What pattern indicates successful LBB placement when viewed in lead V1?

Successful left bundle branch (LBB) pacing is indicated by a specific pattern seen in lead V1 on the electrocardiogram (ECG). This pattern is characterized by a qR or rsR' shape, which reflects the propagation of electrical impulses through the left bundle branch after pacing.

When LBB pacing is effective, the electrical impulse travels down the left bundle branch, resulting in a narrow QRS complex and producing a characteristic morphology in the precordial leads. The qR pattern shows an initial downward deflection (the 'q' wave) followed by a prominent upward deflection (the 'R' wave), indicating proper activation of the left ventricle.

In contrast, patterns such as the M shape or W shape do not distinctly represent LBB pacing and usually suggest different conduction abnormalities or variations. A flat line would indicate a lack of electrical activity or ineffective pacing, which is not a sign of successful placement. Hence, observing a qR or rsR' shape in lead V1 clearly indicates that the LBB has been successfully paced.