Left Ventricular Hypertrophy (LVH) is the thickening of the wall of the left ventricle, which is the heart’s main pumping chamber responsible for sending oxygenated blood to the rest of the body. This physical change can be observed using an Electrocardiogram (ECG). The ECG records the heart’s electrical activity, and the thickening alters the flow of electricity, creating a distinct pattern of changes. By analyzing the amplitude and morphology of the electrical waves, practitioners can identify signs suggesting this structural modification.
What Left Ventricular Hypertrophy Is
Left ventricular hypertrophy is primarily a response by the heart muscle to chronic stress, where the tissue increases in size to handle an excessive workload. This condition is most often caused by long-standing, uncontrolled high blood pressure, known as hypertension. The left ventricle must contract against higher resistance to push blood into the arteries, causing the muscle cells to grow larger and the wall to thicken over time. Another frequent cause is aortic stenosis, a narrowing of the aortic valve that creates a significant barrier to blood flow. The thickened muscle wall becomes less elastic and stiffer, which can impair the heart’s ability to fill properly and eventually lead to heart failure.
How Increased Muscle Mass Affects ECG Voltage
The most direct effect of a thickened left ventricle on an ECG is a significant increase in the amplitude, or voltage, of the recorded electrical signal. A larger muscle mass contains more tissue to electrically activate, which generates a stronger electrical current detectable by the electrodes placed on the skin. This effect is seen as abnormally tall R waves and deep S waves in specific ECG leads. The diagnosis often relies on “voltage criteria,” which are established thresholds for wave height measured in millimeters. For example, the Sokolow-Lyon index measures the depth of the S wave in lead V1 added to the height of the R wave in either lead V5 or V6, with a total measurement greater than 35 millimeters suggesting LVH. These voltage increases are most pronounced in the leads that sit closest to the left side of the heart, such as V5 and V6, and the leads that look at the heart from the left, like lead I and aVL.
Secondary ECG Markers and Repolarization Changes
Beyond the simple increase in voltage, LVH creates secondary markers related to the heart’s electrical recovery phase, known as repolarization. The thickened muscle wall causes the electrical signal to take longer to return to its resting state, resulting in changes to the ST segment and T wave. This abnormality is often referred to as a “strain pattern.” It involves a downsloping ST segment depression and an asymmetrical T-wave inversion in the leads with the tall R waves. This strain pattern is a chronic alteration in the electrical properties of the muscle tissue, typically seen in the lateral leads (V5, V6, I, and aVL).
The increase in muscle mass also shifts the overall direction of the heart’s electrical activity. This shift often leads to Left Axis Deviation (LAD) on the ECG, where the main electrical vector points more horizontally and toward the left side of the body. The electrical activation time may also be slightly prolonged, showing up as a subtle increase in the duration of the QRS complex, because the signal must travel through more tissue.