Cardiac arrest is the sudden cessation of the heart’s pumping function, leading to loss of consciousness as blood flow to the brain and other organs stops. Without prompt restoration of blood flow, lack of oxygen causes irreversible organ damage and death. While cardiac arrest is rare in pregnancy, understanding its causes is important for timely intervention and improved outcomes for both the pregnant individual and the fetus.
Pregnancy’s Physiological Impact
Pregnancy induces profound physiological changes to support fetal development, which can alter susceptibility to cardiac arrest. The cardiovascular system undergoes substantial adaptations, with cardiac output increasing by 30% to 50% above pre-pregnancy levels. Blood volume also expands significantly, leading to a “physiological anemia” where plasma volume increases more than red blood cell mass. These changes create an increased workload on the heart, which can uncover or worsen underlying cardiac issues.
The respiratory system also adapts to meet the increased oxygen demand of pregnancy, which can rise by 15% to 20%. Minute ventilation increases by 40% to 50%, primarily due to a larger tidal volume. These adjustments mean that pregnant individuals have lower oxygen reserves and higher oxygen consumption, making them more vulnerable to rapid oxygen desaturation during an emergency.
Pregnancy creates a hypercoagulable state, meaning there is an increased tendency for blood clot formation. This is due to elevated levels of clotting factors and a reduction in natural anticoagulants. While beneficial for preventing hemorrhage, this altered clotting balance raises the risk of thromboembolic events, such as pulmonary embolism, which can lead to cardiac arrest.
Pregnancy-Specific Complications
Several conditions unique to pregnancy can lead to cardiac arrest. Severe obstetric hemorrhage, characterized by massive blood loss during or after delivery, is a primary cause. Conditions such as placental abruption, placenta previa, or uterine atony can result in hypovolemic shock. Pregnant individuals can compensate for substantial blood loss before showing signs of shock due to their increased blood volume, making early recognition challenging.
Hypertensive disorders of pregnancy, including severe pre-eclampsia and eclampsia, pose a significant risk. Severe pre-eclampsia involves high blood pressure alongside organ dysfunction, which can progress to eclampsia, characterized by seizures. These conditions can lead to cerebral hemorrhage, fluid accumulation in the lungs, or heart dysfunction, causing cardiac arrest.
Amniotic fluid embolism (AFE) is a rare, sudden, and life-threatening event where amniotic fluid enters the maternal circulation. This triggers an acute immune response, causing rapid cardiovascular collapse, respiratory failure, and blood clotting problems, leading to cardiac arrest.
Peripartum cardiomyopathy (PPCM) is a form of heart failure that develops in the final month of pregnancy or within the first few months after childbirth. The heart muscle weakens and struggles to pump blood effectively, which can lead to severe heart failure, irregular heart rhythms, and cardiac arrest.
Other pregnancy-specific complications include ectopic pregnancy rupture and uterine rupture. An ectopic pregnancy occurs when a fertilized egg implants outside the uterus, most commonly in a fallopian tube. If this ruptures, it can cause rapid and severe internal bleeding, leading to hypovolemic shock and cardiac arrest. Uterine rupture, a tear in the uterine wall, is another cause of significant hemorrhage and shock, often occurring during labor, and can result in cardiac arrest.
Pre-existing Conditions Exacerbated by Pregnancy
Chronic medical conditions present before pregnancy can be profoundly affected by the physiological demands of gestation. Pre-existing cardiac disease, encompassing conditions like congenital heart defects, valvular heart disease, or cardiomyopathies, places individuals at higher risk. The substantial increase in cardiac output and blood volume during pregnancy can overwhelm an already compromised heart, leading to heart failure or arrhythmias.
Pulmonary hypertension, a condition of high blood pressure in the arteries of the lungs, can decompensate significantly during pregnancy. The increased blood volume and cardiac output can further elevate pressures in the pulmonary arteries, straining the right side of the heart and leading to heart failure and cardiac arrest.
Diabetes, particularly when poorly controlled and accompanied by vascular complications, increases the risk of cardiovascular events during pregnancy. The metabolic changes and increased stress on the cardiovascular system can accelerate the progression of heart and blood vessel damage, making pregnant individuals more susceptible to events like heart attack or stroke, which can precipitate cardiac arrest.
Severe anemia, a condition where the blood lacks sufficient healthy red blood cells, can be worsened by pregnancy’s physiological anemia. This reduces the blood’s oxygen-carrying capacity, forcing the heart to work harder and potentially leading to heart failure. Chronic kidney disease can lead to fluid and electrolyte imbalances and hypertension, which can further strain the cardiovascular system. Severe asthma or other chronic respiratory conditions can also be exacerbated, leading to respiratory distress that may contribute to cardiac arrest.
Acute Non-Obstetric Causes
Acute medical emergencies that can lead to cardiac arrest in any individual also pose a risk during pregnancy. Sepsis, a severe bloodstream infection, can rapidly progress to septic shock and multi-organ failure. The body’s inflammatory response and widespread infection can compromise cardiovascular function, leading to cardiac arrest.
Anaphylaxis, a severe and sudden allergic reaction, causes a rapid drop in blood pressure and airway constriction. This can lead to cardiovascular collapse and respiratory arrest, culminating in cardiac arrest.
Trauma, such as from motor vehicle collisions, falls, or domestic violence, is a non-obstetric cause of cardiac arrest. Injuries can result in severe hemorrhage, shock, or direct organ damage. Resuscitation efforts in pregnant trauma patients involve specific adjustments, such as displacing the uterus to the side to relieve pressure on major blood vessels.
Drug toxicity or overdose, whether accidental or intentional, can depress respiratory drive or directly affect heart function, leading to cardiac arrest. Stroke, caused by a blood clot or hemorrhage in the brain, can result in neurological collapse that impacts vital functions. Acute myocardial infarction, or heart attack, occurs when blood flow to the heart muscle is blocked. It can occur in pregnant individuals and cause cardiac arrest.