Evaluation of blood flow parameters in addition to blood pressure and electrocardiogram in the conscious telemetered beagle dog

Evaluation of a method utilizing PhysioFlow®, a novel signal morphology-based form of impedance cardiography, to measure cardiac output in the conscious beagle

INTRODUCTION

Currently, standard methods for measuring cardiac output are either invasive (i.e. flow probe) or are limited in terms of short measurement intervals and measurement variability (i.e. echocardiography). The ability to reliably measure cardiac output in a non-invasive manner in large animals would provide a valuable tool to expand functional cardiovascular endpoints in preclinical safety studies. PhysioFlow® is a novel method that uses waveform analysis of an impedance signal to measure cardiac output non-invasively. Unlike cardiac impedance techniques in the past, PhysioFlow® is not dependant on thoracic structure or basal thoracic impedance (Z0) and therefore this methodology is transferrable from human to animal models.

METHODS

Three tool compounds with known effects on cardiac output were administered to conscious beagle dogs to determine if the non-invasive PhysioFlow® system could detect the expected changes in stroke volume and cardiac output as determined by literature references using the current standard methodologies (e.g. aortic blood flow and thermodilution).

RESULTS

The PhysioFlow® system was able to detect increases in cardiac output when dosed with 20μg/kg of Dobutamine, a decrease in cardiac output when dosed with 0.1mg/kg of Acepromazine, and no significant change in cardiac output when dosed with 2mg/kg of Minoxidil. These results are within expected ranges based on published literature (Stepien et al., 1995; Taylor et al., 2007).

DISCUSSION

PhysioFlow®, a signal morphology-based impedance cardiography, can be utilized to reliably and non-invasively measure cardiac output in beagle dogs.

High Definition Oscillometry: Non-invasive Blood Pressure Measurement and Pulse Wave Analysis

Non-invasive monitoring of blood pressure has become increasingly important in research. High-Definition Oscillometry (HDO) delivers not only accurate, reproducible and thus reliable blood pressure but also visualises the pulse waves on screen. This allows for on-screen feedback in real time on data validity but even more on additional parameters like systemic vascular resistance (SVR), stroke volume (SV), stroke volume variances (SVV), rhythm and dysrhythmia. Since complex information on drug effects are delivered within a short period of time, almost stress-free and visible in real time, it makes HDO a valuable technology in safety pharmacology and toxicology within a variety of fields like but not limited to cardiovascular, renal or metabolic research.

Longitudinal hemodynamic measurements in swine heart failure using a fully implantable telemetry system

Chronic monitoring of heart rate, blood pressure, and flow in conscious free-roaming large animals can offer considerable opportunity to understand the progression of cardiovascular diseases and can test new diagnostics and therapeutics. The objective of this study was to demonstrate the feasibility of chronic, simultaneous measurement of several hemodynamic parameters (left ventricular pressure, systemic pressure, blood flow velocity, and heart rate) using a totally implantable multichannel telemetry system in swine heart failure models. Two solid-state blood pressure sensors were inserted in the left ventricle and the descending aorta for pressure measurements. Two Doppler probes were placed around the left anterior descending (LAD) and the brachiocephalic arteries for blood flow velocity measurements. Electrocardiographic (ECG) electrodes were attached to the surface of the left ventricle to monitor heart rate. The telemeter body was implanted in the right side of the abdomen under the skin for approximately 4 to 6 weeks. The animals were subjected to various heart failure models, including volume overload (A-V fistula, n = 3), pressure overload (aortic banding, n = 2) and dilated cardiomyopathy (pacing-induced tachycardia, n = 3). Longitudinal changes in hemodynamics were monitored during the progression of the disease. In the pacing-induced tachycardia animals, the systemic blood pressure progressively decreased within the first 2 weeks and returned to baseline levels thereafter. In the aortic banding animals, the pressure progressively increased during the development of the disease. The pressure in the A-V fistula animals only showed a small increase during the first week and remained stable thereafter. The results demonstrated the ability of this telemetry system of long-term, simultaneous monitoring of blood flow, pressure and heart rate in heart failure models, which may offer significant utility for understanding cardiovascular disease progression and treatment.

How can we improve our understanding of cardiovascular safety liabilities to develop safer medicines?

Given that cardiovascular safety liabilities remain a major cause of drug attrition during preclinical and clinical development, adverse drug reactions, and post-approval withdrawal of medicines, the Medical Research Council Centre for Drug Safety Science hosted a workshop to discuss current challenges in determining, understanding and addressing 'Cardiovascular Toxicity of Medicines'. This article summarizes the key discussions from the workshop that aimed to address three major questions: (i) what are the key cardiovascular safety liabilities in drug discovery, drug development and clinical practice? (ii) how good are preclinical and clinical strategies for detecting cardiovascular liabilities? and (iii) do we have a mechanistic understanding of these liabilities? It was concluded that in order to understand, address and ultimately reduce cardiovascular safety liabilities of new therapeutic agents there is an urgent need to: • Fully characterize the incidence, prevalence and impact of drug-induced cardiovascular issues at all stages of the drug development process. • Ascertain the predictive value of existing non-clinical models and assays towards the clinical outcome. • Understand the mechanistic basis of cardiovascular liabilities; by addressing areas where it is currently not possible to predict clinical outcome based on preclinical safety data. • Provide scientists in all disciplines with additional skills to enable them to better integrate preclinical and clinical data and to better understand the biological and clinical significance of observed changes. • Develop more appropriate, highly relevant and predictive tools and assays to identify and wherever feasible to eliminate cardiovascular safety liabilities from molecules and wherever appropriate to develop clinically relevant and reliable safety biomarkers.

Cardiovascular Function in Nonclinical Drug Safety Assessment

There are several recent examples where clinically significant, safety-related, drug effects on hemodynamics or cardiac function were not apparent until large clinical trials were completed or the drugs entered the consumer market. Such late-stage safety issues can have significant impact on patient health and consumer confidence, as well as ramifications for the regulatory, pharmaceutical, and financial communities. This manuscript provides recommendations that evolved from a 2009 HESI workshop on the need for improved translation of nonclinical cardiovascular effects to the clinical arena. The authors conclude that expanded and improved efforts to perform sensitive yet specific evaluations of functional cardiovascular parameters in nonclinical studies will allow pharmaceutical companies to identify suspect drugs early in the discovery and development process while allowing promising drugs to proceed into clinical development.