Rat  Dual  Pressure  Telemetry   1  

Ultra  High  Fidelity  QT  Interval  in  Conscious  Guinea  Pigs        

-  Recent publications detail a probabilistic method of correcting QT interval in dogs and NHP using intensive telemetry interrogation (Holzgrefe et al) -  log QTc = log QTraw – (β * (log RRraw – log RRref)

- where β is slope of log QT/log RR regression line

- Our laboratories have confirmed the utility of this formula, QTcH, in dog and NHP, including via moxifloxacin administration.

- Our objective was to interrogate whether QTcH is appropriate for small animals, specifically guinea pig

- Six Dunkin-Hartley guinea pigs were instrumented with DSI implant C50-PXT for ECG and pressure.

- QT/RR pairs were acquired on a quasi beat to beat basis for 24h and plotted to obtain β as above.

- QTcH was then determined, and compared against QTcB, QTcF

y  =  0.179x  +  248.1R²  =  0.155

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100 150 200 250 300 350 400QTc  [Bazett's]  interval  (msec)

RR  interval  (msec)

y  =  0.320x  +  152.9R²  =  0.502

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100 150 200 250 300 350 400

QTc  [Frid

ericia's]  interval  

(msec)

RR  interval  (msec)

y  =  0.002x  +  124.1R²  =  0.000

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100 150 200 250 300 350 400

QTc  [H

olzgrefe's]  interval  

(msec)

RR  interval  (msec)

- Slope of QTcH/RR regression is zero, Y-intercept of regression line is the uncorrected QT interval at the reference HR (- 0.5 ms)

- Commonly used QTcB and QTcF are flawed in the correction of guinea pig QT interval

- QTcH accurately corrects the guinea pig QT interval for changes in RR, and should be considered for telemetry studies in this species.