An electrocardiogram (ECG or EKG) is a non-invasive medical test that records the heart’s electrical signals. It helps healthcare professionals assess the heart’s rhythm and overall function, serving as a widely used diagnostic tool.
Understanding the Normal ECG Waveform
A typical, healthy ECG tracing displays a repeating pattern of waves, each representing a specific electrical event within the heart. The P wave marks the electrical activation of the atria, the heart’s upper chambers, as they prepare to contract and pump blood into the ventricles.
Following the P wave is the QRS complex, which signifies the electrical activation and subsequent contraction of the ventricles, the heart’s main pumping chambers. The QRS complex includes three distinct deflections: the Q wave, the R wave, and the S wave. The T wave then represents the electrical recovery or relaxation of the ventricles, as they prepare for the next heartbeat.
Even in a normal ECG, some waves naturally appear as downward deflections from the baseline. For instance, the Q wave is typically a small, initial downward deflection within the QRS complex. The S wave, the final deflection of the QRS complex, also appears as a downward movement.
Identifying Downward Deflections on an ECG
The term “downward spike” is not a precise medical description, but it refers to any part of the ECG tracing that falls below the baseline. Several ECG components are downward deflections, and their characteristics provide important diagnostic clues. Understanding these deflections involves looking at their depth, width, and overall shape.
The Q wave is the initial downward deflection of the QRS complex. A small Q wave is normal, representing the electrical activity as the septum depolarizes. However, a Q wave becomes significant when abnormally deep or wide. Pathological Q waves are typically wider than 0.03 seconds and deeper than 1 millimeter, or greater than 25% of the height of the subsequent R wave.
The S wave is the final downward deflection of the QRS complex, occurring after the R wave. Its size normally varies. While often a normal finding, a very deep S wave can sometimes indicate specific cardiac conditions.
An inverted T wave is another type of downward deflection. The T wave is normally upright in most ECG leads, reflecting ventricular repolarization. When the T wave points downward, it is considered inverted and is a notable finding.
The ST segment, the flat line between the S wave and the T wave, normally rests on the baseline. When this segment drops below the baseline, it is called ST depression. This depression can be horizontal, downsloping, or upsloping.
What Abnormal Downward Deflections Can Indicate
Abnormal downward deflections on an ECG can signal underlying medical conditions that affect the heart’s electrical activity and muscle function. Each type of abnormal deflection offers unique insights into potential cardiac issues.
Pathological Q waves are strongly associated with a previous myocardial infarction, commonly known as a heart attack. These deeper and wider Q waves suggest an area of heart muscle has died and become electrically inactive due to lack of blood flow. While indicating permanent damage, their presence does not necessarily mean the heart attack is recent, as they can persist indefinitely.
While deep S waves are often a normal variation, unusually deep S waves can sometimes be seen in conditions like left ventricular hypertrophy. This condition involves a thickening of the heart muscle, which alters electrical pathways and can result in prominent S waves. Right ventricular hypertrophy might also show deep S waves.
Inverted T waves can indicate a range of cardiac issues, most notably myocardial ischemia (reduced blood flow to the heart muscle). This inversion occurs because ischemia affects how the heart muscle recovers electrically. Electrolyte imbalances, such as low potassium (hypokalemia), can also cause inverted or flattened T waves due to their impact on electrical stability. Cardiomyopathies or central nervous system events can also lead to T wave inversions.
ST depression frequently indicates myocardial ischemia or angina (chest pain from reduced blood flow to the heart). Horizontal or downsloping ST depression is more concerning for ischemia than upsloping depression. This change indicates the heart muscle is not receiving enough oxygen, especially during increased demand. ST depression can also be a reciprocal change, appearing in leads opposite to an area of ST elevation.
The Importance of Professional Interpretation
An ECG provides valuable information about the heart, but it is only one component of a comprehensive medical assessment. Accurate interpretation requires specialized knowledge and training. A qualified healthcare professional integrates ECG findings with a patient’s medical history and results from other diagnostic tests.
Interpreting an ECG independently or relying solely on online information can be misleading and dangerous. The nuances of ECG patterns, including normal variations and subtle abnormalities, necessitate expert evaluation to determine clinical significance. Incorrect self-diagnosis or misinterpretation could lead to unnecessary anxiety or delay appropriate medical care.