Depending on the pathology described:
R/S ratio > 1 (or R/S ratio < 1) in leads V4 and V5

http://www.health.gov.mt/impaedcard/issue/issue1/ipc00103.ht...
The electrocardiogram should be read systematically:
Heart rate
P wave axis
Rhythm
QRS axis
Intervals PR, QRS, QT/QTc
P wave amplitude and duration
QRS amplitude, ***R/S ratio***, Q waves
ST segments and T wave

***R/S Ratio in V5 or V6 < 1***. 3. S ... the three leads V4, V5 and V6. E. ST ? -1mm in two of the three leads V4, V5 and V6. F ...
www.qrsdiagnostic.com/Documents/CardioVi... Guide(1).PDF

Dominant R wave in lead V1 (***R/S ratio > 1***) R wave in lead V1 7 ... ST segment depression and T wave inversion in leads V1 to V4 Deep S waves in leads V5, V6, I, and aVL Other causes ...
www2.kumc.edu/wichita/heartdoc/Topics/Pa...4/ecq_04-01.htm

Example : Fully evolved ... or anteroseptal MI Emphysema and COPD (look for ***R/S ratio in V5-6 <1***) Diffuse infiltrative or myopathic ...
www-medlib.med.utah.edu/kw/ecg/ecg_outli...son9/index.html


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Note added at 9 hrs 47 mins (2004-03-05 14:09:56 GMT)
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It seems that R/S-Umschlag = R/S transition.

A very good ECG glossary: http://www.homecardiographics.com/EcgComp.htm

http://www.homecardiographics.com/EcgR1.htm
R Wave Progression
The R wave in the V leads gradually increases in height from V1 to V4 or V5 where it reaches its maximum. Usually the R = S around V3 or V4 and this becomes the \'transition zone\'.

R/S Ratio
Used especially in V1 where it may suggest right ventricular enlargement or posterior myocardial infarction when > 1.0.

http://www.homecardiographics.com/EcgComp.htm
Transition Zone
In the chest leads, the lead where R = S when going from the small rS of V1 to the qR complex of V6, presumably a transition between a right ventricular epicardial lead and a left ventricular epicardial lead. It normally occurs at V3 or V4. See clockwise and counterclockwise rotation.

Especially the ***R/S transition*** in the precordial leads of the 12-lead surface ECG has been useful to differentiate ...
www.westhertshospitals.nhs.uk/WHC/archiv...-EHJ 2003.pdf

early repolarization, low voltage, ***R/S transition***, early R wave progression, and non ...
www.us.sandostatin.com/hcp/pages/product...duct/warning.do