title: Comparing maximum rate and sustainability of pacing by mechanical vs. electrical stimulation in the Langendorff-perfused rabbit heart.
abstract: OBJECTIVE
  Mechanical stimulation (MS) represents a readily available, non-invasive means of pacing the asystolic or bradycardic heart in patients, but benefits of MS at higher heart rates are unclear. Our aim was to assess the maximum rate and sustainability of excitation by MS vs. electrical stimulation (ES) in the isolated heart under normal physiological conditions.
  
  
  RESULTS
  Trains of local MS or ES at rates exceeding intrinsic sinus rhythm (overdrive pacing; lowest pacing rates 2.5±0.5 Hz) were applied to the same mid-left ventricular free-wall site on the epicardium of Langendorff-perfused rabbit hearts. Stimulation rates were progressively increased, with a recovery period of normal sinus rhythm between each stimulation period. Trains of MS caused repeated focal ventricular excitation from the site of stimulation. The maximum rate at which MS achieved 1:1 capture was lower than during ES (4.2±0.2 vs. 5.9±0.2 Hz, respectively). At all overdrive pacing rates for which repetitive MS was possible, 1:1 capture was reversibly lost after a finite number of cycles, even though same-site capture by ES remained possible. The number of MS cycles until loss of capture decreased with rising stimulation rate. If interspersed with ES, the number of MS to failure of capture was lower than for MS only.
  
  
  CONCLUSIONS
  In this study, we demonstrate that the maximum pacing rate at which MS can be sustained is lower than that for same-site ES in isolated heart, and that, in contrast to ES, the sustainability of successful 1:1 capture by MS is limited. The mechanism(s) of differences in MS vs. ES pacing ability, potentially important for emergency heart rhythm management, are currently unknown, thus warranting further investigation.
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, 5850 College St, Halifax, NS B3H 4R2, Canada alex.quinn@dal.ca.
authors.forename: T Alexander
authors.initials: TA
authors.lastname: Quinn
authors.affiliation: Institute for Experimental Cardiovascular Medicine, University Heart Centre Freiburg/Bad Krozingen, Medical School of the University of Freiburg, Elsaesser Str 2Q, 79110 Freiburg, Germany.|National Heart and Lung Institute, Imperial College London, The Magdi Yacoub Institute, Hill End Road, UB9 6JH London, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Kohl
mesh_terms: D000200:Action Potentials; D000818:Animals; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects / Q000379:methods*; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006321:Heart / Q000294:innervation*; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate; D000067268:Isolated Heart Preparation; D020127:Recovery of Function; D013997:Time Factors; D016277:Ventricular Function, Left; D017725:Ventricular Pressure; D056969:Voltage-Sensitive Dye Imaging
keywords:  Cardiac ; Electrophysiology ; Mechano-electric feedback ; Optical mapping ; Strain; Stretch-activated channels 