Evaluation of cardiac function by echocardiography in dogs treated with doxorubicin

Evaluation of cardioprotective effects of carvedilol in dogs receiving doxorubicin chemotherapy: A prospective, randomized, double-blind, placebo controlled pilot study

The aim of this pilot study was to evaluate the cardioprotective effects of carvedilol in dogs receiving doxorubicin chemotherapy and provide suggestions to future studies based on results and limitations of our study. Thirteen dogs were randomized into two experimental groups: 6 dogs in carvedilol group and 7 dogs in placebo group. In carvedilol group, 0.39 mg/kg ± 0.04 twice-daily oral carvedilol was started on the day of the first doxorubicin treatment and continued throughout the chemotherapy protocol until the final cardiological evaluation. Cardiological evaluations were performed before the first doxorubicin administration and then 10 to 15 days after each subsequent dose. Troponin I and oxidative stress tests were performed with serum collected from dogs at the initial and final cardiological evaluation. Carvedilol produced some echocardiographic and electrocardiographic changes (reduced E velocity and E/IVRT ratio, as well reduced heart rate and increased PR and QT interval) due to its beta-block effect. In placebo group Doppler study showed a significant increase in mitral flow deceleration time (EDT), as well increased amplitude of the S wave in the right, and R wave in the left, precordial chest leads. There were significant difference in the EDT, E/IVRT and A' velocity, as well heart rate, PR interval and R wave in V4/CV6LU precordial chest lead between groups. In conclusion, some indexes of diastolic function and in precordial chest leads were less affected by doxorubicin in carvedilol than in control group. This suggests that carvedilol may have a beneficial effect in canine cancer patients receiving doxorubicin.

The Effects of Repeat-Dose Doxorubicin on Cardiovascular Functional Endpoints and Biomarkers in the Telemetry-Equipped Cynomolgus Monkey

Purpose: Doxorubicin-related heart failure has been recognized as a serious complication of cancer chemotherapy. This paper describes a cardiovascular safety pharmacology study with chronic dosing of doxorubicin in a non-human primate model designed to characterize the onset and magnitude of left ventricular dysfunction (LVD) using invasive and non-invasive methods.

Methods: Cynomolgus monkeys (N = 12) were given repeated intravenous injections of doxorubicin over 135 days (19 weeks) with dosing holidays when there was evidence of significantly decreased hematopoiesis; a separate group (N = 12) received vehicle. Arterial and left ventricular pressure telemetry and cardiac imaging by echocardiography allowed regular hemodynamic assessments and determination of LVD. Blood samples were collected for hematology, clinical chemistry, and assessment of cardiac troponin (cTnI) and N-terminal pro b-type natriuretic peptide (NT-proBNP). Myocardial histopathology was a terminal endpoint.

Results: There was variable sensitivity to the onset of treatment effects, for example 25% of doxorubicin-treated animals exhibited LVD (e.g., decreases in ejection fraction) following 50–63 days (cumulative dose: 8–9 mg/kg) on study. All animals deteriorated into heart failure with additional dosing 135 days (total cumulative dose: 11–17 mg/kg). Reductions in arterial pressure and cardiac contractility, as well as QTc interval prolongation, was evident following doxorubicin-treatment. Both cTnI and NT-proBNP were inconsistently higher at the end of the study in animals with LVD. Measurements collected from control animals were consistent and stable over the same time frame. Minimal to mild, multifocal, vacuolar degeneration of cardiomyocytes was observed in 7 of 12 animals receiving doxorubicin and 0 of 12 animals receiving vehicle.

Conclusions: This repeat-dose study of doxorubicin treatment in the cynomolgus monkey demonstrated a clinically relevant pattern of progressive heart failure. Importantly, the study revealed how both telemetry and non-invasive echocardiography measurements could track the gradual onset of LVD.

Lidocaine administered at a continuous rate infusion does not impair left ventricular systolic and diastolic function of healthy rabbits sedated with midazolam

Lidocaine is a versatile drug that not only provides local anesthesia, but also reduces anesthetic requirements of other agents and has antiarrhythmic, pro-kinetic, anti-inflammatory, antiendotoxemic and antioxidant effects. As it is a drug commonly used in critically ill patients, its safety from the cardiovascular system should be ensured. The aim of this study was to determine the effects of a continuous rate infusion (CRI) of lidocaine on left ventricular systolic and diastolic function of healthy rabbits sedated with midazolam by use of transthoracic echocardiography. Ten New Zealand healthy rabbits were sedated with intramuscular midazolam (1 mg/kg) and enrolled in two experimental treatments (control or lidocaine). The control treatment (CT) comprised an intravenous bolus of 0.9% sodium chloride (0.05 mL/kg) followed by CRI at 5 mL/h, whereas the lidocaine treatment (LT) comprised a bolus of 2% lidocaine without epinephrine at 1 mg/kg followed by CRI at 50 µg/kg/minute. Echocardiographic and hemodynamic variables were studied. Variables were recorded at baseline (TB) and 20, 40 and 60 minutes following start of CRI (T20, T40 and T60, respectively). No differences were found between treatments. The results of this study demonstrate that a continuous rate infusion of lidocaine at 50 µg/kg/minute does not impair echocardiographic indices of left ventricular systolic and diastolic function of healthy rabbits sedated with midazolam.

Prospective evaluation of Doppler echocardiography, tissue Doppler imaging and biomarkers measurement for the detection of doxorubicin-induced cardiotoxicity in dogs: A pilot study

The purpose of this pilot study was to evaluate the usefulness of selected echocardiographic parameters, NT-proBNP and cardiac troponin I (cTnI) in the detection of cardiotoxicity in dogs treated with doxorubicin for various malignancies. Echocardiographic studies and biomarker measurements were performed before each administration of doxorubicin, then 1 and 3 months after completion of therapy. Thirteen dogs were included, with a total cumulative dose of doxorubicin ranging from 30 to 150 mg/m(2). E/A ratio significantly decreased during doxorubicin administration (p=0.047). cTnI level was also significantly affected by treatment (p=0.046), increasing above normal at least at one time point in 11 of 13 dogs. The results of this pilot study suggest that monitoring of left ventricular diastolic function and cTnI level measurement might be useful in the early detection of cardiotoxic signs of doxorubicin therapy in dogs.

Hemodynamic and biochemical alterations in dogs with lymphoma after induction of chemotherapy

Background

Doxorubicin is a common antineoplastic agent with dose‐dependent cardiotoxic adverse effects, and pre‐existing myocardial dysfunction is a contraindication to its use.

Objectives

To systematically define the hemodynamic and biochemical alterations in dogs undergoing chemotherapy for newly diagnosed lymphoma and assess the reversibility of these alterations with fluid administration.

Animals

Twenty‐one client‐owned dogs with newly diagnosed lymphoma were evaluated 1 week after induction of chemotherapy. Underlying degenerative valve disease was exclusionary. Eighteen healthy age‐ and weight‐matched dogs were used as controls.

Methods

Physical examination, blood pressure by Doppler, echocardiography, and biochemical evaluation (routine serum biochemistry, plasma renin activity and aldosterone concentrations, plasma and urine osmolalities, and urine electrolyte concentrations) were measured in dogs with lymphoma and compared to controls. Dogs with lymphoma received crystalloids IV at 6 mL/kg/h for 24 hours. All variables were reassessed at 4 and 24 hours. Deuterium oxide dilution and bromide dilution were used to determine total body water and extracellular water space, respectively.

Results

Baseline echocardiograms showed significantly smaller chamber dimensions in dogs with lymphoma compared to controls. These changes were reversed by fluid administration. Systolic blood pressure and urine sodium concentration were significantly increased, and bromide dilution space, PCV, urine specific gravity, and urine potassium concentration were significantly decreased compared to controls.

Conclusion and Clinical Importance

Echocardiographic and biochemical abnormalities in dogs with lymphoma appear consistent with volume depletion, and may be the result of systemic hypertension and subsequent pressure natriuresis.

Cardiac imaging approaches to evaluate drug-induced myocardial dysfunction

The ability to make informed benefit-risk assessments for potentially cardiotoxic new compounds is of considerable interest and importance at the public health, drug development, and individual patient levels. Cardiac imaging approaches in the evaluation of drug-induced myocardial dysfunction will likely play an increasing role. However, the optimal choice of myocardial imaging modality and the recommended frequency of monitoring are undefined. These decisions are complicated by the array of imaging techniques, which have varying sensitivities, specificities, availabilities, local expertise, safety, and costs, and by the variable time-course of tissue damage, functional myocardial depression, or recovery of function. This White Paper summarizes scientific discussions of members of the Cardiac Safety Research Consortium on the main factors to consider when selecting nonclinical and clinical cardiac function imaging techniques in drug development. We focus on 3 commonly used imaging modalities in the evaluation of cardiac function: echocardiography, magnetic resonance imaging, and radionuclide (nuclear) imaging and highlight areas for future research.

Value of echocardiography and electrocardiography as screening tools prior to Doxorubicin administration

The dose-limiting toxicity of doxorubicin is cardiotoxicosis. The authors of this report hypothesized that by using their institution's adopted guidelines (that involve prescreening echocardiography and electrocardiography), they would detect pre-existing cardiac abnormalities that preclude doxorubicin administration in <10% of dogs. Of 101 dogs, only 6 were excluded from doxorubicin administration based on electrocardiogram abnormalities, with a majority of those arrhythmias classified as ventricular premature contractions. One patient was excluded based on echocardiogram alone due to hypertrophic cardiomyopathy. The incidence of cardiotoxicity in treated dogs was 8% (8/101). Additional pretreatment and ongoing studies are indicated to identify risk factors for cardiotoxicity.

Sudden death in a dog after doxorubicin chemotherapy

A case is reported of fatal cardiomyopathy in an 8-year-old female German Shepherd after standard chemotherapy with doxorubicin for splenic hemangiosarcoma. The main gross lesion was a moderate bilateral cardiac ventricular dilation with diffusely pale myocardium. Histological analysis revealed severe multifocal vacuolar degeneration of cardiomyocytes, myocytolysis, myofibril loss, myocardial fibrosis, and edema. Myocardial fiber vacuolization and myocytolysis were highly suggestive of doxorubicin cardiotoxicity.

Biomedical imaging in the safety evaluation of new drugs

Toxicology accounts for approximately one-third of attrition in new drug development and is a major concern in the pharmaceutical industry. This paper reviews the role of biomedical imaging in the safety evaluation of new candidate drugs. Ex vivo high-resolution three-dimensional imaging of specimens can provide a quick overview of the specimens. Volumetric measurements of tissue structures and lesions can be made with higher precision and reproducibility than histology approaches. As opposed to histology, in vivo animal imaging permits longitudinal studies of the same animals over an extended period of time, with individual animals serving as their own control. Therefore, the number of animals required for a study can be significantly reduced and the intra-subject variability is minimized. Repeated in vivo imaging allows monitoring of the occurrence and progression, or regression, of various structural and functional abnormalities. Compared with other biological assays, imaging can provide anatomically specific information about tissue abnormality. Imaging offers the opportunity to carry forward the same methodology in animal experiments into human studies and has an important role in clinical trials when other safety biomarkers for early toxicities are not available.

Preclinical cardiac safety assessment of drugs

The heart is a frequent site of toxicity of pharmaceutical compounds in humans, and when developing a new drug it is critical to conduct a thorough preclinical evaluation of its possible adverse effects on cardiac structure and function. Changes in cardiac morphology such as myocardial necrosis, hypertrophy or valvulopathy are assessed in regulatory toxicity studies in laboratory animals, although specific models may be needed for a more accurate detection of the risk. The potential proarrhythmic risk of new drugs is a major subject of concern and needs to be fully addressed before treatment of volunteers or patients takes place. In vitro assays are conducted to determine the effects on cardiac ion channels, in particular I(Kr) potassium channel antagonism. Prolongation of the QT interval is assessed in vivo, generally in telemetered dogs. Together, these two tests are considered to detect most arrhythmic drugs. The results of this core battery can be refined by additional studies, in particular assays on isolated cardiac tissues determining changes in cardiac action potential duration, shape and variability over time. Triggering of arrhythmia is assessed in hypokalaemic dogs with artificially created bradycardia, or in vitro in isolated whole hearts. The proarrhythmic risk of the new compound is then evaluated by integrating the results of these different tests. Drug adverse effects on cardiac electrophysiological function, in particular impulse formation and conduction, are evaluated through changes in ECG, generally recorded in dogs, pigs or monkeys. Changes in cardiac contractility occurring either as a primary effect of the drug on cardiac function or as a consequence of cardiac lesions should also be carefully assessed. In telemetered or anaesthetised animals, cardiac contractility is evaluated by measurement of left ventricular pressure and its first derivative over time. Echocardiography allows non-invasive measurement of drug-induced changes in ventricular wall movements and cardiac haemodynamics indicative of effects on contractility. In conclusion, a reliable and accurate evaluation of the cardiac safety of a new pharmaceutical agent is based on the results of in vitro tests, with overall moderate to high throughput, and in vivo experiments assessing the effects of the drug on the heart in its physiological environment. The specific sensitivities of the animals used in these assays to cardiac adverse effects should also be considered. The final evaluation of the cardiac risk is therefore based on an integrated analysis of the results from a battery of tests.

Left ventricular volume and function in cynomolgus monkeys using real-time three-dimensional echocardiography

BACKGROUND

The purpose of this study was to investigate the feasibility of evaluating cardiac function by real time three-dimensional (RT3D) echocardiography in isoflurane-anesthetized male cynomolgus monkeys. Additionally differences between inhibitory effects of beta-blockers and a Ca channel blocker on left ventricular (LV) function were examined.

METHODS AND RESULTS

End-diastolic volume (EDV), end-systolic volume (ESV) and ejection fraction (EF) in the control (without any drug effect) were not significantly changed by repetitive measurement at a 30-day interval. Propranolol and metoprolol (0.1 and 0.3 mg/kg/10 minutes, i.v.) caused a dose-dependent increase in ESV, but little effect on EDV, resulting in a decrease in EF. Verapamil (0.1 and 0.3 mg/kg/10 minutes, i.v.) increased both EDV and ESV, but decreased EF was noted at 0.3 mg/kg.

CONCLUSIONS

These results demonstrate the feasibility of RT3D echocardiography in providing reproducible estimations of LV volume and EF in monkeys when evaluating drugs that may affect cardiac function.

Neurohormonal, hemodynamic, and electrocardiographic evaluations of healthy dogs receiving long-term administration of doxorubicin

OBJECTIVE

To evaluate diagnostic testing that could be used to establish an early diagnosis of cardiotoxicosis induced by long-term administration of doxorubicin.

ANIMALS

13 adult mixed-breed dogs. Procedures-7 dogs were administered doxorubicin chloride (30 mg/m(2), IV, q 21 d for 168 days [cumulative dose, 240 mg/m(2)]), and 6 dogs received saline (0.9% NaCl) solution (5 mL, IV, q 21 d for 168 days; control group). Echocardiography, ECG, arterial blood pressure, plasma renin activity (PRA), and plasma concentrations of norepinephrine and brain natriuretic peptide (BNP) were assessed before each subsequent administration of doxorubicin and saline solution.

RESULTS

Dogs that received doxorubicin had a significant decrease in R-wave amplitude, compared with values for the control group, from 30 to 210 mg/m(2). Doxorubicin-treated dogs had decreases in fractional shortening and left ventricular ejection fraction evident as early as 30 mg/m(2), but significant differences between groups were not detected until 90 mg/m(2)was reached. There was also a significant increase in PRA (>or= 120 mg/m(2)) and left ventricular end-systolic and end-diastolic dimensions (>or= 60 and >or= 180 mg/m(2), respectively). Systemic arterial pressure, remaining echocardiographic variables, and concentrations of norepinephrine and BNP had significant variations, but of no clinical importance, during doxorubicin administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Doxorubicininduced cardiotoxicosis developed at 120 mg/m(2), but there were no clinical signs of dilated cardiomyopathy or congestive heart failure. Echocardiography and determination of PRA were able to detect early cardiac alterations during the development of dilated cardiomyopathy, despite apparently differing degrees of sensitivity to development of doxorubicin-induced cardiotoxicosis.

An ovine model of chronic heart failure: echocardiographic and tissue Doppler imaging characterization

BACKGROUND AND AIM OF THE STUDY

Heart failure in the western world is a major health-care issue. In order to validate novel surgical or pharmacological treatments, reproducible animal models of left ventricular dysfunction are necessary. In the current study, we report our data and experience with a model of toxin-induced heart failure in the sheep.

METHODS

Sequential intracoronary injections of doxorubicin (0.75 mg/kg) were carried out every 2 weeks until standard echocardiographic and tissue Doppler imaging detection of myocardial systolic dysfunction. The animals were assessed 1 month later and harvested. Indices of cardiac function from baseline to last day of protocol were recorded and their differences were evaluated by a Wilcoxon rank test for paired data.

RESULTS

Ten sheep received 2.5 +/- 0.7 intracoronary injections of a cumulative dose of 88.8 +/- 25 mg/m2 doxorubicin. All available parameters demonstrated signs of severe cardiac dysfunction with statistical significance. All hearts demonstrated severe histological lesions, some of which were consistent with doxorubicin-induced toxicity.

CONCLUSIONS

The present study shows that this ovine model is reproducible and stable. It can therefore be relevant to the study of chronic heart failure. It will be incorporated in our future studies concerning novel treatments (such as cell therapy) of nonischemic dilated cardiomyopathy.

Evaluation of cardiac function in primates using real-time three-dimensional echocardiography as applications to safety assessment

INTRODUCTION

A timed non-invasive determination of cardiac function is potentially important for safety pharmacology and toxicity studies. The objectives of this study were to evaluate the accuracy of real-time three-dimensional (RT3D) echocardiography measurements of the left ventricular (LV) volume and LV function and to investigate the effects of some drugs on LV function in cynomolgus monkeys.

METHODS

RT3D echocardiography was performed (SONOS 7500, Philips Med Sys) under isoflurane inhalation. RT3D echocardiography measurements and reconstructions were obtained using Tom-Tec (4DLV analysis). We determined end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), stroke volume (SV), cardiac output (CO) and heart rate as assessments of LV function. EDV, calculated from two-dimensional (2D) echocardiography and RT3D echocardiography, and the actual LV volume were evaluated and compared. Furthermore, each parameter was determined before and after intravenous infusion (5 or 10 min) of propranolol, verapamil and dobutamine.

RESULTS

A strong correlation was found between the actual LV volume and that calculated from RT3D echocardiography (r=0.96, p<0.001). Propranolol (0.1 mg/kg/10 min, n=5) caused an increase in ESV, but not EDV, resulting in a decrease in EF and SV, while verapamil produced increases in both EDV and ESV. Dobutamine (0.01 mg/kg/5 min, n=5) produced decreases in both EDV and ESV and thereby the increased CO resulted from the increased SV.

DISCUSSION

These results demonstrate that RT3D echocardiography provides a feasible and accurate estimation of LV volume and EF for safety pharmacology and toxicity studies.

Alterações ecocardiográficas em cães sob tratamento prolongado com doxorrubicina

Avaliou-se a cardiotoxicidade da doxorrubicina utilizando-se sete cães adultos, clinicamente normais, que receberam 30mg/m² de cloridrato de doxorrubicina (Adriblastina®) por via intravenosa, a cada 21 dias, durante 168 dias (grupo A), perfazendo dose cumulativa total de 240mg/m². Em outros sete cães (grupo B) administraram-se 5ml de solução salina 0,9% estéril por via intravenosa, seguindo-se o esquema de aplicação proposto anteriormente. Os animais foram avaliados, periodicamente, por meio de exames ecocardiográficos em modo-M e bidimensional. Verificou-se aumento (P<0,01) no diâmetro e volume do ventrículo esquerdo, inicialmente em sístole e, posteriormente, em diástole, hipocinesia do septo interventricular e da parede livre do ventrículo esquerdo, reduções de aproximadamente 65% nas frações de encurtamento e de ejeção, além de aumento da separação do septo do ponto E do folheto anterior da válvula mitral nos animais do grupo A. As alterações cardíacas decorrentes do tratamento crônico com doxorrubicina foram semelhantes àquelas descritas em cães com cardiomiopatia dilatada, e os índices ecocardiográficos puderam ser utilizados no acompanhamento e na prevenção da cardiotoxicidade pelo quimioterápico.

Effect of milrinone on echocardiographic parameters after single dose in Beagle dogs and relationship with drug-induced cardiotoxicity

The aim of this study was to further investigate the mechanism of development of cardiac lesions occurring under treatment with milrinone in dogs, by using echocardiography for assessing the effects of this drug on cardiac function. Milrinone is a cAMP phosphodiesterase 3 inhibitor having positive inotropic and vasodilatory effects. We treated groups of three dogs with milrinone at a single dose of 0.5 or 1 mg/kg and recorded M-mode and Doppler parameters at different time points before and after treatment. The hearts of the high-dose animals were histopathologically examined. The treatment with milrinone at 1 mg/kg produced mild cardiac lesions at two different locations. In the left ventricle, haemorrhages in the subendocardium and myocardium occurred in all three dogs. In the right atrium, subepicardial haemorrhages occurred in one dog and inflammation of the epicardium was observed in two dogs. These lesions were considered to be related to changes in the cardiac function, which were investigated by echocardiography. Milrinone treatment produced a moderate tachycardia and changes in M-mode parameters indicating an increase in contractility, in particular, a decrease in end-systolic volume, an increase in ejection fraction and an increase in the rate of circumferential fiber shortening. In addition, there was an increase in the maximal aortic flow velocity evaluated by Doppler measurements, which is thought to represent a haemodynamic correlate of an increase in left ventricular contractility. This increase in myocardial work is considered to play a key role in the development of the lesions observed in the left ventricle. Doppler measurements also revealed changes in the right atrioventricular flow, probably resulting from cardiac stimulation produced by milrinone. In particular, there was an increase in the Vmax of the A-wave of the tricuspid flow, suggesting an increase in contractility of the right atrium. This change, by increasing blood flow in atrial wall, may be involved in the induction of the lesions observed in the right atrium. In conclusion, Doppler and M-mode echocardiography are useful tools to assess haemodynamic changes occurring upon treatment with vasodilators or cardiac stimulants in order to further understand the mechanism of development of cardiac lesions produced by such compounds.