Low cardiac output syndrome (LCOS) is a serious medical condition where the heart struggles to pump enough blood to meet the body’s needs. This inadequacy means organs and tissues may not receive the oxygen and nutrients necessary for proper function.
What is Low Cardiac Output Syndrome
Cardiac output is the amount of blood the heart pumps into the circulatory system each minute, measured in liters per minute. It is determined by two main factors: heart rate (beats per minute) and stroke volume (blood ejected with each beat). A healthy heart adjusts this output to meet the body’s changing demands, such as during physical activity.
When cardiac output is low, organs and tissues do not receive enough oxygenated blood. This can lead to tissue hypoxia, where cells are deprived of oxygen, potentially causing organ dysfunction. The body attempts to compensate by increasing heart rate, but this may not be enough to restore proper blood supply.
Low cardiac output is commonly defined as a cardiac index below 2.2 liters per minute per square meter of body surface area, accompanied by specific symptoms. In severe cases, like cardiogenic shock, the cardiac index can drop below 1.8 liters per minute per square meter, leading to organ failure.
Common Causes and Risk Factors
Low cardiac output syndrome can arise from various underlying conditions affecting the heart’s ability to contract, the resistance it pumps against, or the blood volume returning to it. A common cause is complications following heart surgery, especially after procedures like coronary artery bypass grafting or valve surgery involving cardiopulmonary bypass. This can occur within 4 to 6 hours post-bypass.
Severe heart failure, whether chronic or acute, is another cause, as the weakened heart muscle struggles to pump blood efficiently. Conditions directly affecting heart contractility, such as myocardial ischemia (reduced blood flow to the heart muscle), cardiomyopathy, or acute myocarditis, can also lead to LCOS. Severe aortic stenosis, which narrows the heart’s outflow, can also contribute.
Beyond direct heart conditions, critical illnesses can also precipitate LCOS. These include septic shock, where widespread infection leads to circulatory collapse, severe hypovolemia (significant decrease in blood volume), or pericardial tamponade (fluid around the heart restricting pumping).
Several factors increase the risk of developing LCOS:
Pre-existing heart conditions, especially with reduced left ventricular ejection fraction.
Advanced age, particularly over 70 years.
Metabolic conditions like diabetes mellitus.
Prolonged time on a cardiopulmonary bypass machine during surgery.
Reoperation.
Systemic inflammation.
Electrolyte imbalances.
Significant coronary artery disease.
How Low Cardiac Output Syndrome is Identified
Low cardiac output syndrome manifests through signs and symptoms indicating insufficient blood flow to the body’s tissues. Patients might experience fatigue, dizziness, cold extremities, and prolonged capillary refill time. Other symptoms include decreased urine output and altered mental status, such as confusion.
Low blood pressure (systolic under 90 mmHg or a significant drop from baseline) is a common sign. The pulse may feel weak or thready, and heart rate often increases to compensate for low output.
Medical professionals diagnose LCOS through clinical evaluation and specific diagnostic tools. A physical examination helps identify signs like cool skin and a rapid, weak pulse. Blood tests can reveal metabolic acidosis, an imbalance in the body’s acid-base levels, occurring when tissues are not receiving enough oxygen.
Echocardiograms, ultrasound examinations of the heart, are useful for assessing cardiac function directly. This imaging technique allows clinicians to visualize the heart’s pumping ability, measure ejection fraction, and identify structural abnormalities. Electrocardiograms (ECGs) can detect arrhythmias or signs of myocardial ischemia.
Hemodynamic monitoring, measuring pressures within the heart and blood vessels, provides real-time data on cardiac output and systemic perfusion.
Managing and Treating the Syndrome
The primary goals in managing low cardiac output syndrome are to improve the heart’s pumping ability and support vital organ function. Treatment strategies are individualized, focusing on addressing the specific underlying cause to stabilize the patient and restore adequate blood flow.
Medications play a significant role in immediate management. Inotropes, such as dobutamine or milrinone, are administered to strengthen heart contractions, increasing stroke volume and cardiac output. Vasopressors may also be used to maintain blood pressure by constricting blood vessels, ensuring blood reaches organs despite reduced pumping efficiency.
Fluid management is a nuanced aspect of treatment. Careful administration of intravenous fluids can optimize preload, while excessive fluid can worsen the condition by overstretching the heart muscle. Diuretics may be used to reduce fluid overload if it contributes to heart strain.
For severe cases, mechanical support devices might assist the heart. An intra-aortic balloon pump (IABP) inflates and deflates in sync with the heart’s rhythm, increasing blood flow to the heart muscle and reducing left ventricular workload. Extracorporeal membrane oxygenation (ECMO) provides cardiac and respiratory support by oxygenating blood outside the body.
Addressing identified risk factors or co-existing conditions is also part of the comprehensive treatment plan. This involves managing electrolyte imbalances, controlling blood glucose levels in diabetic patients, or treating ongoing infections.