Right axis deviation is present – the QRS is upright in aVF, but negative in I (for those counting, it is somewhere between 120 and 150 degrees). Perhaps the most common 'cause' of RAD is switched left and right arm leads! Once that is excluded, consider RVH, pulmonary hypertension (acute as in pulmonary embolism can produce the classic S1Q3 seen here, but there is no Tw inversion with strain seen here; or chronic pulmonary hypertension), or dextrocardia.
Finally, remember that the rare left POSTERIOR fascicular block can also produce this pattern (LPFB is much rarer than LAFB which is pretty common). Without chest leads, you cannot say definitively which this is, and sometimes even with chest leads it can be hard to say definitely what is causing the RAD. For example, one must exclude RVH before diagnosing posterior fascicular block.
NOTE: EKG's are for internal educational purposes of the University of Massachusetts Department of Family Medicine. Please do not forward without permission from Dr. Golding!
