Feasibility and clinical utility of transvenous intracardiac echocardiography in conscious, sedated horses.

INTRODUCTION/OBJECTIVES: Intracardiac echocardiography (ICE) is a method of obtaining echocardiographic images with a steerable ultrasound catheter placed within the heart via a venous or arterial approach. The objectives of this study were to assess the feasibility of a 5-10 MHz, 8 French, 90 cm ICE catheter to evaluate cardiac structures and function in standing, sedated horses, and describe standard views in this species. ANIMALS: Ten apparently healthy horses weighing 458.1-618.2 kg from a university teaching herd. MATERIALS AND METHODS: Each horse had a physical examination, transthoracic echocardiography, and ICE performed through a 10 French introducer percutaneously placed in the right jugular vein in the proximal third of the neck with continuous ECG monitoring using telemetry. RESULTS: Three intracardiac echocardiography positions (cranial right atrium, mid right atrium, and right ventricle) with seven views were described with the associated 2D, pulse wave Doppler, continuous wave Doppler, color Doppler, and M-mode image acquisition standardized by referencing the intracardiac positions and common landmarks. The positions were confirmed with simultaneous transthoracic echocardiography. The procedure was well tolerated with only mild, occasional ventricular, and supraventricular arrhythmias that resolved with intracardiac echocardiography catheter repositioning. CONCLUSIONS: Intracardiac echocardiography is feasible, safe, and allows for the acquisition of diagnostic images in conscious, sedated horses.

Serum concentrations of lidocaine and its metabolites after prolonged infusion in healthy horses.

REASONS FOR PERFORMING STUDY: Continuous-rate infusions (CRI) of lidocaine are often used for prolonged duration but, to date, only limited time/concentration relationships administered as a short term (24 h) CRI have been reported. OBJECTIVE: To determine the time/concentration profile of lidocaine and its active metabolites glycinexylidide (GX) and monoethylglycinexylidide (MEGX) during a 96 h lidocaine infusion. METHODS: Lidocaine was administered to 8 mature healthy horses as a continuous rate infusion (0.05 mg/kg bwt/min) for 96 h. Blood concentrations of lidocaine, GX and MEGX were determined using high performance liquid chromatography during and after discontinuation of the infusion. RESULTS: Serum lidocaine concentrations reached steady state by 3 h and did not accumulate thereafter. Concentrations were above the target therapeutic concentration (980 ng/ml) only at 6 and 48 h, and did not reach the range described as potentially causing toxicity (>1850 ng/ml) at any time. MEGX did not accumulate over time, while the GX accumulated significantly up to 48 h and then remained constant. The serum concentrations of lidocaine, MEGX and GX were below the limit of detection within 24 h of discontinuation of the infusion. None of the horses developed any signs of lidocaine toxicity during the study. CONCLUSIONS: The metabolism of lidocaine was not significantly impaired by prolonged infusion and no adverse effects were observed. Prolonged infusions appear to be safe in normal horses but the accumulation of GX, a potentially toxic active metabolite, is cause for concern.