Some types of SVT’s include: Sinus Tachycardia Atrial Tachycardia Atrial Flutter Atrial Fibrillation AVNRT (Atrioventricular Nodal Reentry Tachycardia), and AVRT (Atrioventricular Reentry Tachycardia) Tachyarrhythmias that originate within the ventricles are classified as either Ventricular Tachycardias or Ventricular Fibrillation. Ventricular tachycardias can be further classified as being monomorphic or polymorphic, as previously discussed.
In Sinus Tachycardia, the EKG deflection will show a normal P and R-wave depolarization, with a rapid tachycardic rate Sinus Tachycardia rates range between 100-180 BPM The underlying Mechanism for Sinus Tachycardia is Abnormal Automaticity (Hyper-Automaticity)
Atrial flutter produces an atrial rate between 250 and 400 BPM . The ventricular rate may increase, but it is always slower than the atrial rate. During atrial flutter, atrial impulses are conducted to the ventricles in various ratios. Even conduction ratios (2:1, 4:1) are more common than odd ratios (3:1, 5:1). In a 2:1 ratio, there are two flutter waves for every QRS complex. A constant conduction ratio (e.g., 2:1) results in a regular ventricular rhythm (most common). A variable ratio (e.g., 4:1 to 2:1 to 5:1) results in an irregular ventricular rhythm.
Atrial Fibrillation (AF) is characterized by random, chaotic contractions of the atrial myocardium. Patients have an atrial rate of 400 BPM or more , often too fast to measure on an EKG. A surface EKG shows atrial fibrillation as irregular, wavy deflections (fibrillatory waves) between narrow QRS complexes. The fibrillatory waves vary in shape, amplitude, and direction. The chaotic nature of atrial fibrillation results in a grossly irregular ventricular rhythm . The rhythm is considered controlled if the ventricular rate is less than 100 BPM; uncontrolled if the ventricular rate conducts to greater than 100 BPM. Mechanism: In AF, the multiple wavelets of reentry do not allow the atria to organize. The ectopic focus or foci are said to be located around or within the pulmonary veins. Drugs such as flecainide, sotalol and amiodarone can terminate and prevent atrial fibrillation. Drug therapy can be used before or after DC cardioversion to maintain sinus rhythm after cardioversion.
The primary mechanism of atrial fibrillation is thought to be multiple wavelet reentry . It occurs when adjacent cells in the atrial myocardium have different refractory periods (uneven recovery times). During multiple wavelet reentry: An electrical impulse passing through the atrial myocardium depolarizes excitable cells and moves around refractory cells The rerouted electrical impulse then stimulates any adjacent cells that have recovered their excitability By this time, the cells first stimulated are again excitable. The electrical impulse re-excites the cells and continues to move through the atria, exciting and re-exciting the cells it encounters Unlike a normal depolarization wave that travels from cell to cell in one direction, reentry waves wander across the myocardium, randomly splitting off and following different reentrant pathways (see illustration). This random movement causes the chaotic, uncoordinated contractions of atrial fibrillation.
Atrial fibrillation can also result from the rapid discharge of impulses from one or many ectopic (non-sinus) sites in the atria. The ectopic cells (called foci) depolarize independently of the sinus node and disrupt the normal sinus rhythm. Multifocal firing takes place at multiple atrial ectopic sites. The cells produce many depolarization waves that activate different areas of the atrial myocardium at different times. AF occurs because the myocardial cells do not contract and relax rhythmically, in normal synchronization with the sinus node. *Note: Because a mechanism of AF may be Mulifocal Firing, some would argue that AF is a disorder of Impulse Formation (abnormal automaticity), rather than Impulse Conduction (multiple wavelets of reentry). Some argue still that while ectopic or mulifocal firing may begin AF, it is reentry that sustains it. For purposes of laying out rhythm disorders in this presentation, AF has been identified as a disorder of Impulse Conduction due to how it is sustained. May it be understood, however, that it could arguably be classified under both disorder descriptions.
This summary table allows you to review and compare the disease characteristics of atrial flutter and atrial fibrillation. Keep in mind that: Atrial flutter and atrial fibrillation are closely associated and may occur alternately in the same patient Long episodes (a day or more) of atrial flutter can degenerate into atria fibrillation Once atrial fibrillation develops, it is likely to persist and increase in frequency and duration Early identification and treatment of atrial arrhythmias is critical for preventing disease progression.
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