Today's Veterinary Practice

MAY-JUN 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 30 CE: CONGESTIVE HEART FAILURE IN CANINES stimuli for aldosterone release; therefore, ACE inhibition should reduce aldosterone levels. While this may true in the short term for some dogs, many dogs experience aldosterone escape and levels rapidly rise again. 10 These patients will probably benefit from additional aldosterone blockade from spironolactone. In humans, ACE inhibitors may cause cough, and these patients are generally switched to an angiotensin receptor blocker, such as losartan. These drugs have been used in dogs, but as canine patients are coughing anyway, it is difficult to justify the increased costs or identify increased coughing. Spironolactone, an aldosterone antagonist, is an extremely mild diuretic—it is difficult to document an increase in thirst in a dog given this drug. As a single agent, spironolactone is rarely sufficiently potent to control CHF, and clinical improvements are unlikely to be seen. However, there is good evidence that dogs with DMVD live longer if they receive spironolactone. 11 If not started right away, spironolactone can be introduced at the first or second recheck visit to allow the owner to come to terms with the number and frequency of the dog's medications before adding another tablet. The dose of spironolactone is 1 to 2 mg/kg PO q24h with food, as it is fat soluble, and absorption is increased with a meal. The main side effect of spironolactone in humans, gynecomastia, has not been reported in dogs. However, dogs should be monitored for the development of hyperkalemia. Additional Options If an arrhythmia is present, antiarrhythmic drugs may be indicated. Ventricular arrhythmias severe enough to require treatment are more common in DCM than mitral regurgitation; class 1 and 3 agents are used, with drugs such as mexiletine and sotalol being the most effective. 12 Side effects of mexiletine are usually gastrointestinal. Sotalol can exacerbate bradyarrhythmias and should be used with caution in patients with CHF. Atrial premature complexes, caused by stretching of the atrial myocardium, may not require specific treatment if they are infrequent. However, sustained atrial tachycardia and atrial fibrillation ( FIGURE 3 ) which is characterized by an irregularly irregular rhythm usually require rate control, as the sustained fast rate can result in a chronic tachy cardiomyopathy. A combination of digoxin and diltiazem gives better rate control in atrial fibrillation than either drug alone, but it has yet to be demonstrated that this combination results in an increased life expectancy. 13 Beta-blockers may seem a logical approach to rate control as they are used extensively in human patients with CHF and improved longevity is well documented. Unfortunately, the negative inotropic effects can be significant, particularly in canine patients with poor systolic function (eg, DCM). Furthermore, in the acute setting, the patient may require the extra inotropic and chronotropic support that beta stimulation provides to maintain output. For that reason, beta-blockers should never be administered to patients with acute CHF. FIGURE 3. Electrocardiogram from a dog in atrial fibrillation. There is a lack of P waves on any limb lead and a supraventricular tachycardia with an irregularly irregular rhythm. 50 mm/sec and 1 cm/mV. FIGURE 4. Echocardiogram from right parasternal long axis showing the left side of the heart and the mitral valve from a dog with degenerative mitral valve disease. A flail anterior mitral valve leaflet can be seen prolapsing back into the left atrium during systole.

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