatedly, using the hypertonic saline injection method, at three different levels of lung insufflation: continuous positive airway pressure (PPLI) 0, 5, and 10 cm H(2)O.

RESULTS

V(c)s measured at PPLI 0, 5 and 10 cm H(2)O were 70.9 +/- 4.8, 70.7 +/- 5.5 and 70.5 +/- 5.9 ml, respectively. The corresponding uncalibrated end-diastolic volumes (EDV(u)) were 115.5 +/- 7.1, 117.0 +/- 7.5 and 117.5 +/- 7.7 ml, respectively. Mean coefficients of variance for V(c) and EDV(u) at all three PPLI levels were 3.8% and 1.25%, respectively.

DISCUSSION

Several levels of PPLI demonstrated no systematic change in parallel conductance for LV dual-field conductance volume signal. We concluded that lung inflation at these levels does not generate changes in V(c).

Force- and relaxation-frequency relations in patients with diastolic heart failure

BACKGROUND

Chronotropic effects on myocardial contractility (the positive force-frequency relation) and relaxation (the positive relaxation-frequency relation) are impaired in patients with congestive heart failure and depressed left ventricular (LV) ejection fraction (systolic heart failure [SHF]). However, the force- and relaxation-frequency relation and LV-arterial coupling in patients with diastolic heart failure (DHF) has not been fully investigated.

METHODS AND RESULTS

To examine inotropic and lusitropic responsiveness to atrial pacing, LV pressure-volume relations were measured using a conductance catheter and microtip manometer in patients with DHF (n = 18) and SHF (n = 11). In patients with SHF, an increase in heart rate by 40 beat/min did not affect LV end-systolic elastance (Ees), which reflects LV contractility, or the time constant of LV relaxation. By contrast, in patients with DHF, an increase in heart rate by 40 beat/min significantly enhanced Ees (2.1 vs 2.9 mm Hg/mL, P < .05) but not the time constant. Furthermore, LV-arterial coupling, quantified as Ees/arterial elastance, was impaired during pacing in patients with DHF (1.1 vs 0.8, P < .05) as well as SHF.

CONCLUSIONS

In patients with DHF, the force-frequency relation was preserved, but the relaxation-frequency relation was impaired. Furthermore, LV-arterial coupling was impaired as heart rate increased, which may be related to the impaired LV function. These results suggest that the impaired relaxation-frequency relation and exacerbated LV-arterial coupling during tachycardia may be an important therapeutic target in patients with DHF.

Left ventricular dyssynchrony in patients with heart failure: pathophysiology, diagnosis and treatment

The number of patients with chronic heart failure is increasing rapidly in the Western world. Despite the introduction of new pharmacologic therapies, the prognosis of these patients remains poor. Left ventricular (LV) dyssynchrony is a frequently observed feature in patients with heart failure, and is recognized as an important predictor of poor outcome if left untreated. The presence of LV dyssynchrony leads to inefficient LV contraction with a decreased cardiac output. Moreover, patients with LV dyssynchrony are at increased risk of adverse cardiac events. New therapeutic options targeted at restoring normal mechanical synchrony, such as cardiac resynchronization therapy, have been shown to improve clinical symptoms and prognosis in patients with heart failure. The beneficial effects of cardiac resynchronization therapy are predominantly mediated by this treatment's ability to reduce LV dyssynchrony. Given these results, adequate identification of LV dyssynchrony in patients with heart failure is of paramount importance. Several new imaging techniques are proving useful for diagnosis of LV dyssynchrony. In particular, advanced echocardiographic techniques (e.g. tissue Doppler imaging) and conductance catheter techniques are two accurate methods for quantification of LV dyssynchrony. In this review, we discuss the pathophysiology, diagnosis and treatment of LV dyssynchrony in patients with heart failure.

Coronary vasospasm–induced acute diastolic dysfunction in a patient with Raynaud’s phenomenon

We present the case of a patient with severe dyspnea and Raynaud's phenomenon. We could clarify, using invasive techniques including left ventricular conductance catheterization and coronary ergonovine provocation, that isolated diastolic dysfunction induced by coronary vasospasm were responsible for the symptoms. Systolic function was not affected. Short-term infusions with the prostacyclin analogue iloprost, known to act as a disease-modifying agent in patients suffering from Raynaud's phenomenon, led to an improvement of cardiac function. Thus, episodes of dyspnea in patients with Raynaud's phenomenon might be also interpreted as a coronary ischemia equivalent, which may belong to a visceral form of Raynaud's phenomenon and which are sensitive to iloprost infusions.

Ventriculovascular coupling in systolic and diastolic heart failure

Pressure-volume analysis has provided critical insight into ventricular mechanics, and it has elucidated the underlying mechanisms of heart failure (HF). Renewed interest in ventriculovascular coupling, the interaction of the left ventricle and the arterial system, has developed from recent investigations focusing on the importance of heart rate control in systolic HF, blood pressure lability in the elderly, and acute pulmonary edema in patients with HF and a normal ejection fraction. These data suggest that abnormal ventriculovascular coupling may be an additional pathophysiologic mechanism underlying the development of HF with a normal ejection fraction and may provide a target for novel therapies.

Intramyocardial injection of skeletal myoblasts: long-term follow-up with pressure–volume loops

The human heart has a limited capacity for self-repair because, unlike most other cells, cardiomyocytes do not regenerate. Therefore, if a substantial number of myocytes is lost after a myocardial infarction, the performance of the heart may become severely limited, leading to a condition of heart failure. Recently, cell transplantation has emerged as a potential therapy for patients with end-stage heart failure. Of the various cell types being investigated for this purpose, skeletal myoblasts are an attractive option, because they are readily available from muscle biopsies and, if autologous cells are used, immunosuppression is not required and ethical issues are avoided. Several studies have shown that the cells can survive and differentiate after transplantation, and promising clinical results have been reported. However, effects of this therapy on left ventricular function remain largely unknown. In the present study, we investigated the long-term hemodynamic effects of intramyocardial injection of autologous skeletal myoblasts in patients with ischemic heart failure. Our findings indicate hemodynamic improvement after follow-up for up to 1 year, which is especially promising in view of the expected decline in left ventricular function in these patients.

Effects of human atrial natriuretic peptide on cardiac function and hemodynamics in patients with high plasma BNP levels

Both atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) bind preferentially to the natriuretic peptide A receptor. Therefore, we hypothesized that the positive inotropic and lusitropic effects of ANP might be blunted in patients with moderate congestive heart failure and high BNP levels. Micromanometers and conductance catheters were used to obtain relatively load-insensitive left ventricular pressure-volume analysis in order to compare the myocardial and load-altering actions of ANP in 20 patients with low and high plasma BNP levels. In the low-BNP group (plasma BNP levels <230 pg/ml), ANP infusion significantly decreased end-systolic pressure and end-diastolic pressure and volume, increased end-systolic elastance, and shortened left ventricular relaxation. By contrast, in the high-BNP group (plasma BNP levels >230 pg/ml), the effect of ANP infusion on LV contractility was blunted but its beneficial effects on LV diastolic function and LV-arterial coupling remained. Thus, ANP infusion may improve LV diastolic function even in patients with moderate heart failure and high plasma BNP levels.

Continuous left ventricular ejection fraction monitoring by central aortic pressure waveform analysis

Left ventricular ejection fraction (EF) is perhaps the most clinically significant index of global ventricular function. EF is measured in clinical practice via imaging methods such as echocardiography. However, these methods generally require a well-trained operator and expensive capital equipment. Thus, EF measurements are only obtained in the clinical setting and are usually made few and far between. To expand the measurement of this critical hemodynamic variable, our overarching hypothesis is that EF may be continuously (i.e., automatically) monitored by mathematical analysis of routinely measured blood pressure waveforms. Here, we introduce a novel technique for estimating the absolute EF by model-based analysis of only a central aortic pressure (CAP) waveform. We then demonstrate the validity of the technique with respect to five conscious dogs in which reference EF was independently measured before and after chronic pacing induced heart failure. With further successful testing, the technique may potentially be utilized for continuous EF monitoring in research and clinical settings in which an aortic catheter is employed as well as for ambulatory EF monitoring in conjunction with recently developed implantable devices for measuring CAP.

Ventriculovascular coupling in systolic and diastolic heart failure

Pressure-volume analysis has provided critical insight into ventricular mechanics, and it has elucidated the underlying mechanisms of heart failure (HF). Renewed interest in ventriculovascular coupling, the interaction of the left ventricle and the arterial system, has developed from recent investigations focusing on the importance of heart rate control in systolic HF, blood pressure lability in the elderly, and acute pulmonary edema in patients with HF and a normal ejection fraction. These data suggest that abnormal ventriculovascular coupling may be an additional pathophysiological mechanism underlying the development of HF with a normal ejection fraction and may provide a target for novel therapies.

Strut chordal-sparing mitral valve replacement preserves long-term left ventricular shape and function in pigs

OBJECTIVE

Mitral valve replacement with preservation of the entire subvalvular apparatus entails superior postoperative left ventricular function compared with other techniques. However, this option is often not possible because of valve pathology. We hypothesized that preservation of only 4 mitral valve secondary ("strut") chordae would be functionally and geometrically equivalent to total valve preservation in the long-term setting. In a porcine mitral valve replacement model we investigated the long-term effects of 3 surgical techniques on left ventricular function and geometry: (1) total preservation of the native valve, (2) strut chordal preservation, and (3) total excision of the subvalvular apparatus.

METHODS

Forty 60-kg pigs were randomized to 1 of the 3 techniques. Global and regional left ventricular function and dimensions were assessed with cardiovascular magnetic resonance and conductance catheter 90 days after mitral valve replacement. Groups were compared by multivariate analysis of variance.

RESULTS

There was no overall difference between groups 1 and 2. Group 3 animals had (1) greater base-apex diastolic and systolic lengths, and smaller short-axis diameters, and (2) lower sphericity indices, and greater base-apex and short-axis fractional shortening than groups 1 and 2. Regional analysis showed slimming and elongation to occur primarily in the basal left ventricular segments. Left ventricular contractility and hemodynamic parameters did not differ between groups.

CONCLUSIONS

Strut chordal preservation was equivalent to total valve preservation during mitral valve replacement, whereas total chordal resection caused significant left ventricular slimming with compensatory increases in fractional shortening. Therefore, to preserve left ventricular geometry, special attention must be paid to maintain the valvular-ventricular continuity through the strut chordae during mitral valve replacement. This concept may have important therapeutic implications for chordal-sparing mitral valve replacement.

Nonlinear conductance-volume relationship for murine conductance catheter measurement system

The conductance catheter system is a tool to determine instantaneous left ventricular volume in vivo by converting measured conductance to volume. The currently adopted conductance-to-volume conversion equation was proposed by Baan, and the accuracy of this equation is limited by the assumption of a linear conductance-volume relationship. The electric field generated by a conductance catheter is nonuniform, which results in a nonlinear relationship between conductance and volume. This paper investigates this nonlinear relationship and proposes a new nonlinear conductance-to-volume conversion equation. The proposed nonlinear equation uses a single empirically determined calibration coefficient, derived from independently measured stroke volume. In vitro experiments and numerical model simulations were performed to verify and validate the proposed equation.

Myocardial contractility in the echo lab: molecular, cellular and pathophysiological basis

In the standard accepted concept, contractility is the intrinsic ability of heart muscle to generate force and to shorten, independently of changes in the preload or afterload with fixed heart rates. At molecular level the crux of the contractile process lies in the changing concentrations of Ca²⁺ ions in the myocardial cytosol. Ca²⁺ ions enter through the calcium channel that opens in response to the wave of depolarization that travels along the sarcolemma. These Ca²⁺ ions "trigger" the release of more calcium from the sarcoplasmic reticulum (SR) and thereby initiate a contraction-relaxation cycle.

In the past, several attempts were made to transfer the pure physiological concept of contractility, expressed in the isolated myocardial fiber by the maximal velocity of contraction of unloaded muscle fiber (Vmax), to the in vivo beating heart. Suga and Sagawa achieved this aim by measuring pressure/volume loops in the intact heart: during a positive inotropic intervention, the pressure volume loop reflects a smaller end-systolic volume and a higher end-systolic pressure, so that the slope of the pressure volume relationship moves upward and to the left. The pressure volume relationship is the most reliable index for assessing myocardial contractility in the intact circulation and is almost insensitive to changes in preload and after load. This is widely used in animal studies and occasionally clinically. The limit of the pressure volume relationship is that it fails to take into account the frequency-dependent regulation of contractility: the frequency-dependent control of transmembrane Ca²⁺ entry via voltage-gated Ca2⁺ channels provides cardiac cells with a highly sophisticated short-term system for the regulation of intracellular Ca²⁺ homeostasis. An increased stimulation rate increases the force of contraction: the explanation is repetitive Ca²⁺ entry with each depolarization and, hence, an accumulation of cytosolic calcium. As the heart fails, there is a change in the gene expression from the normal adult pattern to that of fetal life with an inversion of the normal positive slope of the force-frequency relation: systolic calcium release and diastolic calcium reuptake process is lowered at the basal state and, instead of accelerating for increasing heart rates, slows down. Since the force-frequency relation uncovers initial alteration of contractility, as an intermediate step between normal and abnormal contractility at rest, a practical index to measure it is mandatory.

Measuring end-systolic elastance for increasing heart rates is impractical: increasing heart rates with atrial pacing has to be adjunct to the left ventricular conductance catheter, to the left ventricular pressure catheter, to the vena cava balloon, and to afterload changes. Furthermore, a noninvasive index is needed. Noninvasive measurement of the pressure/volume ratio for increasing heart rates during stress in the echo lab could be the practical answer to this new clinical demand in the current years of a dramatic increase in the number of heart failure patients.

Assessment of systolic and diastolic ventricular properties via pressure-volume analysis: a guide for clinical, translational, and basic researchers

Assessment of left ventricular systolic and diastolic pump properties is fundamental to advancing the understanding of cardiovascular pathophysiology and therapeutics, especially for heart failure. The use of end-systolic and end-diastolic pressure-volume relationships derived from measurements of instantaneous left ventricular pressure-volume loops emerged in the 1970s as a comprehensive approach for this purpose. As invasive and noninvasive techniques for measuring ventricular volume improved over the past decades, these relations have become commonly used by basic, translational, and clinical researchers. This review summarizes 1) the basic concepts underlying pressure-volume analysis of ventricular and myocardial systolic and diastolic properties, 2) deviations from ideal conditions typically encountered in real-life applications, 3) how these relationships are appropriately analyzed, including statistical analyses, and 4) the most common problems encountered by investigators and the appropriate remedies. The goal is to provide practical information and simple guidelines for accurate application and interpretation of pressure-volume data as they pertain to characterization of ventricular and myocardial properties in health and disease.

Nitroglycerin improves left ventricular relaxation by changing systolic loading sequence in patients with excessive arterial load

Nitroglycerin abbreviates left ventricular (LV) relaxation through improved hemodynamics as well as by direct actions on the myocardium. The aim of this study was to examine whether the changing systolic loading sequence during nitroglycerin administration affects LV relaxation in patients with excessive arterial load. By use of a conductance catheter with microtip manometer, the effects of intravenous nitroglycerin (0.3-0.5 microg/kg/min) on LV function and hemodynamics were examined in 39 patients with various degrees of LV contractility. Patients were divided into two groups according to LV-arterial coupling, the ratio of end-systolic elastance (Ees) to effective arterial elastance (Ea). In patients with Ees/Ea ratio > 1, nitroglycerin had no effect on the time to peak force or on the time constant of LV relaxation (tau). On the other hand, in patients with Ees/Ea < 1, which represented excessive arterial load, nitroglycerin significantly shortened the time to peak force, shifted the peak of the loading sequence from late to early systole, and significantly decreased tau without any changes in Ees. Thus, nitroglycerin improved LV relaxation in patients with excessive arterial load partly by changing the systolic loading sequence.

Noninvasive assessment of left ventricular contractility by pacemaker stress echocardiography

BACKGROUND

Estimating contractility of the left ventricle with noninvasive techniques is an important yet elusive goal. Positive inotropic interventions are mirrored by smaller end-systolic volumes and higher end-systolic pressures. An increased heart rate progressively increases the force of ventricular contraction (Bowditch treppe or staircase phenomenon).

AIM

To assess the feasibility of a noninvasive estimation of force-frequency relation (FFR) during pacing stress in the echo lab in patients with permanent pacemaker (PM).

METHODS

Transthoracic stress pacing echocardiography was performed in 26 patients with a permanent pacemaker (age 69+/-11 years; 21 men, 5 women). Seven patients had normal function at baseline and during stress ("normals"); eight had angiographically assessed coronary artery disease (three with and five without induced ischemia with stress echo); eleven patients had dilated cardiomyopathy (DC). To build the FFR, the force was determined at different steps as the ratio of the systolic pressure (SP, cuff sphygmomanometer)/end-systolic volume index (ESV, biplane Simpson rule/body surface area). Heart rate was determined from ECG.

RESULTS

The absolute value of the FFR slope was highest in controls and lowest in DC patients. A flat-downsloping FFR was found in 12/19 patients but not for normals (p<0.01).

CONCLUSIONS

Noninvasive pacemaker stress echocardiography (PASE) is a simple and efficient option to assess left ventricular (LV) contractility in patients with permanent pacemaker.

Change in filling pattern with preload reduction reflects left ventricular relaxation

BACKGROUND

The early diastolic mitral valve pressure gradient and the rate of left ventricular filling are determined by the rate of left ventricular relaxation and left atrial pressure at the time of mitral valve opening. Accordingly, we hypothesized that the left ventricular filling pattern with preload reduction can be used to estimate left ventricular relaxation in patients with preserved systolic function.

METHODS

We evaluated the relationship between the logistic time constant of left ventricular relaxation and left ventricular filling pattern calculated from the time derivative of left ventricular volume using a microtipmanometer and a conductance catheter in 26 consecutive patients with preserved left ventricular ejection fraction (>45%). Left ventricular filling patterns were determined from the maximal rates of early diastolic left ventricular filling (E velocity) and atrial filling (A velocity) before and after preload reduction by inferior venal caval occlusion.

RESULTS AND CONCLUSIONS

There was no significant relationship between the logistic time constant of left ventricular relaxation and the E/A velocity ratio at baseline. However, the time constant was correlated with the E/A velocity ratio after venal caval occlusion (r=-0.47, p=0.02). Furthermore, the time constant was correlated with %E/A velocity change, which was defined as the rate of change of E/A before and after caval occlusion divided by E/A after caval occlusion, more significantly (r=-0.67, p<0.01) than with the E/A velocity ratio after caval occlusion. Thus, the left ventricular filling pattern with preload reduction can be used to estimate left ventricular relaxation in patients with preserved left ventricular ejection fraction.

Pressure-independent cardiac effects of angiotensin II in pigs

BACKGROUND

Angiotensin II (Ang II) is a potent vasoconstrictor with an important role in the development of cardiovascular disease. Earlier results have shown a positive acute inotropic effect of Ang II in anaesthetized pigs together with significant vasoconstriction. This investigation was designed to study cardiac effects of Ang II, when blood pressure was maintained constant by experimental means.

METHODS

Ang II (200 microg h(-1)) was infused in anaesthetized pigs (n = 10) at two different arterial blood pressures, the first determined by the effects of Ang II alone, and the second maintained at baseline blood pressure with nitroprusside. Cardiac systolic and diastolic function was evaluated by analysis of left ventricular pressure-volume relationships.

RESULTS

Heart rate, end-systolic elastance (Ees) and pre-load adjusted maximal power (PWRmax EDV(-2)) increased at both blood pressure levels, although less when blood pressure was kept constant with nitroprusside. The time constant for isovolumetric relaxation (tau(1/2)) was prolonged with Ang II alone and shortened with Ang II infused together with nitroprusside.

CONCLUSION

Ang II infusion in the pig has inotropic and chronotropic properties independent of arterial blood pressure levels, although the effects seem to be blunted by pharmacological actions of the nitric oxide donor nitroprusside.

Quantification of left ventricular mechanical dyssynchrony by conductance catheter in heart failure patients

Mechanical dyssynchrony is an important codeterminant of cardiac dysfunction in heart failure. Treatment, either medical, surgical, or by pacing, may improve cardiac function partly by improving mechanical synchrony. Consequently, the quantification of ventricular mechanical (dys)synchrony may have important diagnostic and prognostic value and may help to determine optimal therapy. Therefore, we introduced new indexes to quantify temporal and spatial aspects of mechanical dyssynchrony derived from online segmental conductance catheter signals obtained during diagnostic cardiac catheterization. To test the feasibility and usefulness of our approach, we determined cardiac function and left ventricular mechanical dyssynchrony by the conductance catheter in heart failure patients with intraventricular conduction delay ( n = 12) and in patients with coronary artery disease ( n = 6) and relatively preserved left ventricular function. The heart failure patients showed depressed systolic and diastolic function. However, the most marked hemodynamic differences between the groups were found for mechanical dyssynchrony, indicating a high sensitivity and specificity of the new indexes. Comparison of conductance catheter-derived indexes with septal-to-lateral dyssynchrony derived by tissue-Doppler velocity imaging showed highly significant correlations. The proposed indexes provide additional, new, and quantitative information on temporal and spatial aspects of mechanical dyssynchrony. They may refine diagnosis of cardiac dysfunction and evaluation of interventions, and ultimately help to select optimal therapy.

Impact of left ventricular function on the pulmonary vein Doppler spectrum: nonsimultaneous assessment with load-insensitive indices

Pulmonary vein Doppler spectrum is highly load-dependent and thus has been used to estimate left ventricular (LV) filling pressure. However, the impact of LV function on pulmonary vein Doppler spectrum remains obscure because only load-sensitive indices were studied previously. In the present study, measurements of the pulmonary vein Doppler spectrum were correlated with load-insensitive LV systolic (end-systolic elastance [Ees]) and diastolic (relaxation time constant [tau] and beta coefficient of the end-diastolic pressure volume relationship) function indices obtained from an invasive catheterization study nonsimultaneously. The peak velocity, velocity time integral, and duration of systolic forward spectrum were significantly correlated with Ees (r = 0.35, r = 0.36, and r = 0.41, respectively;P < 0.05). The pulmonary vein diastolic velocity time integral (PVDVTI) and duration of the diastolic forward spectrum were significantly correlated with Ees (r = 0.51 and r = 0.57, respectively;P < 0.01). PVDVTI was correlated with tau and the end-diastolic pressure-volume relationship (EDPVR) (r = 0.42 and r = 0.40 respectively,P < 0.05). On the other hand, the systolic fraction of the forward spectrum was significantly correlated with ejection fraction (for peak velocity,r = 0.63, P < 0.01; for velocity time integral,r = 0.37, P < 0.05) but not with Ees, and the diastolic fraction of the forward spectrum was significantly correlated with minimum pressure derivative over time (for peak velocity,r = 0.48, P < 0.05; for velocity time integral,r = 0.44, P < 0.05, respectively) but not with tau or EDPVR. In summary, the systolic and diastolic components of the pulmonary vein Doppler spectrum are affected variably by LV systolic and diastolic function, independent of the loading condition. The systolic and diastolic fraction of pulmonary vein Doppler spectrum appears to depend more on the loading condition than the LV systolic or diastolic function.

Reducing errors in parallel conductance measurement

Conductance (COND) measures left ventricle (LV) and right ventricle (RV) volume continuously during the cardiac cycle. COND measurement of the ventricle can be impaired by electrically conductive factors extrinsic to the heart that cause an artifactual increase in COND. This is known as parallel COND. A hypertonic saline injection has traditionally been used to measure parallel COND. The entry of hypertonic saline into the ventricle causes a rise (ascending region) in ventricular COND tracing, whereas its dissipation causes a fall (descending region). The hypothesis of this study is that parallel COND measurement can vary based on the region of COND tracing (ascending versus descending versus both) chosen for calculations. Parallel COND was measured in the LV (15 pigs and 5 sheep) and the RV (13 pigs and 5 sheep). In the LV, average +/- standard error of mean (SEM) parallel COND measured from the ascending region (55.4 +/- 9.2) was significantly different (p < 0.05) from the descending region and from both regions (72.2 +/- 10.3 and 66.4 +/- 9.2, respectively). Additionally, LV parallel COND measured from the descending region and from both regions were not different (p = NS; 72.2 +/- 10.3 and 66.4 +/- 9.2, respectively). In the RV, there was no significant difference (p = NS) among parallel COND calculated from ascending, descending, and both regions (102.9 +/- 8.1, 105.6 +/- 10.0, and 103.9 +/- 7.5, respectively). Average +/- SEM number of points used for parallel COND calculation (N) in the LV for each region (ascending versus descending versus both) were significantly different (p < 0.05) from one another (8 +/- 1 vs 11 +/- 1 vs 18 +/- 1). Similarly, N values used for the calculation of RV parallel COND in ascending versus descending versus both regions were significantly different (p < 0.05) from one another (6 +/- 1 vs 9 +/- 1 vs 14 +/- 1). In conclusion, there were significant differences in parallel COND calculation based on varying regions of LV COND. This was not true for the RV. To reduce errors that are caused by the differences cited here, one region should be used consistently to measure parallel COND. More study will be required to determine the optimal region of the COND tracing for the determination of parallel COND.

Continuous on-line measurement of absolute left ventricular volume by transcardiac conductance: angiographic validation in sheep

OBJECTIVE

Validation of the transcardiac conductance method for continuous, on-line measurement of absolute left ventricular volume by comparison with biplane angiography.

DESIGN

Controlled, prospective animal study.

SETTING

Catheterization laboratory of the Leiden University Medical Center.

SUBJECTS

Six anesthetized sheep.

INTERVENTIONS

Subjects were studied at baseline, during infusion of dobutamine, and during volume loading and beta blockade. In a pilot experiment, a coronary artery was occluded by a balloon, and the behavior of the transcardiac conductance signals during ischemia was tested.

MEASUREMENTS AND MAIN RESULTS

Calibration factors alpha and V(p) were determined by thermodilution and hypertonic saline dilution, respectively. Calibrated transcardiac conductance volume was compared with angiographic volume in four different hemodynamic conditions, and transcardiac conductance measurements were registered during a period of ischemia. Results showed a good linear correlation between transcardiac conductance and angiographic volume (r =.77, p <.01) with an intercept of 12.5 +/- 5.6 mL (interanimal variability, 17.8 mL) and a slope of 1.49 +/- 0.15 (interanimal variability, 0.34). Mean alpha and V(p) were 0.12 +/- 0.01 (interanimal variability, 0.07) and 104 +/- 3 mL (interanimal variability, 38 mL), respectively. V(p) did not vary significantly between conditions, and alpha varied only during propranolol (p =.04). Transcardiac conductance enabled immediate visualization of acute left ventricular volume changes during coronary occlusion in a pilot experiment.

CONCLUSIONS

Transcardiac conductance is a method to register an on-line, continuous, left ventricular volume signal, which correlates well with angiography. However, calibration factors need to be determined in individual subjects. The method appears promising to monitor absolute volume in the intensive care unit.

The cardiac effects of intracoronary angiotensin II infusion

Angiotensin II (Ang II) is a potent vasoconstrictor, which recently has been shown to also have significant inotropic effects. Previous results regarding the mechanisms of the acute inotropic effects of Ang II are not conclusive. We designed this study to investigate the local cardiac effects of intracoronary Ang II infusion in doses not affecting systemic circulation. Ang II (2.5-40 microg/h) was infused in the left coronary artery of Yorkshire pigs (n = 9) reaching calculated intracoronary Ang II concentrations of 842 +/- 310, 3342 +/- 1238, and 12448 +/- 4393 pg/mL, respectively. Cardiac systolic and diastolic function was evaluated by analysis of the left ventricular pressure-volume relationship. Coronary flow was measured by using a coronary sinus catheter and the retrograde thermodilution technique. No significant changes were seen in the systolic and diastolic function variables of heart rate, end-systolic elastance, preload recruitable stroke work, the time constant for isovolumetric relaxation, or in coronary vascular resistance and flow. The positive inotropic and chronotropic effects of Ang II seen in previous studies seem thus to be mediated via extracardiac actions of Ang II. Coronary vascular tone is not affected by local Ang II infusion in anesthetized pigs.

IMPLICATIONS

The positive inotropic and chronotropic effects of angiotension II (Ang II) seen in previous studies seem to be mediated via extracardiac actions of Ang II. Coronary vascular tone is not affected by local Ang II infusion in anesthetized pigs.

The effects of hypothermia on human left ventricular contractile function during cardiac surgery

OBJECTIVES

We investigated the interaction of heart rate (HR), temperature and contractility using a validated load independent method.

BACKGROUND

Temperature manipulation is an integral part of cardiac surgery, and postoperative hypothermia is extremely common. Myocardial contraction is a series of enzymatic and physico-chemical reactions that may be differentially affected by temperature.

METHODS

Ten patients undergoing coronary artery bypass grafting were studied during moderately hypothermic cardiopulmonary bypass. After conduit procurement and heparinization but before grafting, the patient was placed on cardiopulmonary bypass and rewarmed to 37 degrees C, and the left ventricle (LV) was instrumented with a conductance catheter allowing continuous pressure and volume measurement. The LV pressure volume relationship was examined to assess the contractility at 37, 35, 33 and 31 degrees C, with fixed atrial pacing (100 beats/min) in five patients and at 80 and 120 beats/min, at 33 and 37 degrees C in five patients.

RESULTS

At a HR of 100 beats/min, lower temperature resulted in a highly significant decrease in maximal elastance (100% at 37 degrees C, 29 +/- 3.5% at 31 degrees C, p < 0.0001). At 37 degrees C, increasing HR increased contractility (80 beats/min 100%, 120 beats/min 205.9%, p = 0.0021); however, at 33 degrees C contractility fell with increasing HR (80 beats/min 100%, 120 beats/min, 53.7%, p = 0.0014).

CONCLUSIONS

At normothermia LV contractility has a direct relationship with HR. In hypothermic conditions this relationship inverses. Clinical strategies maintaining higher HRs at colder temperatures result in reduced contractility. These factors are important in the management of cardiac surgical patients.

Effects of therapeutic doses of human atrial natriuretic peptide on load and myocardial performance in patients with congestive heart failure

The benefits of atrial natriuretic peptide (ANP) in patients with congestive heart failure (CHF) have been demonstrated. However, the myocardial actions of ANP remain unclear. Using relatively load-insensitive left ventricular pressure-volume analysis, the myocardial and load-altering actions of ANP in patients with moderate CHF were studied. After obtaining steady-state data using micromanometers and conductance catheters, ANP was infused in 9 patients with CHF at 0.01 and 0.1 microg/kg/min for 30 minutes, respectively. Hemodynamic variables, plasma ANP, and cyclic guanosine monophosphate (cGMP) levels were determined before and 30 minutes after each ANP infusion. ANP at 0.01 microg/kg/min increased plasma ANP and cGMP levels from 73 +/- 34 to 139 +/- 34 pg/ml and from 4 +/- 1 to 8 +/- 2 pmol/ml, respectively. ANP infusion caused a significant decrease in end-systolic pressure without any changes in heart rate. End-diastolic pressure was significantly decreased but there was no significant change in left ventricular end-diastolic volume. The time constant for isovolumetric relaxation was decreased. ANP infusion at 0.1microg/kg/min caused further decreases in end-systolic pressure, end-diastolic pressure and volume, and the time constant for isovolumetric relaxation (p <0.05) without any changes in heart rate. The slope of the end-systolic pressure-volume relation was increased from 1.3 +/- 0.2 to 1.6 +/- 0.3 mm Hg/ml (p <0.05), indicating increased contractility. Plasma ANP and cGMP levels were increased to 422 +/- 44 pg/ml and 16 +/- 3 pmol/ml, respectively. Thus, ANP infusion increased cGMP generation, decreased afterload and preload, and improved left ventricular systolic and diastolic function.

Acute effects of angiotensin II on myocardial performance

BACKGROUND

Specific angiotensin II (Ang II) receptors exist in many organs including peripheral blood vessels, cardiac myocytes and the central nervous system. This suggests multiple sites of actions for Ang II throughout the cardiovascular system. Cardiac effects of Ang II are not completely understood, though its prominent vasoconstrictor actions are well described. This study was designed to assess left ventricular function during administration of Ang II using relatively load-independent methods in a whole-animal model.

METHODS

Ang II was infused in incremental doses (0-200 microg x h(-1)) in anaesthetised instrumented pigs (n=10). Cardiac systolic and diastolic function were evaluated by analysis of the left ventricular pressure-volume relationship.

RESULTS

Heart rate (HR), mean arterial pressure (MAP) and systemic vascular resistance (SVR) increased dose-dependently with Ang II, while cardiac output (CO) remained unchanged. Systolic function indices, end-systolic elastance (Ees) and preload recruitable stroke work (PRSW), demonstrated dose-dependent increases. The diastolic function parameter tau (tau) did not change with increasing Ang II dose.

CONCLUSION

Ang II infusion caused increases in contractility indices in anaesthetised pigs in the doses used in this study. The mechanisms for these systolic function effects may be a direct myocardial effect or modulated through changes in autonomic nervous system activity.

Hypertonic saline method accurately determines parallel conductance for dual-field conductance catheter

Conversion of conductance catheter data to absolute ventricular volumes requires assessment of parallel conductance (G(P)). We determined the accuracy of GP obtained by the hypertonic saline method (G(P)saline) compared with angiographically derived GP (G(P)Angio) and quantified the variabilities of GP for the dual-field conductance catheter method in nine anesthetized sheep studied at baseline, treated with dobutamine, and subjected to volume loading and beta-blockade. G(P)saline and G(P)Angio showed an excellent linear correlation (G(P)saline = 1.002 x G(P)Angio + 0.001 Omega(-1), R2 = 0.92), and Bland-Altman analysis yielded a nonsignificant bias and narrow limits of agreement (bias +/- 2SD = 0.002 +/- 0.112 Omega(-1)). Within-animal variability of GP was very similar with both methods and was due to changes in blood conductivity rather than geometrical changes. Variability between animals was significant (26.3% of mean for G(P)saline and 25.7% for G(P)Angio) and thus warrants individual assessment. Variations during the cardiac cycle were not significantly different from zero. With biplane angiography used as gold standard, the hypertonic saline method accurately determines GP for the dual-field conductance catheter over a wide range of hemodynamic conditions.

Assessment of LV systolic function in atrial fibrillation using an index of preceding cardiac cycles

The clinical assessment of left ventricular (LV) systolic function during atrial fibrillation (AF) is unreliable and difficult because of beat-to-beat variability. We evaluated an index for the estimation of LV systolic function in AF that is based on the relationship between the preceding (R-R1) and prepreceding (R-R2) R-R intervals. LV Doppler stroke volume (SV), ejection fraction (EF), peak aortic flow rate (AoF) and the maximum value of the first derivative of the LV pressure curve (dP/dt(max)) were evaluated in 13 healthy open-chest dogs during triggered AF. All parameters showed a significantly strong positive linear relationship with the ratio of R-R1/R-R2 (r = 0.65, 0.74, 0.75, and 0.70 for SV, EF, AoF, and dP/dt(max), respectively). The calculated value of LV systolic parameters at R-R1/R-R2 = 1 in the linear regression line showed a good relationship and an agreement with the measured average value of the parameter over all cardiac cycles (SV, 12.1 vs. 12.8 ml; EF, 49.6 vs. 51.2%; AoF, 1.37 vs. 1.48 l/min; and dP/dt(max), 2,323 vs. 2,454 mmHg/s). Using the LV systolic parameters estimated at R-R1/R-R2 = 1 in the linear regression line allows the LV contractile function to be accurately and reproducibly evaluated during AF and obviates the less-reliable process of averaging multiple cardiac cycles.

Inferior vena cava occlusion catheter for pediatric patients with heart disease: for more detailed cardiovascular assessments

Traditional evaluation of cardiac function is too often limited by reliance on measurements with complex interdependence between cardiac properties and loading factors. Analysis by ventricular pressure-volume (P-V), -area (P-A), or -dimension (P-D) relations during inferior vena caval (IVC) occlusion independently quantifies ventricular properties and loading conditions, providing detailed information about cardiovascular dynamics. However, there has been no appropriate size of balloon catheter that can effectively occlude IVC of pediatric patients, hindering the application of P-V (P-A, or P-D) analysis to children with heart disease despite its potential benefit. To address this problem, we have developed a new balloon catheter for IVC occlusion in children. The catheter effectively occluded IVC in 92 pediatric patients with varying forms of heart disease who underwent cardiac catheterization, yielding end-systolic pressure-area relations. Thus a newly developed balloon catheter would contribute to establishing more accurate and detailed cardiovascular assessments in children with heart disease. Cathet Cardiovasc Intervent 2001;53:392-396.

Heart-lung interactions during positive pressure ventilation: left ventricular pressure-volume momentary response to airway pressure elevation

BACKGROUND

Left ventricular (LV) pressure and volume changes are known to occur in response to positive airway pressure (PAP). We aimed to further describe the immediate LV response to increased PAP as demonstrated in successive heart cycles with LV pressure and volume alterations. We postulated that these acute systematic LV events during institution of PAP can follow a distinct pattern that would allow calculation of parameters of systolic function, including end-systolic elastance (Ees) and preload recruitable stroke work (PRSW). We also aimed to examine the relationship of PAP-derived Ees and PRSW to the same parameters derived from vascular occlusion.

METHODS

Eight anesthetized adult pigs were studied with invasive circulatory measurements including LV pressure and volume (conductance). The PAP intervention was an airway pressure plateau of 15 cm H2O for 6 s (APP). Venous occlusion was performed by transient balloon inflation in the inferior vena cava (IVCO). Ees and PRSW were derived for each APP and IVCO intervention.

RESULTS

Central circulatory variables during APP and IVCO are reported. LV systolic function parameters could be derived from each of the heart-lung interactions during APP sequences. Ees and PRSW derived from APP showed a significant positive bias in relation to those derived from the IVCO sequence.

CONCLUSIONS

We conclude that the heart-lung interactions during APP of the magnitude and duration shown here can allow derivation of Ees and PRSW. These parameters are not interchangeable with Ees and PRSW derived from IVCO.

Validation and utility of novel volume reduction technique for determination of parallel conductance

The parallel conductance volume, created by the conductivity of structures surrounding the ventricular blood pool, can be estimated by using a saline dilution technique. This paper examines the use of a novel volume reduction method, during a standard vena caval preload reduction maneuver, as an alternative to the routinely used saline dilution method to calibrate conductance catheter measurements in the left (LV) and right ventricle (RV) of animals and humans. The serial reproducibility of both methods was examined by measurement of percent difference, and by assessing the coefficient of repeatability 1) between two measurements within the same subject, 2) between the two techniques, and 3) interobserver variability. The effect of ventricular size and contractile state on the volume reduction technique was also observed. It was essential to ensure the technique was not affected by inotropic state. The volume reduction technique and saline dilution method were repeated at three different loading states (baseline, 5, and 10 microg x kg(-1) x min(-1) of dobutamine). The coefficient of repeatability between serial measurements was similar for both the volume reduction and saline dilution methods, and good interobserver variability was demonstrated. The volume reduction technique was compared with the saline dilution technique over a large range of ventricular sizes. No significant difference was observed in the RV or LV of adult humans or in the LV of neonatal pigs and children. There was no significant effect on either the saline dilution or the volume reduction technique as the inotropic state increased. In conclusion, the volume reduction technique is neither affected by ventricular size nor contractile state, is repeatable between different observers, and can be used to substitute the saline dilution method when preload reduction of the ventricle is being employed.

Single-beat estimation of end-systolic elastance using bilinearly approximated time-varying elastance curve

BACKGROUND

Although left ventricular end-systolic elastance (E(es)) has often been used as an index of contractility, technical difficulties in measuring volume and in changing loading conditions have made its clinical application somewhat limited. By approximating the time-varying elastance curve by 2 linear functions (isovolumic contraction phase and ejection phase) and estimating the slope ratio of these, we developed a method to estimate E(es) on a single-beat basis from pressure values, systolic time intervals, and stroke volume.

METHODS AND RESULTS

In 11 anesthetized dogs, we compared single-beat E(es) with that obtained with caval occlusion. Although the decrease (but not the increase) in contractility (5.3 to 11.4 mm Hg/mL) and the change in loading conditions (3.7 to 34.0 mm Hg/mL) over wide ranges significantly altered the slope ratio, the estimation of E(es) was reasonably accurate (y=0.97 x 0.46, r=0. 929, SEE=2.1 mm Hg/mL).

CONCLUSIONS

E(es) can be estimated on a single-beat basis from easily obtainable variables by approximating the time-varying elastance curve by a bilinear function.

Pressure-volume relationships in pediatric systolic and diastolic heart failure

The left ventricular pressure-volume relationship has been used to examine ventricular systolic and diastolic function as well as to evaluate myocardial energetics and ventricular-vascular coupling. Preload, afterload and contractility can be separately examined using indices derived from simultaneous pressure and volume measurement. Due to the development of new instrumentation and diagnostic tools, these techniques now can be more readily applied to the evaluation of patients in heart failure. Indices of function can be examined on-line during diagnostic cardiac catheterization. Pharmacologic interventions can be evaluated using these methods, allowing for assessment of therapeutic interventions. Medical therapy can be optimized during these studies, allowing more effective and individualized treatment.

Right ventricular volume measurement: can conductance do it better?

The measurement of right ventricular volume will be reviewed with special reference to the conductance catheter technique. The historical development of the intracavitary impedance technique will be described along with the theory of the multielectrode conductance method. The major potential advantage of this technique is its ability to measure dynamic volume change during the cardiac cycle. This enables a real time beat to beat assessment of ventricular volume in addition to providing continuous recordings during loading manoeuvres performed on the ventricle. However, the conductance catheter technique is based on the assumption that the electric field produced by the catheter is homogeneous and parallel to the long axis of the ventricle, and the current, created by the excitation electrodes of the catheter, is contained within the ventricular cavity. The measurement of these two calibration factors (known as parallel conductance volume (V(C)) and dimensionless slope factor (alpha)), along with the effects of changes in blood resistivity and the orientation of the catheter on the measurement of absolute volume, will be described. Furthermore, some of the clinical applications of the technique in adults and children with heart disease will be outlined.

Clinical overview of the novel inotropic agent toborinone

Toborinone (OPC-18790, Otsuka Pharmaceutical Co. Ltd, 2(1H) -quinolone,6-[3-[ [3,4-dimethoxyphenyl)methyl] amino]-2-hydroxy prop oxyl]-,(.+-.)-) is a novel iv. inotropic agent. Positive inotropic effects are produced by PDE inhibition with the resulting increase in cAMP and intracellular calcium levels. Unlike other inotropic agents that increase cAMP, there is an absence of positive chronotropic effects, which are attributed to prolongation of the action potential due to blockade of delayed rectifier currents. There is also marked venous and arterial vasodilating properties. The absence of heart rate increases results in decreased myocardial oxygen consumption compared with conventional inotropes. Studies in human heart failure patients have been consistent with previous work in animal studies, confirming the effects of toborinone as being positive inotropy (relatively weak), marked arterial and venous vasodilatation and absence of increase in myocardial oxygen consumption. Data regarding safety in larger clinical trials, particularly regarding arrhythmias, is at present unavailable. This information will determine whether this agent becomes an accepted iv. therapeutic option for congestive heart failure.

Evaluation of a new transcardiac conductance method for continuous on-line measurement of left ventricular volume

OBJECTIVE

To evaluate a new, less invasive, conductance method to measure continuous on-line left ventricular volume. End-systolic and end-diastolic volumes obtained with this transcardiac conductance method were compared with simultaneous measurements using the conventional intracardiac conductance catheter.

DESIGN

Controlled animal study.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Six sheep.

INTERVENTIONS

Anesthetized sheep were instrumented and inotropic condition was varied by beta-receptor stimulation (5 microg/kg/min of dobutamine) and beta-receptor blockade (1 mg/kg of propranolol). In each condition (control, dobutamine, repeat control, propranolol), ventricular volume was varied over a wide range by gradual preload reduction using a vena caval balloon catheter.

MEASUREMENTS AND MAIN RESULTS

We compared the two methods by performing linear regression analysis on simultaneous end-systolic and end-diastolic volumes obtained during gradual caval occlusions. We statistically analyzed the intercepts, slopes, and correlation coefficients of the regression equations relating the transcardiac and conductance catheter measurements to determine the effects of interanimal variability, inotropic condition, and cardiac phase on the relationship between the two methods. The results show an excellent linear correlation between the two methods (mean intercept, -1.82+/-1.24 mL; mean slope, 0.787+/-0.024 and r2 = .94). Both slope and intercept of the relationship between the two methods show a significant interanimal and cardiac phase related variability but no significant dependence on inotropic condition.

CONCLUSIONS

The significant interanimal variability indicates that the new method requires individual calibration in each subject. However, the small variability of the regression coefficients with changes in condition indicates that after initial calibration, end-systolic and end-diastolic volume can be followed accurately even in the presence of large changes in volume and inotropic state. This new method may facilitate quantitative continuous assessment of cardiac function in clinical practice, for example, in the intensive care unit.

Computerized left ventricular pressure-volume relationships (pV-loops) using disposable angiographic tip transducer pigtail catheters

Left ventricular pressure-volume relationships expressed as pV loops could yield important hemodynamic information in the cardiac catheterization laboratory. Many clinical situations might benefit from a quantitative assessment of left ventricular function. Potential applications of pV loops include the assessment of vasoactive and inotropic drugs, balloon valvuloplasty, coronary angioplasty, and surgical treatment of valvular heart disease. For many years the clinical use of pV loops has been hindered by logistical difficulties. The ability to merge on-line concurrent digital imaging data for computation of left ventricular volume and digital left ventricular pressure wave forms obtained from high fidelity tip-transducer angiocatheters has allowed us to develop a technique which can generate pV loops during cardiac catheterization procedures. The method offers an automated measurement of left ventricular volume independent of edge detection or an interactive technique for tracing endocardial borders by a trained operator. Illustrative case studies are included to demonstrate the potential of the method during ventricular angiographic procedures. Implementation and computational time requirements of the method are discussed. The concept and the value of pV loop generation to study left ventricular performance has been known for many years. Combining digital imaging and digital physiologic data obtained with disposable tip-transducer angiocatheters with modern networking technology, the technique can more easily be applied to catheterization procedures and could enhance invasive hemodynamic assessment of left ventricular function.

Single-beat determination of preload recruitable stroke work relationship: derivation and evaluation in conscious dogs

OBJECTIVES

To derive and evaluate a method of estimating the slope (Mw) of the preload recruitable stroke work (PRSW) relationship between left ventricular stroke work (SW) and end-diastolic volume (EDV) from a single beat.

BACKGROUND

Mw is a load-insensitive index of contractile function, but its clinical application has been limited by the need to record multiple beats over a wide volume range.

METHODS

Pressure-volume loops were recorded over a variable preload and afterload range by vena caval and aortic constrictions in 12 conscious dogs instrumented with epicardial dimension transducers and micromanometers. Single-beat Mw (SBMw) was determined as the ratio SW/(EDV-Vw), where the volume-axis intercept of the PRSW relationship (Vw)(EDV at zero SW) was estimated as k x EDVB + (k - 1)LVwall, k is the ratio of the epicardial shell volumes corresponding to Vw and baseline EDV (EDVB) and LVwall is wall volume.

RESULTS

In the first six dogs, k was found to be essentially constant at 0.7, SBMw estimates were insensitive to wide preload variation, and the relationship between SBMw and multibeat Mw determined during caval and aortic constrictions did not differ significantly from the line of identity. When the same constant k value was applied to SBMw estimation in a different group of six dogs, SBMw did not differ significantly from multibeat Mw (83 +/- 12 erg x cm(-3) x 10(3) and 77 +/- 12 erg x cm(-3) x 10(3), respectively), neither changed significantly during aortic constriction and both increased significantly with calcium infusion (107 +/- 18 erg x cm(-3) x 10(3) and 95 +/- 19 erg x cm(-3) x 10(3), respectively, both p < 0.05). Single-beat Mw was less load-dependent, more reproducible and a more sensitive index of inotropic state than two previously described single-beat indexes, single-beat elastance and maximum power divided by EDV2.

CONCLUSIONS

Mw can be determined accurately from a single, steady-state beat in the normal canine heart and is sensitive to inotropic alterations while being insensitive to wide variations in preload and afterload. Single-beat Mw estimation should facilitate noninvasive, load-independent assessment of contractile function.

Acute and chronic effects of airway obstruction on canine left ventricular performance

We used a canine model of chronic obstructive sleep apnea (OSA) to examine the effects of intermittent airway occlusion during sleep on left ventricular (LV) performance. Studies were performed in four dogs. The effects of acute airway occlusion on LV pressure and volume (on a background of chronic OSA) were determined with an impedance catheter and a high fidelity manometer. In conscious animals (n = 3), experiencing spontaneous episodes of sleep, acute airway occlusion caused significant increases in LV transmural systolic pressure that were associated with increased end-systolic volume and reduced stroke volume. To determine the effects of chronic OSA on baseline LV function, two-dimensional echocardiograms were performed in conscious animals (n = 4) during unobstructed breathing before and after a 1- to 3-mo period of OSA. During chronic OSA, there was a significant decrease in LV ejection fraction as a result of increases in end-systolic volume. We conclude that in chronic OSA acute airway occlusion during sleep is associated with increases in LV afterload and decreases in fractional shortening. Chronic OSA also leads to sustained decreases in LV systolic performance that could be caused by the development of systemic hypertension and/or transient increases in LV afterload during episodes of airway obstruction.

Left ventricular chamber function during inhaled nitric oxide in patients with dilated cardiomyopathy

Inhaled nitric oxide is a potent and selective pulmonary vasodilator. However, when used in patients with congestive cardiac failure, the decrease in pulmonary vascular resistance is associated with an increase in pulmonary capillary wedge pressure (PCWP). This study examined load-independent indexes of left ventricular chamber function during inhaled nitric oxide in 10 patients with dilated cardiomyopathy (mean ejection fraction, 30.2+/-7.8%, mean +/- SD). Etiology of cardiomyopathy was idiopathic in six and ischemic in four. Pulmonary hemodynamics in seven patients revealed normal resting pulmonary vascular resistance. Chamber function was defined by recording pressure-volume loops at steady state and during inferior vena caval occlusion during inhalation of 20 ppm nitric oxide for 10 min. We found no effect of inhaled nitric oxide on steady-state left ventricular pressures, volumes, contractility (end-systolic elastance or preload recruitable stroke work), contraction duration, or active (tau, dP/dt(min)) or passive (end-diastolic pressure-volume relation) diastolic function. Right heart filling pressures did not change. We therefore conclude that 20 ppm inhaled nitric oxide does not affect left ventricular chamber function in patients with controlled heart failure. Previously described elevations in PCWP during inhaled nitric oxide are most likely due to altered left ventricular loading conditions related to secondary pulmonary hypertension in severe heart failure.

Parallel conductance estimation by hypertonic dilution method with conductance catheter: effects of the bolus concentration and temperature

The conductance catheter has gained momentum since its introduction in cardiovascular dynamics back in 1980. However, measuring errors are still blurring its clinical acceptance. The main objective here was to study the effects of the injected saline concentration and temperature on the evaluation of the parallel conductance, Gp, and thus, on the correction volume Vp. That conductance, Gp, and its associated volume, Vp, were computed using 167 saline dilution curves obtained with boluses at different concentrations and temperatures, injected in seven anesthetized closed-chest dogs. The excursion of the total conductance relative to the steady-state value during a saline maneuver showed good correlation with the injected concentration at both studied temperatures. The reference parallel volume (one reference per dog) was defined as the average value obtained with three successive maneuvers, at 6-M concentration and at body temperature; therefore, the method acted as its own reference. The variation of Vp relative to the reference value was clearly dependent on the injected concentration and on its temperature; dispersion was greater at 22 degrees C than at 40 degrees C. The variability would recognize also other causes, such as uncertainty of the extrapolation procedure and the thoracic redistribution of electrical field lines. As conclusion, it is recommended to characterize each maneuver by its concentration and temperature. Body temperature and 6-M concentration appear as the most recommendable combination for the injectate in most animals. Finally, these results intend to characterize the Vp estimation procedure in order to minimize errors. The variability of Vp, in different experimental conditions, demonstrated that both concentration and temperature are additional parameters that may modify the Gp estimate.