title: Impedance cardiography: a useful and reliable tool in optimization of cardiac resynchronization devices.
abstract: OBJECTIVE
  Optimizing cardiac resynchronization therapy (CRT) devices has become more complex since modification of both atrioventricular (AV) and interventricular (VV) stimulation intervals has become possible. The current paper presents data from the routine use of impedance cardiography (IC)-based cardiac output (CO) measurements to guide the optimization of AV- and VV-interval timing of CRT devices.
  
  
  RESULTS
  Forty-six patients with heart failure (left ventricular ejection fraction <35%, New York Heart Association (NYHA) III-IV) and left bundle branch block (>130 ms) in sinus rhythm were evaluated 3-5 days after implantation of a CRT device by means of IC. CO was measured without pacing and with biventricular pacing using a standard protocol of VV- and AV-interval modification from -60 to +60 ms and 80 to 140 ms, respectively, in 20 ms steps. Mean CO without pacing was 3.66 +/- 0.85 L/min and significantly increased to 4.40 +/- 1.1 L/min (P<0.05) with simultaneous biventricular pacing and an AV interval of 120 ms. 'Optimizing' both VV and AV intervals further increased CO to 4.86 +/- 1.1 L/min (P<0.05). Maximum CO was measured in most patients with left ventricular pre-excitation. The proportion of 'non-responders' to CRT was reduced by 56% following AV- and VV-interval modification using IC guidance.
  
  
  CONCLUSIONS
  Modification of both AV and VV intervals in patients with a CRT device significantly improves CO compared with standard simultaneous biventricular pacing and no pacing. IC is a useful non-invasive technique for guiding this modification. Marked variability of optimal AV and VV intervals between patients requires optimization of these intervals for each patient individually.
authors.affiliation: Department of Medicine III/Cardiology, Martin-Luther-University Halle-Wittenberg, E, rnst-Grube-Strasse 40, 06097, Halle (Saale), Germany. konstantin.heinroth@medizin.uni-halle.de
authors.forename: Konstantin M
authors.initials: KM
authors.lastname: Heinroth
authors.forename: Marcel
authors.initials: M
authors.lastname: Elster
authors.forename: Sebastian
authors.initials: S
authors.lastname: Nuding
authors.forename: Frithjof
authors.initials: F
authors.lastname: Schlegel
authors.forename: Arnd
authors.initials: A
authors.lastname: Christoph
authors.forename: Justin
authors.initials: J
authors.lastname: Carter
authors.forename: Michael
authors.initials: M
authors.lastname: Buerke
authors.forename: Karl
authors.initials: K
authors.lastname: Werdan
mesh_terms: D000368:Aged; D002302:Cardiac Output / Q000502:physiology; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D002307:Cardiography, Impedance / Q000295:instrumentation / Q000379:methods*; D002309:Cardiology / Q000379:methods; D017147:Defibrillators, Implantable; D015150:Echocardiography, Doppler; D005260:Female; D006333:Heart Failure / Q000000981:diagnostic imaging / Q000628:therapy*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction; D010138:Pacemaker, Artificial