Assessment of cardiac function during mechanical circulatory support: the quest for a suitable clinical index.
ABSTRACT A new index to assess left ventricular (LV) function in patients implanted with continuous flow left-ventricular assist devices (LVADs) is proposed. Derived from the pump flow signal, this index is defined as the coefficient (k) of the semilogarithmic relationship between "pseudo-ejection" fraction (pEF) and the volume discharged by the pump in diastole, (V d). pEF is defined as the ratio of the "pseudo-stroke volume" (pSV) to V d. The pseudo-stroke volume is the difference between V d and the volume discharged by the pump in systole (V s), both obtained by integrating pump flow with respect to time in a cardiac cycle. k was compared in-vivo with others two indices: the LV pressure-based index, M(TP), and the pump flow-based index, I(Q). M(TP) is the slope of the linear regression between the "triple-product" and end-diastolic pressure, EDP. The triple-product, TP = LV SP.dP/dt(max). HR, is the product of LV systolic pressure, maximum time-derivative of LV pressure, and heart rate. I(Q) is the slope of the linear regression between maximum time-derivative of pump flow, dQ/dt(max), and pump flow peak-to-peak amplitude variation, Q(P2P). To test the response of k to contractile state changes, contractility was altered through pharmacological interventions. The absolute value of k decreased from 1.354 ± 0.25 (baseline) to 0.685 ± 0.21 after esmolol infusion. The proposed index is sensitive to changes in inotropic state, and has the potential to be used clinically to assess contractile function of patients implanted with VAD.
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ABSTRACT: The clinical application of rotary blood pumps (RBPs) for bridge-to-recovery and destination therapy has focused interest on the remaining contractile function of the heart and its course. This study reports a method to determine contractility that uses readily measured variables of the RBP. The proposed index (I(Q)) is defined as the slope of a linear regression between the maximum derivative of the pump flow and its peak-to-peak value. I(Q) was compared with the maximal derivative of ventricular pressure (dP/dt(max)) vs end-diastolic volume (EDV) and the pre-load-recruitable stroke work. All indices were evaluated using computer simulations and animal experiments. For in vivo studies, a MicroMed-DeBakey ventricular assist device (VAD) was implanted in 7 healthy sheep. Ventricular contractility was examined under normal conditions and after pharmacologic intervention. For the computer simulation, variations of ventricular contractility, ventricular pre-load and after-load, and pump speeds were studied. In vivo and computer simulations showed the I(Q) index to be sensitive to changes of cardiac contractility, similar to other classic indices. For reduced cardiac contractility, it decreased to 9.3 +/- 3.9 (s(-1)) vs 15.3 +/- 4.0 (s(-1)) in the control condition (in vivo experiments). The I(Q) index was only marginally influenced by pre-load and after-load changes: a variation of 7.0% +/- 8.9% and 1.3% +/- 7.1%, respectively, was observed in computer simulations. The I(Q) index, which can be derived from pump data only, is a useful parameter for continuous monitoring of the cardiac contractility in patients with RBP support.The Journal of heart and lung transplantation: the official publication of the International Society for Heart Transplantation 09/2009; 29(1):37-44. · 3.54 Impact Factor
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ABSTRACT: Left ventricular function on patients with heart disease is now evaluated by echocardiography, but these dimensional changes are erroneous in the patient supported by left ventricular assist device because of mechanical unloading for the failing heart. Left ventricular end-systolic pressure-volume relationship provides theoretically most reliable left ventricular contractility. Recently, some patients have weaned from the device because of unexpected recovery of myocardial contractility. But it is very important to evaluate the left ventricular function just before the weaning, and to predict the longevity of the recovered function to keep the good quality of life. Current clinical situation in the patients with ventricular assist device, and theoretical limitations to evaluate the recovering myocardium are discussed.Annals of thoracic and cardiovascular surgery: official journal of the Association of Thoracic and Cardiovascular Surgeons of Asia 03/2002; 8(1):1-6. · 0.47 Impact Factor
- The Journal of heart and lung transplantation: the official publication of the International Society for Heart Transplantation 03/2006; 25(2):256-7. · 3.54 Impact Factor