An R wave is an upward deflection displayed on an electrocardiogram (ECG). During an electrocardiogram, the heart’s rhythm is recorded on graph paper via electrodes attached to the skin. The waves or deflections shown on the ECG are named for the letters P, Q, R, S and T. R waves are the first upward deflection within a series known as the QRS complex.
As part of the QRS complex, an R wave is an important indicator of cardiac health. Cardiologists and other health professionals analyze ECGs to diagnose various cardiac diseases. Some common causes of R wave abnormalities on an ECG include a thin chest wall or obesity. The former results in an enlarged R wave, and the latter causes a smaller R wave.
The R wave-to-R wave interval shows the inverse of the patient’s heart rate. The space between the P wave and the R wave within the QRS complex is called the PR interval and normally lasts 120 to 200 milliseconds. A good indicator of atrioventricular (AV) node function, the PR interval reproduces the time for an electrical impulse to travel from the sinus node through the AV node and into the ventricles.
Variations in the duration of PR intervals indicate certain medical issues. Longer PR intervals suggest first-degree heart block. Increasing PR intervals followed by an eventual QRS drop might indicate a second degree block. PR segment dips show pericarditis or atrial injury. Wolff-Parkinson-White syndrome is often indicated by a short PR interval. Wolff-Parkinson-White syndrome is caused by an abnormal electrical current passing between the atria and ventricles, and it often results in sudden cardiac death.
Poor R wave progression on an ECG might indicate several problems. If the overall ECG is normal, however, the lack of R waves might be a normal variant. Possible cardiac issues include left ventricular hypertrophy, left bundle branch block, anterior or anteroseptal myocardial infarction, emphysema, chronic obstructive pulmonary disease (COPD) or pneumothorax.
In a bundle branch block, the QRS complex will contain a second R wave deflection. This is the RSR pattern. The second R wave deflection is named R-prime. In a right bundle branch block, a tall, wide RSR pattern typically is seen on the ECG.
Tall R waves indicate severe right ventricular hypertrophy when seen in certain leads of the ECG. A posterior myocardial infarction or pause in the sinus node also might cause tall R waves. The physiology of hemiblocks such as the left anterior-superior fascicular or left posterior fascicular block results in tall R waves.