Reduced cardiac output indicates a state where the heart struggles to pump an adequate volume of blood to meet the body’s metabolic demands. This fundamental function of the heart, circulating oxygen and nutrients throughout the body, is central to overall health. When compromised, the heart’s pumping ability can impact every organ and tissue, potentially leading to a range of health issues.
What is Cardiac Output?
Cardiac output refers to the total volume of blood the heart ejects into the circulatory system each minute, expressed in liters per minute. It is calculated from two components: heart rate and stroke volume. Heart rate is the number of times the heart beats in one minute, while stroke volume is the amount of blood pumped by one ventricle with each beat.
A healthy heart adjusts its cardiac output to respond to varying bodily needs, such as increasing blood flow during exercise to deliver more oxygen to active muscles. Reduced cardiac output means the heart cannot deliver enough oxygenated blood to maintain normal organ function. This insufficiency can arise if heart rate, stroke volume, or both, become abnormally low or ineffective.
Signs of Reduced Cardiac Output
When the heart struggles to pump sufficient blood, the body exhibits various physical signs and symptoms. Individuals might experience persistent fatigue and weakness, as their muscles and organs do not receive enough oxygen to function efficiently. Shortness of breath (dyspnea) is a common symptom, particularly during physical activity or when lying flat, due to fluid accumulation in the lungs. Swelling (edema) frequently occurs in the legs, ankles, and feet as fluid builds up in tissues.
Other signs include dizziness or lightheadedness from reduced blood flow to the brain. Extremities, such as hands and feet, may feel cold due to diminished circulation. A decrease in urine output can also signal reduced cardiac output, as the kidneys receive less blood flow. Rapid heart rate or palpitations may occur as the heart attempts to compensate by beating faster.
Common Causes
Several medical conditions can decrease the heart’s pumping efficiency. Heart failure, particularly both systolic (pumping) and diastolic (filling) dysfunction, is a frequent cause where the heart muscle is too weak or stiff to effectively pump blood. Arrhythmias, which are irregular heart rhythms, can significantly impair cardiac output; for instance, very slow heart rates (bradycardia) or excessively fast ones (tachycardia) reduce the heart’s ability to fill or eject blood. Heart valve problems, such as aortic stenosis, can obstruct blood flow out of the heart.
A myocardial infarction (heart attack) can damage heart muscle tissue, leading to a permanent reduction in pumping capacity. Severe infections like sepsis can trigger widespread inflammation and affect the heart’s function. Chronic conditions such as uncontrolled hypertension (high blood pressure) force the heart to work harder against increased resistance, eventually weakening it. Diabetes can also contribute to heart muscle damage and blood vessel issues that impair cardiac function.
Diagnosis and Management
Healthcare professionals diagnose reduced cardiac output through clinical assessment and diagnostic tests. A physical examination can reveal signs such as abnormal heart sounds, fluid retention, or changes in pulse. Blood tests provide insights into kidney function, electrolyte balance, and markers of heart stress. An electrocardiogram (ECG) records the heart’s electrical activity, identifying arrhythmias or signs of heart muscle damage.
An echocardiogram, an ultrasound of the heart, visualizes heart structure and function, including ejection fraction, a measure of pumping efficiency. A chest X-ray can show heart enlargement or fluid in the lungs. More advanced imaging or cardiac catheterization may assess blood flow and pressures within the heart chambers. Management aims to address the underlying cause and improve the heart’s pumping ability.
Lifestyle modifications are an initial part of management, including dietary changes, regular physical activity, maintaining a healthy weight, and avoiding tobacco products. Medications are prescribed to improve heart function and manage symptoms. These include diuretics to reduce fluid buildup, ACE inhibitors or ARBs to relax blood vessels, and beta-blockers to slow the heart rate and reduce its workload. Inotropic agents strengthen heart contractions, while antiarrhythmics regulate heart rhythm.
In some cases, medical procedures or devices are necessary. These include pacemakers or implantable cardioverter-defibrillators (ICDs) to control heart rhythm, or surgical interventions like angioplasty, bypass surgery, or heart valve repair/replacement. Advanced cases may require mechanical circulatory support devices, such as left ventricular assist devices.