Spectro-temporal mapping of the surface electrocardiogram in clinically normal dogs.

OBJECTIVES: To establish data for selected variables of the signal-averaged ECG and determine whether sedation affects segment lengths and points within the terminal QRS complex where windows began. SAMPLE POPULATION: Overtly healthy dogs with no detected abnormalities. PROCEDURE: Signal-averaged ECG (600 beats) were obtained from dogs in left-lateral recumbency, using X, Y, and Z leads with 26-gauge subdermal platinum electrodes. Frequency-domain analyses were performed by fast Fourier transform (FFT), using a post-processing computer software package. Analyses were extracted from 30-, 40-, and 50-millisecond windowed (Blackman-Harris) segments of the terminal 10 or 20 milliseconds of the QRS complex and ST segment. Correlation ratios were calculated by cross-correlation of frequency spectra of each FFT in the range of 40 to 200 Hz. The reference spectrum was the last FFT (nearest the T wave). Spectro-temporal maps were plotted for each analysis. RESULTS: Noise levels were < 1 microV. Sedation resulted in less noise and slower heart rate, but did not affect results. Correlation ratios were not different among 30-, 40-, and 50-millisecond segments, but were lower when 20 (vs 10) milliseconds of the terminal QRS was included. Spectro-temporal maps were similar in all subjects. CONCLUSIONS: Use of sedation facilitated the procedure without affecting results. Segment lengths of 40 and 50 milliseconds, beginning 10 milliseconds prior to the end of the QRS complex and analyzed in the range of 40 to 200 Hz, yielded correlation ratios > 67%, 95% of the time. CLINICAL RELEVANCE: Spectro-temporal mapping may identify dogs with ventricular late potentials (high-frequency signals commonly associated with myocardial fibrosis) that may be at increased risk of sudden death.

Effects of acepromazine and buprenorphine on measured indices of the signal-averaged electrocardiogram in healthy dogs.

OBJECTIVES: To determine values for indices of signal-averaged electrocardiograms (SAECG) in healthy dogs, and to determine whether sedation with acepromazine and buprenorphine would alter these indices. ANIMALS: 15 healthy adult dogs. PROCEDURE: SAECG were recorded from each dog twice: prior to sedation and immediately after sedation with acepromazine (0.01 mg/kg of body weight, IV) and buprenorphine (0.007 mg/kg, IV). Time-domain methods were used to analyze the SAECG. All indices were calculated by use of a computer. Measured indices included QRS duration, duration of low-amplitude signals in the terminal part of the QRS complex, root mean square voltages of the terminal 30 and 40 milliseconds of the QRS complex, heart rate, and high-frequency noise levels. RESULTS: We did not detect significant differences between values measured when dogs were not sedated and values measured when dogs were sedated except in regard to heart rate (P = 0.0001) and high-frequency noise levels (P = 0.0004), which were lower when dogs were sedated. Late potentials were not visually identified in SAECG from any dog in this study. CONCLUSION AND CLINICAL RELEVANCE: Sedation facilitated recording of SAECG in dogs without altering the results.

Evaluation of the hemodynamic effects of interpleural bupivacaine in dogs.

The hemodynamic effects of interpleural (IP) bupivacaine were studied in six halothane-anesthetized dogs. On four separate occasions, each dog received IP saline (S), or bupivacaine at a low dosage of 1.5 mg/kg (L), high dosage of 3.0 mg/kg (H), or high dosage of 3.0 mg/kg with epinephrine 5 micrograms/mL (HE). Heart rate, systolic and mean arterial pressures, and base excess were significantly lower in the H dosage group than in the other treatment groups. Cardiac output, expressed as a percentage of change from baseline, was significantly higher in the L group than in the H and S groups. Pulmonary arterial pressure and respiratory rate were significantly higher in the HE group than in the other three groups. Mean plasma concentrations of bupivacaine peaked between 5 and 15 minutes after IP injection. Maximum plasma concentrations in individual dogs were variable; however, mean maximum plasma concentrations in the H and HE groups were not significantly different. Clinically significant hypotension occurred in one dog in the H group and in one dog in the HE group. No pulmonary complications were detected.