Monday, December 19, 2016

ECG Blog #132 (Ventricular Tachycardia - VT - Vfib - Artifact - Cardioversion)

The lead II rhythm strip shown in Figure-1 was obtained from an older adult patient on telemetry. Should the patient be immediately cardioverted?
Figure-1: Lead II rhythm strip obtained from a patient on telemetry. NOTE — Enlarge by clicking on Figures — Right-Click to open in a separate window.
Interpretation: Although at first glance, this tracing prompted much concern on the telemetry unit — prompt cardioversion is not the optimal initial intervention. Instead, there is much baseline aberration with spurious-looking complexes that occur at a rate over 300/minute in parts of the tracing. No real tachyarrhythmia has a ventricular rate this fast in adults.
  • The first thing to do when confronted with a potentially worrisome tracing such as this one is to check on the patient. Doing so revealed that the patient was vigorously coughing at the time this tracing was recorded. The artifact totally disappeared as soon as the patient stopped coughing.
Comment: Artifact is common in clinical practice. At times, it may be extremely difficult to distinguish artifact from a real tracing. The consequences of mistaking artifact for ventricular tachycardia (as was almost done for the tracing in Figure-1) are not trivial. Patients have been shocked, and investigative procedures (such as cardiac catheterization) have been ordered. Remember the following:
  • Check on the patient first. If the patient is alert and hemodynamically stable — then the rhythm is far less likely to be ventricular tachycardia. This means you have at least some time to investigate further.
  • The most likely causes of artifact simulating ventricular tachycardia are inconsistent skin-electrode contact and body movement (scratching, tremor, shivering, coughing, hiccups, brushing teeth, writhing in bed, interference from a mechanical device, etc.).
  • ECG features that suggest artifact as the cause include geometric appearance (unphysiologic vertical deflections) that are unpredictably irregular, often at exceedingly rapid rates. On a 12-lead tracing, one often inexplicably sees highly unusual deflections in some leads, but not in others.
  • Being able to identify an underlying regular rhythm that is undisturbed by artifactual deflections provides proof that the phenomenon is not real. We illustrate this in Figure-2.
Figure-2: Identification of an underlying rhythm undisturbed by artifact proves that the phenomenon is not real (See text).
Discussion of Figure-2: It often helps to step back a bit from the tracing. Doing so suggests the several deflections near the middle of Figure-2 (marked by a red X) might represent underlying QRS complexes. Set you calipers to the interval between these complexes. Doing so allows you to march out regularly-occurring deflections at a rate of ~130/minute throughout the tracing (red arrows). This proves the much smaller, highly variable and overly rapid vertical deflections are artifact.
For More on this Subject: