title: Derivation of indices of left ventricular contractility in the setting of continuous-flow left ventricular assist device support.
abstract: It is important to accurately monitor residual cardiac function in patients under long-term continuous-flow left ventricular assist device (cfLVAD) support. Two new measures of left ventricular (LV) chamber contractility in the cfLVAD-unloaded ventricle include IQ, a regression coefficient between maximum flow acceleration and flow pulsatility at different pump speeds; and K, a logarithmic relationship between volumes moved in systole and diastole. We sought to optimize these indices. We also propose RIQ, a ratio between maximum flow acceleration and flow pulsatility at baseline pump speed, as an alternative to IQ. Eleven patients (mean age 49 ± 11 years) were studied. The K index was derived at baseline pump speed by defining systolic and diastolic onset as time points at which maximum and minimum volumes move through the pump. IQ across the full range of pump speeds was markedly different between patients. It was unreliable in three patients with underlying atrial fibrillation (coefficient of determination R(2) range: 0.38-0.74) and also when calculated without pump speed manipulation (R(2) range: 0.01-0.74). The K index was within physiological ranges, but poorly correlated to both IQ (P = 0.42) and RIQ (P = 0.92). In four patients there was excellent correspondence between RIQ and IQ, while four other patients showed a poor relationship between these indices. As RIQ does not require pump speed changes, it may be a more clinically appropriate measure. Further studies are required to determine the validity of these indices.
authors.affiliation: Heart Failure and Transplant Unit, St. Vincent's Hospital, Sydney, New South Wales, Australia; Faculty of Medicine, The University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Sunil
authors.initials: S
authors.lastname: Gupta
authors.forename: Kavitha
authors.initials: K
authors.lastname: Muthiah
authors.forename: Kei
authors.initials: K
authors.lastname: Woldendorp
authors.forename: Desiree
authors.initials: D
authors.lastname: Robson
authors.forename: Paul
authors.initials: P
authors.lastname: Jansz
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Hayward
mesh_terms: D000328:Adult; D005260:Female; D006333:Heart Failure / Q000503:physiopathology* / Q000601:surgery; D006352:Heart Ventricles / Q000503:physiopathology*; D006353:Heart-Assist Devices; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D011673:Pulsatile Flow / Q000502:physiology*; D016277:Ventricular Function, Left / Q000502:physiology*
keywords: Continuous flow; Contractility; Heart failure.; Left ventricular assist device