Andrea Z. Mitchell

Evaluation of blood pressure measurement using a miniature blood pressure transmitter with jacketed external telemetry in cynomolgus monkeys

INTRODUCTION Current techniques used to accurately determine arterial blood pressure (BP) in conscious, unrestrained monkeys require invasive telemetry. This study evaluated the functionality of an implanted miniature telemetry blood pressure transmitter for the collection of BP measurements in conjunction with electrocardiographic measurements using a jacketed external telemetry (JET) system in conscious, unrestrained cynomolgus monkeys. METHODS Twenty-four animals were surgically implanted with the transmitter in the right femoral artery. Local tolerability to the implant, signal quality, and variability in hemodynamic values were evaluated. On alternate weeks, animals were given single doses of positive control agents to produce hypotensive (clonidine hydrochloride) or hypertensive (L-NAME) effects. Undisturbed telemetry BP data were continuously collected for at least 24h following dosing and analyzed. RESULTS While exhibiting remarkably high signal quality ( approximately 95% data points retained over 24h of data collection) and moderate variability across study weeks in baseline pulse height measurements (changes as small as < 0 mmHg), nine of 18 transmitters were nonfunctional by 19 weeks post-surgery, most likely due to migration of the catheter out of the artery. In animals given positive control agents, L-NAME induced a statistically significant increase (> or = + 8 mmHg) and clonidine hydrochloride induced a statistically significant decrease (-11 mmHg) in mean arterial pressures. Histological analysis revealed femoral arterial thickening near the sites of implantation. DISCUSSION These results demonstrate the ability of the miniature BP transmitter, in conjunction with the JET system, to detect small changes in hemodynamic data continuously collected in conscious unrestrained monkeys. Future optimization of the transmitter includes the addition of a suture rib to the transmitter body and increased catheter size to prevent catheter migration out of the artery, the root cause of failed transmitters. The miniature blood pressure transmitter evaluated provides a minimally invasive technique for continuous collection of hemodynamic data in a toxicology study environment.

Sensitivity of two noninvasive blood pressure measurement techniques compared to telemetry in cynomolgus monkeys and beagle dogs

INTRODUCTION Animals are commonly used in toxicological research for the evaluation of drug effects on the cardiovascular system. Accurate and reproducible determination of blood pressure (BP) in conscious, manually restrained monkeys and dogs is a challenge with current non-invasive cuff techniques. The High Definition Oscillometry (HDO) technique enables real time measurements with immediate visual feedback via PC screen on data validity. HDO measurements are considerably faster with a duration of approximately 8 to 15s than conventional cuff methods that can take several minutes. METHODS HDO Memo Diagnostic Model Science and Cardell BP Monitor Model 9401 measurements were compared for accuracy and reliability with simultaneously recorded direct blood pressure data captured via radiotelemetry. Six monkeys and six dogs implanted with DSI PCT telemetry transmitters were used; BP data were collected by all methods under manual constraint and compared. Measurements were performed with HDO and Cardell in the presence of a BP lowering drug (hexamethonium bromide). Systolic, diastolic, mean arterial pressure, and pulse rate were determined before, during and following up to 10mg/kg hexamethonium administration via intravenous slow bolus injection. RESULTS Drug induced hemodynamic changes could be detected in monkeys and dogs with the HDO method but only in dogs with the Cardell method. Correlation coefficients were generally higher for HDO versus Telemetry than Cardell versus Telemetry comparisons, indicating that this novel, non-invasive technique produces reliable blood pressure data and is able to detect drug-induced hemodynamic changes. DISCUSSION HDO provides an alternative approach for invasive telemetry surgeries to obtain reliable hemodynamic data in animal models for cardiovascular research when invasive techniques are not warranted.

Intravenous solid tip ECG lead placement in telemetry implanted dogs: Part 2: High quality telemetry signals yield high sensitivity to drug-induced changes.

INTRODUCTION Dogs are commonly used in cardiovascular drug safety assessment, and implanted telemetry models include subcutaneous or epicardial electrocardiogram (ECG) electrode placements. The purpose of this study was to determine the sensitivity of a canine telemetry model with intravenous ECG lead placement: the negative ECG lead (solid tip) inserted into the jugular vein and the positive lead sutured to the diaphragm. Reference drugs were administered to test the sensitivity to drug-induced changes. METHODS Twenty-four dogs were implanted with PCT or PCTP transmitters [Data Sciences International (DSI)]. Three reference drugs were administered: sotalol to eight PCT and milrinone to eight PCTP transmitter-implanted dogs. Twenty-four dogs received moxifloxacin (12 dogs/transmitter type). Telemetry data were collected for 25h and analyzed using double Latin squares for sotalol and milrinone data or a 4×4 or 3×6 parallel design for moxifloxacin data. Evaluated parameters were PR, QT, corrected QT (QTc), QRS, heart rate, left ventricular function, and hemodynamic data. Various correction factors for QTc interval were tested. Retrospective power analysis was performed to detect minimal absolute changes comparing a single to a double Latin square or the two parallel designs. RESULTS Expected changes on ECG and hemodynamic parameters were observed after administration of all reference drugs. The individual animal corrected QT (QTci) interval provided the optimal correction factor. Retrospective power analysis confirmed detection of smaller differences in double versus single Latin squares. Minimal detectable differences were smaller in both Latin squares compared to parallel designs, with smaller detectable differences in a 3×6 compared to a 4×4 parallel design. DISCUSSION The solid tip intravenous ECG lead configuration in dogs is a viable radiotelemetry model to detect drug-induced changes with high sensitivity. This model yields comparable signal quality and represents a refinement over epicardial ECG leads and allows for possible reduction in the number of animals if study design and size are selected based on needed assay sensitivity.

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.