Cardiac Resynchronization Therapy in Non–Left Bundle Branch Block Morphology

History

A 62-year-old woman was seen at the cardiology outpatient clinic. Her medical history was significant for the onset of mild heart failure symptoms 2 years previously. She had a past left ventricular ejection fraction (LVEF) of 32% and a diagnosis of nonischemic cardiomyopathy because no significant coronary artery disease was seen on coronary angiography. She was treated medically for heart failure and had undergone implantable cardioverter-defibrillator (ICD) placement. Because she did not have a left bundle branch block (LBBB), she was not considered for cardiac resynchronization therapy (CRT) at the time, with New York Heart Association (NYHA) class II heart failure symptoms. She remained active, working full time, but recently had 6 months of progressive dyspnea on mild exertion, consistent with NYHA class III heart failure symptoms. She was treated with loop diuretics, an angiotensin-converting enzyme inhibitor, and carvidilol. Her medical history is significant for hysterectomy, oophorectomy, appendectomy, tonsillectomy, and mild hypothyroidism. She previously smoked one pack of cigarettes per day but quit smoking 11 years ago.

Current Medications

The patient was taking furosemide 40 mg daily, enalapril 10 mg twice daily, carvedilol 12.5 mg twice daily, atorvastatin 10 mg daily, levothyroxine 25 mcg daily, and aspirin 325 mg daily.

Current Symptoms

The patient was experiencing progressive dyspnea that occurred with everyday activity and occasional ankle swelling. She denied chest pain, paroxysmal nocturnal dyspnea, palpitations, lightheadedness, or syncope.

Physical Examination

• BP/HR: 110/70 mm Hg/65 bpm

• Height/weight: 167.6 cm/72.6 kg

• Neck veins: Jugular vein distention is estimated to be 10 cm

• Lungs/chest: Lungs clear to auscultation, ICD pocket is well healed

• Heart: Slightly irregular rhythm with occasional premature beats, grade 1/6 systolic murmur best heard at the left sternal border and increases with inspiration

• Abdomen: No hepatosplenomegaly, aortic enlargement, or bruit

• Extremities: Pulses are 2+, mild ankle edema, neurologically intact

Laboratory Data

• Hemoglobin: 13.3 g/dL

• Hematocrit/packed cell volume: 38.6%

• Mean corpuscular volume: 89.1 fL

• Platelet count: 279 × 10 ³ /µL

• Sodium: 140 mmol/L

• Potassium: 4.1 mmol/L

• Creatinine: 0.6 mg/dL

• Blood urea nitrogen: 11 mg/dL

Electrocardiogram

Findings

The electrocardiogram (ECG) revealed normal sinus rhythm, occasional premature ventricular complexes, nonspecific intraventricular conduction delay with a QRS width of 140 ms, and nonspecific T-wave changes ( Figure 36-1 )