Congestive Heart Failure (CHF) occurs when the heart is not able to appropriately handle the blood (load) that comes to it and pump it out for distribution around the body (hence the term heart “failure”). The result is back up of blood within the vessels of the lungs (hence the term “congestive”), increasing the pressure with in these vessels. Eventually fluid leaks out into the lungs themselves (pulmonary edema), causing breathing difficulty, distress and eventually death, if not treated aggressively. There are four main causes of congestive failure:
- myocardial – failure due to disease of the heart’s muscle; dilated cardiomyopathy (DCM) occurs when the heart muscle thins and can not contract properly to pump enough blood with each heart beat; DCM is most common in larger beed dogs; hypertrophic (HCM) and restrictive (RCM) cardiomyopathies occur when the heart muscle thickens or scars respectively and can not relax well enough to allow from proper filling of the heart chambers; HCM and RCM are most common in cats; damage to the heart’s muscle from drugs and infections (or any other cause) can lead to myocardial failure in either species;
- volume overload – failure due to too high a blood volume for the heart to manage; this can occur with: disease of the heart’s valves (valvular endocardiosis, endocarditis or dysplasia), whereby the valves do not create a tight seal when they close and blood is regurgitated back into the heart with each beat; congenital heart abnormalities (patent ductus arteriosus, ventricular spetal defects) where blood is shunted back to the heart with each beat, through a communication that is normally not present; systemic disease, such as hyperthyroidism and chronic (long-lasting) anemia;
- pressure overload – failure due to the generation of higher than normal pressures within the heart, in an effort to overcome an obstruction to the outflow of blood; this can be caused when the outflow tracts of the heart are physically narrowed (subaortic or pulmonic stenosis) or when hypertension (high blood pressure) is present, creating a functional obstruction to blood flow out of the heart; heartworm disease causes heart failure in this manner;
- pericardial disease – failure due to disease of the sac surrounding the heart (pericardium) or within the space created by the pericardium between itself and the heart muscle (pericardial space); generally pericardial disease causes pressure on the heart, preventing it from filling properly and sometimes leading to the collapse of weaker areas (cardiac tamponade); examples of pericardial disease include hemorrhage/bleeding into the pericardial space due to abnormal blood clotting (rodenticide intoxication for ex.) or a ruptured tumor on the heart (ie. hemangiosarcoma) and infection of the pericardium.
Dogs and cats of any age and either sex can be affected. Owners may or may not be aware that a problem is present prior to the congestive failure episode. These animals are usually brought to the veterinarian when owners notice acute respiratory/breathing issues due to the pulmonay edema. They show an increase in respiratory rate and/or effort, often with an obvious abdominal component to their breathing and may or may not have clear, peach colored fluid coming from their nose/mouth. The diagnosis of pulmonary edema is usually very straight-forward, based on the clinical signs, sounds on chest auscultation and changes seen on chest radiographs/x-rays. The underlying cause, however, can be very difficult to diagnose. Cardiomyopathy changes are often seen on x-rays, but may not be. Valvular disease, shunts, heartworm infestation and heart tumors require more specific tests for diagnosis. Often evaluation by a cardiologist is indicated for definitive diagnosis and treatment.
Therapy for congestive heart failure primarily revolves around clearing the pulmonary edema that is already present as quickly as possible, preventing new edema from accumulating and supplementing oxygen during the process, all with as little stress to the patient as possible. The diuretic Lasix/Furosemide is the most commonly employed drug for clearing pulmonary edema. Many doses may be necessary. The animal is placed in an oxygen chamber, if possible, to increase the concentration of inspired oxygen. Alternatively, nasal prongs or a nasal canula may be inserted to deliver oxygen to the patient. Minimally an oxygen mask may be placed in front of the patient’s face to deliver flow-by oxygen. Vasodilating agents (blood pressure lowering agents), such as Nitroglycerin ointment or a Nitroprusside infusion, may be used as adjunctive therapies to decrease the load of blood being returned to the heart and/or decrease the pressure against which the heart has to pump. These are the main therapies indicated for CHF. Specific medications to treat the underlying disease process are added to the regimen, once a definitive diagnosis of the underlying problem can be made. Patients must be stablilized before they can be subjected to the stress of a full radiographic series, an echocardiogram, blood pressure monitoring etc.
The prognosis for a patient that presents in CHF is very difficult to predict, as there are different prognoses for the underlying disease processes that may have caused the CHF in the first place. Many animals can be gotten out of congestive failure, if they are caught early enough and treated aggressively. An animal that has very progressed and severe pulmonary edema may not be able to withstand the stress of transport to the hospital and initial handling, diagnostics and treatment. Veterinarians will often leave the prognosis to be discussed by the cardiologist.
Overall, animals suffering from CHF are critical emergencies and must be treated aggressively. Owners must be fully committed to aggressive therapy. Undertreated or poorly treated animals surely suffer greatly. Owners must be aware that, depending on the underlying cause, future episodes of CHF are possible.