The T-wave in lead V1 is usually inverted or flat. When the T-wave is upright, especially if it is tall (taller than the T-wave in lead V6), be worried about cardiac ischemia...especially if the large upright T-wave is a new finding compared to prior ECGs.
LVH, LBBB, and misplaced precordial leads are the other causes of tall upright T-waves in lead V1. In the absence of any of these three conditions, worry about ischemia.
Marriott described this finding many years ago and refers to it as "loss of precordial T-wave balance."
