First of all,  I want to review some biology so you may better understand the normal Physiology of the heart and the disease process.   

The heart is a 4 chambered pump.  The upper two chambers are the right and left atria (plural for atrium) and the two lower chambers are the right and left ventricles.  The period from the end of one heart contraction to the end of the next contraction is called the cardiac cycle.  This cycle consists of a period of relaxation, called diastole, followed by a period of contraction called systole.  Blood returning from the body enters the right atrium, moves to the right ventricle where it is pumped to the lungs via the pulmonary arteries to exchange carbon dioxide for fresh oxygen, returns to the lungs to the left atrium by the pulmonary veins, and is then pumped from the left atrium to the left ventricle, and is pumped back out into the body via the aorta.  Cardiac output is the quantity of blood pumped by the left ventricle into the aorta each minute, and venous return is the quantity of blood flowing from the veins into the right atrium each minute.  

The A-V (atrial-ventricular) valves prevent back flow of blood from the ventricles to the atria during systole, and the semi-lunar valves prevent back flow from the aorta and pulmonary arteries into the ventricles during diastole.  The mitral valve is between the left atrium and the left ventricle of the heart; it is composed of two cusps, anterior and posterior.  It is also known as the bicuspid valve. The tricuspid valve guards the opening between the right atrium and the right ventricle; it has three points or cusps.   

Chronic heart valve disease (called endocardiosis) is common in many aging dogs. The valve leaflets and the cords holding them in place gradually degenerate and become thickened and distorted with age.  Lumps or nodules develop on the valve leaflets, and chemical changes take place that make the valves less flexible (fibrosis).  All heart valves can be affected to some extent, but the mitral valve, in the left (high pressure) side of the heart is most frequently and seriously affected.  When this valve loses its flexibility, it starts to leak causing valve insufficiency or also called regurgitation.  Initially, mild mitral valve insufficiency causes no distress to the animal but a heart murmur may be heard.  Later, as the leak becomes more pronounced, and the heart becomes overstretched by heart failure, the leakage is accentuated.  Further serious complications can include a flail valve, rupture of chordae tendineae and even rupture of the overstretched left atrium, together with heart rhythm disturbances which can cause dramatic flooding of the lungs, collapse or sudden death. 

The difference between heart disease and heart failure :  heart murmurs, arrhythmias (abnormal rhythms), and other cardiac abnormalities provide evidence for heart disease. Those dogs showing these signs will not show signs of heart failure until these disease states are severe.  Many forms of heart disease may not warrant therapy; however all forms of heart failure require therapeutic intervention.  Heart failure is the state wherein the heart fails to meet the metabolic demands or needs of the tissues, therefore cardiac output is not sufficient to meet the needs of the tissues.  This usually occurs in the face of elevated left ventricular pressures at end diastole.  Heart failure may occur in conditions where the heart is producing a normal cardiac output, but the metabolic needs of the tissues are increased, such as in hyperthyroidism or anemia, and so cardiac output fails to meet their needs. It may also occur in conditions where the strength of the heart muscle appears normal. Most conditions that result in heart failure occur as a result of markedly weakened left ventricle or right ventricle or both.  

Congestive Heart Failure (CHF) is the principle complication of heart disease. It is a pathophysiologic state produced by an abnormality in cardiac pump function, either transient or prolonged. The heart is unable to transport blood in a sufficient flow to meet metabolic needs. CHF occurs at some time in most cases of severe heart disease.

CHF occurs when left ventricle pressure at end diastole is elevated and this results in elevated pulmonary venous pressures and pulmonary edema. CHF occurs when the volume of blood presented to the heart is in excess of the heart’s capacity to move it along.  As a result, fluid builds up behind the heart. If the inability to move the blood forward is due to a left heart problem, then pulmonary venous congestion develops and later pulmonary edema. This can then lead to pleural effusion (effusion is the escape of fluid into a part) and abdominal effusion.  If the abnormality lies in the right heart or the pulmonary arteries, they limit the ability to move blood forward and congestion occurs behind the right heart, causing pleural effusion and/or build up of fluid in the abdomen. Many but not all cases of heart failure also have CHF.  Because of the heart’s inability to function normally,  CHF is the retention of fluids (water and salt) causing build-up of fluid in the lungs.  

Understanding Pulmonary edema :  when the left side of the heart fails without the right side failing, blood continues to be pumped into the lungs by the normal right heart, while it is not pumped adequately out of the lungs by the left heart.  As a result, the mean (average) pulmonary pressure rises while the mean systemic pressure fails because of the shift of large volumes of blood from the systemic circulation into the pulmonary (lung) circulation.  As the volume of blood in the lungs increases, the pulmonary vessels enlarge and once the pulmonary capillary pressure rises above a critical point, fluid begins to filter out of the capillaries into the interstitial spaces and alveoli (air sacs in the lungs where the exchange of oxygen and carbon dioxide occurs), resulting in pulmonary edema. With the abnormal accumulation of fluid, the dog may show signs of shortness of breath and open-mouthed breathing, and may stand or assume a sitting position with the elbows held away from the chest only, in preference to lying down. Unless the congestion with serous fluid and blood is checked, the normal respiratory exchange of oxygen and carbon dioxide is cut off, the dog is literally drowning.  

Myocardial oxygen consumption(MVO2) refers to the amount of oxygen required by the heart muscle for a contraction.  Afterload refers to the resistance the left ventricle encounters as it tries to eject blood. Afterload in only conceptual and can’t be measured directly. Preload refers to the stretching of the myocardial cells in a chamber during diastole, prior to the onset of contraction. This is the process of the pump. Preload is measured as the end-diastolic volume or end-diastole pressure. Preload is equal to venous return plus the residual volume left in the cardiac chamber after the last contraction.  

Synonyms used to describe Congested Heart Failure (CHF) are :  heart failure, dropay, circulatory failure, cardiac failure 

Symptoms of CHF

* Early and mild impairment :

          - basilar rales (crackling heard in lungs)

          - positive hepatojugular reflux (distention of jugular vein when direct pressure is             applied to the liver)

- faint S3 gallop (click here to listen to one -  www.chfpatients.com/faq/s3s4.htm  the first sound is from the atrial walls, the second is from the contraction of the atriums and the 3^rd is caused by vibration of the ventricular walls resulting from the first rapid filling so it is heard just after the S2. it is low in frequency and intensity.)

          - nocturia (frequent nighttime urination)

          - dyspnea on exertion (difficulty breathing) – cardinal sign of left heart failure

          - deteriorating exercise capacity

          - fatigue

          - difficulty breathing

          - weakness

          - tachypnea with mild exertion (abnormally fast breathing)

* Moderate impairment :

          - nocturnal non-productive cough

          - orthopnea (the inability to breathe easily unless sitting up straight or standing)

          - paroxysmal nocturnal dyspnea (waking suddenly in night with shortness of                breath and unable to breathe normally lying down)

-  wheezing, especially at night in absence of history)

-  anorexia (weight loss)

-  tachypnea at rest

-  anxiety

-  hepatomegaly with tenderness to palpation (swollen liver with tenderness)

-  cool extremities due to constriction of blood to limbs

-   right pleural effusion

-   edema

-   gallop rhythm

-   diastolic hypertension

-   elevated jugular venous pressure

-   cardiomegaly (enlarged heart)

 

* Severe impairment :

          - cerebral dysfunction

          - abnormal bloating (ascites – bloated abdomen)

          - cyanosis (blueish appearance to mucosal tissue due to lack of sufficient                 oxygen)

-  hypotension

-  frothy and/or pink sputum

-  increased P2

-  cardiac cachexia (cardiac muscle atrophy or wasting)

-  Cheyne-Stokes respirations (abnormal breathing pattern characterized by periods of breathing with gradually increasing and decreasing tidal volume with periods of apnea which are no breaths at all)