[in Japanese]

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To determine the chronic effects of β-blocker on hemodynamics, left ventricular (LV) function and geometry in dogs with chronic heart failure due to mitral regurgitation (MR), metoprolol (MP) was administered to dogs with experimentally produced severe (n =4) and mild (n =3) MR. Oral administration of MP was started at a dose of 1.5mg/kg/day and gradually increased up to a maintenance dose of 4.5mg/kg/day. Clinical status, heart rate, arterial blood pressure, and LV function and geometry were evaluated at baseline and after 10 days, 20 days, 1 month, 3 months, and 6 months of treatment. Serum norepinephrine (NE) and atrial natriuretic peptide (ANP) concentrations were also examined. As a result, clinical status was worsened in severe MR group after 3 months of treatment, but not in mild MR group throughout the study. MP reduced heart rate, systolic and diastolic blood pressures, and LV fractional shortening in both MR groups. MP caused a significant increase in regurgitant volume and a decrease in stroke volume in severe MR group. In contrast, such changes were not observed in mild MR group. Relative LV wall thickness to chamber diameter increased in mild MR group, whereas LV chamber dilatation with wall thinning was seen in severe MR group. Serum NE and ANP concentrations were elevated in severe MR group associated with deterioration of clinical status. These results suggest that monotherapy of MP achieve negative chronotrophic and inotrophic effects without aggravation of cardiac function and clinical status in mild MR, whereas these effects may lead to progressive worsening of mitral regurgitation and clinical status in severe MR.

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Thirty-four adult healthy dogs (16 males and 18 females) weighing 4.6 to 18.9 kg (mean±SD, 11.2±3.4 kg) were studied by both two-dimensional and M-mode echocardiography. All tested subjects were mixed-breed companion dogs with the age ranging from 1.3 to 8 years old. During recording, dogs were kept in lateral recumbency without giving any chemical restraint. Two-dimensional echocardiographic images were obtained from left caudal (apical) parasternal location. The M-mode echocardiography was performed from the right parasternal long-axis view. Prior to presenting these values, each set of data was validated by both normality test and descriptive statistics. Parameters were also statistically evaluated to determine whether a correlation to age, gender, heart rate, body weight, and body surface area existed. In conclusion, the presented reference values are useful especially when the tested dogs are fitted in the above categories. Many values, being not correlated to age, sex, and body size, provide good indicators for evaluation of cardiac function. They are ejection fraction, fractional shortening, fractional thickness, interventricular septal thickness/left ventricular posterior wall thickness ratio, left atrial dimension/aortic root dimension ratio, systolic time intervals, indices in MV study (D-E excursion, E-F slope, E-septal separation, E-septal separation/left ventricular diastolic dimension ratio), and stroke volume index.

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Thirty adult healthy dogs (11 males and 19 females) weighing 4.7 to 17.2 kg (mean 10.9±3.3) were studied by spectral Doppler echocardiography. All tested subjects were mixedbreed companion dogs with the age ranging from 1.3 to 8 years old. During recording, dogs were kept in left lateral recumbency without giving any chemical restraint. Blood flows across mitral, tricupsid, pulmonary, and aortic valves were analyzed to understand ventricular systolic and diastolic functions and pressure determination as well. In addition, cardiac output and ventricular stroke volume were calculated. Each set of data was validated with both normality test and descriptive statistics. Parameters were also evaluated to understand whether they were correlated to age, gender, heart rate, body weight, and/or body surface area. The results revealed that Doppler values were correlated to pressure recordings, systolic time intervals, indices of ventricular diastolic function, cardiac output index, and/or stroke volume index. In conclusion, the presented reference values are useful especially when the tested dogs are fitted in the above categories. And the facts that many values either not correlated to age, sex, or body size, appear to be good general references for evaluation of cardiac function for all dogs.

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A case of cardiac myxosarcoma arising from the tricuspid valve is described in a 9-year-old dog that died of right-sided congestive heart failure. At necropsy, an oval-shaped, space-occupying mass of the right heart, measuring 5.5×3×2.5 cm, was found attached to the septal leaflet of the tricuspid valve. The cut surface of the mass was variegated gray, yellow, and red with extensive areas of necrosis and hemorrhage. Histologically, the mass had an amorphous to finely fibrillar myxoid background rich in acid mucopolysaccharides, and was composed of pleomorphic and hyperchromatic cells containing a large number of mitotic figures. Immunohistochemically, the tumor cells showed a tendency toward smooth muscle differentiation.

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