What are the indications for an implantable cardioverter-defibrillator (ICD)?
Because the circuit continues in the same direction and through the same tissue at essentially the same speed, the ventricular electrical activation is the same from one beat to the next in this VT, resulting in the same morphology QRS in every beat (that is, monomorphic VT as shown in Figure 3). Understanding this mechanism is very helpful in understanding one way that an ICD can actually painlessly terminate monomorphic VT (and, as will be discussed below potentially painful therapies, primarily electrical shocks, from an ICD are always a concern): because monomorphic VT is typically based on an electrical circuit which is itself based on the electrical properties of the tissue it traverses, that VT can be interrupted or broken by placing an early beat (such as a ventricular beat that arises due to a pacing stimulus from a wire [or lead] placed in the heart); hence, antitachycardia pacing (or ATP, also discussed below) can effectively terminate VT in some cases. Of note, ATP generall
