Right atrial pressure-volume relationships in tricuspid regurgitation

Clinical relevance and prognostic value of renal Doppler in acute decompensated precapillary pulmonary hypertension

AIMS

We aim to evaluate the clinical relevance and the prognostic value of arterial and venous renal Doppler in acute decompensated precapillary pulmonary hypertension (PH).

METHODS AND RESULTS

The renal resistance index (RRI) and the Doppler-derived renal venous stasis index (RVSI) were monitored at admission and on Day 3 in a prospective cohort of precapillary PH patients managed in intensive care unit for acute right heart failure (RHF). The primary composite endpoint included death, circulatory assistance, urgent transplantation, or rehospitalization for acute RHF within 90 days following inclusion. Ninety-one patients were enrolled (58% female, age 58 ± 16 years). The primary endpoint event occurred in 32 patients (33%). In univariate logistic regression analysis, variables associated with RRI higher than the median value were non-variable parameters (age and history of hypertension), congestion (right atrial pressure and renal pulse pressure), cardiac function [tricuspid annular plane systolic excursion (TAPSE) and left ventricular outflow tract- velocity time integral], systemic pressures and NT-proBNP. Variables associated with RVSI higher than the median value were congestion (high central venous pressure, right atrial pressure, and renal pulse pressure), right cardiac function (TAPSE), severe tricuspid regurgitation, and systemic pressures. Inotropic support was more frequently required in patients with high RRI (P = 0.01) or high RVSI (P = 0.003) at the time of admission. At Day 3, a RRI value <0.9 was associated with a better prognosis after adjusting to the estimated glomerular filtration rate.

CONCLUSION

Renal Doppler provides additional information to assess the severity of patients admitted to the intensive care unit for acute decompensated precapillary PH.

Method for measuring jugular venous pulse with a miniature gyroscope sensor patch

The right internal jugular vein is connected to the right atrium of the heart via the superior vena cava, and consequently its pressure, known as the jugular venous pressure or the jugular venous pulse (JVP), is an important indicator of cardiac function. The JVP can be estimated visually from the neck but it is rather difficult and imprecise. In this article we propose a method to measure the JVP using a motion sensor patch attached to the neck. The JVP signal was extracted from the sensor's 3-axes gyroscope signal and aligned with simultaneously measured ECG and seismocardiogram signals.The method was tested on 20 healthy subjects. The timings of the characteristic JVP waves were compared with the ECG R peaks and seismocardiogram heart sounds S1 and S2. The JVP was reliably measured from 18 subjects with all three waves identified. The timings of the waves were also physiologically plausible when compared to the ECG R peak and the heart sounds. Importantly, the JVP was also found to modulate with respiration, further indicating that the measured signal was indeed the JVP and not the carotid pulse.The results show that the JVP can be measured with a wearable patch-like device registering the delicate motions of the right internal jugular vein. The method has potential to be developed into a clinical tool to measure cardiac health in diseases such as heart failure and chronic obstructive pulmonary disease (COPD).Clinical relevance-The developed method could enable an affordable measurement of clinically important cardiac parameter, jugular venous pulse, as a part of a routine examination.

Tricuspid surgery at the time of LVAD implant: A critique

Tricuspid regurgitation (TR) is a common finding in patients with end stage heart failure referred for implantation of left ventricular assist devices. While functional TR frequently resolves after left ventricular unloading, patients with residual and progressive TR demonstrate increased rates of RV dysfunction and poor survival. Criteria for intervention on the tricuspid valve have focused on the degree of tricuspid annular dilatation and the severity of tricuspid regurgitant volume. The surgical decision making regarding intervention on the tricuspid valve remains obscure and historical cohort data cannot distinguish cause from effect.

Tricuspid Regurgitation in Adults after Repair of Right Ventricular Outflow Obstructive Lesions

We determined the prevalence and factors associated with tricuspid regurgitation (TR) in adults with repair of right ventricular (RV) outflow obstruction. A total of 256 patients (128 males) were studied at 25.7 ± 7.2 years after surgery, of whom 179 had repaired tetralogy of Fallot (TOF), 31 had pulmonary atresia with intact ventricular septum (PAIVS), and 46 had pulmonary stenosis (PS). The mitral and tricuspid annulus diameters, maximum right atrial (RA) area, RV end-systolic and end-diastolic areas, and tricuspid and pulmonary regurgitation were assessed using echocardiography. The prevalence of moderate-to-severe TR was 20.7%. Subgroup analysis revealed that prevalence was greater in patients with repaired TOF (20.7%) and PAIVS (35.5%) than PS patients (10.9%). As a group, severity of TR was found to be correlated with RA area (r = 0.35, p < 0.001), RV end-diastolic (r = 0.28, p < 0.001) and end-systolic (r = 0.22, p = 0.001) areas, and tricuspid valve annulus diameter (r = 0.15, p = 0.022). Moderate-to-severe TR was associated with development of cardiac arrhythmias with an odds ratio of 2.9 (95% CI 1.1 to 8.1, p = 0.031). Multivariate analysis revealed maximum RA area (β = 0.36, p = 0.016) as an independent determinant of severity of TR. Moderate-to-severe TR occurs in about one-fifth of adults with repaired TOF, PAVIS, and PS and is associated with RA dilation and risk of development of cardiac arrhythmias.

Strategies for diagnosis of fetal right atrium dilation: based on fetal cardiac anatomy and hemodynamics

BACKGROUND

Fetal right atrium (RA) dilation is frequently detected in routine screenings while it remains a challenge to clarify the reasons. This study aimed to analyze the cardiac anatomy and hemodynamics of fetal RA dilation and the changes of hemodynamic indexes.

METHODS

In the retrospective study, 420 fetuses with RA dilation were included, which were classified into the physiological group (n = 202), volume overload group (n = 142), and the pressure overload group (n = 76). The ratio of right atrium to left atrium (RA/LA) were measured at four-chamber view. Peak velocity of tricuspid regurgitation (V_TR) was recorded in each case, if existed.

RESULTS

The RA/LA ratio in the volume overload group is significantly higher than both the pressure overload group and the physiological group (both P = 0.000) throughout the pregnancy while no difference presents between the pressure overload group and the physiological group (P = 0.694 for 19-31 GW, and P = 0.974 for 32-36 GW, respectively). The V_TR in the pressure overload group (3.29 ± 0.58 m/s) is significantly higher than both the volume overload group (1.85 ± 0.45 m/s, P = 0.000) and the physiological group (0.88 ± 0.45 m/s, P = 0.000). The volume overload group shows a significantly higher V_TR than the physiological group (P = 0.000). In the volume overload group, the ductal contraction/closure shows a significantly higher V_TR than that in the pulmonary valve stenosis/atresia (3.98 ± 0.41 m/s vs. 3.03 ± 0.38 m/s, P = 0.000).

CONCLUSIONS

A strategy proposed herein is useful to clarify the reasons for RA dilatation by systematically assessing fetal hemodynamics, which may facilitate the sonographers to make an accurate diagnosis of congenital heart disease.

Large animal model of acute right ventricular failure with functional tricuspid regurgitation

BACKGROUND

Functional tricuspid regurgitation (FTR) commonly arises secondary to conditions affecting the left heart and is associated with right ventricular dysfunction and tricuspid annular dilatation. We set out to establish an animal model of acute RV failure (RVF) with FTR resembling the clinical features.

METHODS

Ten adult sheep had pressure sensors placed in the LV, RV, and right atrium while sonomicrometry crystals were implanted around tricuspid annulus and on the RV. Animals were studied open-chest to assess for RV function and FTR after: (1) volume infusion, (2) pulmonary artery constriction, (3) 5 min posterior descending artery occlusion, and (4) combination of all interventions. Hemodynamic, echocardiographic, and sonomicrometry data were collected at baseline and after every intervention. RV dimensions, RV strain, and annular area, perimeter, and size were calculated from crystal coordinates. The model was validated in six additional sheep studied only before and after combined interventions.

RESULTS

Neither volume infusion, pulmonary hypertension, nor ischemia were associated with RVF or clinically significant TR when applied separately but combined resulted in RVF and greater than moderate FTR. In the validation group, maximal RV volume increased (62 ± 14 vs 70 ± 16 ml, p = 0.006), contractility decreased (20 ± 6 vs 12 ± 2%, p = 0.02), and strain increased. FTR increased from 0.4 ± 0.5 to 2.5 ± 0.8 (p < 0.001) and annular area from 652 ± 87 mm² to 739 ± 87 mm² (p = 0.005).

CONCLUSIONS

The developed ovine model of acute RVF was associated with significant annular and RV enlargement and FTR. This novel and clinically pertinent research platform offers insight into the acute RVF pathophysiology and can be utilized to evaluate treatment interventions.

Low Cardiac Output Leads Hepatic Fibrosis in Right Heart Failure Model Rats

Background

Hepatic fibrosis progresses with right heart failure, and becomes cardiac cirrhosis in a severe case. Although its causal factor still remains unclear. Here we evaluated the progression of hepatic fibrosis using a pulmonary artery banding (PAB)-induced right heart failure model and investigated whether cardiac output (CO) is responsible for the progression of hepatic fibrosis.

Methods and Results

Five-week-old Sprague-Dawley rats divided into the PAB and sham-operated control groups. After 4 weeks from operation, we measured CO by echocardiography, and hepatic fibrosis ratio by pathological examination using a color analyzer. In the PAB group, CO was significantly lower by 48% than that in the control group (78.2±27.6 and 150.1±31.2 ml/min, P<0.01). Hepatic fibrosis ratio and serum hyaluronic acid, an index of hepatic fibrosis, were significantly increased in the PAB group than those in the control group (7.8±1.7 and 1.0±0.2%, P<0.01, 76.2±27.5 and 32.7±7.5 ng/ml, P<0.01). Notably, the degree of hepatic fibrosis significantly correlated a decrease in CO. Immunohistological analysis revealed that hepatic stellate cells were markedly activated in hypoxic areas, and HIF-1α positive hepatic cells were increased in the PAB group. Furthermore, by real-time PCR analyses, transcripts of profibrotic and fibrotic factors (TGF-β1, CTGF, procollargen I, procollargen III, MMP 2, MMP 9, TIMP 1, TIMP 2) were significantly increased in the PAB group. In addition, western blot analyses revealed that the protein level of HIF-1α was significantly increased in the PAB group than that in the control group (2.31±0.84 and 1.0±0.18 arbitrary units, P<0.05).

Conclusions

Our study demonstrated that low CO and tissue hypoxia were responsible for hepatic fibrosis in right failure heart model rats.

Tricuspid leaflet resection in an open beating heart for the creation of a canine tricuspid regurgitation model

OBJECTIVES

Outcomes of tricuspid valve replacement are poor, partly due to right heart remodelling. The research on its underlying mechanisms is hampered by a lack of animal models of tricuspid regurgitation (TR). Our objective was to create a reproducible and clinically compatible TR animal model to study right heart remodelling caused by TR.

METHODS

Fourteen juvenile male Beagle dogs were divided randomly into an intervention group (n = 11) and a sham-operated control group (n = 3). The intervention group underwent thoracotomy and right atrial incision following superior and inferior vena caval occlusion. The anterior leaflet, together with the chordae, of the tricuspid valve was resected in eight dogs ('one leaflet' group), whereas both anterior and posterior leaflets, together with the chordae, were resected in three dogs ('two leaflets' group). The right atrium and chest were then closed. The control group underwent the same procedure, except leaflet resection. One dog from the 'two leaflets' group and one control dog were sacrificed and autopsy was performed at 12 months post-surgery.

RESULTS

All dogs survived over the 1-year observation period postoperatively. TR grade IV occurred immediately postoperatively in the 'one leaflet' group, and TR grade IV plus in the 'two leaflets' group. The overall procedure lasted 30-40 min, and the mean time of vena caval occlusion was 87 ± 10 s. Central venous pressure increased from 6 ± 1.2 at baseline to 13 ± 1.7 mmHg (P < 0.01). By 12 months after TR creation, both in the 'one leaflet' group and in the 'two leaflets' group, the right atrial area, tricuspid annular diameter and right ventricular index of myocardial performance increased significantly, right ventricular fractional area change and tricuspid annular plane systolic excursion decreased significantly. Autopsy of the intervention dog revealed oedema, ascites and cirrhosis.

CONCLUSIONS

Our surgical technique to create a TR animal model was reproducible with high success and survival rates. This animal model would prove suitable to investigate the mechanisms of right heart remodelling.

The relationship between tricuspid regurgitation severity and right atrial mechanics: a speckle tracking echocardiography study

The aim at this study was to assess the influence of the tricuspid regurgitation volume (TRvol) in right atrium (RA) reservoir phase myocardial mechanics. We included 55 heart failure (HF) patients referred for transthoracic echocardiography during a 2-month period. 18 Had HF with a reduced ejection fraction (HFREF) and 37 HF with a preserved ejection fraction (HFPEF). TR was chronic and functional. TRvol was calculated according to the PISA method. This study of RA used 2D-speckle tracking echocardiography to measure strain (rεR) and strain rate (rSR(R)). The reference frame coincided with the onset of the QRS. RA stiffness was assessed as the ratio: (rE/e')/rε(R). The median age of the sample was 78 (64-84) years, with female gender predominance (63.6%). The median value of rε(R) was 16% (range, 12.7-24.0) and of rSR(R) was 1.57 s(-1) (range, 1.09-2.05). We observed a significant negative correlation between rε(R) (r = -0.68, p < 0.01) and rSR(R) (r = -0.58, p < 0.01) and TRvol. RA mechanics decreased significantly with an increase in the TR grade. We created two multivariate linear regression models for rε(R) and rSR(R), separately for the patients with sinus rhythm or atrial fibrillation. The TRvol was independently associated with rε(R) after adjusting to the RA area, right ventricular longitudinal systolic function and the estimated pulmonary vascular resistance. We demonstrated an increase in RA stiffness with an increase in TR severity, and an association for functional status (NYHA class) and RA compliance. The HFREF group had a significantly lower rε(R) and rSR(R) that the HFPEF patients. According to our study, in HF patients, a chronic volume overload state significantly reduced the RA reservoir phase mechanics.

Right heart and pulmonary vessels structure and function

The right ventricle (RV) can be described in terms of 3 components: the inlet, the apex, and the infundibulum. In the normal adult, the RV shows an arrangement suited for pumping blood against low resistance, with a mass about one sixth that of left ventricle (LV) mass, and a larger volume than the LV. The RV is able to manage a progressive increase in the afterload by increasing contractility and remodeling. The gold standard measurement of contractility is maximal elastance (Emax), or the ratio between end-systolic pressure (ESP) and end-systolic volume (ESV), and the best measurement of afterload is arterial elastance (Ea), or the ratio between ESP and stroke volume (SV). The ratio Emax/Ea defines RV-arterial coupling. The optimal energy transfer from the RV to the pulmonary circulation is measured at Emax/Ea ratios of 1.5-2. In the presence of pulmonary hypertension, the SV/ESV ratio may be an acceptable surrogate of Emax/Ea. The right atrium (RA) has 3 anatomical components: the appendage, the venous part, and the vestibule. It is a dynamic structure having different functions: reservoir, conduit, and booster pump function. In case of increased afterload, the RA is enlarged, denoting high RA pressure, as a consequence of elevated RV diastolic pressure. RA area is a strong predictor of adverse clinical outcome in pulmonary arterial hypertension. In patients with severe pulmonary hypertension, in several congenital heart diseases, and in Eisenmenger syndrome, symptoms and prognosis are greatly dependent on RV function and its ability to adapt to a chronic increase in afterload.

The jugular venous pressure revisited

Assessment of the jugular venous pressure is often inadequately performed and undervalued. Here, we review the physiologic and anatomic basis for the jugular venous pressure, including the discrepancy between right atrial and central venous pressures. We also describe the correct method of evaluating this clinical finding and review the clinical relevance of the jugular venous pressure, especially its value in assessing the severity and response to treatment of congestive heart failure. Waveforms reflective of specific conditions are also discussed.

Differential impact of short periods of rapid atrial pacing on left and right atrial mechanical function

Current techniques to describe atrial function are limited by their load dependency and hence do not accurately reflect intrinsic mechanical properties. To assess the impact of atrial fibrillation on atrial function, combined pressure-volume relationships (PVR) measured by conductance catheters were used to evaluate the right (RA) and left (LA) atrium in 12 isoflurane-anesthetized pigs. Biatrial PVR were recorded over a wide range of volumes during transient caval occlusion at baseline sinus rhythm (SR), after onset of rapid atrial pacing (RAP), after 1 h of RAP, after conversion to SR, and after 1 h of recovery. Cardiac output decreased by 16% (P = 0.008) with onset of RAP. Mean LA and RA pressures increased by 21 and 40% (P < 0.001), respectively, and remained elevated during the entire recovery period. RA reservoir function increased from 51 to 58% and significantly dropped to 43% after resumption of SR (P = 0.017). Immediately after RAP, a right shift of LA end-systolic PVR-intercept for end-systolic volume required to generate an atrial end-systolic pressure of 10 mmHg (24.4 ± 4.9 to 28.1 ± 5.2 ml, P = 0.005) indicated impaired contractility compared with baseline. Active LA emptying fraction dropped from 17.6 ± 7.5 to 11.7 ± 3.7% (P < 0.001), LA stroke volume and ΔP/Δt(max)/P declined by 22% (P = 0.038 and 0.026, respectively), while there was only a trend to impaired RA systolic function. Stiffness quantified by the ratio of pressure to volume at end-diastole was increased immediately after RAP only in the RA (P = 0.020), but end-diastolic PVR shifted rightward in both atria (P = 0.011 LA, P = 0.045 RA). These data suggest that even short periods of RAP have a differential impact on RA and LA function, which was sustained for 1 h after conversion to SR.

Percutaneous Technique for Creation of Tricuspid Regurgitation in an Ovine Model

Experimental models of tricuspid regurgitation (TR) are needed to study the percutaneous placement of prosthetic atrioventricular valves. The purpose of this study was to develop an appropriate simple and reproducible percutaneous experimental model for creation of tricuspid regurgitation. Tricuspid regurgitation was successfully created through papillary muscle avulsion using a guide-wire loop in seven sheep with regurgitation documented on right ventricular angiograms and a significant increase in heart rate and right atrial pressures. Acute onset of tricuspid regurgitation was poorly tolerated in one animal that died. Autopsy examinations showed avulsion of one papillary muscle in four animals and two papillary muscles in three animals.

Reservoir and conduit function of right atrium: impact on right ventricular filling and cardiac output

The purpose of this study was to investigate the relationship between right atrial (RA) reservoir and conduit function and to determine how hemodynamic changes influence this relationship and its impact on cardiac output. In 11 open-chest sheep, RA reservoir and conduit function were quantified as RA inflow with the tricuspid valve closed versus open, respectively. Conduit function was separated into early (before A wave) and late (after A wave) components. The effects of inotropic stimulation, partial pulmonary artery occlusion, and pericardiotomy were tested. At baseline with the pericardium intact, reservoir function accounted for 0.56 (SD 0.13) of RA inflow, early conduit for 0.29 (SD 0.07), and late conduit (during RA contraction) for 0.16 (SD 0.11). Inotropic stimulation decreased conduit function and increased reservoir function, but these effects did not reach statistical significance. With partial pulmonary artery occlusion, early conduit function fell to 0.20 (SD 0.11) ( P < 0.04), and the conduit-to-reservoir ratio decreased by 41% ( P < 0.03). Similarly, after pericardiotomy, early conduit function fell to 0.14 (SD 0.09) ( P < 0.004), reservoir function increased to 0.72 (SD 0.08) ( P < 0.04), and, consequently, the early conduit-to-reservoir ratio decreased by 63% ( P < 0.006). Cardiac output was inversely related to the conduit-to-reservoir ratio ( r = 0.39, P < 0.001). This study demonstrated that the right atrium adjusts its ability to act more as a reservoir than a conduit in a dynamic manner. The RA conduit-to-reservoir ratio was directly related to the right ventricular pressure-RA pressure gradient at the time of maximum RA volume, with increased ventricular pressures favoring conduit function, but it was inversely related to cardiac output, with an increase in the reservoir contribution favoring improved cardiac output.

Right atrial dimension-pressure relation during volume expansion is unaltered by pregnancy in the rat

Blood volume expands significantly during pregnancy, but afferent signals from cardiac receptors are reduced. In addition, during exogenous volume expansion, right atrial pressure (RAP) increases more for equivalent volumes in pregnant animals, implying reduced atrial compliance. To examine possible gestational alterations in atrial dimension during volume expansion, we compared the effects of volume expansion on RAP and right atrial dimension (RAD) in pregnant vs. virgin rats. Anesthetized animals were ventilated and catheterized for measurement of arterial pressure and RAP and for drug infusion. Through a parasternal incision, ultrasonic crystals were glued to the medial and lateral surfaces of the right atrium for measurement of RAD. Plasma volume and hematocrit were determined before experimentation. RAP, RAD, and arterial pressure were recorded at baseline and during progressive volume expansion (6% dextran, 60% of initial blood volume). Baseline RAP was similar in the two groups: 2.82 ± 0.40 and 2.72 ± 0.47 mmHg in pregnant and virgin rats, respectively. Basal RAD was significantly larger in pregnant than in virgin rats: 4.36 ± 0.66 vs. 3.36 ± 0.48 mm. Despite increased basal RAD in pregnant rats, the slope of the RAD-RAP relation during volume expansion was similar in the two groups. Results indicate that resting RAD is increased in pregnant rats and that the change in dimension during volume loads is similar to that in virgin rats. Thus, during pregnancy, the right atrium appears to accommodate the increased blood volume, and reduced afferent signaling most likely is due to mechanisms other than mechanical alterations of the atrium by expanded volume.

Impact of pericardial restraint on right atrial mechanics during acute right ventricular pressure load

Optimization of right atrial (RA) mechanics is important for maintaining right ventricular (RV) filling and global cardiac output. However, the impact of pericardial restraint on RA function and the compensatory role of the right atrium to changes in RV afterload remain poorly characterized. In eight open-chest sheep, RA elastance (contractility) and chamber stiffness were measured (RA pressure-volume relations) at baseline and during partial pulmonary artery (PA) occlusion. Data were collected before and after pericardiotomy. With the pericardium intact and partial PA occlusion, RA elastance increased by 28% (P < 0.04), whereas RA stiffness tended to rise (P = 0.08). However, after pericardiotomy, there was a significant fall in both RA elastance (54%, P < 0.04) and stiffness (39%, P < 0.04), and subsequent PA occlusion failed to induce a change in elastance (P > 0.19) or stiffness (P > 0.84). After pericardiotomy, RA elastance and stiffness fell dramatically, and the compensatory response of the right atrium to elevated RV afterload was lost. The ability of the right atrium to respond to changes in RV hemodynamics is highly dependent on pericardial integrity.

Right atrial function in hypertensive patients: effects of antihypertensive therapy

OBJECTIVES

The effects (16 weeks) of oral antihypertensive drugs on right atrial (RA) function were evaluated by two-dimensional and Doppler echocardiography in 64 patients with mild-to-moderate essential hypertension. Thirty-two age- and sex-matched normal subjects served as controls.

BACKGROUND

Hypertension alters the diastolic properties of the left ventricle and disturbs the left atrial contractile activities. RA performance may also alter in essential hypertension.

METHODS

From the tricuspid flow velocity curves the E/A ratio, the velocity-time integrals (Ei and Ai, respectively) as well as the sum, TTi = Ei + Ai, were measured. RA active contribution (RAAC) was expressed as the ratio RAAC = Ai/TTi.

RESULTS

RA-A/E ratio, RA-Ai and RAAC were increased while RA-TTi were decreased in hypertensives compared to controls, P < 0.0001 for all comparisions. After therapy TTi increased (from 13.2 +/- 1.6 to 16.2 +/- 2.0 cm with ramipril, and from 12.9 +/- 1.1 to 14.4 +/- 1.2 cm with amlodipine, P < 0.001) and RAAC decreased (from 0.19 +/- 0.01 to 0.13 +/- 0.01, with ramipril and from 0.19 +/- 0.01 to 0.16 +/- 0.00, with amlodipine P < 0.001) while RA dimensions did not change. the decrease in RAAC was significantly greater with ramipril (P < 0.001) and was significantly influenced by the decrease in left ventricular mass (P < 0.001) and right ventricular relaxation (P < 0.001).

CONCLUSIONS

RA function is deteriorated in patients with essential hypertension. The fall in the arterial blood pressure produced by antihypertensive treatment was associated with improved RA performance and reduced left ventricular mass without changes in RA dimensions. The left ventricular mass and the right ventricular relaxation influenced the changes in RA performance.

Effects of physical parameters on the cylindrical model for volume measurement by conductance

Despite its undisputed utility for determining changes in ventricular pressure-volume relationships, the conductance catheter technique has not been proven reliable for measuring absolute volume. This limitation is due to violations of the assumptions inherent in the cylindrical model on which the method is based (i.e., homogeneous electric field and no leakage current). The purpose of this investigation was to relate cylindrical model correction factors to the physical environment of the catheter and to the cylindrical equation. Physical measurements of saline-filled, nonconductive cylinders using a four-electrode conductance catheter were compared with a three-dimensional finite element model of the physical apparatus. These measurements were incorporated into a parallel conductance model to relate physical parameters to corrections in the cylindrical equation for volume measurement. Excellent agreement between measured and modeled data was found. Results demonstrated a nonlinear relationship between the field nonhomogeneity correction factor (alpha) and cylinder diameter. The relationship between alpha and diameter was consistent with a theoretical extrapolation of cylinder diameter toward infinity. An inverse relationship between alpha and the parallel conductance volume (Vp) was also clarified. The parallel conductance model was able to demonstrate opposite effects of the physical presence of the catheter body and electrodes, which tended to cancel out any net effect on measured conductance. Results of this investigation and the developed finite element model clarify the nature of the correction terms in the cylindrical model and may lead to greater application of the conductance technique.

Right atrial ischemia exacerbates hemodynamic compromise associated with experimental right ventricular dysfunction

To determine the importance of right atrial function with acute right ventricular dysfunction, sequential right ventricular and right atrial ischemia were induced in 15 dogs. Right ventricular ischemia resulted in right ventricular free wall dyskinesia, right ventricular dilation by ultrasound, elevated right ventricular filling pressure and paradoxic septal motion. There were decrements in right ventricular systolic pressure (28.9 +/- 5.5 to 25.5 +/- 4.6 mm Hg) (p less than 0.05 for these and all subsequent values) and stroke work (5.66 +/- 0.94 to 2.66 +/- 0.62 g.m/m2), resulting in reductions in left ventricular preload, systolic pressure (123 +/- 11 to 97 +/- 12 mm Hg) and stroke volume (24.2 +/- 4.3 to 19.1 +/- 5.2 ml). Right atrial contractility was augmented, as indicated by increases in peak A wave amplitude (ratio of peak A wave to mean right atrial pressure 1.22 +/- 0.02 to 1.46 +/- 0.3) and right atrial stroke work (0.11 +/- 0.02 to 0.25 +/- 0.05 g.m/m2). Right atrial ischemia depressed right atrial contraction, as indicated by decreased A wave amplitude (ratio of peak A wave to mean right atrial pressure 1.46 +/- 0.3 to 1.04 +/- 0.2) and stroke work (0.25 +/- 0.05 to 0.04 +/- 0.01 g.m/m2).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced atrial contribution to left ventricular filling in patients with severe tricuspid regurgitation after tricuspid valvulectomy: a Doppler echocardiographic study

Patients undergoing valvulectomy for isolated tricuspid valve endocarditis offer the unique opportunity to study the effects of acquired right ventricular volume overload on left ventricular filling in persons free of pulmonary hypertension and preexisting left heart disease. Eleven patients who had undergone total or partial removal of the tricuspid valve were compared with 11 age-matched control subjects; Doppler echocardiographic techniques were used to quantify changes in left ventricular filling and to relate them to changes in left ventricular and left atrial geometry caused by right ventricular and right atrial distension. The late diastolic fractional transmitral flow velocity integral, a measure of the left atrial contribution to left ventricular filling, was significantly decreased in patients undergoing tricuspid valvulectomy compared with control subjects (0.22 +/- 0.11 versus 0.32 +/- 0.09; p less than 0.04). Severe tricuspid regurgitation in these patients resulted in marked right atrial distension, reversal of the normal interatrial septal curvature and compression of the left atrium such that left atrial area was significantly smaller than in control subjects (5.9 +/- 2.2 versus 8.6 +/- 1.2 cm2/m2; p less than 0.005). Acting as a receiving chamber, the left ventricle was maximally compressed by the volume-overloaded right ventricle in late diastole, coincident with the timing of atrial systole, resulting in a significant increase in the left ventricular eccentricity index compared with that in control subjects (1.35 +/- 0.14 versus 1.03 +/- 0.1; p less than 0.001). Thus, right ventricular volume overload due to severe tricuspid regurgitation results in left heart geometric alterations that decrease left atrial preload, impair left ventricular receiving chamber characteristics and reduce the atrial contribution to total left ventricular filling.

Assessment of right atrial pressure-volume relations in patients with and without an atrial septal defect

Assessment of the complex relations between pressure and volume in the right atrium has been hampered in the past by difficulties in the measurement of atrial volume. Accordingly, in the present study the dynamics of right atrial pressure-volume relations were examined (with the use of an impedance catheter to measure right atrial volume) in patients with and without an atrial septal defect. Right atrial pressure and impedance volume were measured in 16 patients at the time of cardiac catheterization with the use of a multi-electrode impedance catheter to provide continuous, on-line, pressure-volume data. Eleven patients without evidence of an interatrial shunt were examined during normal respiration and during the Valsalva maneuver and contrasted with five patients with an atrial septal defect documented by oxygen saturation step-up and echocardiographic studies. Right atrial pressure-volume diagrams in patients without an atrial septal defect exhibited the normal figure eight pattern, with an A loop (atrial contraction) and a V loop (passive filling), corresponding to the A wave and V wave of right atrial pressure, respectively. During inspiration, mean right atrial pressure decreased and mean right atrial volume increased, consistent with augmented venous return. With the Valsalva maneuver, right atrial pressure increased and both right atrial stroke volume and mean right atrial volume decreased compared with baseline. Patients with an atrial septal defect demonstrated baseline pressure-volume diagrams similar to those of patients without an interatrial shunt. However, no change in mean right atrial volume occurred with either respiration or the Valsalva maneuver despite changes in right atrial pressure similar to those seen inpatients without an atrial septal defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of respiration and vasodilation on venous volume in animals and man, as measured with an impedance catheter

Venous return determines cardiac preload and is in turn affected by respiration and vasodilation. The purpose of the present study was to examine the dynamics of venous return and venous volume, using impedance volume measurements in the venous system. In order to develop a methodology for the assessment of venous volume and venous return in man, we first studied 17 endotracheally intubated and ventilated anesthetized closed-chest dogs. We measured central venous and inferior vena cava (IVC) pressure (micromanometer) and volume (impedance catheter). Studies were done above and below the diaphragm with normal ventilation, with positive end-expiratory pressure (PEEP), and with beta-adrenergic blockade and i.v. nitroglycerin. Intrathoracic IVC volume fell and extrathoracic IVC volume rose with lung inflation, while PEEP raised extrathoracic IVC volume and lowered intrathoracic IVC volume. Nitroglycerin lowered intrathoracic IVC volume. Beta blockade did not affect IVC volume, ventilatory variation, or response to PEEP and nitroglycerin. We performed similar studies in 14 human subjects during normal quiet respiration, with measurements above and below the diaphragm, and with interventions including Valsalva maneuver and i.v. nitroglycerin. Intrathoracic IVC volume fell and extrathoracic IVC volume rose with expiration and Valsalva maneuver. Nitroglycerin again lowered intrathoracic IVC volume. We conclude that venous volume and the dynamics of venous return can be assessed in animals and man with an impedance catheter. Specifically, we show the divergent effects of respiration, ventilation, PEEP, and nitroglycerin on IVC volumes above and below the diaphragm. Beta-adrenergic blockage does not appear to play a role in altering any of these effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of aortic pressure-volume relationships with an impedance catheter

Volume measurements obtained with an impedance catheter (impedance volume measurements) have been used previously in determining pressure-volume relationships in the right and left ventricles and in the right atrium. The purpose of the present study was to determine the utility of impedance volume techniques in the assessment of aortic pressure-volume relationships in animals and humans. Experiments to develop this methodology were first performed in ten anesthetized dogs, with simultaneous measurements of aortic pressure (micromanometer), diameter (ultrasonic crystals), and impedance volume. Transient (20 sec) inferior vena cava (IVC) occlusion and nitroprusside infusion resulted in a reproducible series of aortic pressure-volume and pressure-diameter points. In each case changes in impedance volume closely paralleled changes in diameter. From the wide range of pressure-volume points, it was possible to construct pressure-volume plots for a single cardiac cycle, as well as longer loops over a 20-40 mm Hg pressure range. End-systolic and end-diastolic pressure-volume points could subsequently be identified, which outlined a more precise pressure-volume relationship that was linear in six cases and curvilinear in four cases, depending on the level of aortic pressure. We extended these techniques to human subjects undergoing diagnostic cardiac catheterization. Studies using the impedance catheter in the aorta were performed in 11 patients. Aortic pressure-volume curves were elicited during Valsalva maneuver to obtain data over a range wider than that of a single cardiac cycle. Measurements of relative volume were calibrated with simultaneous M-mode echocardiography in three patients. We conclude that pressure-volume relationships in the aorta can be assessed with impedance volume techniques, making possible in vivo measurements of arterial compliance. Potential nonlinearities in aortic P-V relationships require that the assessment of aortic compliance encompass as much as possible of the physiologic range of pressure and volume.

The effect of VVI pacing and resultant atrioventricular dyssynchrony on segmental volumes

Left and right ventricular volumes were monitored simultaneously in four anesthetized dogs by intracardiac impedance ventriculography during normal sinus rhythm, spontaneous ventricular rhythm, and VVI and VDD pacing. Cardiac output was found to increase with VVI pacing rate but remained somewhat lower than normal sinus or VDD values. The dissynchronous atrial contraction was found to distort the volume waveforms but had little effect on right ventricular volumes. Left atrial contraction had the greatest impact on left ventricular filling at near normal AV delays. Cardiac output during VDD pacing was found to be a maximum at 170 msec and decreased in three of four dogs at 220 msec. Examination of volume waveforms during "filling" indicates that the right ventricle is dominated by passive filling while the left ventricle demonstrates a large active or "fast" filling phase.