Chapter 31: Cardiac Resynchronization Therapy in the treatment of Heart Failure

PATIENT CASE

A 55-year-old woman presented to your clinic for a follow-up. She was diagnosed with nonischemic cardiomyopathy diagnosed9 months ago after she presented to the emergency department (ED) with New York Heart Association (NYHA) class IV heart failure (HF) symptoms. Coronary angiography then revealed no obstructive coronary artery disease (CAD). Echocardiogram at the time of her initial evaluation revealed moderately dilated left ventricle, and global hypokinesis with an ejection fraction of 20%, with no gross valvular abnormalities. Cardiac magnetic resonance imaging (MRI) showed midwall fibrosis consistent with nonischemic cardiomyopathy. During her clinic visit, she reported symptoms of effort intolerance and exertional dyspnea with mild exertion. She denied resting or exertional chest pain. An echocardiogram at the time of her visit showed left ventricular ejection fraction (LVEF) of 25%. Her current medications include carvedilol 25 mg twice daily, lisinopril 10 mg twice daily, aldactone 25 mg by mouth once a day, Lipitor 80 mg by mouth once daily, Aspirin (ASA) 81 mg by mouth once daily, and Plavix 75 mg by mouth once daily. Electrocardiogram showed normal sinus rhythm, left bundle branch block with QRS duration of 155 ms. Blood Pressure is 90/60 mm Hg and heart rate is 70 beats per minute. Her cardiovascular examination was unremarkable.

INTRODUCTION

Cardiac resynchronization therapy (CRT) is a device-based treatment for HF that emerged over the last few decades to be a major contributor to reducing morbidity and mortality. The concept of this therapy is to restore synchronous activation of both ventricles in select patients who had evidence of prolonged depolarization evident by prolongation of the QRS segment on the surface electrocardiogram (ECG). Stimulation of the right ventricle is achieved with the standard transvenous leads used in traditional pacemakers and implantable cardioverter defibrillators (ICDs). Early CRT systems required thoracotomy and epicardial left ventricular (LV) lead placement by open surgical approach. This practice was replaced by a transvenous approach in which implantation of the LV lead is achieved by cannulation of the coronary sinus and targeting a lateral or posterior branch. Given the recent advancement in lead and delivery system technologies, the transvenous approach has become the standard technique worldwide. The epicardial technique is still used but reserved for patients with difficult venous anatomy or suboptimal target vessels.

CARDIAC DYSSYNCHRONY

Cardiac dyssynchrony has deleterious effects on the heart’s performance as a pump. It can occur between the left and right ventricles and within the left ventricle itself.¹ A left bundle-branch blockade (LBBB) with prolongation of the QRS duration ≥120 ms has been used as a universal measure of electrical dyssynchrony in most clinical trials. LBBB is present in approximately one-third of HF patients in whom the septum is activated earlier than the lateral or posterior walls, resulting in paradoxical septal motion and ineffective contraction (Figure 31-1). Furthermore, dyssynchronous contraction increases LV end-systolic and end-diastolic volumes and reduces ...