Clay A. Calvert

Heart Rate Variability

Heart rate variability (HRV), usually performed from 24 hour ambulatory ECG recordings, measures the variability of the heart rate. Alterations in autonomic balance and baroreceptor function, increased plasma norepinephrine levels, and reduced HRV have been associated with progressive myocardial failure. Not only has reduced HRV been associated with the degree of myocardial failure, possibility of prognostic significance, but also increased sudden death risk in both ischemic and nonischemic cardiomyopathy in humans. Heart rate variability analysis in the dog is confounded by pronounced sinus arrhythmia, and whether or not this technique has clinical utility in the dog remains to be demonstrated.

Feline diabetes mellitus: a retrospective mortality study of 55 cats (1982-1994).

Signalment, concomitant diseases, prognostic factors, and mortality were evaluated, retrospectively, in 55 diabetic cats (mean age, 11 years; range, five to 18 years). Sixty-seven percent of the cats were between 7.5 and 15 years of age. One-year mortality (n = 23) was high; most early deaths were due to comorbid disease, and the rate of death diminished in cats surviving beyond one year. The median survival time for all cats was 29 months; among cats that died, the median survival time was 11 months. Of the cats surviving more than one year, 16 were alive at a mean of 41 months. Only 13 of 37 cats died due to diabetes mellitus; the majority died due to concomitant diseases, with renal failure (n = 8) and hepatopathies (n = 6) being the most common causes. No clinical data was identified as being of prognostic significance.

Influence of antiarrhythmia therapy on survival times of 19 clinically healthy Doberman pinschers with dilated cardiomyopathy that experienced syncope, ventricular tachycardia, and sudden death (1985-1998).

Overtly healthy Doberman pinschers, having moderate to severe myocardial failure secondary to dilated cardiomyopathy, which experienced ventricular tachycardia, syncope or collapse, and sudden death were studied to determine the effect of antiarrhythmic medication on their clinical outcome. Antiarrhythmia drug therapy may have retarded sudden death in 13 treated dogs compared to the six dogs not administered antiarrhythmia drugs.

Hypertrophic cardiomyopathy in a litter of five mixed-breed cats

A litter of five, 18-month-old, mixed-breed cats were determined to have hypertrophic cardiomyopathy (HCM). Although no overt clinical signs were present in any cat, systolic heart murmurs were present in each. Electrocardiograms were normal, while subjective interpretations of heart enlargement on radiographs were made on four cats. Echocardiographic analyses indicated abnormalities consistent with HCM. Overt clinical signs are absent two years following diagnosis.

Toxicity in Doberman Pinchers with Ventricular Arrhythmias Treated with Amiodarone (1996–2005)

BACKGROUND Asymptomatic Doberman Pinschers with dilated cardiomyopathy (DCM) often die suddenly owing to ventricular tachycardia that degenerates into ventricular fibrillation. A safe and effective antiarrhythmic drug treatment is needed. This will require a large, well-controlled, prospective study. HYPOTHESIS Amiodarone toxicity is common in Dobermans with occult DCM and ventricular tachyarrhythmias refractory to antiarrhythmia therapy. Infrequent monitoring of hepatic function is inadequate. Frequent monitoring may be useful to determine dogs in which the dosage should be decreased or the drug withdrawn. METHODS Medical records from the University of Georgia and Cornell University were searched for Doberman Pinschers diagnosed with preclinical DCM that received amiodarone for severe ventricular arrhythmias refractory to other antiarrhythmic agents. Echocardiographic data, Holter recording data, hepatic enzyme serum activity, and serum amiodarone concentrations were recorded. The presence of clinical signs of toxicity was recorded. Serum amiodarone concentrations were obtained in some dogs. RESULTS Reversible toxicity was identified in 10 of 22 (45%) dogs. CONCLUSION AND CLINICAL IMPORTANCE Adverse effects from amiodarone were common and were, in part, dosage related. Patients should be monitored for signs of toxicity and liver enzyme activity should be measured at least monthly.

Bradycardia-associated syncope in 7 Boxers with ventricular tachycardia (2002-2005).

BACKGROUND Syncope is a recognized problem in Boxers and often is the result of rapid ventricular tachycardia (VT). Affected dogs may have echocardiographic evidence of dilated cardiomyopathy, but frequently have normal echocardiograms. Although VT is probably the most common cause of syncope in Boxers, neurocardiogenic bradycardia can also occur. OBJECTIVE We describe 7 Boxers with comorbid VT and neurocardiogenic bradycardia, wherein the syncope was secondary to bradycardia rather than VT. ANIMALS Seven Boxers were selected from a larger population of Boxers with Holter-documented VT because these dogs had documented bradycardia at the time of syncope. METHODS Retrospective study. RESULTS Although all dogs had Holter-documented VT, the etiology of the syncopal episodes was consistent with neurocardiogenic bradycardia. CLINICAL IMPORTANCE Neurocardiogenic bradycardia or VT can occur as isolated problems in Boxers. In some Boxers, VT and potential or manifest neurocardiogenic bradycardia coexist. The administration of a beta-blocker or sotalol to such dogs can aggravate or precipitate neurocardiogenic bradycardia-related syncope.

Evaluation of Extended-Release Diltiazem Once Daily for Cats With Hypertrophic Cardiomyopathy

Serum diltiazem concentrations were evaluated following either 30 mg or 60 mg of an extended-release diltiazem administered orally once daily to 13 cats. Sequential blood samples were obtained over 24 hours. Both dosages usually resulted in elevated serum concentrations of >200 ng/mL at 6, 12, 18, and 24 hours. The 30-mg dosage was sometimes associated with low serum concentrations of <50 ng/mL at 18 and 24 hours. The 60-mg dosage (9.3 to 14.8 mg/kg) was associated with lethargy, gastrointestinal disturbances, and weight loss in nine (36%) of 25 client-owned cats. Gastrointestinal disturbances were recognized within 1 week, and weight loss was detected after 2 to 6 months of treatment.

Unfavorable influence of anesthesia and surgery on Doberman pinschers with occult cardiomyopathy.

Exacerbation of heart rhythm disturbances or deterioration of left-ventricular function occurred in six Doberman pinschers with occult cardiomyopathy following anesthesia and surgery. These abnormalities improved over time in surviving dogs, supporting a causal relationship between anesthesia/surgery and exacerbation. Moderate myocardial failure and ventricular tachyarrhythmias of variable severity existed prior to anesthesia and surgery in each dog. The incidence of these adverse effects is uncertain but probably significant. Exacerbation of arrhythmias may be life-threatening or lethal. Embarrassment of left-ventricular function may be inapparent or, if function already is marginal, may precipitate congestive heart failure.

Pulmonary Manifestations of Heartworm Disease

The clinical signs associated with heartworm disease are the result of changes in the pulmonary arterial system. These clinical signs are the result of either pulmonary hypertension or lung parenchymal disease associated with vascular changes. An increase in pulmonary arterial pressure produces an increase in right ventricular afterload, which may lead to exercise intolerance, syncope, and right-sided congestive heart failure. Coughing, dyspnea, and hemoptysis are the results of pulmonary parenchymal disease.

Effect of medical therapy on survival of patients with dilated cardiomyopathy.

Few studies have been conducted that focus on survival as the end point of medical therapy of CHF. No vigorous studies have been conducted in dogs. It is generally accepted that diuretic therapy is an essential component of the therapy of CHF in cardiomyopathic dogs. Significant symptomatic improvement is afforded by diuretics, and acute death may be prevented. In this context diuretics can be said to improve survival. However, diuretics do not alter the natural progression of cardiomyopathy and in this context do not favorably influence long-term survival. Digitalis glycosides have been shown in humans to improve various parameters of CHF in a subset of patients with either atrial fibrillation or third heart sounds. In dogs, these gallop heart rhythms due to third heart sounds are usually associated with myocardial failure due to dilated cardiomyopathy. In spite of symptomatic improvement, no study has demonstrated an unequivocal favorable effect of digoxin on survival of patients with dilated cardiomyopathy. Likewise, there is no convincing evidence of an adverse effect on survival. Newer, powerful inotropes, such as milrinone, often demonstrate impressive short-term improvements in left ventricular function, clinical signs, and exercise tolerance in patients with CHF. However, their long-term benefits are much less impressive, they are arrhythmogenic, and they have not been shown to prolong survival. In fact, long-term milrinone therapy in humans has had an unfavorable influence on mortality. Vasodilators offer the potential advantage of increasing left ventricular performance without an associated increase in myocardial oxygen demand and cardiac rhythm disturbances. The only vigorous survival study that unequivocally demonstrated improved survival of patients with advanced CHF due to myocardial failure, including dilated cardiomyopathy, was the Consensus Trial. Survival of patients receiving enalapril was significantly better than those receiving placebo. In fact, the trial was stopped prematurely by the ethical review committee when it became obvious that the results favored the enalapril group. Although the use of beta-adrenergic blocking drugs in cardiomyopathic patients with CHF is controversial and associated with a risk of short-term deterioration of left ventricular function, their use in human medicine is gaining acceptance. Although hemodynamic and clinical evidence of improvement has been demonstrated along with withdrawal-associated deterioration, the only study purporting a beneficial effect on survival used retrospective controls.(ABSTRACT TRUNCATED AT 400 WORDS)