Pacemaker Upgrade to Cardiac Resynchronisation Therapy in Patients With Left Ventricular Dysfunction Dependant Upon Right Ventricular Pacing.

Background

1. Chronic heart failure Chronic heart failure (CHF) is a common syndrome of breathlessness and fatigue associated with left ventricular systolic dysfunction. It affects 2% of individuals between 50 and 60 years of age, and increases in prevalence to 10% over the age of 80 years.
2. Cardiac resynchronisation therapy Cardiac resynchronisation therapy (CRT) involves the implantation of a pacemaker capable of stimulating the heart (specifically the left ventricle) from both the front of the heart, the right ventricle RV (as is usual with conventional pacemakers) and from the back of the heart (known as the lateral wall) via the coronary sinus, aiming to improve the timing of cardiac contraction (dyssynchrony) and hence the pumping function of the heart in order to improve symptoms of breathlessness and fatigue.

Early data in patients with left bundle branch block and severe heart failure, suggested improved exercise capacity and left ventricular function. More recent data have demonstrated not only improved symptoms, but also reduced hospital admissions, and improved overall mortality.

Current guidelines drawn up using the data from randomised trials, suggest that CRT should be offered to patients with left bundle branch block with a QRS > 150ms and severe (class III and IV) heart failure despite optimal medical therapy. Patients with a QRS duration of between 120 and 150ms should be assessed for mechanical dyssynchrony before being offered a device. 3. Heart failure in the pacemaker population

• Prevalence In 307 patients with pacemakers, 94 (31%) had left ventricular ejection fraction (LVEF) < 40% and 83 (27%) had symptoms of heart failure. RV pacing is associated with an increase in heart failure-related hospitalisation and mortality, and in patients with left ventricular dysfunction the presence of a right ventricular apical pacemaker is a strong predictor of future deterioration in left ventricular function.
• Aetiology of pacemaker-related heart failure Many patients receiving RV pacemakers are elderly with a background of ischaemic heart disease or hypertension, both of which contribute to the development of heart failure. In addition RV pacing induces dyssynchrony, no different to that of left bundle branch block (LBBB). Dyssynchrony leads to altered regional blood flow and wall stress. The severity of these perfusion abnormalities, the regional wall motion abnormalities and the associated deterioration in global left ventricular function are directly related to the duration of pacing. These changes can be identified after only 18 months of pacing. The induction of dyssynchrony by RV apical pacing seems therefore to lead to adverse LV remodeling, LV dilatation, asymmetrical hypertrophy.
• Management of pacemaker-related heart failure In any one patient the exact aetiology of a deterioration of LV dysfunction is often unclear. What has become routine practice however, is an attempt to avoid RV pacing unless absolutely necessary and several programmes within commercially available devices now exist to facilitate this. The options in patients with a high degree of heart block on the other hand remain limited to aggressive medical therapy with beta-blockers and angiotensin converting enzyme inhibitors.