Atrial fibrillation with a controlled ventricular response is often considered to be atrial fib that has been controlled with medication.  While this is often true, it is possible to see atrial fib with a ventricular rate between 50 and 100 bpm in a patient who has not been treated.  The hallmark signs of atrial fib are:  no P waves and irregularly-irregular rhythm.

Multiple, simultaneous leads are advised to be sure there are no P waves, and a long rhythm strip is often needed to prove the irregularly-irregular rhythm.  Remember, even though this rate is adequate (about 90 bpm), the loss of P waves means no "atrial kick".  The atria are not filling the ventricles with a forceful pumping action. Patients can lose a significant percentage - up to 25% - of their cardiac output because of this.  Coupled with the risk of stroke from the formation and embolization of blood clots from the sluggish circulation in the atria, it is much preferable to have sinus rhythm at the same rate.

A good example of ventricular fibrillation.  The patient is pulseless, CPR has been performed, and the ED staff is about to defibrillate.  Characteristics of V Fib are:  a chaotic, wavy baseline without clear P waves, QRS complexes, or T waves.  Baseline artifact (baseline going up and down) can be seen with CPR and other movement of the electrodes on the patient's body as resuscitation efforts are underway.  The patient will ALWAYS be unconscious and pulseless in V Fib.  If this rhythm is seen in a patient who is awake or has pulses, it is ARTIFACT - check your electrodes!  

This rhythm strip illustrates a junctional escape rhythm.  The sinus rhythm has slowed or stopped, and the junctional tissue has taken over as the pacemaker of the heart.  The "junction" is loosely defined as the area between the AV node and the Bundle of His.  The intrinsic rate of the pacemaking tissue in this area is 40 - 60 beats per minute.  This slow rate is usually overridden by the sinus node, and the junction is not allowed to express itself as a pacemaker.  Should the sinus node fail or fall below the junctional rate, the junction "escapes" and takes control of the heart.  The QRS complex in junctional rhythm will normally be narrow, because the impulse follows the bundle branches down through the ventricles in a normal fashion, resulting in quick and normal ventricular depolarization.  If the QRS complex is wide in a junctional rhythm, there is another, separate cause, such as bundle branch block.

 If the junctional impulse is able to penetrate the AV node and depolarlize the atria, the P wave will be deflected downward in Leads II, III, and aVF, as the impulse is travelling in a retrograde direction (backward).  The P wave could end up slightly before the QRS, during the QRS, or after the QRS. In this strip, the P waves are seen after the QRS complexes.

This is a rhythm strip from a NIPS procedure (non-invasive programmed stimulaltion), which is a programming test for an implantable cardioverter defibrillator (ICD).  The test is done under light anesthesia, similar to that used for colonoscopy.   In this example, the patient is in normal sinus rhythm at the beginning of the procedure.  The pacemaker technician overdrives the patient's rate to observe the pacing function, then a stimulus is delivered to cause ventricular fibrillation (V Fib).  Initially, the ventricular rhythm is somewhat organized and coarse (V flutter), but it will rapidly deteriorate if not corrected.  Before it deteriorates, the ICD delivers a shock, and the patient's rhythm is restored.  In this example, bi-ventricular pacing was conducted for a few minutes before the patient resumed NSR.  The patient is then recovered from the anesthesia and discharged home.

For your students, this is a good example of the relative safety of shocking the well-perfused heart.  Although it is possible to put the heart into an intractable V Fib with this test, the ICD usually is able to convert the potentially lethal rhythm easily.  It is a good reminder that we need to perfuse the heart well before performing defibrillation on a person with unwitnessed cardiac arrest.