Angina is chest pain or discomfort occurring when the heart muscle doesn’t receive enough oxygen-rich blood. This condition results from narrowed or blocked blood vessels supplying the heart, often a sign of coronary artery disease. Many wonder if an electrocardiogram (ECG) can detect angina. While an ECG is a valuable tool, its ability to definitively diagnose angina depends on factors like timing and type.
Understanding the Electrocardiogram
An electrocardiogram (ECG) is a quick test that records the heart’s electrical activity. Electrodes are placed on the chest, arms, and legs to measure the electrical signals that trigger heart contractions and relaxations, displaying them as wavy lines. These patterns provide information about the heart’s rate, rhythm, and the timing and strength of electrical impulses. Healthcare providers interpret these patterns to identify abnormal heart activity or damage.
ECG Changes During Angina
When the heart muscle experiences reduced blood flow (myocardial ischemia), specific changes can appear on an ECG. While a resting ECG may appear normal, these alterations are more likely during an angina episode or a stress test. One common change is ST-segment depression, a downward shift in the tracing. This indicates subendocardial ischemia, affecting the inner heart muscle layer, and is seen during exertional angina. A significant indicator is horizontal or downsloping ST depression.
Another change is ST-segment elevation, a rise above the baseline. This signals transmural ischemia, affecting the entire heart muscle wall, and is characteristic of conditions like Prinzmetal’s angina. T-wave inversions, where the T-wave appears upside down, also accompany ischemic events. In acute situations, very early ischemia might present with hyperacute T-waves, which are symmetrically tall and broad. For Prinzmetal’s angina, peaked T-waves can precede transient ST-segment elevation.
Limitations of ECG for Angina
Despite its utility, an ECG has limitations when it comes to diagnosing angina. A normal ECG result does not definitively rule out the presence of angina, especially stable angina. This is because a standard ECG captures only a brief “snapshot” of the heart’s electrical activity at a specific moment. If an angina episode is not occurring at the exact time the ECG is performed, the tracing may show no abnormalities.
Certain types of angina may not consistently produce clear ECG changes. Microvascular angina involves issues with the heart’s tiny blood vessels; while stress tests might reveal ST segment changes, a resting ECG may remain unremarkable. Prinzmetal’s angina, caused by coronary artery spasms, produces transient ECG changes visible only during the actual spasm. Other heart conditions, such as left ventricular hypertrophy, pericarditis, or certain rhythm disturbances, can also cause ECG patterns resembling ischemic changes, making interpretation complex. A comprehensive clinical assessment, including a detailed symptom history, is important.
Other Tests for Angina Diagnosis
Given the limitations of a standalone ECG, healthcare providers often use a combination of tests to diagnose angina and assess heart health. Stress tests, which can involve exercise on a treadmill or medication to simulate exertion, are frequently employed. During these tests, an ECG continuously monitors heart activity. They may be combined with imaging techniques like echocardiography or nuclear imaging to observe how blood flows to the heart muscle under stress. An echocardiogram uses sound waves to create moving images of the heart, allowing visualization of blood flow and heart muscle function.
For detailed visualization of coronary arteries, cardiac CT angiography (CCTA) is a non-invasive option. This test uses X-rays and contrast dye to create detailed images, helping identify blockages. Coronary angiography is a definitive test, an invasive procedure where a catheter is inserted into a blood vessel and dye is injected to directly visualize any blockages or narrowing. Blood tests, such as those measuring cardiac troponin, can help rule out a heart attack, though they do not directly diagnose angina.