An electrocardiogram (EKG or ECG) is a non-invasive diagnostic tool for evaluating heart health. It quickly assesses cardiac function by recording the heart’s electrical activity, providing immediate insights, especially when a heart attack is suspected.
Understanding the EKG Basics
An EKG measures the electrical signals that coordinate the heart’s pumping actions. These impulses trigger the heart muscle to contract and relax in a rhythmic pattern. The standard EKG tracing displays a characteristic waveform, consisting of several distinct components.
The P wave represents the electrical activity for the contraction of the heart’s upper chambers (atria). The QRS complex signifies the electrical activity causing the powerful contraction of the ventricles (heart’s lower chambers). The T wave indicates the electrical recovery, or repolarization, of the ventricles as they prepare for the next beat.
Specific EKG Indicators of a Heart Attack
During a heart attack, the EKG can display distinct changes that reflect damage to the heart muscle due to inadequate blood flow. ST-segment elevation, where the segment between the S wave and the T wave rises above the baseline, is a significant indicator. This often suggests a complete blockage of a coronary artery, leading to severe muscle damage.
ST-segment depression, where this same segment drops below the baseline, is another pattern. This finding can indicate myocardial ischemia (heart muscle not receiving enough oxygen) or suggest a non-ST-elevation myocardial infarction (NSTEMI).
T-wave inversion, where the T wave appears downward instead of its typical upright position, is also associated with ischemia or evolving heart muscle damage. Inverted T waves deeper than 1.0 mm are considered abnormal.
Pathological Q waves indicate past or ongoing myocardial damage. These appear as abnormally deep and wide Q waves, typically at least 0.03 seconds in width and 1 mm in depth in at least two adjacent leads. Their presence suggests a portion of the heart muscle has undergone necrosis (tissue death). These EKG changes collectively provide important clues about the extent and location of heart muscle injury.
Differentiating Heart Attack Types by EKG
EKG patterns help medical professionals distinguish between different types of heart attacks, guiding immediate treatment strategies. A ST-Elevation Myocardial Infarction (STEMI) is characterized by significant ST-segment elevation, indicating a complete and sustained blockage of a coronary artery. This finding suggests extensive heart muscle damage and requires urgent intervention to restore blood flow.
A Non-ST-Elevation Myocardial Infarction (NSTEMI) typically presents with ST-segment depression, T-wave inversion, or no specific EKG changes, despite evidence of heart muscle damage found through blood tests. This pattern usually points to a partial or temporary blockage of a coronary artery. Both STEMI and NSTEMI are serious events, but the distinct EKG findings help healthcare providers tailor their approach to patient care.
Other Factors Influencing EKG Readings
While an EKG is a diagnostic tool for heart attacks, its readings can be influenced by various other factors, making a comprehensive interpretation necessary. Conditions such as pericarditis (inflammation of the sac surrounding the heart) can cause widespread ST-segment elevation that might resemble a heart attack. Early repolarization, a normal variant in some individuals, can also present with ST elevation.
Left ventricular hypertrophy (LVH), a thickening of the heart’s main pumping chamber, can lead to changes like ST depression and T-wave inversion. Imbalances in electrolytes (e.g., potassium or calcium) can significantly alter the heart’s electrical activity and manifest as abnormal EKG patterns. Certain medications can also affect EKG readings, causing changes that might be misinterpreted.
EKG results are always considered alongside a patient’s symptoms, medical history, and other diagnostic tests, including blood tests for cardiac enzymes. This integrated approach helps ensure an accurate diagnosis and appropriate management.