CARDIAC PACING - pediagenosis
Article Update
Loading...

Thursday, May 15, 2025

CARDIAC PACING

CARDIAC PACING

CARDIAC PACING


When patients are symptomatic because of symptomatic bradycardia (e.g., syncope, dizziness, lethargy), a cardiac pacemaker can effectively decrease or eliminate symptoms because it treats the pathophysiologic problem: slow heart rate, which can result from sinus node dysfunction or A-V block. Some devices pace only the atrium, some only the right ventricle, and some pace both the atrium and the ventricle sequentially. Some pacemakers also are combined with an implantable cardioverter-defibrillator (ICD), and others can improve cardiac synchronization (e.g., BiV pacemakers).

 

CURRENT TRANSVENOUS PACEMAKERS

A modern pacemaker generator (usually a lithium battery) is placed subcutaneously under the clavicle. This generator is sealed so as not to imbibe body fluids and can deliver electrical impulses to the electrode leads within the right atrial appendage and right ventricle and to the left ventricle by way of a coronary sinus electrode lead (BiV pacing). The pacemaker generator is immunologically inert.

Permanent Pacing

The pacemaker implant procedure is performed under fluoroscopy, usually by a trained cardiologist or cardiac surgeon. Most often, percutaneous access to the left subclavian lead is used to pass the electrode leads into the heart, but the right subclavian vein can be used when the left is not available. Fluoroscopy confirms the positioning of the pacing leads in the right atrial or right ventricular chambers and of the left ventricular epicardial lead when BiV pacing is employed.

Pacemaker Types

Pacemakers can be of three types and are used to pace a single or multiple chambers of the heart. A single-chamber pacemaker involves the placement of a single lead into an atrium or ventricle, which then can sense and pace either the atrium or the ventricle. The most common reason for pacing only the atrium is dysfunction of the sinus node, such as sick sinus syndrome. The most frequent reason for pacing only the right ventricle is atrial fibrillation.

In contrast, a dual-chamber pacemaker consists of two leads inserted into the heart (see Plate 2-29). One lead can be inserted into the right atrial appendage and fixated in that position, pacing the atrium. Another pacing lead can be inserted into the right ventricle and fixated in that position. When activated and functioning, these two pacing leads pace the atrium and ventricle sequentially, closely simulating the natural conduction system of the heart. This type of pacing is the most common type currently used.

A rate-responsive pacemaker is usually a dual-chamber pacemaker (can be single chamber) that responds to increased demand for an increased heart rate. The patient’s increased physical activity (exercise) increases pectoral muscle activity, which is sensed by the pacemaker generator. Once this physical activity is detected, the pacemaker increases the rate of electrical impulses and increases heart rate to meet the patient’s physiologic demands for increased cardiac output. Rate- responsive pacemakers are often used for patients with symptomatic bradycardia.

Biventricular Pacing

In contrast to standard two-lead A-V sequential pacing, biventricular (BiV) pacing consists of three leads: RA appendage lead, RV lead, and a lead introduced into the coronary sinus and advanced to a lateral vein on the epicardial surface of the LV free wall. The position of the epicardial lead corresponds to the position of an obtuse marginal artery. This lead system, in addition to A-V pacing, enables pacing of the LV free wall (see Plate 2-29).

Cardiac resynchronization therapy (CRT) uses BiV pacing because the lead system paces both the septal LV wall and the lateral LV wall. When viable tissue is present in these areas, the left ventricle resynchronizes the contraction of a heart whose opposing walls do not contract in synchrony. Dyssynchrony frequently occurs in patients with systolic heart failure, many with QRS duration longer than 120 msec, which qualifies a patient for CRT. These patients are at high risk for sudden cardiac death because many have an LV ejection fraction of 35% or less. The BiV lead system can be combined with an ICD to prevent sudden cardiac death from ventricular tachycardia or ventricular fibrillation, a common companion to severe heart failure.


Share with your friends

Give us your opinion

Note: Only a member of this blog may post a comment.

Notification
This is just an example, you can fill it later with your own note.
Done