Pacemakers

We know that SAN (Sino Atrial Node) and AVN (Atrio Ventricular Node) are the natural pacemakers of the heart that maintains the rhythm of the heart. But in some patients, the impulses from the SAN become inconsistent or weak resulting in irregular heartbeats. For that purpose, a Pacemaker needs to implanted into the patient that can provide the necessary electrical impulse to the heart to beat normally.

Let us know understand the different types of Pacemakers and how they function:

Single Chamber Pacemaker: These types of pacemakers have only one lead in them. This lead is inserted into the right ventricle

Double Chamber Pacemaker: Here there are two leads. One lead is present at the Right Ventricle. The second lead is inserted into the Right Atrium. This actually mimics the actual signaling system from the natural pacemaker of the heart.

Biventricular Pacemaker: This Pacemaker has 3 leads. One lead is in the Right Ventricle, Second lead in the Right Atrium and the Third Lead is inserted into the Left Ventricle. Therefore the name Biventricular Pacemaker as it is pacing both the ventricles. This is required in those patients whose right and left ventricles fail to contract simultaneously. This happens if there is a Left Bundle Branch block. Therefore for such kind of patients, a Biventricular Pacemaker is used. A Biventricular Pacemaker is also called as CRT-P (Cardiac Resynchronization Therapy Pacemaker).

ICD (Implantable Cardioverter Defibrillator): An implantable defibrillator is designed to monitor the heart rhythm 24 hours a day. If the heart is beating too fast or irregularly, the device will first send small painless electrical signals to correct your heart rate. If the fast heart rate continues, the defibrillator will deliver a shock to restore your heart to a normal rate. ICDs can have One lead-into the Right Ventricle, Two Leads-Right Ventricle and Right Atrium or 3 Leads. So essentially, ICDs along with pacing the heart is also capable of delivering a shock (defibrillation) if there is ventricular tachycardia or fibrillation

CRT-D (Cardiac Resynchronization Therapy Defibrillator): This is nothing but an ICD with three leads. The third lead is inserted into the Left Ventricle ( same as we saw in CRT-P), but unlike CRT-P, if the heart rate rises abruptly to more than 180 beats per minute, then it will attempt an ATP (Anti-tachycardia pacing). But if still, the heart rate further increases to greater than 240 beats, this condition is called Ventricular Fibrilation which is a life threatening condition and there it delivers a shock which lasts for few milliseconds which can be felt by the patient. This brings back the rhythm of the heart.