title: The systolic index: a noninvasive approach for the assessment of cardiac function: implications for patients with DDD and CRT devices.
abstract: BACKGROUND
  Our objective was to evaluate the systolic index (SI), the ratio between rate-corrected left ventricular ejection time (LVETc), and a preejection period surrogate (PEPsu), to assess cardiac function in patients with DDD and cardiac resynchronization therapy (CRT) pacemakers.
  
  
  METHODS
  LVETc and PEPsu were automatically measured from electrocardiogram and finger photoplethismography. Atrioventricular (AV) and mode switch (CRT to DDD) were used as hemodynamic challenges. Performance of SI, beat-by-beat systolic blood pressure (SBP), and Doppler aortic velocity/time integral (AoVTI) were compared in 36 patients, and SI's detection of CRT to DDD mode switch in nine patients, responders to CRT. AVs were changed from 30 ms to 250 ms (20 ms steps) at constant paced heart rate, alternating with a reference AV (RefAV), to reduce hemodynamic drift. The coefficient of variation (standard deviation/mean) of SI, SBP, and AoVTI during all RefAVs were used as error marker. The percentage detection of hemodynamic changes during AV transitions was a marker of sensitivity.
  
  
  RESULTS
  Fifty-five patients (males 62%, age 69.6 ± 17) were studied. SI detected 441 of 544 transitions (81%) versus 361 (66%) of SBP (P = 0.005). Error during RefAVs was smaller for SI (3.4%) as compared to AoVTI (7.8%, P = 0.015) and to SBP (5.7%, P = 0.005). SIs correlated with AoVTI (R from 0.71 to 0.98, all P < 0.001). SI detected all CRT to DDD changes (P < 0.001).
  
  
  CONCLUSIONS
  The noninvasive SI obtained with a simple, observer-independent hemodynamic assessment procedure has higher accuracy than SBP and AoVTI and better sensitivity than SBP. It detects mechanical resynchronization in CRT and allows programming a suitable AV delay.
authors.affiliation: Servicio de Cardiología, Hospital Fernández, Buenos Aires, Argentina.
authors.forename: Raul
authors.initials: R
authors.lastname: Chirife
authors.forename: G Aurora
authors.initials: GA
authors.lastname: Ruiz
authors.forename: Enrique
authors.initials: E
authors.lastname: Gayet
authors.forename: Claudio
authors.initials: C
authors.lastname: Muratore
authors.forename: Héctor
authors.initials: H
authors.lastname: Mazzetti
authors.forename: Alejandro
authors.initials: A
authors.lastname: Pellegrini
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Tentori
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D058409:Cardiac Resynchronization Therapy Devices; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D006333:Heart Failure / Q000175:diagnosis* / Q000503:physiopathology / Q000517:prevention & control*; D006334:Heart Function Tests; D006801:Humans; D008875:Middle Aged; D010138:Pacemaker, Artificial; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013318:Stroke Volume; D055815:Young Adult
keywords: CRT and DDD optimization; cardiac performance; systolic index; systolic intervals