A 68-year-old man with 5 year history of congestive cardiomyopathy is in his family physician’s office for a routine assessment. His condition is stable and he has no symptoms or signs of heart failure:

• Sinus rhythm, 84/min
• Right superior axis deviation
• Nonspecific intraventricular block

The QRS duration is markedly increased to 165 msec. There are no findings of right bundle branch block or left bundle branch block.