Continuous assessment of cardiac function during rotary blood pump support: a contractility index derived from pump flow.
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.
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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.Artificial Organs 03/2014; · 1.87 Impact Factor
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ABSTRACT: Monitoring of cardiac rhythms is of major importance in the treatment of heart failure patients with left ventricular assist devices (LVADs) implanted. A continuous surveillance of these rhythms could improve out-of-hospital care in these patients. The aim of this study was to investigate cardiac rhythms using available pump data only. Datasets (n = 141) obtained in the normal ward, in the intensive care unit, and during bicycle ergometry were analyzed in 11 recipients of a continuous flow LVAD (59.1 ± 9.7 years; male 82%). Tachograms and arrhythmic patterns derived from the pump flow waveform, and a simultaneously recorded ECG were compared, as well as heart rate variability parameters such as: the average heart beat duration (RR interval), the standard deviation of the beat duration (SDNN), the root-mean-square of the difference of successive beat durations (RMSSD), and the number of pairs of adjacent beat duration differing by >50 ms divided by the number of all beats (pNN50). A very good agreement of cardiac rhythm parameters from the pump flow compared with ECG was found. Tachycardia, atrial fibrillation, and extrasystoles could be accurately identified from the tachograms derived from the pump flow. Also, Bland-Altman analysis comparing pump flow with ECG indicated a very small difference in average RR interval of 0.3 ± 1.0 ms, in SSDN of 0.5 ± 2.7 ms, in RMSSD of 1.0 ± 5.6 ms, and in pNN50 of 0.3 ± 1.0%. Continuous monitoring of cardiac rhythms from available pump data is possible. It has the potential to reduce the out-of-hospital diagnostic burden and to permit a more efficient adjustment of the level of mechanical support.Artificial Organs 08/2013; · 1.87 Impact Factor
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ABSTRACT: Recent outstanding clinical advances with new mechanical circulatory systems (MCS) have led to additional strategies in the treatment of end stage heart failure (HF). Heart transplantation (HTx) can be postponed and for certain patients even replaced by smaller implantable left ventricular assist devices (LVAD). Mechanical support of the failing left ventricle enables appropriate hemodynamic stabilisation and recovery of secondary organ failure, often seen in these severely ill patients. These new devices may be of great help to bridge patients until a suitable cardiac allograft is available but are also discussed as definitive treatment for patients who do not qualify for transplantation. Main indications for LVAD implantation are bridge to recovery, bridge to transplantation or destination therapy. LVAD may be an important tool for patients with an expected prolonged period on the waiting list, for instance those with blood group 0 or B, with a body weight over 90 kg and those with potentially reversible secondary organ failure and pulmonary artery hypertension. However, LVAD implantation means an additional heart operation with inherent peri-operative risks and complications during the waiting period. Finally, cardiac transplantation in patients with prior implantation of a LVAD represents a surgical challenge. This review summarises the current knowledge about LVAD and continuous flow devices especially since the latter have been increasingly used worldwide in the most recent years. The review is also based on the institutional experience at Berne University Hospital between 2000 and 2012. Apart from short-term devices (Impella, Cardiac Assist, Deltastream and ECMO) which were used in approximately 150 cases, 85 pulsatile long-term LVAD, RVAD or bi-VAD and 44 non-pulsatile LVAD (mainly HeartMateII and HeartWare) were implanted. After an initial learning curve, one-year mortality dropped to 10.4% in the last 58 patients.Schweizerische medizinische Wochenschrift 01/2012; 142. · 1.88 Impact Factor