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Friday, October 28, 2011

Heart Rhythms Part 4: Ventricular Rhythms

As we learned in Part 3 the AV node will initiate an electrical impulse if it fails to receive one from the atria in a timely manner. This is also true for the ventricles. If they fail to receive an electrical impulse from the AV node they will fire on their own, albeit at a much slower rate (20 to 40 beats a minute). On the heart monitor a ventricular rhythm is characterized by a wide QRS complex. In other words, if it has a wide QRS complex, it's a ventricular rhythm of some sort.

There are several ventricular heart rhythms/arythmias and all of them have the potential to be lethal. Some of them are always deadly.

I'll start with ventricular rhythms. The ventricles have an intrinsic rate between 20 and 40 beats per minute. Clearly, if you're at this point, you are having some major issues medically speaking. So now that you can recognize a ventricular rhythm (by the wide QRS complex) the rate becomes important.
  • <20 - Recheck for a pulse, I bet they're dead.
  • 20 to 40 - Ideoventricular rhythm
  • 40 to 100 - Accelerated ventricular rhythm
  • 100+ Ventricular tachycardia (V-Tach), again, check for pulses. Often a lethal heart rhythm.
An ideoventricular rhythm. Note the wide QRS complexes.
A sinus rhythm going into V-Tach. This photo demonstrates how much wider the QRS complexes really are from a sinus thythm.

Ventricular fibrillation I think is best described as your heart having a seizure. The entire muscle just spasms and ceases to pump blood. This is always a lethal heart rhythm.

A is course V-Fib, B is fine V-Fib

The last ventricular arrhythmia is Torsades De Puentes which means twisting of points. This is a form of V-Tach with some specific characteristics on the EKG:
  • Rotation of the heart's electrical axis by at least 180º
  • Prolonged QT interval
  • Preceded by long and short RR-intervals
  • Triggered by an early premature ventricular contraction (R-on-T PVC)
You can actually see the "twisting of the points" best in leads II, III, and aVR.

Heart Rhythms Part 1: Basic Anatomy
Heart Rhythms Part 2: Sinus Rhythms
Heart Rhythms Part 3: Junctional Rhythms
Heart Rhythms Part 4: Ventricular Rhythms
Heart Rhythms Part 5: Premature Beats
Heart Rhythms Part 6: Heart Blocks

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