Heart failure is a chronic condition where the heart muscle is unable to pump enough blood to meet the body’s metabolic demands. It is a progressive syndrome resulting from damage or stress over time. The condition is classified into two main categories based on the cardiac cycle phase affected: the contraction phase (systole) or the relaxation phase (diastole). Understanding the specific functional problem allows medical professionals to tailor treatment strategies.
Understanding the Functional Difference: Ejection Fraction
A measurement called Ejection Fraction (EF) is the primary metric used to differentiate the two major types of heart failure. EF represents the percentage of blood that the left ventricle, the heart’s main pumping chamber, pushes out with each contraction. In a healthy heart, EF typically falls within a range of 55% to 70%. Heart failure is categorized based on this measurement. Heart failure with reduced Ejection Fraction (HFrEF) indicates systolic dysfunction, a problem with the heart’s pumping ability. Heart Failure with preserved Ejection Fraction (HFpEF) points to diastolic dysfunction, a problem with the heart’s ability to fill. An EF of 50% or higher is considered preserved, while an EF of 40% or lower is considered reduced. A third, intermediate category, Heart Failure with mildly reduced Ejection Fraction (HFmrEF), exists for patients with an EF between 41% and 49%.
Systolic Heart Failure: The Pumping Problem
Systolic heart failure (HFrEF) is characterized by a weakened heart muscle that cannot contract forcefully enough to eject a sufficient volume of blood. The heart muscle often becomes thin, stretched, and enlarged, a condition known as dilated cardiomyopathy. This structural change reduces the force of contraction, causing the Ejection Fraction to fall below 40%.
The underlying issue is a failure of output, meaning the heart struggles to move oxygenated blood effectively into the systemic circulation. This reduced force results in a backup of blood pressure in the chambers, which can eventually lead to fluid accumulation in the lungs and extremities.
Common primary causes for this loss of contractile force include damage from a previous myocardial infarction, or heart attack. Long-term, uncontrolled high blood pressure can also damage and thin the muscle fibers over time. Other factors like coronary artery disease, faulty heart valves, and certain arrhythmias can also initiate the process that leads to a weakened and dilated ventricle.
Diastolic Heart Failure: The Filling Problem
Diastolic heart failure (HFpEF) occurs when the heart muscle is stiff and unable to relax properly between beats, even though its pumping strength may remain normal. The left ventricle becomes rigid and thickened, preventing it from adequately expanding to receive blood returning from the lungs. Although the heart can still squeeze out a normal percentage of blood, the total amount of blood filling the chamber is less because the chamber cannot fully relax.
This inability to relax creates high pressure inside the heart during the filling phase, which pushes backward. This elevated pressure leads to the classic heart failure symptoms of fluid congestion in the lungs and body.
The primary drivers of this stiffness often involve chronic conditions that cause the heart wall to become hypertrophic, or abnormally thick. Long-standing, uncontrolled hypertension is a major cause, as the heart must constantly push against high resistance. Metabolic conditions like diabetes and obesity are also strongly associated with HFpEF, contributing to muscle stiffening, especially in older patients.
How Doctors Distinguish the Two Conditions
The definitive way doctors distinguish between systolic and diastolic heart failure is by using an echocardiogram, a non-invasive ultrasound of the heart. This imaging test provides a precise measurement of the Ejection Fraction, which immediately classifies the patient into the HFrEF or HFpEF category. The echocardiogram also visually assesses the heart’s structure, showing whether the left ventricle is enlarged and thin (HFrEF) or thickened and stiff (HFpEF).
Clinical evaluation also considers the patient’s specific profile and primary risk factors, which often differ between the two types. Patients with HFrEF are more likely to have a history of major coronary events, such as a heart attack, which caused direct muscle damage. Conversely, patients with HFpEF are often older and have a long history of chronic conditions like high blood pressure, diabetes, and obesity. Both types present with shortness of breath and fluid retention, making clinical distinction based on symptoms alone challenging.
Beyond imaging, blood tests measuring biomarkers like B-type natriuretic peptide (BNP) or its precursor (NT-proBNP) can support a heart failure diagnosis and help assess severity.
Classifying the heart failure type is a practical measure, as HFrEF is often more responsive to medications that directly improve pumping strength. HFpEF treatment focuses more on managing the underlying risk factors that cause stiffness and controlling fluid balance. Accurate classification is necessary because a treatment that helps one type may be ineffective or even detrimental to the other.