Heart failure (HF) is a chronic, progressive medical condition where the heart muscle cannot pump blood efficiently enough to meet the body’s metabolic demands. Although the term suggests a complete stoppage, it describes a diminished pumping function where the heart cannot keep up with its workload. The body relies on the heart’s pumping action to deliver oxygen- and nutrient-rich blood throughout the circulatory system. When the heart struggles, this insufficiency results in inadequate circulation and often causes a backup of fluid in the body.
Mechanics of Left-Sided Failure
The left side of the heart, specifically the left ventricle, is responsible for pumping oxygenated blood out through the aorta to the rest of the body. Left-sided heart failure (LSHF) occurs when the left ventricle’s function is impaired, which is the more common form of the condition. This impairment can manifest in two primary ways: systolic failure, where the ventricle cannot contract with enough force to eject blood, or diastolic failure, where the muscle becomes stiff and cannot relax and fill properly between beats.
In either case, the left ventricle cannot move blood forward efficiently, causing a backlog. The unexpelled blood pools and increases pressure, backing up into the left atrium and, subsequently, into the pulmonary veins that return blood from the lungs. This mechanical failure results in a buildup of pressure in the lungs, a condition known as pulmonary congestion. This congestion impedes the lungs’ ability to exchange oxygen and carbon dioxide effectively.
Mechanics of Right-Sided Failure
The right side of the heart, primarily the right ventricle, receives deoxygenated blood from the body and pumps it into the lungs to be re-oxygenated. In right-sided heart failure (RSHF), the right ventricle is too weak to efficiently push blood into the lungs’ pulmonary arteries. This inability to move blood forward causes it to accumulate in the right atrium and subsequently back up into the major veins of the body’s systemic circulation.
The resulting mechanical failure leads to an increase in pressure within the veins, known as central venous pressure. This elevated pressure forces fluid to seep out of the blood vessels and into the surrounding tissues and organs. This systemic congestion is the defining characteristic of RSHF, as fluid is retained in various parts of the body. The right ventricle must work harder against this resistance.
Observable Differences in Symptoms
The distinct mechanical failures of the two sides of the heart lead to different physical manifestations. Left-sided failure causes signs related to the backup of fluid into the pulmonary circuit. This pulmonary congestion manifests as shortness of breath (dyspnea), particularly during physical activity or when lying flat, a symptom called orthopnea.
Fluid accumulation in the lungs can be detected as crackles or rales upon listening to the chest. A persistent cough or wheezing, sometimes producing pink or white blood-tinged phlegm, also reflects the fluid saturation in the lungs. This respiratory distress is a hallmark of LSHF, as the body struggles to oxygenate the blood.
Conversely, right-sided failure produces symptoms related to the backup of blood into the systemic circulation. The increased venous pressure causes fluid to collect in the lower extremities, resulting in pitting peripheral edema. Fluid retention can also occur in the abdomen, a condition known as ascites, and cause congestion in the liver (hepatomegaly). Swelling of the jugular veins in the neck, known as jugular venous distension (JVD), is a direct sign of elevated central venous pressure.
Primary Causes and Interrelation
The underlying conditions that damage the heart often determine which side fails first. The most common primary causes of left-sided heart failure are long-standing conditions that increase the workload on the left ventricle, such as coronary artery disease, which limits blood flow to the heart muscle, and chronic high blood pressure (hypertension). A past heart attack, which damages a portion of the left ventricular muscle, is also a frequent cause.
Right-sided heart failure most often develops as a consequence of advanced left-sided failure. When the left ventricle fails, the resulting increased pressure in the lungs is transmitted backward, creating high resistance for the right ventricle to pump against.
Other Causes of RSHF
RSHF can also be caused by primary lung conditions, such as severe chronic lung disease or pulmonary hypertension. These conditions directly increase the pressure in the pulmonary arteries without initial left-sided involvement.