Ouabain-induced hypertension enhances left ventricular contractility in rats

Chronic ouabain treatment produces hypertension acting on the central nervous system and at vascular levels. However, cardiac effects in this model of hypertension are still poorly understood. Hence, the effects of hypertension induced by chronic ouabain administration ( approximately 8 microg day(-1), s.c.) for 5 weeks on the cardiac function were studied in Wistar rats. Ouabain induces hypertension but not myocardial hypertrophy. Awake ouabain-treated rats present an increment of the left ventricular systolic pressure and of the maximum positive and negative dP/dt. Isolated papillary muscles from ouabain-treated rats present an increment in isometric force, and this effect was present even when inotropic interventions (external Ca(2+) increment and increased heart rate) were performed. However, the sarcoplasmic reticulum activity and the SERCA-2 protein expression did not change. On the other hand, the activity of myosin ATPase increased without changes in myosin heavy chain protein expression. In addition, the expression of alpha(1) and alpha(2) isoforms of Na(+), K(+)-ATPase also increased in the left ventricle from ouabain-hypertensive rats. The present results showed positive inotropic and lusitropic effects in hearts from awake ouabain-treated rats, which are associated with an increment of the isometric force development and of the activity of myosin ATPase and expression of catalytic subunits of the Na(+), K(+)-ATPase.     

Effects of changes in left ventricular contractility on indexes of contractility in mice

Measurement of left ventricular (LV) function is often overlooked in murine studies, which have been used to analyze the effects of genetic manipulation on cardiac phenotype. The goal of this study was to address the effects of changes in LV contractility on indexes of contractility in mice. LV function was assessed in vivo in closed-chest mice by echocardiography and by LV catheterization using a conductance pressure-volume (P-V) catheter with three different interventions that alter contractility by 1) atrial pacing to increase inotropy by augmentation of the force-frequency relation (modest increment of inotropy), 2) dobutamine to maximize inotropy, and 3) esmolol infusion to decrease contractility. Load-independent parameters derived from P-V relations, such as slope of end-systolic P-V relations (ESPVR) and slope of the first maximal pressure derivative over time (dP/dt(max))-end-diastolic volume relation (dP/dt-EDV), and standard echocardiographic parameters were measured. The dP/dt-EDV changed the most among parameters after atrial pacing and dobutamine infusion (percent change, 162.8 +/- 95.9% and 271.0 +/- 44.0%, respectively). ESPVR was the most affected by a decrease in LV contractility during esmolol infusion (percent change, -49.8 +/- 8.3%). However, fractional shortening failed to detect changes in contractility during atrial pacing and esmolol infusion and its percent change was <20%. This study demonstrated that contractile parameters derived from P-V relations change the most during a change in LV contractility and should therefore best detect a small change in contractility in mice. Heart rate has a modest but significant effect on P-V relationship-derived indexes and must be considered in the evaluation of murine cardiac physiology.     

Acidaemia reduces cardiac output and left ventricular contractility in conscious lambs

We studied the effects of HCI-induced metabolic acidaemia on cardiac output, contractile function, myocardial blood flow, and myocardial oxygen consumption in nine unanaesthetized newborn lambs. Through a left thoracotomy, catheters were placed in the aorta, left atrium and coronary sinus. A pressure transducer was placed in the left ventricle. Three to four days after surgery, we measured cardiac output, dP/dt, left ventricular end diastolic and aortic mean blood pressures, heart rate, aortic and coronary sinus blood oxygen contents, and left ventricular myocardial blood flow during a control period, during metabolic acidaemia, and after the aortic pH was restored to normal. We calculated systemic vascular resistance, myocardial oxygen consumption and left ventricular work. Acidaemia was associated with reduction in cardiac output, maximal dP/dt, and aortic mean blood pressure. Left ventricular end diastolic pressure and systemic vascular resistance increased, and heart rate did not change significantly. The reduction in myocardial blood flow and oxygen consumption was accompanied by fall in cardiac work. Cardiac output returned to control levels after the pH had been normalized but maximal dP/dt was incompletely restored. Myocardial blood flow and oxygen consumption increased beyond control levels. This study demonstrates that HCI-induced metabolic acidaemia in conscious newborn lambs is associated with a reduction in cardiac output which could have been mediated by the reduction in contractile function and/or the increase in systemic vascular resistance. The decreases in myocardial blood flow and oxygen consumption appear to reflect diminished cardiac work. The restoration of a normal cardiac output after normalization of the pH appears to have resulted from the increases in heart rate and left ventricular filling pressures in conjunction with an incomplete restoration of contractile function.     

Histamine decreases left ventricular contractility in normal human subjects.

To determine whether histamine alters human left ventricular contractility we measured heart rate, calibrated carotid arterial pressure, and left ventricular dimensions (echocardiogram) in nine healthy volunteers. We assessed baseline contractility using the end-systolic pressure-dimension relationship and the end-systolic meridional wall stress-rate-corrected velocity of circumferential fiber shortening relationship determined over a wide range of afterloads using phenylephrine and nitroprusside infusions. We then infused histamine for 3-5 min at a dose predetermined to decrease mean arterial pressure by 20%, both before and after H1 receptor antagonist pretreatment (diphenhydramine 50 mg i.v.). Histamine decreased end-systolic pressure but, unlike an equally hypotensive infusion of nitroprusside, did not decrease end-systolic dimension or increase fractional shortening. Histamine also decreased velocity of circumferential fiber shortening at the same end-systolic meridional wall stress as controls (P < 0.05). These effects of histamine were inhibited by H1 antagonist pretreatment. We conclude that the dominant effect of histamine on the human heart is to decrease left ventricular contractility and that this decrease in contractility is dependent, at least partially, on H1-receptor activation.     

Pressure-volume-based single-beat estimations cannot predict left ventricular contractility in vivo

The end-systolic pressure-volume relationship is regarded as a useful index for assessing the contractile state of the heart. However, the need for preload alterations has been a serious limitation to its clinical applications, and there have been numerous attempts to develop a method for calculating contractility based on one single pressure-volume loop. We have evaluated four of these methods. Pressure-volume data were obtained by combined pressure and conductance catheters in 37 pigs. All four methods were applied to 88 steady-state pressure-volume files, including eight files sampled during dopamine infusions. Estimates of single-beat contractility (elastance) were compared with preload-varied multiple-beat elastance [E(es(MB))]. All methods had a low average bias (-0.3 to 0.5 mmHg/ml) but limits of agreement (+/-2 SD) were unacceptably high (+/-2.6 to +/-3.8 mmHg/ml). In the dopamine group, E(es(MB)) showed an increase of 1.7 +/- 0.8 mmHg/ml (mean +/- SD) compared with baseline (P < 0.001). None of the single-beat methods predicted this increase in contractility. It is therefore doubtful whether any of the methods allow for single-beat assessment of contractility.     

Effects of left ventricular contractility and coronary vascular resistance on coronary dynamics

Wave-intensity analysis, which separates upstream from downstream events and defines their interaction, has been used to study the effects of changes in left ventricular (LV) contractility (E(max)) and left circumflex coronary artery resistance (R(LCx)) on the coronary systolic flow impediment (CSFI). In 10 anesthetized, open-chest dogs, we measured coronary, aortic, and LV pressures, coronary velocity (Flowire), and flow. E(max) was increased by paired pacing and R(LCx) was modulated by intracoronary infusions of vasodilators (adenosine and nitroglycerin) and a vasoconstrictor (phenylephrine). When both E(max) and R(LCx) were varied, CSFI and the energy of the backward-going compression wave (I(W-)) were greatest at the highest levels of E(max) and the lowest levels of R(LCx). I(W-) was proportional to the CSFI. We conclude that contractility and coronary resistance change CSFI by modulating the backward-going compression wave.     

Halothane alters contractility and Ca2+ transport in ventricular myocytes from streptozotocin-induced diabetic rats

General anaesthetics have previously been shown to have profound effects on myocardial function. Moreover, many patients suffering from diabetes mellitus are anaesthetised during surgery. This study investigated compromised functioning of cardiac myocytes from streptozotocin (STZ)-induced diabetic rats and the additive effects of halothane on these dysfunctions. Ventricular myocytes were isolated from 8 to 12 weeks STZ-treated rats. Contraction and intracellular free calcium concentration ([Ca2+]i) were measured in electrically field-stimulated (1 Hz) fura-2-AM-loaded cells using a video-edge detection system and a fluorescence photometry system, respectively. L-type Ca2+ current was measured in whole cell, voltage-clamp mode. Halothane significantly (p < 0.01) depressed the amplitude and the time course of the Ca2+ transients in a similar manner in myocytes from control and STZ-treated rats. However, the effect of halothane on the amplitude of shortening and L-type Ca2+ current was more pronounced in myocytes from STZ-treated animals compared to age-matched controls. Myofilament sensitivity to Ca2+ was significantly (p < 0.01) increased in myocytes from STZ-treated rats compared to control. However, in the presence of halothane the myofilament sensitivity to Ca2+ was significantly (p < 0.05) reduced to a greater extent in myocytes from STZ-treated rats compared to controls. In conclusion, these results show that contractility, Ca2+ transport and myofilament sensitivity were all altered in myocytes from STZ-treated rats and these processes were further altered in the presence of halothane suggesting that hearts from STZ-induced diabetic rats are sensitive to halothane.     

Halothane alters contractility and Ca2+ transport in ventricular myocytes from streptozotocin-induced diabetic rats

General anaesthetics have previously been shown to have profound effects on myocardial function. Moreover, many patients suffering from diabetes mellitus are anaesthetised during surgery. This study investigated compromised functioning of cardiac myocytes from streptozotocin (STZ)-induced diabetic rats and the additive effects of halothane on these dysfunctions. Ventricular myocytes were isolated from 8 to 12 weeks STZ-treated rats. Contraction and intracellular free calcium concentration ([Ca²⁺] _i ) were measured in electrically field-stimulated (1 Hz) fura-2-AM-loaded cells using a video-edge detection system and a fluorescence photometry system, respectively. L-type Ca²⁺ current was measured in whole cell, voltage-clamp mode. Halothane significantly (p < 0.01) depressed the amplitude and the time course of the Ca²⁺ transients in a similar manner in myocytes from control and STZ-treated rats. However, the effect of halothane on the amplitude of shortening and L-type Ca²⁺ current was more pronounced in myocytes from STZ-treated animals compared to age-matched controls. Myofilament sensitivity to Ca²⁺ was significantly (p < 0.01) increased in myocytes from STZ-treated rats compared to control. However, in the presence of halothane the myofilament sensitivity to Ca²⁺ was significantly (p < 0.05) reduced to a greater extent in myocytes from STZ-treated rats compared to controls. In conclusion, these results show that contractility, Ca²⁺ transport and myofilament sensitivity were all altered in myocytes from STZ-treated rats and these processes were further altered in the presence of halothane suggesting that hearts from STZ-induced diabetic rats are sensitive to halothane. (Mol Cell Biochem 261: 251–261, 2004)     

Validation of a novel noninvasive cardiac index of left ventricular contractility in patients

Although there are several excellent indexes of myocardial contractility, they require accurate measurement of pressure via left ventricular (LV) catheterization. Here we validate a novel noninvasive contractility index that is dependent only on lumen and wall volume of the LV chamber in patients with normal and compromised LV ejection fraction (LVEF). By analysis of the myocardial chamber as a thick-walled sphere, LV contractility index can be expressed as maximum rate of change of pressure-normalized stress (d sigma*/dt(max), where sigma* = sigma/P and sigma and P are circumferential stress and pressure, respectively). To validate this parameter, d sigma*/dt(max) was determined from contrast cine-ventriculography-assessed LV cavity and myocardial volumes and compared with LVEF, dP/dt(max), maximum active elastance (E(a,max)), and single-beat end-systolic elastance [E(es(SB))] in 30 patients undergoing clinically indicated LV catheterization. Patients with different tertiles of LVEF exhibit statistically significant differences in d sigma*/dt(max). There was a significant correlation between d sigma*/dt(max) and dP/dt(max) (d sigma*/dt(max) = 0.0075 dP/dt(max) - 4.70, r=0.88, P<0.01), E(a,max) (d sigma*/dt(max) = 1.20E(a,max) + 1.40, r=0.89, P<0.01), and E(es(SB)) [d sigma*/dt(max)=1.60 E(es(SB)) + 1.20, r=0.88, P<0.01]. In 30 additional individuals, we determined sensitivity of the parameter to changes in preload (intravenous saline infusion, n = 10 subjects), afterload (sublingual glyceryl trinitrate, n = 10 subjects), and increased contractility (intravenous dobutamine, n=10 patients). We confirmed that the index is not dependent on load but is sensitive to changes in contractility. In conclusion, d sigma*/dt(max) is equivalent to dP/dt(max), E(a,max), and E(es(SB)) as an index of myocardial contractility and appears to be load independent. In contrast to other measures of contractility, d sigma*/dt(max) can be assessed with noninvasive cardiac imaging and, thereby, should have more routine clinical applicability.     

Effect of temperature on isoproterenol-induced increases in left ventricular developed pressure

The goal of this project was to determine the effects of elevated cardiac temperature on preload-dependent and preload-independent regulation of left ventricular developed pressure (LVDP) in Langendorff-perfused, electrically paced (420 bpm), Sprague-Dawley rat hearts. LVDP responses to steady-state isoproterenol infusions (10⁻⁸ M) were determined at 37, 38, 39, and 40 °C. Preload-dependent LVDP was determined at 37 and 40 °C. Isoproterenol-induced LVDP and preload-dependent LVDP time controls were conducted in a separate group maintained at 37 °C. The percent increase in LVDP during isoproterenol infusion significantly decreased at 40 °C to 42±6 (SE), compared to 55±9, 55±6, and 53±7% at 37, 38, and 39 °C, respectively. No significant differences were observed in the percent increase in LVDP to isoproterenol among the corresponding time controls (50±6, 47±3, 56±4, and 56±5%). Preload-dependent LVDP decreased across the experimental protocol, but there were no cardiac temperature effects. These data indicate that β-adrenergic mediated contractility is not altered by moderate heating from normothermia but is compromised at very high temperatures (40 °C). Cardiac temperatures from 37 to 40 °C do not alter the inherent preload-dependent LVDP, indicating that the Frank–Starling relation is not directly affected within this temperature range.     

PYK2 expression and phosphorylation increases in pressure overload-induced left ventricular hypertrophy

Proline-rich tyrosine kinase 2 (PYK2) is a member of the focal adhesion kinase (FAK) family of nonreceptor protein tyrosine kinases. PYK2 has been implicated in linking G protein-coupled receptors to activation of mitogen-activated protein kinase cascades and cellular growth in a variety of cell types. To determine whether PYK2 expression and phosphorylation is altered in left ventricular (LV) myocardium undergoing LV hypertrophy (LVH) and heart failure in vivo, suprarenal abdominal aortic coarctation was performed in 160-g male Sprague-Dawley rats. Immunohistochemistry and Western blotting were performed on LV tissue 1, 8, and 24 wk after aortic banding. Aortic banding produced sustained hypertension and gradually developing LVH. PYK2 levels were increased 1.8 +/- 0.2-, 2.7 +/- 0.6-, and 2.0 +/- 0.2-fold in 1-, 8-, and 24-wk banded animals compared with their respective sham-operated controls. The increase in PYK2 expression was paralleled by an increase in PYK2 phosphorylation, both of which preceded the development of LVH. Immunohistochemistry revealed that enhanced PYK2 expression occurred predominantly in the cardiomyocyte population. Furthermore, there was a high degree of correlation (R = 0.75; P < 0.001) between the level of PYK2 and the degree of LVH in 24-wk sham and banded animals. In contrast, FAK levels and FAK phosphorylation were not increased before the development of LVH. However, there was a high degree of correlation (R = 0.68; P < 0.001) between the level of FAK and the degree of LVH in 24-wk sham and banded rats. There was also a significant increase in the ratio of phosphospecific anti-FAK to FAK at this time point. These data are consistent with a role for PYK2 in the induction of pressure overload-induced cardiomyocyte hypertrophy, and suggest that PYK2 and FAK have distinctly different roles in LVH progression.     

Effects of pericardial constraint and ventricular interaction on left ventricular hemodynamics in the unloaded heart

Pericardial constraint and ventricular interaction influence left ventricular (LV) performance when preload is high. However, it is unclear if these constraining forces modulate LV filling when the heart is unloaded, such as during upright posture, in humans. Fifty healthy individuals underwent right heart catheterization to measure pulmonary capillary wedge (PCWP) and right atrial pressure (RAP). To evaluate the effects of pericardial constraint on hemodynamics, transmural filling pressure (LVTMP) was defined as PCWP-RAP. Beat-to-beat blood pressure (BP) waveforms were recorded, and stroke volume (SV) was derived from the Modelflow method. After measurements at -30 mmHg lower body negative pressure (LBNP), which approximates the upright position, LBNP was released, and beat-to-beat measurements were performed for 15 heartbeats. At -30 mmHg LBNP, RAP and PCWP were significantly decreased. During the first six beats of LBNP release, heart rate (HR) was unchanged, while BP increased from the fourth beat. RAP increased faster than PCWP resulting in an acute decrease in LVTMP from the fourth beat. A corresponding drop in SV by 3% was observed with no change in pulse pressure. From the 7th to 15th beats, LVTMP and SV increased steadily, followed by a decreased HR due to the baroreflex. A decreased TMP, but not PCWP, caused a transient drop in SV with no changes in HR or pulse pressure during LBNP release. These results suggest that the pericardium constrains LV filling during LBNP release, enough to cause a small but significant drop of SV, even at low cardiac filling pressure in healthy humans.     

Regional left ventricular myocardial contractility and stress in a finite element model of posterobasal myocardial infarction

Recently, a noninvasive method for determining regional myocardial contractility, using an animal-specific finite element (FE) model-based optimization, was developed to study a sheep with anteroapical infarction (Sun et al., 2009, "A Computationally Efficient Formal Optimization of Regional Myocardial Contractility in a Sheep With Left Ventricular Aneurysm," ASME J. Biomech. Eng., 131(11), p. 111001). Using the methodology developed in the previous study (Sun et al., 2009, "A Computationally Efficient Formal Optimization of Regional Myocardial Contractility in a Sheep With Left Ventricular Aneurysm," ASME J. Biomech. Eng., 131(11), p. 111001), which incorporates tagged magnetic resonance images, three-dimensional myocardial strains, left ventricular (LV) volumes, and LV cardiac catheterization pressures, the regional myocardial contractility and stress distribution of a sheep with posterobasal infarction were investigated. Active material parameters in the noninfarcted border zone (BZ) myocardium adjacent to the infarct (T(max_B)), in the myocardium remote from the infarct (T(max_R)), and in the infarct (T(max_I)) were estimated by minimizing the errors between FE model-predicted and experimentally measured systolic strains and LV volumes using the previously developed optimization scheme. The optimized T(max_B) was found to be significantly depressed relative to T(max_R), while T(max_I) was found to be zero. The myofiber stress in the BZ was found to be elevated, relative to the remote region. This could cause further damage to the contracting myocytes, leading to heart failure.     

Chronic intermittent hypoxia exposure improves left ventricular contractility in transgenic mice with heart failure

We previously reported the unexpected finding that 4 wk of exposure to intermittent hypoxia (IH), which simulates the hypoxic stress of obstructive sleep apnea, improved LV cardiac function in healthy, lean C57BL/6J mice. The purpose of the present study was to assess the impact of 4 wk of IH on cardiac function in a transgenic murine model that exhibits a natural history of heart failure. We hypothesized that IH exposure would exacerbate cardiac decompensation in heart failure. Adult male FVB (wild type) and transgenic mice with cardiac overexpression of tumor necrosis factor α (TNF-αTG) at 10-12 wk of age were exposed to 4 wk of IH (nadir inspired oxygen 5-6% at 60 cycles/h for 12 h during light period) or intermittent air (IA) as control. Cardiac function was assessed by echocardiography and pressure-volume loop analyses, and mRNA and protein expression were performed on ventricular homogenates. TNF-αTG mice exposed to IA exhibited impaired LV contractility and increased LV dilation associated with markedly elevated cardiac expression of atrial natriuretic peptide and brain natriuretic peptide compared with wild-type mice. When wild-type FVB mice were exposed to IH, they exhibited increases in arterial pressure and dP/dt(max), consistent with our previous report in C57BL/6J mice. Surprisingly, we found that TNF-αTG mice exposed to IH showed a reduction in end-diastolic volume (38.7 ± 3.8 to 22.2 ± 2.1 ul; P < 0.01) and an increase in ejection fraction (29.4 ± 2.5 to 41.9 ± 3.1%; P < 0.05). In contrast to our previous study in C56Bl/6J mice, neither FVB nor TNF-αTG mice exhibited an upregulation in β-adrenergic expression or cAMP in response to IH exposure. We conclude that 4 wk of exposure to IH in mice induces adaptive responses that improve cardiac function in not only healthy animals but also in animals with underlying heart failure.     

Acute hypothyroidism slows the rate of left ventricular diastolic relaxation

The effect of acute thyroid hormone deficiency on left ventricular diastolic filling was studied by radionuclide ventriculography with simultaneous right heart catheterization in nine athyreotic patients without cardiovascular disease. The patients were studied when they were hypothyroid and when they were euthyroid on replacement therapy. Peak filling rate and the time to peak filling were used to characterize diastolic function. The time to peak filling was defined as the interval from end-systole on the radionuclide time-volume curve to the time of occurrence of peak filling. The peak filling rate was determined in absolute terms from the normalized radionuclide peak filling rate and from the end-diastolic volume, which was derived from the radionuclide ejection fraction and from the thermodilution stroke volume. In all patients, the values for peak filling rate were lower in the hypothyroid than in the euthyroid state (287 +/- 91 mL/s vs. 400 +/- 118 mL/s, delta = 41 +/- 13%, p less than 0.01). Peak filling always occurred during the first half of the diastolic interval. The time to peak filling was not significantly affected by the thyroid state (170 +/- 10 ms vs. 159 +/- 21 ms, delta = 7 +/- 10%). Left ventricular filling pressure as reflected by the pulmonary capillary wedge pressure and end-systolic volume were similar in both thyroid states (6 +/- 2 mmHg vs. 8 +/- 2 mmHg (1 mmHg = 133.32 Pa) and 32 +/- 11 mL vs. 32 +/- 7 mL, respectively). The data suggest that the rate of active diastolic relaxation is decreased in short-duration hypothyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute left ventricular failure in a patient with hydroxychloroquine-induced cardiomyopathy

We present the case of a 75-year-old woman with a medical history of rheumatoid arthritis treated with hydroxychloroquine, who was admitted with acute left-sided heart failure due to a hydroxychloroquine-induced cardiomyopathy as supported by endomyocardial biopsy.