Indication
Strength of indication
Sinus rhythm, LVEF ≤35 %, LBBB, QRS duration ≥150 ms, and NYHA class II, III, or ambulatory IV symptoms
Class I
Sinus rhythm, LVEF ≤35 %, LBBB, QRS duration 120–149 ms, and NYHA class II, III, or ambulatory IV symptoms
Class IIa
Sinus rhythm, LVEF ≤35 %, non-LBBB pattern, QRS duration ≥150 ms, and NYHA class III or ambulatory IV symptoms
Class IIa
Atrial fibrillation, LVEF ≤35 %, patient requires ventricular pacing, and AV nodal ablation or pharmacologic rate control will allow near 100 % ventricular pacing with CRT
Class IIa
LVEF ≤35 % and undergoing new or replacement device placement with anticipated requirement for significant (>40 %) ventricular pacing
Class IIa
Sinus, rhythm, LVEF ≤30 %, LBBB, QRS duration ≥150 ms, ischemic etiology of heart failure, and NYHA class I symptoms
Class IIb
Sinus, rhythm, LVEF ≤35 %, non-LBBB pattern, QRS duration 120–149 ms, and NYHA class III or ambulatory IV symptoms
Class IIb
Sinus, rhythm, LVEF ≤35 %, non-LBBB pattern, QRS duration ≥150 ms, and NYHA class II symptoms
Class IIb
Contraindications
There are two circumstances under which CRT carries a Class III recommendation (no benefit and may cause harm). These are patients who do not fulfill implant criteria (NYHA class I or II symptoms, non-LBBB pattern, and QRS duration <150 ms) and patients with estimated survival <1 year based on comorbidities and/or frailty [3].
Equipment
CRT devices, like the majority of cardiac implantable electronic devices, consist of two basic components, the pulse generator and the leads (Fig. 24.1). There are two main categories of CRT devices, BiV pacemakers and BiV ICDs. The majority of devices implanted are BiV ICDs, as the majority of patients who are candidates for CRT also have an indication for an ICD for primary prevention of sudden cardiac death.
Fig. 24.1
PA and lateral radiographic images of a biventricular implantable cardioverter defibrillator. PA (Panel a) and lateral (Panel b) chest x-rays showing a biventricular implantable cardioverter defibrillator. Both images show the device (thick white arrow) implanted in the left chest, the atrial lead (thin white arrow) positioned in the right atrial appendage, the right ventricular lead (thick black arrow) positioned in the right ventricular apex, and the left ventricular lead (thin black arrow) positioned in a lateral branch of the coronary sinus
CRT devices are typically larger than standard pacemakers or ICDs. However, even the largest devices are smaller than an average deck of playing cards. The device contains two main components, the electronics that control the device function and a compact battery.
All CRT devices have at least two leads, and most have three leads. Typically there is an atrial lead to facilitate AV synchrony, though in some circumstances this may not be necessary (chronic atrial fibrillation). By definition, these devices must have two ventricular leads. Typically one lead is placed in the right ventricular (RV) apex or elsewhere in the RV along the interventricular septum. Unique to BiV devices, is the presence of a pacing lead in the coronary sinus. The coronary sinus lead can have as many as four pacing electrodes on it (Fig. 24.2). This allows for multiple possible pacing vectors, so as to produce the most synchronous contraction of the LV.
