Electrocardiogram, hemodynamics, and core body temperatures of the normal freely moving laboratory beagle dog by remote radiotelemetry

Detection of contractility changes in the heart from arterial blood pressure data using symmetric Projection Attractor Reconstruction

The potential for unintended drug induced changes in cardiac contractility is a major concern in medicines development. Whilst direct left ventricular pressure (LVP) measurement is the gold standard for measuring cardiac contractility in vivo, it is resource intensive and poses a welfare burden on research animals. In contrast, arterial blood pressure (BP) measurement has fewer challenges. Symmetric Projection Attractor Reconstruction (SPAR) is a signal processing technique which transforms physiological time-series signals into a corresponding visual image ('attractor'), amplifying morphology changes within physiological waveforms. It was hypothesized that SPAR analysis of BP signals would provide a surrogate measure of cardiac contractility by specifically amplifying the maximum slope of the systolic upstroke. BP (abdominal aorta) signals obtained from beagle dogs, treated with positive and negative inotropes, were retrospectively analysed to identify signal features that correlated with the maximum upslope of the LVP signal from simultaneously acquired LVP recordings. SPAR transformation of BP signals quantified drug induced changes in the maximum slope of the systolic upstroke. We identified key SPAR metrics that provided >0.8 correlation with the LVP maximum upslope, outperforming the BP systolic upstroke alone. This was observed for all 4 different drugs, doses and time points evaluated across studies. Thus, we conclude that the SPAR measures derived from the BP signal could be used as a first pass in vivo screen to flag any risk of drug induced changes in cardiac contractility during the conduct of non-clinical medicines development, potentially reducing or replacing the need to perform direct left ventricular measurements.

Reference intervals and method sensitivity for electrocardiology, hemodynamics, and body temperature parameters in healthy cynomolgus monkeys

In nonclinical studies, electrocardiograms (ECG) of cynomolgus monkey are recorded intermittently by external leads in manually restrained animals (snapshot recording) or continuously by jacketed external telemetry (JET) or implanted radiotelemetry transmitter in freely moving animals. With the implanted device, blood pressure and core body temperature can be monitored simultaneously. Despite the frequent use of cynomolgus monkeys in nonclinical safety pharmacology testing, few reference data are available for this species, comparisons of the ECG recording methods are limited, and power analyses are seldom conducted. In this study, pretreatment data were recorded from 406, 663, and 131 healthy experimentally naïve monkeys using the snapshot, JET, and implantable method, respectively, from 2019 to 2021. Reference intervals were determined for ECG, blood pressure, and body temperature parameters. Diurnal effects were observed in these parameters, with the exception of QRS and pulse pressure. The QRS, QT, and heart rate-corrected QTc intervals, as well as blood pressure, had a weak positive relationship with age and/or body weight. There were no sex differences in these parameters, and the country of origin only had minimal influences. Compared to telemetry, snapshot ECG data had shorter RR, PR, and QT intervals and longer QRS interval. The JET and implanted telemetry ECG data were comparable. Effect size analysis was conducted to estimate the method sensitivity for each parameter in common non-clinical study design scenarios. Snapshot recording, JET, and implanted telemetry were sensitive to detect 7-15 milliseconds of changes in QTc intervals in standard study designs, indicating these are powerful methods for assessment of QT prolongation in vivo.

Nonclinical safety assessments of a novel synthetic toll-like receptor 4 agonist and saponin based adjuvant

A full nonclinical safety package was performed to support the clinical use of SPA14, a novel liposome-based vaccine adjuvant containing the synthetic toll-like receptor 4 agonist E6020 and saponin QS21. E6020 and QS21 were tested negative for their potential genotoxic effects in Ames, micronucleus, or mouse-lymphoma TK (thymidine kinase) assay. To evaluate the potential local and systemic effects of SPA14, two toxicity studies were performed in rabbits. In the first dose range finding toxicity study, rabbits received two intramuscular injections of SPA14 at increasing doses of E6020 combined with two antigens, a control (saline), the two antigens alone, or the antigens adjuvanted with a liposome-based adjuvant AS01B. No systemic toxicity was detected, supporting the dose of 5 μg of E6020 for the subsequent pivotal study. In the second repeated dose toxicity study, rabbits received four intramuscular injections of SPA14 alone, a control (saline), SPA14 combined with two antigens, the two antigens alone, or the antigens combined with AF03 adjuvant, which is a squalene-based emulsion. SPA14 alone or in combination with the antigens was well tolerated and did not cause any systemic toxicity. Finally, two safety pharmacology studies were conducted to assess potential cardiovascular and respiratory effects of E6020 and SPA14 in conscious telemetered cynomolgus monkeys and beagle dogs, respectively. One subcutaneous injection of E6020 in monkeys and one intramuscular injection of SPA14 in dogs had no consequences on respiratory and cardiovascular functions. Altogether these results support the clinical development of SPA14.

"Digital biomarkers" in preclinical heart failure models - a further step towards improved translational research

Innovations in the development of novel heart failure therapies are essential to further increase the predictive value of early research findings. Animal models are still playing a pivotal role in 'translational research'. In recent years, the transferability from animal studies has been more and more critically discussed due to persistent high attrition rates in clinical trials. However, there is an increasing trend to implement mobile health devices in preclinical studies. These devices can increase the predictive value of animal models by providing more accurate and translatable data and protect from confounding factors. This review outlines the current prevalence and opportunities of these techniques in preclinical heart failure research studies to accelerate the integration of these important tools. A literature screening for preclinical heart failure studies in large animals implementing telemetry devices over the last decade was performed. Twelve out of 43 publications were included. A variety of different hemodynamic and cardiac parameters can be recorded in conscious state by means of telemetry devices in both, the animal model and the patient. The measurement quality is consistently rated as valid and robust. Mobile health technologies functioning as digital biomarkers represent a more predictive approach compared to the traditionally used invasive measurement techniques, due to the possibility of continuous data collection in the conscious animal. Furthermore, they help to implement the 3R concept (reduction, refinement, replacement) in animal research. Despite this, the use of these techniques in preclinical research has been restrained to date.

Investigational New Drug Enabling Nonclinical Safety Pharmacology Assessment of the Iminosugar UV-4, a Broad-Spectrum Host-Targeted Antiviral Agent

UV-4 (N-(9-methoxynonyl)-1-deoxynojirimycin) is a broad-spectrum antiviral drug candidate with demonstrated activity in vitro and in vivo against multiple, diverse viruses. Nonclinical safety pharmacology studies were conducted to support the filing of an Investigational New Drug (IND) application. Preliminary in vitro pharmacology testing evaluating potential for binding to "off-target" receptors and enzymes indicated no significant liability for advanced development of UV-4. The safety pharmacology of UV-4 was evaluated in the in vitro human ether-à-go-go-related gene (hERG) assay, in a central nervous system (CNS) study in the mouse (modified Irwin test), in a respiratory safety study in conscious mice using whole body plethysmography, and in a cardiovascular safety study in conscious, radiotelemetry-instrumented beagle dogs. There were no observed adverse treatment-related effects following administration of UV-4 as the hydrochloride salt in the hERG potassium channel assay, on respiratory function, in the CNS study, or in the cardiovascular assessment. Treatment-related cardiovascular effect of decreased arterial pulse pressure after 50 or 200 mg of UV-4/kg was the only change outside the normal range, and all hemodynamic parameters returned to control levels by the end of the telemetry recording period. These nonclinical safety pharmacology assessments support the evaluation of this host-targeted broad-spectrum antiviral drug candidate in clinical studies.

Radio-Telemetric Assessment of Cardiac Variables and Locomotion With Experimentally Induced Hypermagnesemia in Horses Using Chronically Implanted Catheters

The objective of this study was to characterize the pharmacokinetics and pharmacodynamics of intravenous administration of magnesium sulfate to horses using a novel radio-telemetry system for physiologic signal capture. Five Horses were surgically implanted with a radio-telemetric carotid catheter. Implants were paired with a non-invasive telemetric unit which acquired a six lead ECG and 3-axis acceleration to assess activity acquired wirelessly in real-time for future analysis. Horses were exposed to a new stall environment before (baseline) and after 60 mg/kg (30 mL) of magnesium sulfate (MgSO₄), or the same volume of 0.9% saline, administered intravenously in a blinded, random crossover design. Blood for pharmacokinetics, telemetric data, and body temperature were recorded serially for 24 h. Data were analyzed across time and between treatments. Significance was set at P < 0.05. Ionized magnesium concentration (Mg²⁺) increased and the Ca²⁺ to Mg²⁺ ratio decreased and persisted for 5 h after MgSO₄ administration. Heart rate (HR) increased and mean arterial blood pressure (MAP) decreased for at least 6 h. Electrocardiogram (ECG) intervals (RR) decreased and (PR and QTc) increased in duration compared to controls indicating an increase in heart rate, and slower myocardial conduction in the MgSO₄ group. Acceleration in all planes was less in the MgSO₄ group compared to controls indicating decreased locomotion. This novel method permitted collection of physiologic signals without interference by handlers or animal restraint. An intravenous bolus of MgSO₄ produced cardiac variable changes associated with the reduction of locomotion in these horses, and in a direction that may be causal. Locomotion was decreased when horses were first introduced into a new environment which reflects the calming effect desired in sport horses. Telemetric monitoring can be used as a model to elucidate the behavior and physiologic effects of other drugs. The administration of MgSO₄ may be detected for regulatory purposes with the monitoring of Mg²⁺ and Ca²⁺ concentrations and their ratio.

Social housing of non-rodents during cardiovascular recordings in safety pharmacology and toxicology studies

INTRODUCTION

The Safety Pharmacology Society (SPS) and National Centre for the Replacement, Refinement & Reduction of Animals in Research (NC3Rs) conducted a survey and workshop in 2015 to define current industry practices relating to housing of non-rodents during telemetry recordings in safety pharmacology and toxicology studies. The aim was to share experiences, canvas opinion on the study procedures/designs that could be used and explore the barriers to social housing.

METHODS

Thirty-nine sites, either running studies (Sponsors or Contract Research Organisations, CROs) and/or outsourcing work responded to the survey (51% from Europe; 41% from USA).

RESULTS

During safety pharmacology studies, 84, 67 and 100% of respondents socially house dogs, minipigs and non-human primates (NHPs) respectively on non-recording days. However, on recording days 20, 20 and 33% of respondents socially house the animals, respectively. The main barriers for social housing were limitations in the recording equipment used, study design and animal temperament/activity. During toxicology studies, 94, 100 and 100% of respondents socially house dogs, minipigs and NHPs respectively on non-recording days. However, on recording days 31, 25 and 50% of respondents socially house the animals, respectively. The main barriers for social housing were risk of damage to and limitations in the recording equipment used, food consumption recording and temperament/activity of the animals.

CONCLUSIONS

Although the majority of the industry does not yet socially house animals during telemetry recordings in safety pharmacology and toxicology studies, there is support to implement this refinement. Continued discussions, sharing of best practice and data from companies already socially housing, combined with technology improvements and investments in infrastructure are required to maintain the forward momentum of this refinement across the industry.

Rat cardiovascular telemetry: Marginal distribution applied to positive control drugs

Cardiovascular effects are considered frequent during drug safety testing. This investigation aimed to characterize the pharmacological response of the conscious telemetered rat in vivo model to known cardiovascular active agents. These effects were analyzed using statistical analysis and cloud representation with marginal distribution curves for the contractility index and heart rate as to assess the effect relationship between cardiac variables. Arterial blood pressure, left ventricular pressure, electrocardiogram and body temperature were monitored. The application of data cloud with marginal distribution curves to heart rate and contractility index provided an interesting tactic during the interpretation of drug-induced changes particularly during selective time resolution (i.e. marginal distribution curves restricted to Tmax). Taken together, the present data suggests that marginal distribution curves can be a valuable interpretation strategy when using the rat cardiovascular telemetry model to detect drug-induced cardiovascular effects. Marginal distribution curves could also be considered during the interpretation of other inter-dependent parameters in safety pharmacology studies.

Intravenous solid tip lead placement in telemetry implanted dogs. Part 1: Surgical methods, signal quality, and pathological endpoints

INTRODUCTION

Electrocardiogram (ECG) signals in safety pharmacology studies are generally collected via subcutaneous or epicardial leads. Subcutaneous placement is an easier procedure, but signals often contain artifacts. Epicardial leads offer improved quality but require additional surgical expertise. Signal quality and tolerability of intravenous (IV)/diaphragmatic ECG leads were investigated as a less invasive alternative to the epicardial ECG lead approach for cardiovascular assessment in dogs.

METHODS

Twenty-eight beagle dogs were implanted with PCT (n=14) or PCTP (n=14) transmitters with IV (negative)/diaphragmatic (positive) ECG leads arranged in approximate Lead II configuration. Surgical time for previous epicardial and current IV lead placement approaches was compared. The ECG signals were assessed for up to 32 weeks post-surgery. Signal quality was assessed based on good wave/total wave (GW/TW) ratios calculated using ECG PRO (Ponemah Physiology Platform, Version 4.8) and variability in ECG parameter measurements for each surgical model. Clinical pathology was assessed on all animals before surgery and approximately 2 and 12 weeks post-surgery. A specialized necropsy was conducted on four animals (two PCT and two PCTP) to assess the tolerability of telemetry equipment; selected tissues were examined microscopically.

RESULTS

Surgical time using the IV lead method was approximately 18% shorter than the epicardial lead method. The GW/TW ratio for IV lead-implanted dogs indicated good durability of signal that was similar to epicardial leads. Intra- and inter-animal variability in ECG parameter measurements was similar between IV lead-implanted and epicardial lead-implanted dogs. Clinical pathology revealed no noteworthy findings, and the IV/diaphragmatic surgical approach had minimal consequences on local vasculature and associated implantation sites.

DISCUSSION

Advantages of the IV/diaphragmatic lead model include a less invasive and shorter surgical procedure; high tissue tolerance, ECG signal quality, and durability; and data processing procedures similar to that of epicardial leads. Therefore, the IV/diaphragmatic lead configuration is a viable alternative to more invasive surgical approaches for telemetry device implantation in dogs.

An integrated system for video and telemetric electroencephalographic recording to measure behavioural and physiological parameters

INTRODUCTION

The combined evaluation of physiology and behaviour allows a complete and more comprehensive pre-clinical assessment of central nervous system (CNS) function. An integrated video-telemetric electroencephalography (Video-tEEG) system, which allows the simultaneous and continuous recording of EEG and video images for long periods, was developed.

METHODS

This study focuses on the refinement of the surgical methodology for the combined recording of cortical, hippocampal EEG and electromyogram (EMG) waveforms in freely moving rats. The post-operative recovery of animals was monitored by recording EEGs by telemetry and the general activity by video, on days 1, 6 and 15 after surgery, for approximately 24h, on each occasion.

RESULTS

The results suggested that the applied surgical technique for the implantation of the telemetric transmitter, allowed for a gradual recovery of the animals within 15days. During the recovery period the behavioural and locomotor parameters measured, indicated that there were no changes to the light-dark circadian cycle, and these parameters gradually tended to reach background levels within a 15-day period. Using a mechanical connection between the deep and the telemetric electrodes, 15days after surgical implantation the recording system was able to acquire cortical and hippocampal EEG traces of good quality.

DISCUSSION

This present study is concerned with the refinement of the surgical technique, as well as the integration and synchronisation of the commercially available Dataquest telemetry system and the Noldus video system, in order to study cortical, hippocampal EEG waveforms, in combination with behaviour and locomotion. The application of this integrated Video-tEEG system could provide advantages in the ethical use of animals in different pre-clinical research areas.

Interferences of the autonomic nervous system with drug induced QT prolongation: a point to consider in non-clinical safety studies

INTRODUCTION

QT interval assessment by telemetry has become one of the most useful models in testing strategies adopted for detection of drug induced QT prolongation in non-clinical safety pharmacology studies. This study reports experimental data showing that the autonomic nervous system might influence drug induced QT prolongation.

METHODS

Animals were instrumented with telemetric transmitters and epicardial ECG leads. Effects on QT interval of reference drugs such as thioridazine and terfenadine were analysed with different approaches, the Holzgrefe's probabilistic method, the QT shift method and an individual analysis of beat-to-beat QT/RR pair distribution visualised as points-cloud.

RESULTS

Two cases of unexpected absence of QT interval prolongation are reported with thioridazine and terfenadine in conscious beagle dogs under conditions of concomitant tachycardia. The pro-arrhythmic properties of these two molecules were unmasked by co-treatment with sympatholytic agents, atenolol and clonidine respectively suggesting that sympathetic activation and/or parasympathetic withdrawal might impair a drug induced QT prolongation.

DISCUSSION

The apparent absence of changes in the QT interval due to novel drug candidates should be interpreted cautiously under conditions of concomitant tachycardia or elevated heart rate levels in non-clinical safety studies.

Nonclinical safety assessment of the histone deacetylase inhibitor vorinostat

Vorinostat (SAHA, Zolinza), a histone deacetylase inhibitor, is assessed in nonclinical studies to support its approval for cutaneous T-cell lymphoma. Vorinostat is weakly mutagenic in the Ames assay; is clastogenic in rodent (ie, CHO) cells but not in normal human lymphocytes; and is weakly positive in an in vivo mouse micronucleus assay. No effects are observed on potassium ion currents in the hERG assay up to 300 microM (safety margin approximately 300-fold the approximately 1 microM serum concentration associated with the 400 mg/d maximum recommended human dose. No rat respiratory or central nervous system effects are found at 150 mg/kg (>2-fold maximum recommended human dose). No cardiovascular effects, including effects on QTc interval, are observed after a single oral dose (150 mg/kg) in dogs. Vorinostat is orally dosed daily in rats (controls, 20, 50, or 150 mg/kg/d) and dogs (controls, 60, 80, or 100/125/160 mg/kg/d) for 26 weeks with a 4-week recovery. Rat vorinostat-related adverse findings are decreased food consumption, weight loss, and hematologic changes; a no observed adverse effects level is not established. In dogs, adverse effects are primarily gastrointestinal; the no observed adverse effects level is 60 mg/kg/d (approximately 6-fold maximum recommended human dose). Toxicities are reversible and can be monitored in the clinic.

Electrocardiographic reference values in whippets

The aim of this study was to determine the electrocardiographic characteristics of whippets and to compare the results with published reference values for a general dog population. Electrocardiographic parameters from 105 healthy whippets were used to establish reference values for the breed. The most important differences compared to published reference values were the higher median R-wave amplitudes in leads II, CV(6)LL and CV(6)LU. For some parameters (P-wave amplitude, ST-segment deflection and T-wave amplitude in lead II; R-wave amplitude in CV(5)RL), a marked percentage of the whippet values were above the published maximum reference data. The results confirmed that whippets have electrocardiographic characteristics similar to those reported in athletic heart syndrome in humans. Some of these characteristics could be erroneously taken as evidence of cardiac disease and clinicians should be aware of these factors to prevent unnecessary investigations in healthy dogs.

Beyond the safety assessment of drug-mediated changes in the QT interval... what's next?

Assessing drug-induced changes (particularly prolongation) in the QT interval has been the major preoccupation of safety pharmacology since its inception, under the assumption that QT widening represents a surrogate biomarker for torsades de pointes (TdeP) liability. While evidence of changes in QT remains a bane to the development of novel therapeutic agents, non-clinical and clinical methods have been developed (with a certain amount of validation) to limit this potential liability of a new chemical entity (NCE). Because of the associated withdrawal of numerous drugs from clinical use, determining whether or not a drug development candidate exhibits a TdeP liability has been the motivation in the implementation of discussions between 'pharmaceutical companies', academicians, clinicians and regulatory authorities worldwide that has led to the development of the ICHS7A and ICHS7B guidance documents (Anon, 2001, 2005). Simultaneously, it has resulted in the firm establishment of safety pharmacology as a standalone discipline within the drug development scheme (Pugsley et al., 2008). As far as TdeP liability is concerned, QT widening remains the most poignant issue, in that QT widening in humans is immediately regarded as a cause for concern, yet QT widening in preclinical models (and indeed in man) is not a quantitative predictor of TdeP liability (and indeed may not even be a qualitative predictor by itself (Pugsley et al., 2008). The present focused issue of the journal returns to safety pharmacology, and contains papers arising from the 8th annual SPS Meeting that was held in Madison, WI in 2008. Indeed, so many papers have arisen from the meeting that this issue of the Journal is only part 1. Part 2 will be published as the next issue of the Journal. Some topics which have been addressed include whether an assessment method for drugs that produce a shortened QT interval is needed, what the role of the slow component of the delayed rectifier K current (I(Ks)) should be in a safety assessment and whether safety pharmacology endpoints can or should be added to repeat dose Toxicology studies.

Calculation of QT shift in non clinical safety pharmacology studies

INTRODUCTION

Drug-induced QT interval prolongation is a major concern in new drug candidate development. This study presents a method of assessment of drug-induced QT interval prolongation without need for QT correction in conscious Beagle dogs and Cynomolgus monkeys monitored by telemetry. Accuracy and reliability are analysed by comparison with a reference QT correction method (Holzgrefe) from experiments performed with reference substances terfenadine, thioridazine and sotalol.

METHODS

The QT shift method principle is assessment of any drug-induced QT interval shift directly from the individual QT/RR relationship. The individual QT/RR relationship is built from a treatment-free 24-hour recording period. QT and RR intervals are determined from a beat-to-beat analysis. A probabilistic method is used to define the individual QT/RR relationships. Checks were performed to compare results obtained with the QT shift method and the QT correction methods. The robustness of the QT shift method was tested under various conditions of drug-induced heart rate change (i.e. normal, bradycardia and tachycardia).

RESULTS

The extent of agreement with the used reference QT correction method, Holzgrefe formula, was excellent (3-4 ms) in both animal species under the various drug induced effects on heart rate. The statistical sensitivity threshold for detection of QT prolongation according to a standard safety pharmacology study design was 7-8 ms.

DISCUSSION

When combined with the probabilistic determination of individual QT/RR relationships, this simple method provides a direct assessment of a drug-induced effect on QT interval, without any curve fitting or application of correction formula. Despite noticeably different shapes in QT/RR relationships, the QT shift method is applicable to both Beagle dogs and Cynomolgus monkeys. It is likely that the QT shift method will be particularly helpful in problematic cases, enabling detection of drug-induced prolongation of less than 10 ms.

A highly sensitive canine telemetry model for detection of QT interval prolongation: Studies with moxifloxacin, haloperidol and MK-499

INTRODUCTION

Preclinical evaluation of delayed ventricular repolarization manifests electrocardiographically as QT interval prolongation and is routinely used as an indicator of potential risk for pro-arrhythmia (potential to cause Torsades de Pointes) of novel human pharmaceuticals. In accordance with ICH S7A and S7B guidelines we evaluated the sensitivity and validity of the beagle dog telemetry (Integrated Telemetry Services (ITS)) model as a preclinical predictor of QT interval prolongation in humans.

METHODS

Cardiovascular monitoring was conducted for 2 h pre-dose and 24 h post-dosing with moxifloxacin (MOX), haloperidol (HAL), and MK-499, with a toxicokinetic (TK) evaluation in a separate group of dogs. In both cardiovascular and TK studies, MOX (0, 10, 30 and 100 mg/kg), HAL (0, 0.3, 1, 3 mg/kg) and MK-499 (0, 0.03, 0.3 and 3 mg/kg) were administered orally by gavage in 0.5% methylcellulose. Each dog received all 4 doses using a dose-escalation paradigm. Inherent variability of the model was assessed with administration of vehicle (0.5% methylcellulose) alone for 4 days.

RESULTS

Significant increases in QT(c) were evident with 10, 30 and 100 mg/kg of MOX (C(max)< or =40 microM), 0.3, 1 and 3 mg/kg of HAL (C(max)< or =0.36 microM) and 0.3 and 3 mg/kg of MK-499 (C(max)< or =825 nM) with peak increases of 45 (20%), 31 (13%), and 45 (19%) ms, respectively (p< or =0.05).

DISCUSSION

In conclusion, we have demonstrated that the ITS-telemetry beagle dog exhibits low inherent intra-animal variability and high sensitivity to detect small but significant increases in QT/QT(c) interval ( approximately 3-6%) with MOX, HAL and MK-499 in the same range of therapeutic plasma concentrations attained in humans. Therefore, this dog telemetry model should be considered an important preclinical predictor of QT prolongation of novel human pharmaceuticals.

Analysis of the nonclinical telemetered ECG: Impact of logging rate and RR bin width in the dog and cynomolgus monkey

INTRODUCTION

Species-dependent ECG differences may affect QT interval analysis. Among these are the range of QT and RR values, heart rate variability, and respiratory sinus arrhythmia (SA). Importantly, the effects of data logging rates and RR bin width (BW) on QT analysis have not been characterized in dogs and nonhuman primates.

METHODS

Digital ECGs were collected for 18-21 h in telemetered dogs (n=7) and cynomolgus monkeys (n=7) employing epicardial ECG leads and analyzed by computerized algorithms. ECG intervals were determined employing beat-to-beat (1 ms BW) and 10 s logging rates (for 1, 10, 20, and 50 ms BW). Diurnal heart rate variability was defined as the beat-to-beat RR ratio (VR) where SA was defined as >+/-10% change in VR.

RESULTS

Canine beat-to-beat QT-RR data were curvilinear and plateaued, with multiple RR values associated to any given QT for RR>or=900 ms. Cynomolgus QT-RR data collected as beat-to-beat or at a 10 s logging rate were linear for all RR intervals. During the day, SA comprised 62.9+/-2.4% and 11.4+/-6.1% of total beats in the dog and cynomolgus, respectively, with no diurnal/nocturnal differences in either species. QT interval changes varied with BW such that 5 ms resolution was maintained for BW <or=11.5 and 41 ms in the dog and cynomolgus, respectively.

DISCUSSION

Differences in the QT interval, primarily due to SA, were responsible for skewed canine beat-to-beat QT-RR relationships. A 10 s logging rate eliminated this confounding factor, enabling the derivation of accurate QT rate-corrections. Thus, the uniform application of a 10 s logging rate in conjunction with a 10 ms RR BW ensured consistent and accurate QT analysis in both species. In conclusion, optimal BWs were defined which maintained beat-to-beat accuracy, while maximizing the number of QT-RR observations incorporated into QT-RR rate-correction models, a critical factor for robust probabilistic QT rate-corrections.

A canine model used to simultaneously assess potential neurobehavioural and cardiovascular effects of candidate drugs

INTRODUCTION

Unwanted effects of drugs on neurobehavioural and cardiovascular functions are normally assessed in separate studies and using different animals. A new model using dogs which allows for the integration of these assessments into a single study was established and validated, adopting the most sophisticated technologies for both monitoring behaviour by video recordings and cardiovascular parameters by telemetry.

METHODS

Conscious male beagle dogs (n=4) were given single oral doses of vehicle, and D-amphetamine (0.25, 0.75, 1.5 mg/kg) or acepromazine (0.05, 0.3, 2 mg/kg) within two different studies. Blood pressure, heart rate, electrocardiogram (EKG), body temperature, motor activity and behaviour (by video) were monitored continuously for 24 h post-dose. Animals underwent a full neurobehavioural examination the day before dosing, at the time to the maximal plasma concentration (Tmax) and 24 h post-dose.

RESULTS

D-Amphetamine: a dose-dependent increase in arterial blood pressure was noted at all doses and was generally associated with an increase in the QA interval, an index of cardiac contractility. Heart rate also increased but only at the 1.5 mg/kg dose. A dose-dependent general excitatory state of the nervous system was observed, characterised mainly by hyper-reactivity, and stereotyped activities. Acepromazine: a decrease in systolic blood pressure was detected at 0.3 and 2 mg/kg generally associated with a decrease in pulse pressure reflecting a negative inotropic effect. A dose-related increase in heart rate accompanied this effect. Dose-dependent general depression of the nervous system was noted; mainly characterised by half-closed eyes, subdued behaviour and impaired posture. In both studies, all dogs completely recovered at approximately 16 h after treatment.

DISCUSSION

Cardiovascular and neurobehavioural changes expected from the pharmacology of test substances were accurately detected. No significant fluctuations of the telemetric parameters recorded were noted as a consequence of the handling associated with the direct neurobehavioural examination. These results confirm the validity of this combined model capable of providing a reliable neurobehavioural and cardiovascular assessment of drugs.

Novel probabilistic method for precisely correcting the QT interval for heart rate in telemetered dogs and cynomolgus monkeys

INTRODUCTION

QT intervals are not regulated on a beat-to-beat cadence, but are strongly influenced by the preceding heart rate history (hysteresis). ECG sampling, when performed over sufficiently long periods, results in the detection of ranges of different QT values for each discrete RR interval. Given the potential impact of QT hysteresis in QT interval rate-correction procedures, we hypothesized that, physiologically, the QT interval exists as a probabilistic variable where the exact value corresponding to any RR interval is precisely estimated from the associated QT population.

METHODS

Digital ECGs were collected for 18-21 h in telemetered dogs (n=7) and cynomolgus monkeys (n=7) employing epicardial ECG leads for accurate T(end) detection, and analyzed by computerized algorithms. Descriptive statistics were calculated for raw QT values in 10 ms RR increments. Individual rate-corrected QT (QTc) formulae were derived from the slopes of log-transformed QT-RR data where each QT point was the mean of >250 beats/RR increment. The aptness of this QTc model was assessed by residual analysis.

RESULTS

Beat-to-beat ECG analysis demonstrated that for all discrete cycle lengths, the associated raw QT intervals were normally distributed populations, spanning approximately 30-40 and 45-100 ms in the dog and cynomolgus monkey, respectively. In both species, QTc was stable (< or =5 ms variation) over all physiological RR intervals.

DISCUSSION

The probabilistic treatment of raw QT interval populations natively associated to any RR interval provides hysteresis-free raw QT estimates which can be accurately modeled, allowing the derivation of a precise QTc value. Previous unawareness of the probabilistic nature of the QT interval explains the historical failure of numerous QT rate-correction formulae to correctly solve this scientific issue. Importantly, QT distribution analysis has the potential to provide, for the first time, a universal and sensitive method for QT heart rate-correction, providing a robust method for nonclinical and clinical cardiac safety investigations of repolarization delay.