A cardiac pacemaker is an electronic device that delivers direct electrical stimulation to stimulate the myocardium to depolarize, initiating a mechanical contraction. The pacemaker initiates and maintains the heart rate when the heart’s natural pacemaker is unable to do so. Pacemakers can be used to correct bradycardias, tachycardias, sick sinus syndrome, and second- and third-degree heart blocks, and for prophylaxis. Pacing may be accomplished through a permanent implantable system, a temporary system with an external pulse generator and percutaneously threaded leads, or a transcutaneous external system with electrode pads placed over the chest.
Types of pacing:
- Permanent Pacemakers- used to treat chronic heart conditions; surgically placed, utilizing a local anesthetic, the leads are placed transvenously in the appropriate chamber of the heart and then anchored to the endocardium. The pulse generator is placed in a surgically made pocket in subcutaneous tissue under the clavicle or in the abdomen. Once placed, it can be programmed externally as needed.
- Temporary pacemakers- usually placed during an emergency, such as when a patient demonstrates signs of decreased cardiac output. It indicated for patients with high-grade AV blocks, bradycardia, or low cardia output. They serve as a bridge until the patient becomes stable enough for placement of a permanent pacemaker. It can be placed transvenously, epicardially, transcutaneously, and transthoracically.
- Biventricular Pacemakers- referred to as cardiac resynchronization therapy. used to treat moderate to severe heart failure as result of left ventricular dyssynchrony. Intraventricular conduction defects result in an uncoordinated contraction of the left and right ventricle, which causes a wide QRS complex and is associated with worsening heart failure and increased mortality. Biventricular pacemakers utilize three leads (one in the right atrium, one in the right ventricle, and one in the left ventricle via the coronary sinus) to coordinate ventricular contraction and improve cardia output. Biventricular pacemakers can incorporate implantable cardioverter defibrillators or be used alone.
A LVAD (Left ventricular assist device) is not a pacemaker but is a mechanical device that assumes the function of the heart in patients with end-stage heart failure. It is implanted in the patient with a lead that exits the body and is attached to an external battery source. A 2015 study showed a mortality rate of 65% of patients within 3 years of implantation and an 82% mortality rate within 4 years of implantation.
