WILTIMS #217: The EKGs Strike Back

Today we revisited a topic we covered back in physiology: EKGs. I definitely don't remember everything involved, but it's nice that at least the concepts are familiar this time. I'll need to really master interpreting those squiggly lines this time though, because now we are not just looking at what a healthy heart looks like, but how each of the innumerable heart dysfunctions look from an electrical perspective.

One totally useless slide from lecture today was particularly interesting to me: a ye olde EKG machine, circa 1895. The patient sat with three limbs in buckets of salt solution (these were the equivalent of the little sticky paper/metal leads of today) while the electrocardiographer looked through a viewer so as to draw by hand a vague approximation of what the electrical signal was showing.

TIL: A bunch of slight differences in terminology:

Sinus tachycardia vs supraventricular tachycardia: Tachycardia is an elevated heart rate. A sinus rhythm is simply any rhythm where all the peaks are in the right places. A problem comes, however, if an otherwise sinus rhythm is just too fast; the beats are so close together that they overlap and you can't see all the peaks distinctly. Since you can't at that point say whether it is or is not a sinus rhythm, you have to call it something else: the deceptively vague "supraventricular" tachycardia (because, just like in sinus rhythm, the rhythm generating pacemaker is in the atrium, hence supra- (above) the ventricle). 

Atrial flutter vs atrial fibrillation: A flutter occurs when the atrium is beating too fast and the ventricle can't keep up, so it only beats every 3 atrial beats (sometimes 2, sometimes 4, but always consistent). Afib occurs when the atrium is essentially beating non-stop so that there isn't even a signal that the ventricles can go off of. The ventricle then tries its best to keep a rhythm, but fails at it, resulting in an erratic heartbeat.

Atrial vs junctional vs ventricular escape: The heart has three normal pacemakers: the SA node, in the atrium; the AV node, between the atria and ventricles; and a baseline rhythm by the ventricles. The SA node overrides the AV node and either node overrides the ventricular rhythm, so that usually, the whole heart goes off the SA node. If for whatever reason, the SA node fails to fire, other nearby atrial cells can pick up the slack and make a new rhythm (atrial escape). If the whole atrium is slacking, then the AV node will lead the way (junctional escape). Lastly, if something is horribly wrong and nothing above is giving it a signal, the ventricles will beat on their own (ventricular escape).