Influence of coronary occlusion during PTCA on end-systolic and end-diastolic pressure-volume relations in humans

Frequent cyclic variation of heart rate is associated with left ventricular diastolic dysfunction in patients without ischemia

BACKGROUND

Cyclic variation of heart rate (CVHR) associated with sleep-disordered breathing reflects cardiac autonomic responses to apneic/hypoxic stress. However, the association of CVHR with cardiac function is unclear.

METHODS

We investigated a total of 181 patients who underwent both 24-hour Holter electrocardiography (ECG) and quantitative gated single-photon emission computed tomography (SPECT) myocardial functional imaging, excluding patients with atrial fibrillation, myocardial infarction, structural heart disease, and implantable devices, from January 2017 to July 2018. The number of CVHR per hour (CVHR index) in sleeping-time Holter ECG was compared with the parameters of left ventricular (LV) systolic and diastolic functions assessed by cardiac SPECT functional imaging, peak filling rate (PFR), first-third mean filling rate (1/3 MFR), and time to peak filling rate (TTPF).

RESULTS

In all patients, the CVHR index was not associated with any parameters of cardiac functions. However, in a propensity score-matched subgroup of patients without ischemia (N = 39), the CVHR index was negatively correlated with PFR (r = -0.35, P < .05) and 1/3 MFR (r = -0.37, P < .05) but positively correlated with TTPF (r = 0.43, P < .01) and was not correlated with LV ejection fraction. Multivariate linear regression analysis revealed that high CVHR index was independently associated with LV diastolic dysfunction, even after adjusting for the relative wall thickness and LV mass index assessed by echocardiography.

CONCLUSION

These results indicate that the high frequency of CVHR in sleeping time is associated with LV diastolic dysfunction in nonischemic patients, irrespective of LV geometry.

Model-Based Quantification of Left Ventricular Diastolic Function in Critically Ill Patients with Atrial Fibrillation from Routine Data: A Feasibility Study

Introduction

Left ventricular diastolic dysfunction (LVDD) and atrial fibrillation (AF) are connected by pathophysiology and prevalence. LVDD remains underdiagnosed in critically ill patients despite potentially significant therapeutic implications since direct measurement cannot be performed in routine care at the bedside, and echocardiographic assessment of LVDD in AF is impaired. We propose a novel approach that allows us to infer the diastolic stiffness, β, a key quantitative parameter of diastolic function, from standard monitoring data by solving the nonlinear, ill-posed inverse problem of parameter estimation for a previously described mechanistic, physiological model of diastolic filling. The beat-to-beat variability in AF offers an advantageous setting for this.

Methods

By employing a global optimization algorithm, β is inferred from a simple six parameter and an expanded seven parameter model of left ventricular filling. Optimization of all parameters was limited to the interval ]0, 400[ and initialized randomly on large intervals encompassing the support of the likelihood function. Routine ECG and arterial pressure recordings of 17 AF and 3 sinus rhythm (SR) patients from the PhysioNet MGH/MF Database were used as inputs.

Results

Estimation was successful in 15 of 17 AF patients, while in the 3 SR patients, no reliable estimation was possible. For both models, the inferred β (0.065 ± 0.044 ml⁻¹ vs. 0.038 ± 0.033 ml⁻¹ (p=0.02) simple vs. expanded) was compatible with the previously described (patho) physiological range. Aortic compliance, α, inferred from the expanded model (1.46 ± 1.50 ml/mmHg) also compared well with literature values.

Conclusion

The proposed approach successfully inferred β within the physiological range. This is the first report of an approach quantifying LVDF from routine monitoring data in critically ill AF patients. Provided future successful external validation, this approach may offer a tool for minimally invasive online monitoring of this crucial parameter.

Left Ventricular Diastolic Myocardial Stiffness and End-Diastolic Myofibre Stress in Human Heart Failure Using Personalised Biomechanical Analysis

Understanding the aetiology of heart failure with preserved (HFpEF) and reduced (HFrEF) ejection fraction requires knowledge of biomechanical factors such as diastolic myocardial stiffness and stress. Cine CMR images and intra-ventricular pressure recordings were acquired in 8 HFrEF, 11 HFpEF and 5 control subjects. Diastolic myocardial stiffness was estimated using biomechanical models and found to be greater in HFrEF (6.4 ± 1.2 kPa) than HFpEF (2.7 ± 0.6 kPa, p < 0.05) and also greater than control (1.2 ± 0.4 kPa, p < 0.005). End-diastolic mid-ventricular myofibre stress derived from the personalised biomechanics model was higher in HFrEF (2.9 ± 0.3 kPa) than control (0.9 ± 0.3 kPa, p < 0.01). Chamber stiffness, measured from the slope of the diastolic pressure-volume relationship, is determined by the intrinsic tissue properties as well as the size and shape of the heart, and was unable to distinguish between any of the three groups (p > 0.05). Personalised biomechanical analysis may provide more specific information about myocardial mechanical behaviour than global chamber indices, which are confounded by variations in ventricular geometry.

Pathophysiology of coronary collaterals

While the existence of structural adaptation of coronary anastomoses is undisputed, the potential of coronary collaterals to be capable of functional adaptation has been questioned. For many years, collateral vessels were thought to be rigid tubes allowing only limited blood flow governed by the pressure gradient across them. This concept was consistent with the notion that although collaterals could provide adequate blood flow to maintain resting levels, they would be unable to increase blood flow sufficiently in situations of increased myocardial oxygen demand.

However, more recent studies have demonstrated the capability of the collateral circulation to deliver sufficient blood flow even during exertion or pharmacologic stress. Moreover, it has been shown that increases in collateral flow could be attributed directly to collateral vasomotion.

This review summarizes the pathophysiology of the coronary collateral circulation, ie the functional adapation of coronary collaterals to acute alterations in the coronary circulation.

Heart failure with preserved ejection fraction: current understandings and challenges

Heart failure (HF) is the leading cause of hospitalization among older adults and the prevalence is growing with the aging populations in western countries. Approximately one-half of patients with HF have preserved ejection fraction (HFpEF). In contrast to HF with reduced EF (HFrEF), there is no proven effective treatment for HFpEF. The pathophysiology of HFpEF is complex, and the dominant mechanisms leading to symptoms of HF often vary between afflicted patients, confounding efforts to apply "one-size fits all" types of therapeutic approaches. Current treatment strategies focus on control of volume status and comorbidities, but future research aimed at individualized therapies holds promise to improve outcomes in this increasingly prevalent form of cardiac failure.

Improving the stability of cardiac mechanical simulations

In the field of cardiac modeling, the mechanical action of the heart is often simulated using finite element methods. These simulations are becoming increasingly challenging as the computational domain is customized to a patient's anatomy, within which large heterogeneous tension gradients are generated via biophysical cell models which drive simulations of the cardiac pump cycle. The convergence of nonlinear solvers in simulations of large deformation mechanics depends on many factors. When extreme stress or irregular deformations are modeled, commonly used numerical methods can often fail to find a solution, which can prevent investigation of interesting parameter variations or use of models in a clinical context with high standards for robustness. This paper outlines a novel numerical method that is straightforward to implement and which significantly improves the stability of these simulations. The method involves adding a compressibility penalty to the standard incompressible formulation of large deformation mechanics. We compare the method's performance when used with both a direct discretization of the equations for incompressible solid mechanics, as well as the formulation based on an isochoric/deviatoric split of the deformation gradient. The addition of this penalty decreases the tendency for solutions to deviate from the incompressibility constraint, and significantly improves the ability of the Newton solver to find a solution. Additionally, our method maintains the expected order of convergence under mesh refinement, has nearly identical solutions for the pressure-volume relations, and stabilizes the solver to allow challenging simulations of both diastolic and systolic function on personalized patient geometries.

Implications of coronary artery disease in heart failure with preserved ejection fraction

OBJECTIVES

This study investigated the characteristics, evaluation, prognostic impact, and treatment of coronary artery disease (CAD) in patients with heart failure and preserved ejection fraction (HFpEF).

BACKGROUND

CAD is common in patients with HFpEF, but it remains unclear how CAD should be categorized, evaluated for, and treated in HFpEF.

METHODS

Clinical, hemodynamic, echocardiographic, treatment, and outcome characteristics were examined in consecutive patients with previous HFpEF hospitalizations who underwent coronary angiography.

RESULTS

Of the 376 HFpEF patients examined, 255 (68%) had angiographically-proven CAD. Compared with HFpEF patients without CAD, patients with CAD were more likely to be men, to have CAD risk factors, and to be treated with anti-ischemic medications. However, symptoms of angina and heart failure were similar in patients with and without CAD, as were measures of cardiovascular structure, function, and hemodynamics. Compared with patients without CAD, HFpEF patients with CAD displayed greater deterioration in ejection fraction and increased mortality, independent of other predictors (hazard ratio: 1.71, 95% confidence interval: 1.03 to 2.98; p = 0.04). Complete revascularization was associated with less deterioration in ejection fraction and lower mortality compared with patients who were not completely revascularized, independent of other predictors (hazard ratio: 0.56, 95% confidence interval: 0.33 to 0.93; p = 0.03).

CONCLUSIONS

CAD is common in patients with HFpEF and is associated with increased mortality and greater deterioration in ventricular function. Revascularization may be associated with preservation of cardiac function and improved outcomes in patients with CAD. Given the paucity of effective treatments for HFpEF, prospective trials are urgently needed to determine the optimal evaluation and management of CAD in HFpEF.

Right ventricular dysfunction in systemic sclerosis-associated pulmonary arterial hypertension

BACKGROUND

Systemic sclerosis–associated pulmonary artery hypertension (SScPAH) has a worse prognosis compared with idiopathic pulmonary arterial hypertension (IPAH), with a median survival of 3 years after diagnosis often caused by right ventricular (RV) failure. We tested whether SScPAH or systemic sclerosis–related pulmonary hypertension with interstitial lung disease imposes a greater pulmonary vascular load than IPAH and leads to worse RV contractile function.

METHODS AND RESULTS

We analyzed pulmonary artery pressures and mean flow in 282 patients with pulmonary hypertension (166 SScPAH, 49 systemic sclerosis–related pulmonary hypertension with interstitial lung disease, and 67 IPAH). An inverse relation between pulmonary resistance and compliance was similar for all 3 groups, with a near constant resistance×compliance product. RV pressure–volume loops were measured in a subset, IPAH (n=5) and SScPAH (n=7), as well as SSc without PH (n=7) to derive contractile indexes (end-systolic elastance [Ees] and preload recruitable stroke work [Msw]), measures of RV load (arterial elastance [Ea]), and RV pulmonary artery coupling (Ees/Ea). RV afterload was similar in SScPAH and IPAH (pulmonary vascular resistance=7.0±4.5 versus 7.9±4.3 Wood units; Ea=0.9±0.4 versus 1.2±0.5 mm Hg/mL; pulmonary arterial compliance=2.4±1.5 versus 1.7±1.1 mL/mm Hg; P>0.3 for each). Although SScPAH did not have greater vascular stiffening compared with IPAH, RV contractility was more depressed (Ees=0.8±0.3 versus 2.3±1.1, P<0.01; Msw=21±11 versus 45±16, P=0.01), with differential RV-PA uncoupling (Ees/Ea=1.0±0.5 versus 2.1±1.0; P=0.03). This ratio was higher in SSc without PH (Ees/Ea=2.3±1.2; P=0.02 versus SScPAH).

CONCLUSIONS

RV dysfunction is worse in SScPAH compared with IPAH at similar afterload, and may be because of intrinsic systolic function rather than enhanced pulmonary vascular resistive and pulsatile loading.

Measuring Left Ventricular Volumes in Two-Dimensional Echocardiography Image Sequence Using Level-set Method for Automatic Detection of End-Diastole and End-systole Frames

BACKGROUND

Identifying End-Diastole (ED) and End-Systole (ES) frames is highly important in the process of evaluating cardiac function and measuring global parameters accurately, such as Ejection Fraction (EF), Cardiac Output (CO) and Stroke Volume.

OBJECTIVES

The current study aimed to develop a new method based on measuring volume changes in Left Ventricle (LV) during cardiac cycle.

MATERIAL AND METHODS

For this purpose, the Level Set method was used both in detecting endocardium border and quantifying cardiac function of all frames.

RESULTS

Demonstrating LV volumes displays ED and ES frames and the volumes used in calculating the required parameters.

CONCLUSIONS

Since ES and ED frames exist in iso-volumic phases of the cardiac cycle with minimum and maximum values of LV volume signals, such peaks can be utilized in finding related frames.

The effect of hydrogel injection on cardiac function and myocardial mechanics in a computational post-infarction model

An emerging therapy to limit adverse heart remodelling following myocardial infarction (MI) is the injection of polymers into the infarcted left ventricle (LV). In the few numerical studies carried out in this field, the definition and distribution of the hydrogel in the infarcted myocardium were simplified. In this computational study, a more realistic biomaterial distribution was simulated after which the effect on cardiac function and mechanics was studied. A validated finite element heart model was used in which an antero-apical infarct was defined. Four infarct models were created representing different temporal phases in the progression of a MI. Hydrogel layers were simulated in the infarcted myocardium in each model. Biomechanical and functional improvement of the LV was found after hydrogel inclusion in the ischaemic models representing the early phases of MI. In contrast, only functional but no mechanical restitution was shown in the scar model due to hydrogel presence.

Coronary collaterals provide a constant scaffold effect on the left ventricle and limit ischemic left ventricular dysfunction in humans

Coronary collaterals preserve left ventricular (LV) function during coronary occlusion by reducing myocardial ischemia and may directly influence LV compliance. We aimed to re-evaluate the relationship between coronary collaterals, measured quantitatively with a pressure wire, and simultaneously recorded LV contractility from conductance catheter data during percutaneous coronary intervention (PCI) in humans. Twenty-five patients with normal LV function awaiting PCI were recruited. Pressure-derived collateral flow index (CFI(p)): CFI(p) = (P(w) - P(v))/(P(a) - P(v)) was calculated from pressure distal to coronary balloon occlusion (P(w)), central venous pressure (P(v)), and aortic pressure (P(a)). CFI(p) was compared with the changes in simultaneously recorded LV end-diastolic pressure (ΔLVEDP), end-diastolic volume, maximum rate of rise in pressure (ΔLVdP/dt(max); systolic function), and time constant of isovolumic relaxation (ΔLV τ; diastolic function), measured by a LV cavity conductance catheter. Measurements were recorded at baseline and following a 1-min coronary occlusion and were duplicated after a 30-min recovery period. There was significant LV diastolic dysfunction following coronary occlusion (ΔLVEDP: +24.5%, P < 0.0001; and ΔLV τ: +20.0%, P < 0.0001), which inversely correlated with CFI(p) (ΔLVEDP vs. CFI(p): r = -0.54, P < 0.0001; ΔLV τ vs. CFI(p): r = -0.46, P = 0.0009). Subjects with fewer collaterals had lower LVEDP at baseline (r = 0.33, P = 0.02). CFI(p) was inversely related to the coronary stenosis pressure gradient at rest (r = -0.31, P = 0.03). Collaterals exert a direct hemodynamic effect on the ventricle and attenuate ischemic LV diastolic dysfunction during coronary occlusion. Vessels with lesions of greater hemodynamic significance have better collateral supply.

Pressure-volume relation analysis of mouse ventricular function

Nearly 40 years ago, the Sagawa laboratory spawned a renaissance in the use of instantaneous ventricular pressure-volume (P-V) relations to assess cardiac function. Since then, this analysis has taken hold as the most comprehensive way to quantify ventricular chamber function and energetics and cardiovascular interactions. First studied in large mammalian hearts and later in humans employing a catheter-based method, P-V analysis was translated to small rodents in the late 1990s by the Kass laboratory. Over the past decade, this approach has become a gold standard for comprehensive examination of in vivo cardiac function in mice, facilitating a new era of molecular cardiac physiology. The catheter-based method remains the most widely used approach in mice. In this brief review, we discuss this instrumentation, the theory behind its use, and how volume signals are calibrated and discuss elements of P-V analysis. The goal is to provide a convenient summary of earlier investigations and insights for users whose primary interests lie in genetic/molecular studies rather than in biomedical engineering.

The effect of repeated ischaemic periods on left ventricular dynamics during percutaneous coronary intervention

AIMS

To study online left ventricular (LV) dynamic effects of transmural ischaemia and reperfusion during consecutive balloon coronary occlusions in the setting of percutaneous coronary intervention (PCI).

METHODS AND RESULTS

In 10 consecutive unselected patients with stable angina (seven males, mean age 62 ± 3 years) who underwent elective PCI, LV dynamics were continuously recorded using a pressure-conductance catheter to simultaneously measure pressure and volume (PV-loop). The effects of a prolonged balloon coronary occlusion (148 ± 19 s) and a second occlusion on various LV function parameters were studied, as well as recovery of these parameters after reperfusion. Ischaemia caused an immediate (<5 s) decrease in diastolic function, followed by a decrease in contractile function, indicated by a rightward shift of the PV-loop, and a decreased dP/dtmax and ejection fraction. All parameters recovered within two minutes after reperfusion. The second occlusion caused a more rapid and more pronounced decrease in systolic and global LV function, while the 12-lead ECG showed less ST-segment deviation.

CONCLUSIONS

Online LV pressure-volume measurements during elective PCI show that prolonged balloon coronary occlusion causes a phased ischaemic response of diastolic dysfunction, and then systolic dysfunction with more pronounced deterioration during a consecutive ischaemic period, paradoxical to the ischaemic electrocardiographic signs.

Stunning and cumulative left ventricular dysfunction occurs late after coronary balloon occlusion in humans insights from simultaneous coronary and left ventricular hemodynamic assessment

OBJECTIVES

We aimed to investigate whether left ventricular (LV) stunning could be detected late after coronary occlusion when coronary flow has normalized.

BACKGROUND

Stunning and cumulative LV dysfunction after ischemia reperfusion has been clearly demonstrated in animal models but has been refuted in several angioplasty models in humans. However, these studies have assessed LV function early, during the reactive hyperemic phase, which might have augmented LV function.

METHODS

We recruited 20 male subjects with single-vessel, type A coronary disease, and normal ventricular function. We simultaneously measured LV function with a conductance catheter and coronary flow velocity with a Combowire (Volcano Therapeutics, Inc., Rancho Cordova, California) at baseline (BL), for 30 s after a low-pressure coronary balloon occlusion for 1 min and again after 30 min, before a second balloon occlusion.

RESULTS

Stunning was detected at 30 min after a 1-min balloon occlusion: stroke volume (ml) BL1: 88.4 (22.8) versus BL2: 79.4 (24.0), p = 0.04; tau (ms) BL1: 49.8 (9.0) versus BL2: 52.5 (8.9), p = 0.02, despite full recovery of coronary average peak velocity (p = 0.62). A second balloon occlusion caused cumulative LV dysfunction: stroke volume (ml) BO1: 77.3 (34.6) versus BO2 64.9 (22.9), p = 0.01. Reactive hyperemia significantly augmented early recovery systolic function: dP/dt max 30 s: +5.8% versus 30 min - 5.4%, p = 0.0009.

CONCLUSIONS

Coronary occlusion for 1-min results in late stunning and cumulative LV dysfunction after 30 min. Reactive hyperemia augments stunned LV systolic function in early recovery.

Heart failure with preserved ejection fraction: pathophysiology and emerging therapies

Approximately half of patients with heart failure (HF) have a preserved ejection fraction (HFpEF). Morbidity and mortality are similar to HF with reduced EF (HFrEF), yet therapies with unequivocal benefit in HFrEF have not been shown to be effective in HFpEF. Recent studies have shown that the pathophysiology of HFpEF, initially believed to be due principally to diastolic dysfunction, is more complex. Appreciation of this complexity has shed new light into how HFpEF patients might respond to traditional HF treatments, while also suggesting new applications for novel therapies and strategies. In this review, we shall briefly review the pathophysiologic mechanisms in HFpEF, currently available clinical trial data, and finally explore new investigational therapies that are being developed and tested in ongoing and forthcoming trials.

Relationship between post-systolic motion during dobutamine stress echocardiography and functional recovery of myocardium after successful percutaneous coronary intervention

BACKGROUND AND OBJECTIVES

Doppler myocardial imaging (DMI) has been suggested as a method of quantifying inducible ischemia during dobutamine stress echocardiography (DSE). Post-systolic motion (PSM) detected by DMI is related to peri-infarct ischemia during DSE. We hypothesized that PSM during DSE would predict recovery of dysfunctional myocardium after successful percutaneous coronary intervention (PCI).

SUBJECTS AND METHODS

Thirty patients with dysfunctional myocardium in the left anterior descending coronary artery (LAD) territory were divided into two groups according to improvement of wall motion score index (WMSI) in the LAD territory at 6 months after successful PCI of the LAD. DMI was evaluated in the LAD territory during DSE. Fifteen patients showed improved WMSI (1.42+/-0.39) while the other 15 had unchanged WMSI (1.75+/-0.46) 1 month after PCI. Myocardial velocity was measured in the mid-septal, apico-septal, and basal anterior segments of the LAD artery territory. PSM was defined as a positive wave appearing after the curve of systolic ejection had reached the zero line.

RESULTS

Although there was no difference between resting PSMs in both groups, PSM during DSE was significantly higher in the improved WMSI group than in the WMSI group where it was unchanged.

CONCLUSION

PSM during DSE predicts recovery of dysfunctional myocardium after successful PCI.

'Dynamic' Starling mechanism: effects of ageing and physical fitness on ventricular-arterial coupling

Cardiovascular diseases increase with advancing age, associated with left ventricular and arterial stiffening in humans. In contrast, daily exercise training prevents and/or improves both ventricular and arterial stiffening with ageing. We propose a new approach to quantify the dynamics of the Starling mechanism, namely the beat-to-beat modulation of stroke volume (SV) caused by beat-to-beat alterations in left ventricular filling, which we propose reflects the complex interaction between ventricular and arterial stiffness. We hypothesized that the dynamic Starling mechanism would be impaired with ageing, and that this impairment would be prevented and restored by daily exercise training. Two different approaches were employed: (1) a cross-sectional study to assess the effects of ageing and life-long exercise training; and (2) a longitudinal study to assess the effects of one-year endurance training in the elderly. Spectral transfer function gain between beat-to-beat changes in left ventricular end-diastolic pressure and SV was used as an index of the dynamic Starling mechanism. Gain was significantly lower in the sedentary elderly (70 +/- 3 years) than in both young individuals (27 +/- 6 years) and Masters athletes (68 +/- 3 years), and it was significantly lower in Masters athletes than in young controls (elderly: 0.37 +/- 0.11; Masters athletes: 0.96 +/- 0.55; young: 1.52 +/- 0.42 ml m(-2) mmHg(-1), mean +/- s.d.). Gain increased by 65% after one-year exercise training in the elderly, although the response was quite variable (P = 0.108). These findings suggest that the dynamic Starling mechanism is impaired with human ageing possibly due to ventricular-arterial stiffening. Life-long daily exercise training may minimize this impairment, although the effect may be limited particularly when started later in life.

Mechanisms of Diastolic Dysfunction in Heart Failure

Abnormalities of diastole are common to most forms of congestive heart failure (HF). Diastolic function is broadly defined as the ability of the heart to fill adequately and at normal pressure to charge the ventricular pump for each subsequent contraction. It is determined by both active and passive processes occurring at the level of the myocyte, extracellular matrix, and left ventricular chamber. Forces extrinsic to the myocardium-such as the influence of right heart filling, pericardial and extracardiac constraints, and cardiac preload and afterload also contribute. Nearly half of patients with HF have apparently preserved systolic function, and this has focused attention on diastolic dysfunction as a dominant contributor to symptoms, sparking interest for understanding and treating diastolic abnormalities. This review focuses on the mechanisms determining normal and pathologic cardiac relaxation and distensibility and highlights how these abnormalities may be therapeutically targeted to improve diastolic function in human HF.

Novel method for measurement of medium size arterial lumen area with an impedance catheter: in vivo validation

There is no doubt that the transformation of a cardiac catheter into a conductance catheter that allows reliable and accurate assessment of lumen cross-sectional area (CSA) will provide a powerful diagnostic and treatment tool for the invasive cardiologist. The objective of this study was to develop a method based on the impedance catheter that allows accurate and reproducible measurements of CSA for medium size vessels (e.g., coronary, femoral, and carotid arteries). Two solutions of NaCl (0.5% and 1.5%) with known conductivities were injected directly into the lumen of the artery in eight swine. We showed that the CSA can be determined analytically from two Ohm's law-type algebraic equations that account for the parallel conductance of the current into the surrounding tissue. Excellent agreement was found between the conductance catheter with the proposed two-injection method and B-mode ultrasound (US). The root mean square error for the impedance measurements was 4.8% of the mean US diameter. The repeatability of the technique was assessed with duplicate measurements. The mean of the difference between the two measurements was nearly zero, and the repeatability coefficient was within 2.4% of the mean of the two measurements. The validated method was used to assess the degree of acute vasodilatation of the vessel in response to flow overload.

Effects of dobutamine on left ventriculoarterial coupling and mechanical efficiency in acutely ischemic pigs

This study investigated the effects of dobutamine on left ventriculoarterial (VA) coupling and mechanical efficiency in acutely ischemic pigs. Experiments were performed in 12 pigs in which vascular properties, including peripheral resistance (R2), compliance (C), and arterial elastance (Ea), were estimated with a windkessel model, and left ventricular (LV) function by the slope (Ees) of the end-systolic pressure-volume relationship (ESPVR) and stroke work (SW). VA coupling was defined as Ees/Ea, and mechanical efficiency as SW/pressure-volume area (PVA). In all animals, the left anterior descending coronary artery was ligated after basal measures. The animals were then randomly divided into 2 groups: group CTRL (n = 6) was followed for 180 minutes without other intervention, whereas group DOBU (n = 6) was infused with dobutamine (5 microg x kg(-1) x min(-1)) starting after T60 measures. Coronary occlusion induced a rightward shift of ESPVR and a decrease in Ees from 3.67 +/- 0.33 to 1.92 +/- 0.20 mm Hg x mL(-1), while Ea changed from 3.33 +/- 0.56 to 4.65 +/- 0.29 mm Hg x mL, R2 from 1.72 +/- 0.30 to 2.38 +/- 0.16 mm Hg x s x mL(-1), and C from 0.78 +/- 0.16 to 0.46 +/- 0.08 mL x mm Hg(-1). This altered VA coupling from 1.22 +/- 0.11 to 0.44 +/- 0.07. SW decreased from 4056 +/- 223 to 2372 +/- 122 mm Hg x mL, and PVA and SW/PVA decreased from 5575 +/- 514 to 4830 +/- 317 mm Hg x mL, and from 0.76 +/- 0.04 to 0.49 +/- 0.03, respectively. In group DOBU, dobutamine restored Ees and the position of ESPVR to baseline values, while Ea decreased to 3.39 +/- 0.34 mm Hg x mL(-1) because of an R2 decrease to 1.60 +/- 0.24 mm Hg x s x mL(-1). VA coupling was restored. SW and PVA increased to 3833 +/- 180 mm Hg x mL and to 7498 +/- 442 mm Hg x mL, respectively, while SW/PVA was unchanged. In ischemic pigs, dobutamine restored VA coupling through an increase in LV contractility and decrease in arterial elastance as a result of peripheral vasodilatation. However, myocardial oxygen consumption was increased, and mechanical efficiency impaired.

Diagnosis of viable myocardium using velocity data of Doppler myocardial imaging: comparison with positron emission tomography

To test whether velocity data of Doppler myocardial imaging (DMI) at rest is useful for diagnosis of myocardial viability, 25 consecutive patients (age 64 +/- 10 years) with regional wall-motion abnormalities at the left anterior descending coronary artery territory and left ventricular dysfunction (ejection fraction: 31 +/- 7%) underwent both DMI at rest and positron emission tomography. The peak systolic velocity (Vpeak) and postsystolic thickening (PST) velocity were measured in myocardial segments of left anterior descending coronary artery territory from apical views. A total of 71 segments were classified by positron emission tomography as normal or viable in 38 (group A) and nonviable in 33 (group B). Although Vpeak did not show any difference between groups (1.81 +/- 1.77 vs 1.29 +/- 0.94 cm/s, P =.107), PST velocity was significantly higher in group A (2.48 +/- 1.68 vs 0.89 +/- 0.72 cm/s, P <.001). The sensitivity and specificity of PST velocity > 2.0 cm/s for diagnosis of viability were 61% (23/38) and 97% (32/33), respectively. In segments with PST velocity was < or =2.0 cm/s, Vpeak > 1.8 cm/s could discriminate group A from B with a sensitivity of 67% (10/15) and a specificity of 91% (29/32). The algorithm using both PST velocity and Vpeak of DMI showed sensitivity and specificity of 87% and 88%, respectively, for diagnosis of myocardial viability. Velocity data of DMI at rest provides robust information regarding viability in selected patients, and an advantage of this technique is that no stress testing is needed.

Measurement of Coronary Lumen Area Using an Impedance Catheter: Finite Element Model and in Vitro Validation

The measurement of coronary lumen cross-sectional area (CSA) is important for coronary physiology and cardiology. The general objective of this study is to develop an accurate and reproducible method to measure the lumen CSA of left anterior descending (LAD) artery using an impedance or conductance catheter. The conductance catheter technique is based on a cylindrical model of the chamber of interest. The first aim of this study was to validate the assumptions of the cylindrical model using a finite-element analysis (FEA) of the conductance catheter in the lumen of the vessel that takes into account the conductance of current through the vessel wall and surrounding tissue (parallel conductance, Gp). The FEA was used to determine the heterogeneity of potential and electrical fields and to optimize the design of the catheter relative to the diameter of the vessel. An optimum relationship between vessel and catheter diameter was obtained based on FEA. The second aim was to validate the in vitro CSA of LAD artery obtained from the conductance catheter method using A-mode ultrasound (US). The present study offers a novel approach to correct for the Gp that involves the injection of two solutions of NaCl (0.5% and 1.5%) with known conductivities directly into the lumen of the coronary artery in a porcine heart. In six hearts obtained from a slaughterhouse, we showed that the CSA and Gp can be determined analytically from two Ohm's law-type algebraic equations (cylindrical model) that account for the parallel conductance. The mean difference in diameter between the conductance catheter using the proposed two-injection method and U.S. was -0.02. The root mean square error for the impedance measurements was 2.8% of the mean US diameter. The future application of this technique to the in vivo condition is discussed.

Postsystolic thickening detected by Doppler myocardial imaging: a marker of viability or ischemia in patients with myocardial infarction

BACKGROUND

Postsystolic thickening (PST) of ischemic myocardial segments has been reported to account for the characteristic heterogeneity or regional asynchrony of myocardial wall motion during acute ischemia.

HYPOTHESIS

Postsystolic thickening detected by Doppler myocardial imaging (DMI) could be a useful clinical index of myocardial viability or peri-infarction viability in patients with myocardial infarction (MI).

METHODS

Doppler myocardial imaging was recorded at each stage of a standard dobutamine stress echocardiogram (DSE) in 20 patients (16 male, 60 +/- 13 years) with an MI in the territory of the left anterior descending artery. Myocardial velocity data were measured in the interventricular septum and apical inferior segment of the MI territory. Postsystolic thickening was identified if the absolute velocity of PST was higher than peak systolic velocity in the presence of either a resting PST > 2.0 cm/s or if PST doubled at low-dose dobutamine infusion.

RESULTS

Doppler myocardial imaging data could be analyzed in 38 ischemic segments (95%), and PST was observed in 21 segments (55%), including 3 segments showing PST only at low-dose dobutamine infusion. There was no significant difference of baseline wall motion score index (2.1 +/- 0.3 vs. 2.1 +/- 0.6, p = 0.77) or peak systolic velocity (1.1 +/- 1.1 vs. 1.9 +/- 2.0 cm/s, p = 0.05) between segments with and without PST. Peri-infarction ischemia or viability during DSE was more frequently observed in segments with PST than in those without (86 vs. 24%, p < 0.05). The sensitivity and specificity of PST for prediction of peri-infarction viability or ischemia was 82 and 81%, respectively.

CONCLUSIONS

Postsystolic thickening in the infarct territory detected by DMI is closely related with peri-infarction ischemia or viability at DSE.

Nicardipine or nitroglycerin in patients with failed percutaneous coronary angioplasty: effect on myocardial diastolic function

OBJECTIVE

To evaluate whether intracoronary vasodilators can improve diastolic function in 32 patients with failed percutaneous transluminal coronary angioplasty (PTCA).

DESIGN

Clinical trial.

SETTING

Single-institution, academic hospital.

PARTICIPANTS

Failed PTCA patients undergoing emergency coronary artery bypass grafting surgery.

INTERVENTIONS

Patients were divided into 2 groups: group A received 0.1 mg of intracoronary nicardipine, and group B received 20 microg of intracoronary nitroglycerin. Both drugs were administrated via a coronary dilatation perfusion catheter inserted in the catheterization laboratory by the cardiologist. Subsequently, they were continuously infused via the side port of the introducer of the pulmonary artery catheter and titrated to keep systolic blood pressure at about two thirds of the control value. Transesophageal echocardiography (Power Vision/6000, 9-mm 5MHZ Probe; Toshiba, Elmsford, NY) was used in this study.

MEASUREMENTS AND MAIN RESULTS

Left ventricular ejection fraction, cardiac index, tissue Doppler imaging velocity of the left ventricle and mitral annulus, and troponin levels were measured before and after administration of the 2 vasodilators and after cardiopulmonary bypass. Diastolic dysfunction was found preoperatively in all the patients and responded only to intracoronary nicardipine. Ea of mitral annulus velocity significantly increased in group A patients from 7.5 +/- 0.02 to 11.8 +/- 0.01 (p < 0.005) and decreased in group B patients from 8.0 +/- 0.03 to 7.5 +/- 0.02 after nicardipine or nitroglycerin administration. Left ventricular ejection fraction and cardiac index increased significantly (p < 0.005) only after nicardipine administration. Troponin levels were significantly lower in group A than in group B patients (p < 0.005).

CONCLUSION

Intracoronary nicardipine improves diastolic function and myocardial flow velocity in patients with failed PTCA undergoing emergency coronary artery bypass graft surgery.

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.

Endomyocardial nitric oxide synthase and the hemodynamic phenotypes of human dilated cardiomyopathy and of athlete's heart

OBJECTIVE

In dilated cardiomyopathy and in athlete's heart, progressive LV dilatation is accompanied by rightward displacement of the diastolic LV pressure-volume relation. In dilated cardiomyopathy, an increase in diastolic LV stiffness can limit this rightward displacement thereby decreasing LV systolic performance. Because nitric oxide (NO) reduces diastolic LV stiffness, the present study relates diastolic LV stiffness and LV systolic performance to intensity of endomyocardial NO synthase (NOS) gene expression in dilated cardiomyopathy and in athlete's heart.

METHODS

Microtip LV pressures, conductance-catheter or angiographic LV volumes, echocardiographic LV wall thicknesses and snap-frozen LV endomyocardial biopsies were obtained in 33 patients with dilated cardiomyopathy and in three professional cyclists referred for sustained ventricular tachycardia. Intensity of LV endomyocardial inducible NOS (NOS2) and constitutive NOS (NOS3) gene expression was determined using quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Dilated cardiomyopathy patients with higher diastolic LV stiffness-modulus and lower LV stroke work had lower NOS2 and NOS3 gene expression at any given level of LV end-diastolic wall stress. The intensity of NOS2 and NOS3 gene expression observed in athlete's heart was similar to dilated cardiomyopathy with low LV diastolic stiffness-modulus and preserved LV stroke work.

CONCLUSIONS

High LV endomyocardial NOS gene expression is observed in athlete's heart and in dilated cardiomyopathy with low diastolic LV stiffness and preserved LV stroke work. Favourable effects on the hemodynamic phenotype of high LV endomyocardial NOS gene expression could result from a NO-mediated decrease in diastolic LV stiffness and a concomitant rise in LV preload reserve.

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.

Quantification of left ventricular diastolic pressure-volume relations during routine cardiac catheterization by two-dimensional digital echo quantification and left ventricular micromanometer

BACKGROUND

Currently there is no simple clinical method for quantifying the left ventricular (LV) diastolic pressure-volume relation. Echocardiographic-automated endocardial border detection, however, may be combined with LV micromanometer to construct LV pressure-volume loops. We investigated the feasibility of on-line display and sampling of LV pressure-volume loops by such an approach. For this purpose we used a new echocardiographic digital echo quantification (DEQ) method in combination with LV pressures on-line and in real-time.

METHODS

Eighteen patients were screened by conventional echocardiography and DEQ. Ten of the patients with high quality images were included in the study. Left ventricular pressures and volumes were recorded simultaneously and were displayed on-line as pressure-volume loops. Changes in LV volume were induced by intravenous saline. Left ventricular chamber compliance was estimated as change in volume divided by change in pressure from minimum diastolic pressure to end-diastolic pressure (average LV chamber compliance).

RESULTS

Left ventricular pressure-volume loops were displayed on-line during the examination. When compared with the Simpson's method, DEQ underestimated end-diastolic volume (EDV) by 35% and overestimated end-systolic volume (ESV) by 14%. Beat-to-beat variability for ESV and EDV were 7.4% +/- 0.8% and 7.2% +/- 0.7 %, respectively. Volume loading increased LV end-diastolic pressure (LVEDP) from 14.0 +/- 1.6 to 24.7 +/- 2.0 mm Hg (P <.05) and EDV from 79 +/- 10 to 85 +/- 11 mL (NS), and decreased LV chamber compliance from 4.0 +/- 0.7 to 2.0 +/- 0.3 mL/mm Hg (P <.05).

CONCLUSION

The current study demonstrates that LV pressure-volume loops can be displayed and evaluated in real-time during routine cardiac catheterization. This may represent a clinically useful method for identifying patients with reduced chamber compliance. The underestimation of the volumes by DEQ compared with the Simpson's method suggests that further refinements should be performed to improve the endocardial border detection algorithm.

Acute changes in systolic and diastolic events during clinical coronary angioplasty: a comparison of regional velocity, strain rate, and strain measurement

Ultrasound-derived natural strain rate and strain are new Doppler myocardial imaging (DMI) parameters, which can measure local deformation independently of overall heart motion and thus could better characterize local contractility than DMI velocities alone. This study was undertaken to evaluate the relative benefits of regional velocity, strain rate, and strain measurements in detecting the range of acute changes in regional myocardial function in the "at-risk" zone during coronary angioplasty. Sixty-one patients (aged 63 +/- 12, 18 women) with stable angina pectoris were studied before, at the end of, and during recovery from a 60-second percutaneous transluminal coronary angioplasty (PTCA) balloon occlusion. High frame rate (147 fps) color DMI regional velocity data were derived from basal posterior (parasternal view) and mid, apical septal (apical view) "at-risk" segments as well as from the corresponding segments in healthy subjects and analyzed offline for velocity (VEL), strain rate (SR), and strain (epsilon) measurements. Coronary occlusion resulted in the reduction in VEL(SYS), SR(SYS), and epsilon(SYS) values for both radial (RCA/CX occlusion) and longitudinal data (LAD occlusion) in all segments analyzed. Velocity parameters alone failed to distinguish between baseline and occlusive measurements in the "at-risk" segments with visually abnormal baseline function. SR(SYS) and epsilon(SYS) had a higher diagnostic accuracy (sensitivity 75%, 80% and specificity 80%, 82%, respectively) than VEL(SYS) velocity alone (sensitivity 68%, specificity 65%,) for identifying acute ischemia in either baseline normal and abnormal segments. DMI-derived indexes can identify and quantify the spectrum of acute systolic and diastolic ischemic changes induced during clinical PTCA. The quantitation of regional deformation rather than motion would appear to be more appropriate in detecting and quantifying acute ischemic changes in myocardial function, especially in segments with pre-existing abnormal function.

A novel technique for measurement of pericardial pressure

To determine whether pericardial liquid pressure accurately measures pericardial constraint, we developed a technique in which a catheter was positioned perpendicular to the epicardial surface. This device, which occupies little or no pericardial space, couples the thin film of liquid to a transducer. In six open-chest dogs, we also measured left ventricular (LV) end-diastolic pressure (LVEDP) and anteroposterior and septum-to-free wall diameters. LVEDP was raised incrementally to approximately 25 mmHg by saline infusion. With the use of the product of the two diameters as an index of area (A(LV)), LVEDP-A(LV) relationships were obtained with the pericardium closed and again after the pericardium had been widely opened to obtain the isovolumic difference in LVEDP (DeltaLVEDP). In all dogs, the technique yielded values of pericardial pressure equal to DeltaLVEDP as well as equal to that measured using a previously placed balloon transducer in the same location and at the same A(LV). We conclude that, when the pressure of the pericardial liquid is appropriately measured, it (in addition to the balloon-measured contact stress) defines the diastolic constraining effect of the pericardium. Furthermore, we suggest that earlier measurements of pericardial "liquid pressure" were low, due to an artifact of measurement.

Acute effects of 17beta-estradiol on ventricular and vascular hemodynamics in postmenopausal women

Because premenopausal women have lower cardiovascular morbidity than postmenopausal women, it has been proposed that estrogen may have a protective role. Estrogen is involved in smooth muscle relaxation both through its specific receptor as well as through calcium channel blockade. This study examined the acute effect of estradiol on invasive cardiovascular hemodynamics in 18 postmenopausal women (age 62.6 +/- 7.6 years, means +/- SD). The effect of estradiol on left ventricular chamber performance was studied in 9 women using simultaneous left ventricular pressure-volume recordings. In a further group of 9 women, the acute effect of estradiol on arterial function was assessed using input impedance (derived from simultaneous aortic pressure and flow recordings), pressure waveform analysis, and pulse wave velocity. After 2 mg micronized 17beta-estradiol was administered, serum estradiol levels increased from 50.9 +/- 21.9 to 3,190 +/- 2,216 pmol/l, P < 0.0001. There was no effect of estradiol on either left ventricular inotropic or lusitropic function. There was no acute effect of estradiol on arterial impedance, reflection coefficient, augmentation index, or pulse wave velocity. There was a trend to decreased heart rate and cardiac output in both groups of 9 women. Because heart rate and cardiac output were common to both hemodynamic data sets, results for these parameters were pooled. Across all 18 women, there was a small but significant decrease in heart rate (69.2 +/- 10.4 vs. 67.2 +/- 9.9 beats/min, P = 0.02), as well as a significant decrease in cardiac output (4.82 +/- 1.77 vs. 4.17 +/- 1.56 l/min, P = 0.002). Despite achieving supraphysiological serum levels, this study found no significant effect of acute 17beta-estradiol on ventricular or large artery function.

Assessment of diastolic dysfunction. Invasive modalities

In this article, the author sought to review the two primary components of diastolic function that are most directly and accurately determined using invasive methodologies. For chamber relaxation this is optimally achieved using a micromanometer catheter, whereas for chamber compliance (or its inverse stiffness) this is best achieved by combining this catheter with a measure of instantaneous volume from a conductance catheter, using data from multiple cycles. Even with the ideal data set, the analysis of both properties involves physiologic and often mathematical assumptions, and the extent to which the data do not match these assumptions, the derived indexes may be misleading. Care in the data collection, and awareness of the various factors and pitfalls involved with their analysis can undoubtedly improve the interpretations. As advances in noninvasive methods continue to evolve, reliance on invasive methodologies will continue to fade into the background. At present, however, they remain the gold standard for the two primary diastolic properties described, and have clearly played a central role in the evolution of our understanding of cardiac diastolic disease and its treatment.

Modulation of left ventricular diastolic distensibility by collateral flow recruitment during balloon coronary occlusion

OBJECTIVES

The goals of this study were to elucidate the scaffolding effect of blood-filled coronary vasculature and to determine the functional role of recruited collateral flow in modulating left ventricular (LV) distensibility during balloon coronary occlusion (BCO).

BACKGROUND

Although LV distensibility is an important factor affecting acute dilation after myocardial infarction, the response of LV diastolic pressure-volume (P-V) relations to coronary occlusion is inconsistent in humans.

METHODS

Micromanometer and conductance derived LV P-V loops were serially obtained from 16 patients undergoing percutaneous transluminal coronary angioplasty. Coronary collateral flow recruitment was angiographically evaluated by contralateral and ipsilateral contrast injection during BCO.

RESULTS

In the group with poor collateral flow (grades 0-I; n = 8), BCO resulted in a downward and rightward shift of the diastolic P-V relations, where end-diastolic volume (EDV) increased by 13% (p < 0.05) without appreciable change in end-diastolic pressure (EDP; 18 +/- 6 to 18 +/- 8 mm Hg). In contrast, BCO in the group with good collateral flow (grades II-III; n = 8) shifted the diastolic P-V relations upward to the right with a concomitant increase in minimal pressure (min-P; 6 +/- 4 to 10 +/- 5 mm Hg, p < 0.05), EDP (15 +/- 7 to 21 +/- 9 mm Hg, p < 0.05) and EDV (+/- 10%, p < 0.05). Reactive hyperemia after balloon deflation caused a rapid and parallel upward shift of the diastolic P-V relations with a marked increase in min-P and EDP, especially in the group with poor collateral flow, before any improvement in LV contraction or relaxation abnormalities.

CONCLUSIONS

Grades of coronary filling, either retrograde or anterograde, abruptly modulate LV distensibility through the rapid scaffolding effect of coronary vascular turgor.

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.

Effects of critical coronary stenosis on global systolic left ventricular function quantified by pressure-volume relations during dobutamine stress in the canine heart

OBJECTIVES

In this study we quantified the effects of a critical coronary stenosis on global systolic function using pressure-volume relations at baseline and during incremental dobutamine stress.

BACKGROUND

The effects of coronary stenosis have previously been analyzed mainly in terms of regional (dys)function. Global hemodynamics are generally considered normal until coronary flow is substantially reduced. However, pressure-volume analysis might reveal mechanisms not fully exposed by potentially load-dependent single-beat parameters. Moreover, no systematic analysis by pressure-volume relations of the effects of dobutamine over a wide dose range has previously been presented.

METHODS

In 14 dogs left ventricular volume and pressure were measured by conductance and micromanometer catheters, and left circumflex coronary flow by Doppler probes. Measurements in control and with left circumflex stenosis were performed at baseline and at five levels of dobutamine (2.5 to 20 microg/kg/min). The end-systolic pressure-volume relation (ESPVR) dP/dtMAX vs. end-diastolic volume (dP/dtMAX - V(ED)) and the relation between stroke work and end-diastolic volume (preload recruitable stroke work [PRSW]) were derived from data obtained during gradual caval occlusion.

RESULTS

In control, dobutamine gradually increased heart rate up to 20 microg/kg/min, the inotropic effect blunted at 15 microg/kg/min. With stenosis, the chronotropic effect was similar, however, contractile state was optimal at approximately 10 microg/kg/min and tended to go down at higher levels. At baseline, the positions of ESPVR and PRSW, but not of dP/dtMAX - V(ED), showed a significant decrease in function with stenosis. No differences between control and stenosis were present at 2.5 microg/kg/min; the differences were largest at 15 microg/kg/min.

CONCLUSIONS

Pressure-volume relations and incremental dobutamine may be used to quantify the effects of critical coronary stenosis. The positions of these relations are more consistent and more useful indices than the slopes. The positions of the ESPVR and PRSW show a reduced systolic function at baseline, normalization at 2.5 microg/kg/min and a consistent significant difference between control and stenosis at dobutamine levels of 5 microg/kg/min and higher.

Continuous monitoring of global left ventricular ejection fraction during percutaneous transluminal coronary angioplasty

Continuous monitoring of left ventricular (LV) function during percutaneous transluminal coronary angioplasty (PTCA) was performed in 40 patients (53 +/- 2 years) with a miniature, nuclear detector system after labeling the patients' red blood cells with technetium-99m. Balloon dilation (113 seconds, range 60 to 240) induced on average a 0.12 ejection fraction (EF) unit (19%) decrease in the LVEF, which was explained by a 34% increase in end-systolic counts. Balloon dilation of the left anterior descending artery (n = 23) produced a decrease in the LVEF of 0.17 +/- 0.13 EF units compared with the decrease of 0.06 +/- 0.07 EF units in patients undergoing dilation of the left circumflex artery (n = 9) and 0.05 +/- 0.04 EF units in patients treated for a stenosis of the right coronary artery (n = 8), (p = 0.02). Balloon deflation was associated with an immediate return to pre-PTCA levels. In 10 patients with 2 identical balloon occlusions, the second occlusion led to a significantly less decrease in the LVEF (0.41 +/- 0.14 vs 0.44 +/- 0.15) and electrocardiographic ST-segment deviation (88 +/- 54 microV vs 65 +/- 42 microV) than the first. We conclude that PTCA is associated with an abrupt transient decrease in the LVEF. The effect of balloon occlusion of the left anterior descending artery is more pronounced than balloon occlusion of the left circumflex and the right coronary arteries. Neither single nor multiple balloon occlusions were associated with post-PTCA global LV dysfunction, whereas the lesser degree of LV dysfunction and electrocardiographic signs of myocardial ischemia during the second of 2 identical balloon occlusions suggests that preconditioning can be induced during PTCA.

Effects of calcium on left ventricular function early after cardiopulmonary bypass

OBJECTIVES

Evaluation of the effects of intravenous CaCl2 on systolic and diastolic function early after separation from cardiopulmonary bypass (CPB) DESIGN: Prospective study

SETTING

University hospital

PARTICIPANTS

Twenty patients scheduled for elective coronary artery surgery

INTERVENTIONS

Left ventricular (LV) pressures were measured with fluid-filled catheters. Data were digitally recorded during pressure elevation induced by tilt-up of the legs. Transgastric short-axis echocardiographic views of the LV were simultaneously recorded on videotape. Measurements were obtained before the start of CPB, 10 minutes after termination of CPB, after intravenous administration of CaCl2, 5 mg/kg, and 10 minutes later.

MEASUREMENTS AND MAIN RESULTS

Systolic function was evaluated with the slope (Ees, mmHg/mL) of the systolic pressure-volume relation. Diastolic function was evaluated with the chamber stiffness constant (Kc, mmHg/mL) of the diastolic pressure-volume relation. CaCl2 increased Ees from 2.62 +/- 0.46 to 5.58 +/- 0.61 (mean +/- SD), but induced diastolic dysfunction with an increase in Kc from 0.011 +/- 0.006 to 0.019 +/- 0.007. These changes were transient and had disappeared within 10 minutes after administration of CaCl2.

CONCLUSIONS

CaCl2 early after CPB transiently improved systolic function at the expense of an increase in ventricular stiffness, suggesting temporary diastolic dysfunction.

Effect of inhaled nitric oxide on normal human left ventricular function

OBJECTIVES

This study determined the effects of inhaled nitric oxide (NO) on load-independent indexes of normal human left ventricular (LV) function.

BACKGROUND

Inhaled NO is a potent and selective pulmonary vasodilator. However, when it is used in patients with congestive heart failure, the decrease in pulmonary vascular resistance (PVR) is often associated with an increase in pulmonary capillary wedge pressure. NO has been shown to have a negative inotropic action, but it is not known whether it affects LV chamber function when delivered by inhalation.

METHODS

Eleven subjects (51 to 69 years old) with normal LV function (mean ejection fraction 72% [range 60% to 80%]) were studied. Four patients had concomitant coronary artery disease. Pressure-volume loop recordings were used to determine end-systolic and end-diastolic pressure-volume and preload recruitable stroke work relations. NO was delivered at 20 ppm for 10 min. In an additional group of patients with normal LV function, PVR (n = 5) and NO metabolites (n = 9) were measured.

RESULTS

There was no effect of inhaled NO on steady state LV pressures, volumes, contractility, contraction duration, active relaxation (time constant of relaxation, peak negative first derivative of left ventricular pressure), diastolic compliance or PVR. NO metabolites (methemoglobin and nitrate) were present in the LV cavity at the same concentration as right atrial venous blood, suggesting inactivation of free NO before arrival in the LV chamber. This study had a power of 0.995 to detect a 5% change in contractility (slope of preload recruitable stroke work relation) for alpha = 0.05, based on the multiple linear regression model used.

CONCLUSIONS

These results indicate that 20 ppm of inhaled NO does not have significant effects on normal LV function. This lack of effect may be due in part to rapid inactivation of free NO in transit to the heart.

Identifying and tracking a guide wire in the coronary arteries during angioplasty from X-ray images

During angioplasty, a guide wire (GW) is routinely placed in the coronary artery. Balloon inflation during angioplasty causes transient occlusion of the coronary artery and regional dysfunction. Thus, it is of major importance to monitor myocardial function, which may be impaired during this period. Since the GW moves with the coronary arteries, information regarding myocardial function can potentially be extracted from the GW motion. An algorithm is suggested which is a step toward such monitoring. The algorithm presented is a semiautomatic procedure for identifying and tracking the GW using specific characteristics of the GW. This algorithm is based on working in limited active windows. A preprocessing stage which enhances the GW by the use of a modified Laplacian filter or a modified Marr-Hildreth filter is introduced. The second stage of the algorithm is the tracking of the GW, which is based on fitting a second-degree polynomial to the GW using the Hough transform in each window. To further improve the results further modifications of the basic algorithms that were taken. A single set of parameters, which enabled good tracking for a large number of images taken during angioplasty, was fitted to the final algorithm.

Effects of lidoflazine on left ventricular function in patients

OBJECTIVE

The present study evaluated the effects of the nucleoside transport inhibitor, lidoflazine, at a dose of 1 mg/kg, on left ventricular function.

DESIGN

Patients were randomly assigned to receive either lidoflazine or saline in a double-blind manner.

SETTING

A university hospital.

PARTICIPANTS

The study was performed in 32 patients scheduled for elective coronary artery bypass surgery.

INTERVENTIONS

Left ventricular pressures were measured with fluid-filled catheters. Data were digitally recorded during pressure elevation induced by tilt-up of the legs. Transgastric short-axis echocardiographic views of the left ventricle were simultaneously recorded on videotape. Systolic function was evaluated with the slope (Ees, mmHg/mL) of the systolic pressure-volume relationship. Diastolic function was evaluated with the chamber stiffness constant (Kc, mmHg/mL) of the diastolic pressure-volume relationship. Cardiac function was assessed at baseline and after administration of either lidoflazine (group A [n = 16]) or placebo (group B [n = 16]). Data were compared using two-factor analysis of variance.

MEASUREMENTS AND MAIN RESULTS

At baseline, diastolic and systolic function were comparable in both groups. Lidoflazine increased Kc from 0.079 +/- 0.015 to 0.125 +/- 0.017 mmHg/mL and decreased Ees from 2.481 +/- 0.213 to 1.217 +/- 0.211 mmHg/mL (p = 0.009 and p = 0.004, respectively). None of these changes occurred when placebo was administered.

CONCLUSIONS

Administration of lidoflazine before the start of cardiopulmonary bypass impaired left ventricular systolic function but also increased diastolic stiffness.

Effect of dobutamine and OPC-18790 on diastolic chamber stiffness in patients with idiopathic dilated cardiomyopathy

We investigated the acute effects of the positive inotropic agents (dobutamine and a novel phosphodiesterase inhibitor OPC-18790) on left ventricular diastolic chamber stiffness in patients with idiopathic dilated cardiomyopathy (DCM). We obtained pressure-volume (PV) data before and after drug administration in 17 patients with DCM by using a conductance catheter with a micromanometer tip. Patients were randomly assigned to receive intravenous infusions of dobutamine (2.5-7.5 micrograms/kg body weight per min, n = 8) or OPC-18790 (5-10 micrograms/kg body weight per min, n = 9). The dynamic diastolic chamber stiffness constant was calculated from a steady-state beat. The passive diastolic chamber stiffness constant was determined from the end-diastolic PV relation determined during transient inferior vena caval occlusion. Dobutamine and OPC-18790 similarly improved left ventricular end-systolic elastance (Ees) and left ventricular isovolumic relaxation time constants. The dynamic diastolic chamber stiffness constant decreased significantly in both the dobutamine (0.0934 +/- 0.0271 to 0.0685 +/- 0.0248; p < 0.01) and OPC-18790 (0.0843 +/- 0.0477 to 0.0569 +/- 0.0246; p < 0.05) groups. The passive diastolic chamber stiffness constant decreased significantly in the OPC-18790-treated group (0.0211 +/- 0.0114 to 0.0144 +/- 0.0117; p < 0.005) but not in the dobutamine-treated group (0.0197 +/- 0.0130 to 0.010186 +/- 0.0102; p > 0.05). Thus both dobutamine and OPC-18790 reduced the dynamic diastolic chamber stiffness constant, but only OPC-18790 reduced the passive diastolic chamber stiffness constant. OPC-18790 had a favorable effect on diastolic function in patients with DCM, compared with that of dobutamine. The passive diastolic chamber stiffness obtained from the end-diastolic PV relations represents more likely passive chamber properties than the dynamic diastolic chamber stiffness obtained from traditional single-beat analysis.

Clinical application of the conductance catheter technique in the adult human right ventricle

This study examines the use of conductance catheters to assess human right ventricular volume. Ten patients undergoing diagnostic cardiac catheterisation underwent right heart catheterisation with a conductance catheter and micromanometer, and a thermodilution catheter before and after fluid loading. Parallel wall conductance (Vc), and the multiplication factor relating conductance and thermodilution derived stroke volumes (å) were derived at each steady state. Pressure-volume cycles were analyzed at steady state and during fluid loading. Fluid loading resulted in a significant increase in cardiac output, and change in maximum and minimum cycle volume. There was no significant change in å (mean 0.40 S.D. 0.20) or Vc (mean 126.4 S.D. 59.6 ml) at higher cardiac outputs or ventricular volumes. Right ventricular pressure-volume cycles were formed demonstrating characteristic lack of clear isovolumic contraction and relaxation phases, and low cycle efficiencies (mean 0.62 S.D. 0.16). Serial cycles recorded during volume loading defined an end systolic pressure-volume relation more reliably than a stroke work end diastolic volume relation. Thus, a conductance derived volume signal can be obtained in the human right ventricle which can be interpreted as a continuous and instantaneous index of right ventricular volume, allowing the construction of real time pressure-volume cycles.

Aminophylline reduces cardiac ischemic pain during percutaneous transluminal coronary angioplasty

OBJECTIVES

We investigated the effect of aminophylline, an antagonist of the adenosine P1 receptor, on cardiac pain experienced during percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Adenosine may mediate cardiac pain because the administration of adenosine provokes cardiac pain like angina. However, it is not known whether endogenous adenosine released during myocardial ischemia is responsible for cardiac pain.

METHODS

This was a single-blind, placebo-controlled randomized study. Of 21 men with stable effort angina with one-vessel coronary artery disease who underwent balloon inflation four times during PTCA, 11 received intravenously administered aminophylline before the fourth balloon inflation and the other 10 were given saline solution. The severity of cardiac pain based on the pain score and ST segment elevation on standard surface and intracoronary electrocardiograms were assessed.

RESULTS

All patients experienced cardiac pain during balloon inflation. Aminophylline significantly prolonged the duration of both the symptom-free interval (from 42 +/- 13 to 64 +/- 27 s, mean +/- SD, p < 0.05) and inflation time (from 79 +/- 23 to 103 +/- 20 s, p < 0.05), and it significantly reduced the pain score from 7.6 +/- 1.4 to 4.6 +/- 2.3 (p < 0.01). However, aminophylline did not affect ST segment elevation. Saline solution did not affect any of these variables. Balloon diameter and pressure were not different between the third and the fourth inflation in either group.

CONCLUSIONS

Aminophylline significantly reduced the severity of cardiac pain during PTCA without affecting ST segment elevation. These findings suggest that the activation of P1 receptors by endogenous adenosine may be partially responsible for cardiac pain during ischemia.

Diastolic aortic pressure rise during percutaneous transluminal coronary angioplasty: an index of left ventricular systolic dysfunction

OBJECTIVES

To investigate the relation between diastolic aortic pressure response and left ventricular systolic dysfunction during percutaneous transluminal coronary angioplasty.

BACKGROUND

The abnormal diastolic blood pressure rise during exercise in patients with coronary artery disease probably reflects left ventricular systolic dysfunction rather than the number of stenosed coronary arteries.

METHODS

Aortic blood pressures and left ventricular systolic function indices were estimated in 26 patients with single proximal stenosis of the left anterior descending coronary artery both before and during angioplasty.

RESULTS

During coronary angioplasty all patients presented an increase in diastolic aortic pressure (P << 0.001), 8-12s before intracoronary electrocardiographic changes. During acute ischaemia there was a decrease in left ventricular ejection fraction (P << 0.001) and stroke volume (P << 0.001) and an increase in end systolic volume (P << 0.001) and left ventricular end diastolic pressure (P << 0.001). No statistically significant changes were observed in systolic blood pressure or heart rate. The aortic diastolic pressure increase was correlated with the decrease in ejection fraction (r = -0.95, P << 0.001) and with the increases in end systolic volume (r = 0.86, P << 0.001) and left ventricular end diastolic pressure (r = 0.85, P << 0.001).

CONCLUSIONS

The rise in diastolic aortic pressure during percutaneous transluminal coronary angioplasty occurs earlier than intracoronary electrocardiographic changes and is related to ischaemic left ventricular systolic dysfunction.