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Episodic weakness and syncope are common in Boxers. Reported causes include ventricular tachycardia (VT) and neurally-mediated bradycardia (NMB). The purpose of this study was to describe the features of presumed NMB in Boxers. A total of 27 Boxer dogs were identified. To be included in the study, each dog must have been overtly healthy with a history of syncope or presyncope; had a normal echocardiogram; had absence of ventricular tachycardia (VT) and fewer than 500 ventricular premature complexes on 24 hour Holter recordings; and been alive and clearly healthy for at least six months following the initial evaluation. Heart rhythm were documented at the time of an episode in only eight dogs (30%) and only once on the first Holter recording. Bradycardia was subsequently recorded in five times during 120 hour Holter recordings and during the 5th day of an event recording. Bradycardia was documented during auscultation in two additional dogs. The heart rate was not documented in 19 (70%) dogs in this study. Documentation of the heart rhythm during episodes of collapse was difficult and was carried out in only 30% of dogs and was unlikely to occur during the first Holter recording. In Boxers with suspected NMB, extended ambulatory monitoring, including implantable loop recorders, may be required for heart rate documentation. [ABSTRACT FROM AUTHOR] more...

Summary: Background: Despite the paucity of data available, orally administered angiotensin‐converting enzyme (ACE) inhibitors are empirically used in horses with valvular regurgitation. Objective: Evaluate the echocardiographic and hormonal changes in response to oral benazepril in horses with left‐sided valvular regurgitation. Study design: Prospective, randomised double‐blind, placebo‐controlled trial. Methods: Horses with mitral valve (MR) and/or aortic valve regurgitation (AR) received oral benazepril (n = 6) at a dosage of 1 mg/kg q 12 h or a placebo (n = 5) for 28 days. Echocardiography was performed before drug administration and after 28 days of treatment. Plasma renin activity, serum ACE activity, angiotensin II concentration, aldosterone concentration and biochemical variables were measured before drug administration and after 7 and 28 days of treatment. Results: Relative to baseline, horses treated with benazepril had statistically significant reduction in left ventricular internal diameter in systole (mean difference between groups = −0.97 cm; 95% CI = −1.5 to −0.43 cm), aortic sinus diameter (−0.31 cm; −0.54 to −0.07 cm), and percentage of the aortic annulus diameter occupied by the base of the AR jet (−17.05%; −31.17 to −2.93%) compared with horses receiving a placebo. In addition, horses treated with benazepril had a significantly greater increase in cardiac output (11.95 L/min; 1.17–22.73 L/min) and fractional shortening (7.59%; 3.3–11.88%) compared with horses receiving a placebo. Despite profound serum ACE inhibition, renin activity and concentrations of angiotensin II and aldosterone were not significantly different between treatment groups or among time points. Main limitations: Very small sample size and short treatment period. Conclusions: Treatment with oral benazepril resulted in statistically significant echocardiographic changes that might indicate reduced cardiac afterload in horses with left‐sided valvular regurgitation. Additional studies with a larger sample size will be necessary to determine if administration of benazepril is beneficial in horses with valvular regurgitation. The Summary is available in Spanish – see Supporting Information [ABSTRACT FROM AUTHOR] more...

Background Benazepril has been shown to inhibit circulating angiotensin-converting enzyme ( ACE) activity in horses but the optimal dosage is unknown. Objectives To determine the lowest tested dose of benazepril that results in ≥75% attenuation in the response of arterial blood pressure ( BP) to exogenous angiotensin I ( ANG-I) administration. Study design Prospective experimental study. Methods A total of 5 healthy horses were instrumented for the direct measurement of BP. Each horse received 4 intragastric doses of benazepril (0.5, 1, 2 and 4 mg/kg bwt) with a washout period of 7 days between doses. Prior to and 2, 12 and 24 h after benazepril administration, each horse received intravenous (i.v.) boluses of ANG-I at 20, 60 and 200 ng/kg. Attenuation of the systolic arterial pressure ( SBP) response to ANG-I and serum ACE activity were quantified and expressed as percentage of inhibition. Results There was a significant effect of benazepril dose (P = 0.004) and time (P = 0.004) on the percentage of inhibition of the systolic pressor response to ANG-I. Regardless of benazepril dose, the percentage of inhibition was significantly greater 2 h after administration of benazepril compared with 12 and 24 h. At an ANG-I dose of 20 ng/kg, the percentage of inhibition after administration of benazepril at 1 mg/kg bwt (46.6 ± 18.9%) was significantly greater than that achieved after 0.5 mg/kg bwt (19 ± 14%) but not significantly different from that achieved at higher doses of benazepril. Benazepril doses ≥1 mg/kg bwt resulted in serum ACE inhibition of at least 90%. Main limitations Small sample size and resulting low statistical power. Conclusions Attenuation of the rise in SBP in response to ANG-I after administration of benazepril is modest in horses despite adequate serum ACE inhibition. A dose of 1 mg/kg bwt would be recommended for future investigations of benazepril for the management of cardiovascular diseases in horses. [ABSTRACT FROM AUTHOR] more...

Reasons for performing study: Pimobendan is an inodilator used in dogs for the management of heart failure due to myxomatous valve disease or dilated cardiomyopathy. The lack of data regarding the effects of pimobendan in horses prevents the rational use of this drug. Objective: To determine the cardiovascular effects of pimobendan in healthy mature horses. Study design: Randomised experimental study. Methods: Five horses were fasted overnight prior to receiving i.v. pimobendan (0.25 mg/kg bwt), intragastric (i.g.) pimobendan (0.25 mg/kg bwt) or i.g. placebo with a washout period of one week between each administration. Horses were instrumented for the measurement of right ventricular (RV) minimum pressure, RV maximum pressure, RV end diastolic pressure, and maximum rate of increase and decrease in RV pressure before and 0.5, 1, 2, 4, and 8 h after drug administration. Arterial blood pressure, central venous pressure, cardiac output and heart rate were measured at the same time points. Data were expressed as a maximum percentage of change over baseline values. Results: There were no adverse effects associated with administration of pimobendan. The percentage increase in heart rate was significantly greater for horses given pimobendan i.g. (33 ± 4%) and i.v. (36 ± 14%) than for those given a placebo (-2 ± 7%). The percentage increase in maximum rate of increase in RV pressure (35 ± 36%) and the percentage decrease in minimum pressure (47 ± 24%) and end diastolic pressure (34 ± 13%) were significantly greater in horses given pimobendan i.v. than in those given placebo. Other variables measured were not significantly different between treatment groups. Conclusion: Pimobendan administered i.v. has positive chronotropic and inotropic effects in healthy mature horses and warrants further investigation for the treatment of heart failure in horses. [ABSTRACT FROM AUTHOR] more...