Heart failure occurs when the heart cannot pump enough blood to meet the body’s demands. Diastolic Heart Failure (DHF) is overwhelmingly associated with a problem in the left side. This condition involves the heart’s inability to relax and fill with blood, contrasting with a failure to pump blood out forcefully. It is often referred to as Heart Failure with Preserved Ejection Fraction.
The Heart’s Filling and Pumping Cycle
The heart operates in a continuous, two-part cycle known as the cardiac cycle. The first phase is systole, the period of contraction when the heart pushes blood out to the body. The second phase is diastole, the period of relaxation when the chambers refill with blood.
Diastolic failure specifically identifies an issue during the relaxation and filling period. The heart has trouble fully expanding after a contraction, which prevents the chamber from accepting the normal volume of blood needed for the next beat.
Why Diastolic Failure Involves the Left Ventricle
The left ventricle (LV) is the largest and most muscular chamber, tasked with pumping oxygenated blood to the entire body. Because it supplies the systemic circulation, the left ventricle operates under the highest pressure load in the heart. Long-term stress from conditions like chronic high blood pressure (hypertension) causes the muscle of the LV to adapt. This adaptation involves the heart muscle thickening and becoming less pliable over time, a process called hypertrophy.
This stiffening of the ventricular walls is the defining mechanism of diastolic heart failure. The thickened muscle is unable to relax fully and stretch adequately during the diastolic phase. Consequently, the left ventricle’s capacity to fill with blood is significantly reduced. Although the LV may still contract with force, the insufficient filling volume means less blood is delivered to the body with each beat.
The heart attempts to compensate for this reduced filling by generating higher pressures inside the ventricle to draw in blood. This mechanism, while initially helpful, ultimately increases the overall workload and stress on the chamber. The sustained high pressure results from the heart muscle’s reduced compliance, or inability to stretch and accommodate incoming blood.
Consequences of Impaired Left-Sided Filling
The primary consequence of the stiff, poorly filling left ventricle is a backward buildup of fluid pressure. Since the left ventricle cannot efficiently accept blood from the left atrium, the pressure is transmitted back through the left atrium and into the pulmonary veins. These veins carry oxygenated blood from the lungs, meaning the backup directly impacts the pulmonary circulation. This increased pressure forces fluid out of the blood vessels and into the lung tissue, a condition known as pulmonary edema.
The fluid in the lungs leads to common symptoms experienced by patients with DHF. Individuals frequently report shortness of breath, particularly during physical exertion. A specific symptom is orthopnea, which is difficulty breathing when lying flat, forcing the person to sleep propped up on pillows. This occurs because the horizontal position allows the pooled fluid to distribute more widely across the lungs, worsening gas exchange.
The chronic high pressure in the pulmonary circulation can eventually affect the right side of the heart. The right ventricle, which pumps blood only to the lungs, must work harder against the back pressure coming from the left side. Over time, the right ventricle can weaken and fail, leading to symptoms of right-sided heart failure, such as swelling (edema) in the legs, ankles, and abdomen.