EKG: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

In examining a rhythm strip or EKG tracing, the health care professional must understand the waves, complexes, and straight lines that represent the different aspects of the cardiac cycle on the paper. Every waveform has a distinct name and normals that are particular for each. In the previous chapter, the different leads, or views of the heart, were discussed. Since each of these leads looks at a distinct viewpoint of the heart, the waveforms created on each lead will appear differently. Sometimes these variances in positive or negative deflection and shape are significantly different and sometimes they are minor. For purposes of discussion in this chapter, lead II will be used as a reference point. The letters PQRST are used to denote each of the waves on the EKG tracing. Isoelectric lines are present in between and these lines are known as segments. When two or three waves come together, they form a complex. Once a clear understanding of the waves, complexes, and straight lines is achieved, information regarding the components of interpretation of the rhythms will be presented.

It is important to remember that every patient is an individual as well. Sometimes there are anatomical differences that are reflected in various inconsistencies in waveforms. These deviations then may not be indicative of disease processes, but rather simply distinctive variations of normal waveforms.

Contents

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: Waves and Complexes

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The P Wave

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

The P wave is the first element of the EKG waveform. This represents depolarization of the atria. (Repolarization is not seen as it has less strength than depolarization of the ventricles and is therefore hidden in the QRS complex.) The beginning upstroke of this wave corresponds to the right atrial activity and the down-stroke denotes left atrial activity. In lead II this is characterized by a positive deflection meaning that the wave will be above the isoelectric line. Depending on which lead is viewing the activity of the atria, the P wave can be clearly defined, smaller than others, or have a biphasic configuration. When the electrical activity moves toward the positive pole, a positive deflection will occur. In general, leads I, II, aVL, aVF, and V2-V6 usually have an upward appearing P wave. aVR demonstrates a negative deflection and lead V1 and III commonly have a biphasic (both directions) appearance, although lead III can be variable. The lead depicted in The P wave is from lead II.

The P wave should have a smooth, round appearance. The normal width for a P wave is 0.12 seconds or less or 3 small boxes on the EKG paper. (1 mm on the horizontal plane of the EKG paper is equal to 0.04 seconds.) The normal amplitude or height of a P wave is about 0.5 to 2.5 mm depending on the view. In normal sinus rhythm a P wave should be present before each QRS complex. When the P wave is of normal amplitude and length, is upright in lead II, and precedes each QRS, it can be assumed that the original impulse was initiated by the sino-atrial (SA) node. P waves can also originate from different locations of the atria. The term used to describe these altered pacemaker sites is ectopic. This ectopic impulse can come from different parts of the atria or from the atrio-ventricular (AV) junction. Ectopic waveforms may appear as smaller than normal, as a wavy line, or may have a sawtooth pattern. P waves that originate from the AV junction will have negative deflections (be seen below the isoelectric line) or may appear either after or be hidden within the QRS. When these ectopic P waves occur, certain dysrhythmias, to be discussed later in this book, are created (Abnormal P waves).

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The P wave

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: Abnormal P waves

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Clinical Alert

Abnormal P waves can also occur with certain disease processes such as chronic obstructive pulmonary disease (COPD), a pulmonary embolus (blood clot in the lung), valvular problems inside the heart, atrial enlargement, or heart failure. These P waves may appear to be peaked, notched, or unusually large.

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The QRS Complex

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

When the ventricles depolarize, the QRS complex is generated. It is much larger than the P wave because the ventricles have a much larger muscle mass. Three separate wave deflections comprise this complex known as the QRS. The Q wave and the S wave are smaller negative deflections. The R wave is a larger positive deflection (sometimes called inflection when it is positive) that is present between the Q and S wave. Lead II is again a good view of the QRS complex because the R wave is represented as a strong positive deflection. Other leads in which the R wave is positive are: leads I, III, aVL, aVF, V4, V5, and V6. Negative R waves are seen in leads aVR, V1, V2, and V3 (The normal QRS complex).

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The normal QRS complex

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

There are several different varieties of the QRS complex. The Q wave is always the first negative deflection. The R wave is considered to be the first positive deflection and the S wave is the final negative deflection. Sometimes there is a total QRS complex containing all three deflections and sometimes there is an absence of any one of the components. When looking at this complex, always denoted as the QRS complex, the health care professional may note that it is in reality a QS segment, a QR segment, an RS segment, etc. When one or the other of these waveforms has small amplitude, below 5 mm, then a lower case letter is used to denote it. Those with higher amplitude, greater than 5 mm, are designated with a capital letter. In dealing with this aspect, those segments mentioned above may then become a qs segment, a qR segment, an Rs segment, etc. At times there may only be an R wave present (Diverse forms of the QRS complex).

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: Diverse forms of the QRS complex

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Another feature that might be present in the QRS complex is the presence of an extra R or S wave. When this happens, it is called R prime or S prime. In order to be labeled as R or S prime, the wave must actually touch and cross the baseline (the isoelectric line). If it simply changes directions it is called a “notch”. R prime is written as R1 and S prime is written as S1. Both R and S prime and notching of these waves can be important in diagnosing bundle branch blocks which will be further discussed in Chapter 6 (Recognition of R prime (R1), S prime (S1), and notched R and S waves).

Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The T Wave

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Another important aspect of the QRS segment has to do with R wave progression. The R wave should be at its lowest amplitude in V1 and the largest in V6. This evolution of the R wave, as it progresses across the chest from right to left, is significant for different diagnostic reasons. One of the most common reasons for poor R-wave progression is the simple misplacement of the chest leads especially leads V1 and V2. One of the more common patients for this to occur with is the obese female. There is also a transition point on the EKG when the R wave begins to become more positive than negative. This usually occurs in either V3 or V4. Etiologies of Poor R-Wave Progression describes some of the etiologies for poor R-wave progression. Normal R-wave progression shows normal progression. Poor R-wave progression depicts poor R-wave progression.

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: Etiologies of Poor R-Wave Progression

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

The normal duration for the QRS complex is 0.06 to 0.10 seconds. The measurement begins at the Q wave and ends at the end of the S wave. If no Q wave is present, begin the measurement at the beginning of the R wave.

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: Normal R-wave progression

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: Poor R-wave progression

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

This measurement is also known as the QRS interval (The QRS interval). Widened QRS complexes can suggest delays in ventricular conduction, bundle branch blocks, premature ventricular contractions, and aberrant atrial impulses. The absence of a QRS complex could mean ventricular standstill or a conduction block, both requiring emergent intervention. Amplitude or height varies with each lead.

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The QRS interval

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Clinical Alert

The Q wave carries special significance for a patient experiencing a myocardial infarction. Deep and/or wide Q waves are evidence of infarcted myocardium.

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The T Wave

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Ventricular repolarization is noted on the EKG as the T wave. The normal T wave is approximately 0.5 mm in height in leads I, II, and III. In the anterior, V3 and V4 and lateral views, V5, and V6, the amplitude is higher, up to 10 mm. These waves are normally smooth and rounded but are slightly asymmetric as they have an upward slope to the top of the wave and then returns to the baseline or isoelectric line (The normal T wave). Remember that the T wave carries the refractory periods and during the relative refractory period stimuli can produce dangerous ventricular dysrhythmias.

Many different processes can cause changes in the T wave. Common Etiologies of T Wave Abnormalities lists some of these pathological diseases. Most of these abnormalities will either have T wave elevation or T wave inversion. Pericarditis, an inflammatory condition of the sac around the heart, actually has both T wave elevation and inversion as patients go through several phases of this disease process. Pericarditis can also cause a notched or pointed T wave configuration.

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The normal T wave

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: Common Etiologies of T Wave Abnormalities

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Normally the T wave will have the same deflection as the prior QRS, that is, if the QRS was positive (above the isoelectric line) the T wave will also run in the positive direction. However, when there is an abnormal ventricular beat or complex, the direction of the T wave will be opposite that of the QRS. This can occur in ventricular dysrhythmias or bundle branch blocks.

Clinical Alert

Patients with significant cerebral bleeding such as that seen with a subarachnoid hemorrhage can have “giant” T wave inversion. These are seen as deeply inverted T waves and are also associated with a prolonged QT interval. This pattern can mimic that of an acute myocardial infarction (T wave changes with cerebral hemorrhage).

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 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: T wave changes with cerebral hemorrhage

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The U Wave

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

The U wave is not always seen and its presence is not necessarily an indicator of disease or wellness. When it is present, it follows the T wave and its background is not totally understood. Theories regarding its origin include repolarization of the Purkinje fibers and late repolarization of the ventricles. Normally these are small (<1.5 mm high). Fast heart rates create a situation where the U wave is very difficult to locate. It is best seen in slower heart rates in leads V2 and V3. The deflection or direction of the waveform usually correlates with that of the T wave. It is important to look at these carefully as they may appear to be a P wave. Close examination will reveal a different shape than the P wave (The U wave).

 Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting: The U wave

Focus topic:  Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

Focus topic: Waves, Complexes, Straight Lines, and Intervals/Labeling and Interpreting

 

Clinical Alert

Disorders that can cause tall U waves include: hypokalemia, hypercalcemia, digitalis toxicity, cardiomyopathy, left ventricular hypertrophy, certain medications such as procainamide (Pronestyl), quinidine, and amiodarone (Cordarone), hyperthyroidism, central nervous system diseases, and long QT syndrome.

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