Orthodromic = ortho + dromos.
Ortho- is a prefix denoting normal, straight, proper order, correct.
Dromos is a Gr. word meaning course
Orthodromic, therefore, means conducting impulses in the normal or correct direction.
Orthodromic denotes the propagation of an impulse along a conduction system (for example, nerve fiber) in the direction it normally travels. Compare: antidromic.
In the heart, orthodromic refers to an impulse going in the correct direction from the atria to the ventricles, in contrast to some impulses in re-entry.
For example, in AVRT, the impulse typically “traverses down the AV node and returns to the atrium via the accessory pathway (orthodromic conduction). On ECG, the P wave appears after the QRS complex, although it is often obscured by the T wave.
Conduction that sends the impulse down the accessory pathway first, with activation of the entire ventricular myocardium before involving the AV node (therefore without conduction through the His-Purkinje system), creates a wide QRS complex (antidromic conduction) and is less common.” AAFP 2015
Reference
Am Fam Physician. 2015 Nov 1;92(9):793-802. http://www.aafp.org/afp/2015/1101/p793.html