Q. If someone has problems concentrating and he knows he wont be able to concentrate even on the first bracha of the amida, is he exempt from tefila?
A. Mishna Berura (101: 3) indeed rules that one should not daven if he cannot concentrate at least on the first brocho (See Talmud Brochos 30b). However, the end of the first brocho in case of great need suffices.
Piskei Teshuvos (ibid. 3) quotes opinions that in our days, due to the lack of paying attention so common in our times, one should daven anyway, and try his uttermost to at least focus on the last part of the first brocho.
Horav Shlomo Miller’s Shlit’a opinion is similar.
The above is based on the Tur (O.H. 101, mentioned in the last question) and on the explanation of the Baal Haturim at the end of Parshas Pekudei that the eighteen repetitions of the posuk “He did as Hashem ordered Moshe,” are the reason for the eighteen blessings of the amida. The 113 words in those psukim also correspond to the 113 words that constitute the ending brocho of those blessings. He adds that 113, is the number of times that the word “Lev” or heart is mentioned in the Torah, teaching us that at least that part requires kavanah.”
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a