American Journal of Critical Care. 2005;14: 249-250
A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses ECG interpretation for clinical practice. We welcome letters to the Editors regarding this feature.
Relative Refractory Period
By
Mary G. Adams, RN, PhD and
Michele M. Pelter, RN, PhD.
From the School of Nursing at State University of New York at Buffalo (MGA) and Washoe Health System and the School of Nursing, University of Nevada, Reno, NV (MMP).
Scenario: This rhythm strip was obtained in an 18-year-old woman admitted to the intensive care unit (ICU) following a motor vehicle accident; her sister, the passenger, was dead on arrival. Although the patient was in critical condition, she was hemodynamically stable with mechanical ventilation and sedation. Unexpectedly, the central monitor alarmed for the ECG strip below. Immediate assessment of the patient revealed that she had no palpable carotid pulse.
Interpretation: Sinus tachycardia at 120 beats per minute with sustained pulseless ventricular tachycardia triggered by R-on-T.
Rationale
Careful evaluation of the T waves reveals that there is some variability from beat to beat. For example, the offset of the T wave is distinct with some beats, whereas the offset of the T wave actually extends into the P wave of some beats. Such lengthening extends the relative refractory period of repolarization, thus increasing the risk of an R-on-T phenomenon. Of note, because the patient is receiving mechanical ventilation, the respiratory waveform continues to rhythmically march on despite the lethal arrhythmia.
Nursing Actions
The American Heart Association has developed protocols (ie, Advanced Cardiac Life Support, ACLS) addressing the specific treatment of arrhythmias. Given that the patient is pulseless, the appropriate ACLS algorithm to follow is pulseless ventricular tachycardia. This algorithm emphasizes the importance of quick, prompt, and aggressive intervention beginning with "stacked shocks" (sequential defibrillation) and, if necessary, continuing with pharmacological agents and alternating with defibrillation. In this case, the patient was successfully defibrillated back into sinus tachycardia; however, given the underlying mechanism, it is important to diligently monitor this patient for any lengthening of the QT interval. In addition, because the post-resuscitation phase can be very labile in some patients, standards for post-resuscitation care should be followed. For example, if the patient’s rhythm was successfully converted using amiodarone, then specific orders should be written regarding a loading and maintenance dose for this drug.
