Cardiac Rhythms & Priority Response

The conduction pathway

Impulses originate at the sinoatrial node, travel through the atria producing the P wave, pause at the atrioventricular node creating the PR interval, then race down the bundle of His, the bundle branches and the Purkinje fibers to depolarize the ventricles as the QRS complex. The T wave is ventricular repolarization.

Every rhythm abnormality is a failure somewhere on that path. A missing P wave means the atria are not firing in an organized way. A widened QRS means the impulse is not using the normal conduction highway.

Stability determines the intervention

Instability means the rhythm is compromising perfusion: hypotension, altered mental status, chest pain, signs of shock or acute heart failure. A client in atrial fibrillation at 150 who is awake, talking and normotensive is treated very differently from one who is grey and confused at the same rate.

This is why 'assess blood pressure and level of consciousness' outranks any drug in a priority question about a new tachyarrhythmia.

Rhythms that appear most often

Atrial fibrillation is irregularly irregular with no discernible P waves. The nursing concern is stroke risk from atrial thrombus, which is why anticoagulation questions attach themselves to it.

Ventricular tachycardia is a wide-complex regular rhythm. With a pulse and stability, antiarrhythmics; with a pulse and instability, cardioversion; without a pulse, defibrillation and CPR.

Ventricular fibrillation is chaotic with no organized complexes and is always pulseless. Begin CPR and defibrillate as soon as the device is charged.

Asystole and pulseless electrical activity are never shocked. CPR and epinephrine, while searching for the reversible cause.

• Peaked T waves with a widening QRS → suspect hyperkalemia
• Prolonged QT → risk of torsades de pointes; treat with magnesium sulfate
• New irregular rhythm with a rate over 150 → assess perfusion before anything else