Left-sided heart failure (LSHF) occurs when the heart’s main pumping chamber, the left ventricle, cannot efficiently move oxygen-rich blood out to the rest of the body. This inefficiency causes blood to back up, leading to fluid congestion, most noticeably in the lungs, which results in symptoms like shortness of breath. The question of whether left-sided heart failure is systolic or diastolic has a simple answer: it can be either, or sometimes both. The classification depends entirely on the specific mechanism of failure—whether the problem is with the heart’s ability to squeeze and pump blood or its ability to relax and fill with blood.
Understanding the Left Ventricle’s Dual Roles
The heart functions in a continuous cycle, alternating between two main phases: systole and diastole. Systole is the active phase when the left ventricle contracts forcefully to eject blood into the aorta for distribution throughout the body. Following this powerful contraction, the heart must immediately enter diastole, which is the relaxation and filling phase. During diastole, the left ventricle muscle relaxes and expands, allowing blood returning from the lungs to flow into the chamber. Both phases must be executed properly to maintain the approximately 55% to 60% of blood pumped out with each beat, a measurement known as the ejection fraction (EF).
Left-Sided Systolic Failure (HFrEF)
Systolic failure is defined as a failure of the left ventricle’s pumping action, meaning the problem lies squarely within the contraction phase. This condition is formally known as Heart Failure with Reduced Ejection Fraction, or HFrEF. In HFrEF, the heart muscle is weakened and cannot contract with enough force to push an adequate volume of blood into the systemic circulation. The defining characteristic of HFrEF is a reduced ejection fraction, typically measured at 40% or lower. Common causes of this muscle weakness include damage from a previous heart attack, which scars the muscle tissue, or chronic coronary artery disease that limits blood flow to the heart.
Left-Sided Diastolic Failure (HFpEF)
Diastolic failure represents a problem with the heart’s ability to relax and fill with blood, even though its pumping strength may appear normal. This condition is referred to as Heart Failure with Preserved Ejection Fraction (HFpEF). In HFpEF, the walls of the left ventricle become stiff, thick, or less flexible, preventing the chamber from fully expanding during the diastolic phase. Because the ventricle cannot relax sufficiently, it struggles to fill with the necessary volume of blood coming from the lungs. Even though the heart muscle can still contract strongly enough to eject a normal percentage of the small amount of blood it contains, the total volume of blood pumped out is insufficient for the body’s needs. Chronic high blood pressure (hypertension) is a frequent cause, leading to a thickened, less compliant muscle over many years.
Why Diagnosis Matters: Treatment Implications
Differentiating between HFrEF and HFpEF is important because the underlying mechanisms of failure require different management strategies. The therapeutic approach for HFrEF is focused on improving the weakened pump and reducing the heart’s workload. Treatments for HFrEF include medications like beta-blockers and ACE inhibitors, which are designed to counteract the hormonal signals that cause the heart muscle to weaken and remodel. Conversely, the treatment for HFpEF centers primarily on managing the conditions that cause the heart muscle to become stiff. Management for HFpEF focuses on controlling chronic conditions such as high blood pressure and diabetes, along with using diuretics to control fluid volume and symptoms.