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Technique for measurement of diastolic interval surrogate: Tpeak to QRS onset (TpQ) and APD surrogate: QRS onset to Tpeak (QTp). A. When an S2 arrives after the Tpeak the TpQ and QTp are measured as shown on the left of the diagram. B. If the S2 occurs before the Tpeak the TpQ is effectively negative. In this case it is measured by subtracting the QTp-1 interval (QTp for the last drive cycle beat) from the QQ, in the example above this would give a TpQ close to zero.
