The heart operates through a continuous, two-phase cycle to circulate blood throughout the body. Systole is the contraction or pumping action, where the heart forcefully ejects blood to the organs and tissues. Diastole is the relaxation or filling action, during which the chambers refill with blood in preparation for the next beat. Diastolic dysfunction is a mechanical problem in the filling phase that is closely related to the overarching condition of heart failure.
The Mechanics of Diastolic Dysfunction
Diastolic dysfunction (DD) is a mechanical problem where the left ventricle, the heart’s main pumping chamber, becomes stiff and cannot relax properly during the filling phase. This impaired relaxation prevents the chamber from fully expanding to accept the incoming blood volume. Conditions like long-standing high blood pressure or aging can cause the heart muscle cells to thicken and become less flexible, a process known as myocardial fibrosis or hypertrophy. The consequence of this stiffness is abnormally high pressure within the heart chamber, which causes blood to “back up.” The underlying cellular mechanisms involve impaired calcium handling and changes to a protein called titin, which regulates the muscle cell’s passive stiffness, allowing this malfunction to exist for years without causing noticeable symptoms.
Heart Failure: A Clinical Syndrome
Heart failure (HF) is a complex clinical syndrome where the heart cannot meet the body’s metabolic demands for oxygen and nutrients. It is the cumulative result of various structural or functional impairments of the heart, including DD. The hallmark of heart failure is the presence of systemic symptoms like shortness of breath, fatigue, and fluid retention, which signify that the body’s circulation is compromised. The inability of the heart to effectively circulate blood leads to congestion in the lungs and peripheral tissues. HF is categorized based on which phase of the cardiac cycle is primarily affected, but it always signifies a failure of the circulatory system to maintain adequate function without abnormally high filling pressures.
Diastolic Dysfunction as Heart Failure with Preserved Ejection Fraction (HFpEF)
Diastolic dysfunction is directly related to heart failure when it progresses to a symptomatic state, specifically classified as Heart Failure with Preserved Ejection Fraction (HFpEF). Ejection Fraction (EF) is the percentage of blood pumped out of the left ventricle with each contraction, and a preserved EF is typically defined as 50% or higher. In HFpEF, the heart’s pumping strength (systolic function) remains relatively normal, but the underlying DD prevents adequate filling. The mechanical problem of the stiff ventricle (DD) causes the high pressures characteristic of heart failure, even though the EF is preserved. DD is considered the foundational mechanism for HFpEF, accounting for approximately half of all heart failure cases, and its progression from asymptomatic DD to symptomatic HFpEF is a significant event with a prognosis comparable to that of HFrEF.
How Doctors Diagnose and Differentiate the Conditions
The progression to symptomatic heart failure is typically marked by the onset of symptoms, such as shortness of breath worsened by exertion or when lying flat, and swelling due to fluid retention. The primary non-invasive tool used to diagnose DD and classify the type of heart failure is a specialized ultrasound of the heart called an echocardiogram. This imaging test allows physicians to measure the Ejection Fraction to determine if it is preserved or reduced. The echo also assesses the heart’s filling patterns and the degree of ventricular stiffness through specific measurements, such as the E/e’ ratio. The combined finding of preserved EF and objective evidence of diastolic dysfunction on the echocardiogram confirms the clinical diagnosis of HFpEF. This process helps doctors distinguish the mechanical problem (DD) from the systemic condition (HFpEF) and differentiate it from HFrEF.