title: The acute effects of changes to AV delay on BP and stroke volume: potential implications for design of pacemaker optimization protocols.
abstract: BACKGROUND
  The AV delay optimization of biventricular pacemakers (cardiac resynchronization therapy) may maximize hemodynamic benefit but consumes specialist time to conduct echocardiographically. Noninvasive BP monitoring is a potentially automatable alternative, but it is unknown whether it gives the same information and similar precision (signal/noise ratio). Moreover, the immediate BP increment on optimization has been reported to decay away: it is unclear whether this is the result of an (undesirable) decrease in stroke volume or a (desirable) compensatory relief of peripheral vasoconstriction.
  
  
  RESULTS
  To discriminate between these alternative mechanisms, we measured simultaneous beat-to-beat stroke volume (flow) using Doppler echocardiography, and BP using finger photoplethysmography, during and after AV delay changes from 40 to 120 ms in 19 subjects with cardiac pacemakers. BP and stroke volume both increased immediately (P<0.001, within 1 heartbeat). BP showed a clear decline a few seconds later (average rate, -0.65 mm Hg/beat; r=0.95 [95% CI, 0.86-0.98]); in contrast, stroke volume did not decline (P=0.87). The immediate BP increment correlated strongly with the stroke volume increment (r=0.74, P<0.001). The signal/noise ratio was 3-fold better for BP than stroke volume (6.8±3.5 versus 2.3±1.4; P<0.001).
  
  
  CONCLUSIONS
  Improving AV delay immediately increases BP, but the effect begins to decay within a few seconds. Reassuringly, this is because of compensatory vasodilatation rather than reduction in cardiac function. Pacemaker optimization will never be reliable unless there is an adequate signal/noise ratio. Using BP rather than Doppler minimizes noise. The early phase (before vascular compensation) has the richest signal lode.
authors.affiliation: International Centre for Circulatory Health, Imperial College London, London, UK. cmanisty@ic.ac.uk
authors.forename: Charlotte H
authors.initials: CH
authors.lastname: Manisty
authors.forename: Ali
authors.initials: A
authors.lastname: Al-Hussaini
authors.forename: Beth
authors.initials: B
authors.lastname: Unsworth
authors.forename: Resham
authors.initials: R
authors.lastname: Baruah
authors.forename: Punam A
authors.initials: PA
authors.lastname: Pabari
authors.forename: Jamil
authors.initials: J
authors.lastname: Mayet
authors.forename: Alun D
authors.initials: AD
authors.lastname: Hughes
authors.forename: Zachary I
authors.initials: ZI
authors.lastname: Whinnett
authors.forename: Darrel P
authors.initials: DP
authors.lastname: Francis
mesh_terms: D000368:Aged; D001283:Atrioventricular Node / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology*; D015150:Echocardiography, Doppler; D004562:Electrocardiography; D004867:Equipment Design; D005260:Female; D005500:Follow-Up Studies; D006333:Heart Failure / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D006339:Heart Rate; D006801:Humans; D008297:Male; D010045:Outpatients; D010138:Pacemaker, Artificial / Q000592:standards*; D017156:Photoplethysmography; D013318:Stroke Volume / Q000502:physiology*; D016896:Treatment Outcome
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