Heart failure occurs when the heart can’t pump enough blood to maintain normal bodily function. When circulating blood volume is inadequate weakness and fatigue will be experienced with physical exertion and at rest with disease progression. Edema develops. Blood that the heart can’t pump starts to pool. Initially a weakness of the heart’s right side causes edema in the extremities, liver and abdomen. Left sided failure is demonstrated by pulmonary edema. Pulmonary edema causes shortness of breath increasing in severity as mounting edema decreases oxygen capacity. In advanced heart failure both sides eventually fail.
One of the bodies’ first compensatory mechanisms to low blood volume is increasing heart rate via the release of epinephrine and norepinephrine. This action can benefit a non-diseased heart resuming normal cardiac output. Tachycardia can stress an abnormal heart, which may already be ischemic due to low blood volume and/or coronary artery disease. Another automatic attempt to increase circulating blood volume is for the kidneys to retain salt resulting in water retention. The extra water increases blood volume resulting in improved cardiac output for a while. If heart failure is not corrected by medical intervention this mechanism eventually fails. The excess fluid starts to collect in the lower extremities, back and abdomen.
Lastly the heart muscle enlarges to increase its pumping ability. Again this helps for a while but bigger isn’t always better. As heart muscle increases in size it looses its’ ability to stretch and pump blood. Heart failure can result from any process that interferes with the hearts’ ability to pump. The most common cause is coronary artery disease. The blood vessels that oxygenate the heart become compromised by fatty plaque weakening the heart. Heart valve disease may cause a valve to partially block blood flow or not close properly allowing blood to flow backward.