Ventricular Tacharrhythmias

Ventricular tachyarrhythmias are potentially the most dangerous cardiac arrhythmias, often requiring the most aggressive therapy. However, there are some uncommon forms of ventricular tachycardia that are relatively benign and often easily treated by mild medications or even potentially curable using radiofrequency catheter ablation. A common classification for ventricular tachyarrhythmias is presented below:

• Typical monomorphic ventricular tachycardia
• Atypical monomorphic ventricular tachycardia
• Polymorphic ventricular tachycardia
• Bundle branch reentrant ventricular tachycardia
• Arrhythmogenic right ventricular dysplsia-related ventricular tachycardia
• Long QT syndrome and torsade de pointes
• Brugada Syndrome
• Ventricular fibrillation

In general ventricular tacharrhythmias are classified in two ways: 1) by the appearance of the QRS waves on the ECG recording or, 2) by their prognosis and life-threatening potential, which in turn, is directly related to the degree of the patient's underlying heart disease.

When viewed in any of the recorded 12 ECG leads, monomorphic ventricular tachycardia will exhibit QRS complexes that are identical in size and shape and are unchanging (Figure 1). In technical terms, a cardiac electrophysiologist would say that monomorphic ventricular tachycardia has an unchanging QRS morphology and QRS axis. These ECG findings contrast with those observed during polymorphic ventricular tachycardia (Figure 2), in which the QRS size and shape can change from beat-to-beat, even when viewed using the same ECG lead. Ventricular fibrillation exhibits even more disorganized and chaotic QRS waves when recorded by the 12-lead ECG machine (Figure 3).

In all patients, a finding of polymorphic ventricular tachycardia or ventricular fibrillation triggers an aggressive investigation of the cause(s) and administration of a definitive treatment after completion of diagnostic studies. Polymorphic ventricular tachycardia and ventricular fibrillation may occur in the setting of an acute "heart attack" (myocardial infarction), or may occur without warning in patients with a history of chronic underlying severe heart disease such as cardiomyopathy coronary artery disease, or previous myocardial infarction. Rarely, these arrhythmias may occur secondary to genetically inherited conditions (long QT syndrome) or as uncommon "allergic reaction" to certain medications. Treatment may be as simple as withdrawing the offending medication, but more commonly treatment may require coronary artery bypass surgery, angioplasty with insertion of a coronary stent, or implantation of a cardioverter-defibrillator.

Monomorphic ventricular tachycardia is also classified based upon whether it occurs in patients with structurally normal hearts or in patients with significant heart disease, primarily cardiomyopathy coronary artery disease, or previous myocardial infarction. Fast monomorphic ventricular tachycardia that occurs in a patients with severe heart disease so-called — typical monomorphic ventricular tachycardia — usually requires aggressive diagnostic studies and treatment, just as for the case of patients with polymorphic ventricular tachycardia or ventricular fibrillation. However, patients with normal hearts lacking heart disease who have monomorphic ventricular tachycardia — so-called atypical monomorphic ventricular tachycardia — may be safely treated with less aggressive means, such as medical therapy or possibly curative radiofrequency catheter ablation. These atypical monomorphic tachycardias can be usually be diagnosed by their characteristic ECG appearance and documentation of the absence of structural heart disease by echocardiography.