The Electrocardiogram (EKG) is a common diagnostic instrument used to record the electrical activity of the heart. This test captures the electrical signals generated by heart muscle cells as they depolarize and repolarize, presenting data as a series of waves and complexes. The QRS complex represents the electrical depolarization of the ventricles, the heart’s main pumping chambers, and the R wave is the prominent positive (upward) deflection within this complex. Analyzing the R wave’s progression across the chest leads is a specific method doctors use to assess the electrical flow from the front of the heart.
The Normal Electrical Axis Shift
The R wave progression across the chest leads (V1 through V6) provides a window into the heart’s electrical field as it moves from the right side of the chest to the left. The normal pattern is a gradual increase in the R wave’s positive amplitude and a corresponding decrease in the negative S wave’s depth. This change reflects the normal direction of ventricular depolarization, which moves from the septum toward the dominant left ventricle.
In the right-sided leads, V1 and V2, the electrical forces are primarily directed away from the electrode, resulting in a small R wave and a deep S wave. As the electrical recording moves across the chest to V3 and V4, the QRS complex typically becomes “equiphasic,” where the R wave height approximately equals the S wave depth. This point is known as the transition zone, which should ideally occur between V3 and V4.
By the time the signal is recorded by the left-sided leads, V5 and V6, the electrical vector is largely directed toward these electrodes, resulting in a tall, dominant R wave and a very small S wave. This expected shift from a mostly negative complex to a mostly positive complex indicates that electrical conduction is following the normal anatomical path of the ventricular muscle mass. This systematic increase in R wave size is referred to as good R wave progression.
Defining Poor R Wave Progression
Poor R Wave Progression (PRWP) is a descriptive term used when the expected increase in R wave amplitude fails to materialize across the precordial leads. One common definition of PRWP is an R wave height of 3 millimeters or less in lead V3.
The abnormality can manifest as delayed transition or reversed progression. Delayed transition occurs when the equiphasic complex appears later than expected, such as in lead V5 or V6, indicating that the electrical forces are not moving anteriorly as they should. Conversely, reversed progression describes a pattern where the R wave amplitude decreases from one lead to the next, such as from V2 to V3, or remains abnormally small across all anterior leads.
The failure of the R wave to grow suggests that the electrical signal traveling toward the front of the chest is reduced or blocked, preventing the typical positive deflection from being recorded. The PRWP pattern is a visual clue on the EKG that points to an underlying issue affecting the heart’s electrical forces in the anterior wall.
Underlying Conditions Causing PRWP
Poor R wave progression is not a diagnosis itself but a sign that can be caused by various physiological or anatomical issues. One of the most common causes is a prior anterior wall myocardial infarction, or heart attack. When heart muscle tissue dies due to a blocked coronary artery, it is replaced by scar tissue, which is electrically inert and cannot conduct the electrical signal.
This scar tissue in the anterior wall creates an “electrical hole,” causing the depolarization vector to move away from the chest leads, resulting in a loss of R wave amplitude. The presence of pathological Q waves alongside PRWP can further support the diagnosis of a previous infarction. Another significant cause is left ventricular hypertrophy (LVH), which is an abnormal thickening of the heart’s main pumping chamber wall.
The enlarged muscle mass of the left ventricle can alter the electrical axis, causing the electrical forces to be directed away from the anterior chest leads. Right ventricular hypertrophy (RVH) can also push the heart backward and rotate it, reducing the electrical forces recorded by the anterior leads. PRWP can also be due to technical issues, such as the incorrect placement of precordial electrodes (V1 or V2 placed too high), which artificially reduces the recorded R wave amplitude and creates a false sign of poor progression.
Clinical Interpretation and Next Steps
Poor R wave progression on an EKG is considered a non-specific finding, meaning it is not automatically diagnostic of a specific disease. Because PRWP can result from a range of issues, from serious cardiac disease to simple anatomical variations, it requires careful interpretation in the context of the patient’s overall health and symptoms. In some healthy individuals, PRWP can be a normal variant due to a naturally low cardiothoracic ratio or a more horizontal heart position within the chest.
When PRWP is identified, the physician’s next steps often involve ruling out significant structural heart disease. The first line of investigation is typically an echocardiogram, an ultrasound of the heart. This test is used to evaluate the motion of the heart wall, check for areas of scarring or reduced function, and assess for conditions like left or right ventricular hypertrophy.
If the echocardiogram is inconclusive but the clinical suspicion for coronary artery disease remains high, further testing may be ordered. Advanced evaluations can include a cardiac stress test, which monitors the heart’s response to exertion, or a cardiac CT or MRI, which provide detailed images of the heart muscle and coronary arteries. The ultimate significance of PRWP is determined by correlating the EKG pattern with these additional test results and the patient’s complete medical history.