Mitral regurgitation (Proceedings)
Mitral regurgitation (MR) is the most common heart disease in dogs (seen in approximately 85% of dogs with heart disease); dilated cardiomyopathy (dCMy) is next most common (seen in approximately 5% of dogs with heart disease). If the dog has heart disease and you can pick it up with one hand, it's probably MR; if it takes 2 hands, it's probably dCMy. MR occurs with increasing frequency in dogs over 6 years old, except in Cavalier King Charles Spaniels in which it may occur at 2 to 3 years of age. It is no doubt a familial (hereditary disease), but the genetic transmission is not clear.
Most heart disease of importance affects the left side of the heart: left atrium, left ventricle, aorta, and reduces forward flow (cardiac outpt=CO) and/or cause blood to dam-up in the lungs. Two general formas of heart disease occur: one in which the ventricle lacks enough power, or in the presence of MR or aortic stenosis (narrowing) to pump blood into the aorta—so-called systolic failure; the other in which the ventricle fails to fill properly because it is too stiff—so-called diastolic failure. Symptoms/signs and mortality arise equally from diastolic and systolic failure and it is very hard to tell them apart.
We intend to focus on treatment of disease, so here are a few rules about ordering tests to find out what is wrong and prescribing drugs to improve the quality of life or lengthening it:1. Don't do something just because you can.
2. Don't do something because others do.
3. Don't do something because it's always been done.
4. Do something because there is a reasonable expectation that it will change, favorably, the outcome of the case, or because it will answer a question the owner has.
What do you (the DVM, nurse, assistant) want top know?
1. Diseases you can exclude from consideration.
2. Goals to achieve for therapy.
3. Methods to achieve those goals.
4. Risk—and how you might minimize them—to achieving goals.
5. How do you know when goals are achieved?
6. What do you do if goals are not achieved?
Goals of therapy are:
1. Never to treat a name or a murmur.
2. Generally to prolong life and decrease symptoms/signs.
3. Adjust fluid balance.
4. Improve force of contraction and rate of relaxation of the ventricles.
5. Decrease hindrance to ejection.
6. Regulate rhythm.
7. Improve oxygenation—remember that most animals that die fro heart or ling disease do so from asphyxia resulting from fatigue of muscles of respiration.
8. Diminish remodeling. Remodeling is a change in structure or electrophysiological properties.
9. "Up-regulate" beta receptors
10. Return baroreceptors to normal.
11. "Build a bridge from diagnosis to when the animal has enough beta blockers on board."
Remember that the the sympathetic nervious system may save your life for short spurts, but it is your mortal enemy the rest of the time. Pay attention to it.
The following is an outline of precisely when to use each drug in your pharmacopoeia:
1. left atrial enlarge met—ACE inhibitor
2. left ventriculae enlargement—digoxin, spironolactone, carvedilol, pimobendan
5. refractory edema—add a ....thiazide
6. atrial fibrillation—diltiazem
7. ventricular arrhythmia—sotalolo/procainamide-mexiletine