Premature Ventricular Contraction (PVCs)

Premature Ventricular Contraction (PVCs) Rate: Depends on the underlying rhythm Rhythm: Depends on the underlying rhythm. The PVC beats are premature, so this will make the R to R interval a bit irregular P waves: Not applicable (there are no P waves associated with PVCs) PR Interval: Not applicable QRS Width: > .12 seconds, wide and bizarre in appearance. T wave may be opposite direction of QRS complex Characteristics: A premature ventricular contraction (PVC) is a depolarization that arises in either ventricle before the next expected sinus beat, and is therefore labeled “premature.” They are generally easy to detect because the QRS is wide and bizarre looking. Since PVCs originate in the ventricle, the normal sequence of ventricular depolarization is altered. For example, instead of the two ventricles depolarizing simultaneously, a PVC will cause the ventricles to depolarize at different times or sequentially. In addition, conduction occurs more slowly through the myocardium than through specialized conduction pathways. This results in a wide (0.12 second or greater) and bizarre-appearing QRS. The sequence of repolarization is also altered, usually resulting in an ST segment and T wave in a direction opposite to the QRS complex. After the PVC occurs, you may find a short pause before the next QRS. This is called a compensatory pause. The compensatory pause may or may not be present. Unifocal PVCs: When a PVC originates from a single focus, its morphology or waveform characteristics look the same each time. When a PVC looks the same each time, it is called a unifocal PVC ecause it originates from one area). All of the PVCs from a unifocal source are identical in appearance. The strip below is an example of a unifocal PVC. Multifocal PVCs: In cases of greater irritability, several ventricular foci might begin to initiate ectopic beats. Multifocal PVCs will occur if more than one ectopic area begins to initiate early ventricular beats. For example, if three ectopic ventricular sites began initiating PVCs, each site would produce a slightly different looking PVC waveform. The ECG criteria are basically the same as unifocal PVCs. Multifocal PVCs are considered more dangerous when compared to unifocal PVCs, as this represents a greater amount of myocardial irritability. Below is a sample of a patient in NSR with a couplet of PVCs from two foci (multifocal). PVCs may also occur in succession. When this happens, the PVCs are called a Couplet. (The strip above also shows a couplet.) The term Ventricular Bigeminy is used for a grouped beating pattern when every other beat is a PVC (despite the underlying rhythm). For example, ventricular bigeminy is a when you see a pattern of one PVC, then one normal beat, then one PVC, followed by a normal beat. If every other beat is a PVC, ventricular bigeminy is present. If every third beat is a PVC, the term Ventricular Trigeminy is used; if every fourth beat is a PVC, Ventricular Quadrigeminy is present; and so forth. The strip below is an example of ventricular trigeminy. Keep in mind, PVCs may occur as isolated complexes, or they may occur repetitively in pairs (two PVCs in a row). When three or more PVCs occur in a row, whether unifocal or multifocal, Ventricular Tachycardia (VT) is present. When VT lasts for more than 30 seconds, it is arbitrarily defined as Sustained Ventricular Tachycardia. R on T Phenomenon: The T wave is a sensitive or vulnerable area in the cardiac electrical cycle. Remember that the heart is now repolarizing and does not like to be stimulated at this time. If an early ventricular beat comes in on top of or near the T wave, the early beat could throw the heart into an uncontrollable repetitive pattern called ventricular tachycardia. The term “R on T phenomenon” is used whenever an early ventricular beat lies near the vulnerable T wave. Consult with MD if you see early R waves coming in near the T wave. Early detection can help prevent your patient from developing a life-threatening rhythm. Causes: Caffeine, tobacco, alcohol, Digoxin toxicity, Exercise, Hypocalcemia, Hyperkalemia, New MI, Proarrhythmic effect of antiarrhythmic agents Nursing Priorities: Assess the patient’s response. Many patients are asymptomatic, while others may feel palpitations or light-headed. Potential Treatments: Treatment is required only when PVCs are frequent or the patient has intolerable symptoms. Asymptomatic: Observation. Rule out hypokalemia and hypoxemia (both can trigger PVCs). Oxygen. Correct electrolyte imbalances. Symptomatic: In the setting of an acute myocardial infarction, PVCs indicate the need to aggressively treat the ischemia/infarction with oxygen, nitroglycerin, morphine, and potential antiarrhythmic agents.