Cardiovascular Engineering

, Volume 7, Issue 1, pp 32–38 | Cite as

Novel Means to Monitor Cardiac Performance: The Impact of the Force-frequency and Force-interval Relationships on Recirculation Fraction and Potentiation Ratio

  • Sarah E. Ahlberg
  • Robert C. Hamlen
  • Daniel L. Ewert
  • Paul A. Iaizzo
  • Lawrence J. Mulligan
Original Paper


Insights into intracellular calcium regulation and contractile state can be accomplished by changing pacing rate. Steady-state increases in heart rate (HR) (force-frequency relationship, FFR), and introduction of extrasystoles (ES) (force-interval relationship, FIR) have been used to investigate this relationship. This study focused on the recirculation fraction (RF) and potentiation ratio (PR), obtained from the recovery of the FFR and FIR. These parameters may provide insight on intracellular Ca2+ regulation. Left ventricular (LV) pressures and HR were assessed in anesthetized canines (n = 7). Intrinsic data were collected prior to and following HR increases to 150, 180, and 200 bpm, as well as following delivery of an ES at 280 ms. The RF was calculated as the slope of dP/dtmax(n + 1) vs. dP/dtmax(n), where n = beat number. The PR was calculated by normalizing dP/dtmax from the first beat following the ES (or the last paced beat) to the steady-state dP/dtmax. The RF due to an ES was not significantly different than that from a HR of 200 bpm. The PR from an ES was not significantly different than from a HR of 150 bpm. The impact of an ES delivered at an interval of 280 ms produces a PR similar to that from a HR of 150 bpm; yet, it recovers similarly to the termination of pacing at 200 bpm, eliciting a similar RF value. The method of measuring RF by an ES versus an increased HR may provide a safer and more feasible approach to collecting diagnostic information.


Intracellular Ca2+ handling Pacing Contractile function Heart failure Diagnostics 



Much gratitude is owed to Monica Mahre for her assistance in the editing of this manuscript. Financial support was provided by Medtronic, Inc. and Biomedical Engineering Institute, University of Minnesota.


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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  • Sarah E. Ahlberg
    • 1
    • 2
  • Robert C. Hamlen
    • 4
  • Daniel L. Ewert
    • 5
  • Paul A. Iaizzo
    • 1
    • 2
    • 3
  • Lawrence J. Mulligan
    • 4
  1. 1.Department of Biomedical EngineeringUniversity of MinnesotaMinneapolisUSA
  2. 2.Department of SurgeryUniversity of MinnesotaMinneapolisUSA
  3. 3.Department of PhysiologyUniversity of MinnesotaMinneapolisUSA
  4. 4.Therapy Delivery, Medtronic, Inc.MinneapolisUSA
  5. 5.Department of Electrical and Computer EngineeringNorth Dakota State UniversityFargoUSA

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