Atrioventricular (Heart) Block
Atrioventricular block or heart block is a failure of the heart’s electrical system to properly coordinate conduction. There are four main types of atrioventricular block: first degree, second degree type I, second degree type II, and third degree heart block. The types of second degree heart block are referred to as Mobitz type I and Mobitz type II. Second degree heart block Mobitz type I is also known as the Wenckebach phenomenon.Heart block is important because it can cause hemodynamic instability and can evolve into cardiac arrest.
First degree atrioventricular block
The PR interval is a consistent size, but longer or larger than it should be in first degree heart block.
Second degree atrioventricular block, Mobitz type I (Wenckebach)
The PR interval increases in size until a QRS complexes dropped, resulting in missed “beat.”
Second degree atrioventricular block, Mobitz type II
A QRS wave will occasionally drop, though the PR interval is the same size.
Third degree (complete) atrioventricular block
Complete dissociation between P waves and the QRS complex. No atrial impulses reach the ventricle.
Pulseless Electrical Activity and Asystole
Pulseless electrical activity or PEA is a cardiac rhythm that does not create a palpable pulse is even though it should. A PEA rhythm can be almost any rhythm except ventricular fibrillation (incl. torsade de pointes) or pulseless ventricular tachycardia.
Asystole is the “flatline” on the ECG monitor. It represents a lack of electrical activity in the heart. It is critically important not to confuse true asystole with disconnected leads or an inappropriate gain setting on an in-hospital defibrillator. Asystole may also masquerade as a very fine ventricular fibrillation. If the ECG device is optimized and is functioning properly, a flatline rhythm is diagnosed as asystole. Note that asystole is also the rhythm one would expect from a person who has died. Consider halting PALS efforts in people who have had prolonged asystole.
It is inappropriate to provide a shock to pulseless electrical activity or asystole. Cardiac function can only be recovered in PEA or asystole through the administration of medications.
Ventricular Fibrillation and Pulseless Ventricular Tachycardia
In ventricular fibrillation or pulseless ventricular tachycardia, the heart’s conduction system exhibits a disordered rhythm that can sometimes be corrected by applying energy to it. This energy may come in the form of an automated external defibrillator (AED) defibrillator paddles, or defibrillator pads. VFib and VTach are treated with unsynchronized cardioversion, since there is no way for the defibrillator to decipher the disordered waveform. In fact, it is important not to provide synchronized shock for these rhythms.
Ventricular fibrillation is recognized by a disordered waveform, appearing as rapid peaks and valleys as shown in this ECG rhythm strip:
Ventricular tachycardia may provide waveform similar to any other tachycardia; however, the biggest difference in cardiac arrest is that the patient will not have a pulse and, consequently, will be unconscious and unresponsive. Two examples of ventricular tachycardia are shown in this ECG rhythm strips. The first is narrow complex tachycardia and the second is wide complex tachycardia:
Atrial fibrillation is the most common arrhythmia. It is diagnosed by electrocardiogram, specifically the RR intervals follow no repetitive pattern. Some leads may show P waves while most leads do not. Atrial contraction rates may exceed 300 bpm. The ventricular rate often range is between 100 to 180 bpm. The pulse may be “irregularly irregular.”
Atrial flutter is a cardiac arrhythmia that generates rapid, regular atrial depolarizations at a rate of about 300 bpm. This often translates to a regular ventricular rate of 150 bpm, but may be far less if there is a 3:1 or 4:1 conduction. By electrocardiogram, or atrial flutter is recognized by a sawtooth pattern sometimes called F waves. These waves are most notable in leads II, III, and aVF.
Narrow QRS complex tachycardias include several different tachyarrhythmias. A narrow QRS complex tachycardia is distinguished by a QRS complex of less than 90 ms. One of the more common narrow complex tachycardias is supraventricular tachycardia, shown below. The heart rate can exceed 220 bpm in infants and 180 bpm in children.
Wide complex tachycardias are difficult to distinguish from ventricular tachycardia. Ventricular tachycardia leading to cardiac arrest should be treated using the ventricular tachycardia algorithm. A wide complex tachycardia in a conscious child should be treated using the tachycardia algorithm. Tissue perfusion will dictate which algorithm to use.