Blood tests measuring Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT) are common health assessment tools. While these enzymes are most frequently discussed in the context of liver function, their levels can also signal problems with the heart. This article explores the connection between elevated AST and ALT and various heart conditions, explaining how cardiac issues can appear in these blood tests.
The Function of AST and ALT Enzymes
Aspartate and alanine aminotransferases are enzymes that help metabolize amino acids, the building blocks of proteins. They facilitate cellular energy production by converting one amino acid into another, a process that occurs inside the cells of various tissues.
The primary difference between these enzymes is their distribution. ALT is found in the highest concentrations in the liver and is a relatively specific indicator of liver cell injury. When liver cells are damaged, ALT is released into the bloodstream, causing its levels to rise.
In contrast, AST is more widespread, with significant amounts in the liver, heart muscle, skeletal muscles, and kidneys. Because of this broad distribution, damage to any of these tissues, including the heart, can cause an increase in blood AST levels.
How Heart Conditions Cause Elevated Liver Enzymes
Certain heart conditions can injure heart and liver cells, releasing AST and ALT into the bloodstream. One direct cause is a myocardial infarction, or heart attack. When the blood supply to the heart is blocked, cardiac muscle cells die and release their contents, including a high concentration of AST, into the blood.
A more indirect mechanism involves chronic heart failure, which can lead to a condition known as congestive hepatopathy. In heart failure, the heart cannot pump blood effectively, causing it to back up and increase pressure in the veins leading to the liver. This congestion stresses liver cells, leading to damage and the release of both AST and ALT.
Acute events like cardiogenic shock can drastically reduce blood flow and oxygen to the liver, a condition called ischemic hepatitis or “shock liver.” This oxygen starvation leads to widespread death of liver cells. The result is a sudden and dramatic spike in both AST and ALT levels.
Medication-Related Enzyme Increases
Elevated liver enzymes in people with heart disease can also be a side effect of medications. The most well-known examples are statins, which are drugs prescribed to lower cholesterol and reduce the risk of heart attack and stroke.
A small percentage of patients starting statins may experience a mild to moderate rise in liver enzyme levels. This increase is often temporary and does not indicate significant liver damage, as the body adapts to the medication. Enzyme levels frequently return to normal with continued use.
Healthcare providers monitor liver enzymes in patients taking these medications. If an elevation is detected, a doctor will assess the situation, balancing the medication’s benefits with potential side effects. The course of action may be to continue monitoring, adjust the dosage, or switch to a different medication.
Interpreting Test Results in a Cardiac Context
Healthcare professionals do not assess AST and ALT levels in isolation. They interpret these results as part of a larger clinical picture to understand a cardiac event. The AST/ALT ratio can offer insights, as a high ratio where AST is much more elevated than ALT suggests a non-liver source, such as the heart.
To distinguish between liver and heart issues, doctors use other specific cardiac markers. Troponin, a protein released from damaged heart muscle, is a definitive marker for a heart attack. If both AST and troponin are high, it strongly points to a cardiac event, while elevated liver-specific tests like GGT suggest liver disease.
The degree of enzyme elevation can also be a prognostic indicator. Extremely high levels, particularly from ischemic hepatitis, signal severe circulatory failure from a major cardiac event. The goal of management is not to lower the enzyme levels directly but to treat the underlying heart condition. As the heart’s function improves, enzyme levels return to normal.