Heart failure (HF) is a complex medical condition where the heart muscle cannot pump enough blood to meet the body’s metabolic demands. This is not a sudden stopping of the heart, but rather a progressive inadequacy of its function as a pump. Understanding heart failure requires differentiating between the location of the issue, most commonly the left side, and the specific functional problem. The heart’s inability to maintain adequate circulation can stem from issues with the contraction phase (systole) or the relaxation phase (diastole). This distinction between location and function is fundamental to diagnosing and managing the condition.
Understanding the Difference Between Systolic and Diastolic Failure
The heart operates in a two-part cycle: systole, the phase of contraction and ejection, and diastole, the phase of relaxation and filling. Heart failure is classified based on which of these two mechanical functions is primarily impaired.
Systolic heart failure, also known as Heart Failure with Reduced Ejection Fraction (HFrEF), occurs when the heart muscle is weakened and cannot contract forcefully enough. This weakness means the heart struggles to eject an adequate volume of blood into the circulation with each beat.
In contrast, diastolic heart failure, or Heart Failure with Preserved Ejection Fraction (HFpEF), involves a problem with the heart’s ability to relax and fill properly. The heart muscle becomes stiff, preventing the chamber from expanding adequately to receive blood during the resting phase. Although the muscle may still contract with near-normal force, the reduced volume of blood available for pumping results in low output.
The primary metric used to distinguish these two types is the Ejection Fraction (EF), which measures the percentage of blood pumped out of the ventricle with each contraction. A normal EF typically falls between 50% and 70%. In HFrEF, the EF is reduced, usually dropping below 40%, indicating a severe pumping problem. Conversely, in HFpEF, the EF remains preserved, often at 50% or higher, reflecting a filling problem rather than a contraction problem.
Why Left Sided Heart Failure Can Be Either Type
Left-sided heart failure refers to a problem originating in the left side of the heart, specifically the left ventricle (LV), which is the body’s main pump. The LV is responsible for receiving oxygenated blood from the lungs and propelling it out to the rest of the body. Because the LV is subjected to the highest workload and pressure, it is the most common chamber to fail.
Left-Sided Heart Failure is a description of the location, meaning the functional impairment within the LV can manifest as either systolic or diastolic dysfunction.
When the failure is systolic (HFrEF), the left ventricle’s muscular wall becomes thin and dilated. This weakened state prevents the muscle from squeezing effectively, resulting in a low volume of blood ejected from the LV.
Alternatively, the LV can suffer from diastolic failure (HFpEF), where the muscle wall becomes thickened and stiff. The ventricle cannot relax sufficiently to accommodate an adequate volume of blood during diastole. Even though the LV may contract normally, the high pressure needed to force blood into the stiff chamber causes blood to back up.
The underlying cause often dictates the type of failure. A history of heart attacks and coronary artery disease frequently leads to the weakened muscle of systolic failure. Long-term, uncontrolled high blood pressure, however, often causes the persistent strain and thickening that results in the stiff muscle characteristic of diastolic failure. Therefore, left-sided heart failure is a broad diagnosis that must be refined by testing the heart’s mechanics to determine if the problem is one of ejection or one of filling.
Primary Effects of Left Ventricular Dysfunction
The clinical presentation of left ventricular dysfunction, regardless of whether it is systolic or diastolic, stems from the failure to move blood forward efficiently. When the left ventricle cannot pump blood out effectively, the blood volume begins to back up into the chambers upstream. This accumulation first affects the left atrium and then the pulmonary veins, which carry blood from the lungs to the heart.
This backward pressure ultimately forces fluid out of the blood vessels and into the air sacs of the lungs, a condition known as pulmonary congestion or pulmonary edema. The presence of fluid in the lungs directly interferes with the exchange of oxygen, leading to the most common symptoms of left-sided failure. Patients often experience shortness of breath, medically termed dyspnea, which can occur during physical activity or even at rest.
Specific breathing difficulties include orthopnea, which is shortness of breath that worsens when lying flat, and paroxysmal nocturnal dyspnea, which involves sudden awakenings due to severe breathlessness. The fluid accumulation can also irritate the airways, causing a persistent cough or wheezing. By contrast, the failure of the right side of the heart causes blood to back up into the systemic circulation, leading to fluid retention and swelling, primarily in the legs and abdomen.