Pacing Developments

The earliest recorded description of pacing was in 1882 and its now over 60 years since the first patients received an implantable cardiac pacemaker. Many lives have been saved and quality of life improved by these early devices and the many subsequent developments implemented over the following decades. Important developments include the implantable cardioverter defibrillator (ICD) in 1980 and then more recently a treatment for heart failure with cardiac resynchronisation therapy (CRT), first described in 1984 followed by the development in recent years of conduction system pacing (CSP).

Pacemakers are indicated for symptomatic bradycardia and also in cases of atrio-ventricular (AV) block for improving prognosis. In the main cardiac resynchronisation pacemakers are indicated in patients who develop significant intraventricular conduction delay (bundle branch block) or those with left ventricular (LV) impairment who are expected to receive a high degree or percentage of heart beats activated from conventional right ventricular (RV) pacing. Right ventricular pacing is associated with the development of LV impairment (pacing induced cardiomyopathy) and has been shown to increase mortality. Particularly at risk are those with pre-existing LV impairment. Approximately 10-20% of patients with normal LV function will develop LV impairment following significant RV pacing (>40% ventricularly paced beats). ICDs were originally inserted for survivors of cardiac arrest (secondary prevention implantation) but it has become apparent that high risk patients could be identified prior to sudden cardiac death (primary prevention implantation). Current practice is therefore to insert the majority of ICDs for those judged to be at high risk of ventricular arrhythmia as a primary prevention measure. However the prediction of sudden death risk remains challenging although this has been assisted greatly by developments in a number of clinical areas including for example, imaging with cardiac MRI to image myocardial fibrosis and in some specific cardiomyopathies, genetic testing.