leads I, aVL, V5 and V6. Pathologic Q waves occur when the electrical signal passes through stunned or scarred heart muscle; as such, they are usually markers of previous myocardial infarctions, with subsequent fibrosis. A pathologic Q wave is defined as having a deflection amplitude of 25% or more of the subsequent R wave, or being (40 ms) in width and in amplitude. However, diagnosis requires the presence of this pattern in more than one corresponding lead. R wave progression Looking at the precordial leads, the R wave usually progresses from showing an rS-type complex in V1 with an increasing R and a decreasing S wave when moving toward the left side. There is usually a qR-type of complex in V5 and V6, with the R-wave amplitude usually taller in V5 than in V6. It is normal to have a narrow QS and rSr' patterns in V1, and this is also the case for qRs and R patterns in V5 and V6. The transition zone is where the QRS complex changes from predominantly negative to predominantly positive (R/S ratio becoming >1), and this usually occurs at V3 or V4. It is normal to have the transition zone at V2 (called "early transition") and at V5 (called "delayed transition"). In biomedical engineering, the maximum amplitude in the R wave is usually called "R peak amplitude", or just "R peak". Accurate R peak detection is essential in signal processing equipment for heart rate measurement and it is the main feature used for arrhythmia detection. The definition of poor R wave progression (PRWP) varies in the literature. It may be defined, for example, as R wave of less than 2–4 mm in leads V3 or V4 and/or presence of a reversed R wave progression, which is defined as R in V4 < R in V3 or R in V3 < R in V2 or R in V2 < R in V1, or any combination of these. Poor R wave progression is commonly attributed to anterior myocardial infarction, but it may also be caused by left bundle branch block, Wolff–Parkinson–White syndrome, right and left ventricular hypertrophy, or a faulty ECG recording technique. R wave peak time R wave peak time (RWPT) represents the time from the onset of QRS complex to the peak of R wave, which is usually measured in aVL and V5 or V6 leads. R-peak time for right ventricle is measured