for my $row ($sheet->{MinRow} .. $sheet->{MaxRow}) {
   my $A_cell = $sheet->{Cells}[$row][$A_col];
   my $B_cell = $sheet->{Cells}[$row][$B_col];
   my $A_val = $A_cell->{Val};
   my $B_val = $B_cell->{Val};
...

##</code><code>##

===|===|
A1 |B1 |
===|===|
A2 |B2 |
===|   |
A3 |   |
===|===|
A4 |B4 |
===|===|