Identification of Ventricular Ectopy

Electrocardiographic (ECG) differentiation of wide QRS complex beats and tachycardias is often challenging. If the abnormality causing the wide QRS complexes is not managed appropriately, a negative outcome may occur. Wide QRS complex beats and tachycardias may be ventricular in origin or may be supraventricular impulses conducted abnormally through the ventricles, resulting in a wide QRS complex with a duration of greater than 0.12 seconds.Marriott and Sandler1 published the foundational evidence for use of QRS morphology to differentiate between ventricular ectopy and ventricular aberration. They discouraged reliance on physical examination skills alone.1 Much of their work and contributions from others related to QRS morphology is still important today. This column is the second in a series examining differentiation of ventricular aberration from ventricular ectopy. Differentiation of aberrantly conducted beats was presented in the previous column.2 In this column, the common ECG characteristics of ventricular ectopy will be reviewed followed by other common clues.Premature ventricular contractions (PVCs) are typically associated with a QRS duration of 0.12 seconds or greater. However, there are instances where the QRS duration may appear to to be normal because a portion of the waveform may be isoelectric in a particular lead. When attempting to determine the origin of these beats, it is important to examine 2 or 3 simultaneously recorded leads to determine the actual width of the QRS.3The ECG morphologic clues for ventricular ectopy apply to PVCs, ventricular tachycardia, and accelerated idioventricular rhythm (AIVR). Recall that selecting the ECG leads that reveal the stronger clues for differentiating between ventricular and aberrantly conducted beats is extremely important. The best leads for this are V1 and V6.3In lead V1 the QRS complex may be positive or negative based on the origin of the ventricular impulse. Left ventricular beats produce positive QRS complexes in lead V1. Common positive QRS configurations for left ventricular beats in lead V1 include a monophasic R wave that may be notched with a peak on the left that is taller than the one on the right. This is sometimes referred to as a “taller left rabbit ear” configuration described by Dr Marriott in the 1970s.4 Figure 1has an example of this. Another positive QRS configuration in lead V1 originating from the left ventricle is a biphasic QRS with a small q wave, large R or large R wave followed by a smaller s wave (Figure 1).4Premature ventricular contractions can also produce negative QRS complexes in lead V1, thought to originate from the right ventricle. The most common form is a small r, large S configuration. The width of the r is usually greater than 0.03 seconds, and the S wave is frequently notched on the downward deflection. The QRS duration is greater than 0.06 seconds from the QRS onset to the peak of the S wave.4In lead V6, left ventricular PVCs are associated with a negative QRS complex, often a QS pattern with notching on the downstroke of the complex. There may be a small r wave preceding the S wave.4 Figure 1provides examples of these. Figure 2is an example of ventricular tachycardia originating from the left ventricle.Right ventricular PVCs may produce positive or negative QRS complexes in lead V6. The positive configuration is a small q, large R wave or the presence of any q wave when the QRS complex is positive in lead V1. Figure 3has examples of QRS configurations associated with right ventricular beats in leads V1 and V6. A negative QRS complex is characterized by either a small r, large S configuration or QS (all negative) complex (Figure 3). From the onset of the QRS to the peak of the r wave or depth of the S wave will be equal to or greater than 0.07 seconds.4 Figure 4is an example of ventricular tachycardia originating from the right ventricle.There are several common ECG clues to assist with the identification of PVCs or ventricular rhythms (AIVR or VT). Refer to the Tablefor a list of these clues. One of the first is to look for the presence of independent P waves that have no relationship to the abnormal QRS complexes or the presence of AV dissociation.4–6 Figure 5is an example of right ventricular tachycardia. Note the independent P waves throughout the rhythm strip.The presence of fusion beats or capture beats is another clue. If an atrial impulse falls at the right time and is conducted, a normal-appearing QRS complex will appear in the midst of all the wide QRS complexes (Figure 6). Fusion beats occur when an atrial impulse depolarizes part of the ventricular tissue simultaneously with the ventricular impulse depolarizing the rest of the tissues.4,6Additional clues include the presence of extreme left-axis deviation beyond −60 degrees (Figure 1), a QRS duration of greater than 0.14 seconds and, lastly, the presence of concordant V leads. Concordant V leads refers to when the QRS complexes in the V leads are either all positive or all negative.4,6 Figure 7is an example of ventricular concordance.Weak clues that are often used to identify PVCs include the presence of an incomplete compensatory pause when examining single beats and constant coupling intervals between the normal QRS and abnormal QRS if frequent premature beats or bigeminy is present. Lastly, if the initial deflection of the abnormal QRS is identical to the normal QRS, clinicians may inaccurately assume that the abnormal beat is an aberrantly conducted supraventricular impulse. Unfortunately, many clinicians continue to use these clues even though they have all been shown to be unreliable and may lead to the wrong interpretation.In the acute clinical setting, approximately 80% of wide QRS complex tachycardias are ventricular in origin while 15%-30% are supraventricular with aberration.6 Unfortunately it is common for clinicians to assume that stable hemodynamics associated with a wide QRS complex tachycardia indicate the rhythm is a supraventricular tachycardia with aberration. If the rhythm is actually ventricular tachycardia, serious consequences can occur if verapamil or diltiazem is given. In one report where patients were given verapamil for an incorrect interpretation of a wide QRS tachycardia, hemodynamic deterioration occurred in 100% of the patients.6 The case example discussed in the previous column involving the 67-year-old male with a history of ischemic heart disease and ventricular dysrhythmias admitted for evaluation of syncopal episodes is an example of what may occur.2 Recall that he had an abrupt onset of a wide QRS tachycardia while reading the newspaper and was hemodynamically stable with a blood pressure of 140/64 mm Hg. He was being monitored in lead II. The assumption was made that he was in a supraventricular tachycardia with aberration, and verapamil 5 mg was administered. His rhythm deteriorated into ventricular fibrillation, and he lost consciousness. He was defibrillated and transferred to the intensive care unit. There are repeated recommendations that the abrupt onset of a wide QRS complex tachycardia in the acute setting should be considered to be ventricular in origin, with steps taken to prove otherwise.6–8It is important that analysis of continuous ECG monitoring be based on published standards and that all staff are adequately educated on the optimal use and interpretation of ECG monitoring.9 Correct placement of ECG electrodes and selection of best leads to monitor based on the patient’s needs cannot be overemphasized, as clinical decisions are made every day based on the data provided.9 Present guidelines recommend that unit protocols, initial education, and staff competency be evaluated on a regular basis.9 Given the nursing shortage and challenges that occurred during the recent pandemic and that continue currently, ensuring ECG monitoring guidelines are known and followed is even more important from a patient safety perspective.Identification and differentiation of ventricular ectopy and ventricular tachycardia from supraventricular tachycardia with aberration is often challenging. Learning and maintaining skills in using differentiating criteria remain important.