The health of many patients who have had a heart attack may deteriorate over time due to progressive heart failure. For example, a heart attack often results in damage to a portion of the heart tissue. To compensate for the reduction in heart function due to damaged heart tissue, walls of the heart wall may thicken to enable the heart to pump harder. However, the resulting enlargement of the heart tends to reduce the ejection fraction of the heart.
Progressive heart failure also may affect the timing of contractions in the heart. For example, the normally coordinated pumping of the right ventricle and the left ventricle may become unsynchronized. Cardiac resynchronization therapy (“CRT”) may be used to treat such a condition in some patients. Here, an implantable cardiac device incorporating appropriate CRT functionality may be implanted in the patient along with associated leads capable of providing stimulation pulses to the heart.
Although CRT may provide some improvement in heart function, the problems caused by progressive heart failure may eventually lead to acute decompensation and associated pulmonary-related conditions. In particular, a condition known as pulmonary edema may develop whereby fluid accumulates in the patient's lungs. In its early stages, a patient may not be aware that he or she has pulmonary edema. If pulmonary edema is not detected and treated in its early stages, however, hospitalization of the patient may be required to treat the condition. Consequently, there is a need for improved techniques for detecting pulmonary edema to reduce the potential impact on the patient's quality of life and to avoid significant hospital expense that may otherwise result from a failure to detect pulmonary edema at an early stage.