Suction due to left ventricular assist: implications for device control and management.
ABSTRACT Left ventricular assist device (LVAD) overpumping is associated with hemolysis, thrombus release, and tissue damage at the pump inlet. However, the impact of LVAD suction on pulmonary circulatory function remains unknown. We investigated LVAD suction as induced by pulmonary artery banding and overpumping in experimental animals and in a computer model. In six sheep, a rotary LVAD was implanted. Before inducing suction, partial support (40-60% of cardiac output) was established and characterized by measuring pressures and flows. In the animals, pulmonary artery occlusion (PAOC) elicited LVAD suction (left ventricular pressure was from -10 to -20 mm Hg) within 5-10 heartbeats. During suction, aortic pressure dropped to 50% and LVAD flow decreased significantly. After releasing the occlusion (20 s), the collapsed state persisted for another 20 s. A similar trend was obtained by simulating PAOC in the computer model. Additional simulations showed that pulmonary vascular resistance (PVR), volume status, and right ventricular (RV) contractility are exponentially related to the persistence of collapse after a suction event. Even modest increases in predisposing factors (elevated PVR, RV dysfunction, hypovolemia) caused sustained hemodynamic collapse lasting in excess of 15 min. Both in selected animals and the computer model, comparable suction-induced collapse was obtained by increasing LVAD speed by about 33%. Attempted compensation by simply decreasing speed was not effective, but temporarily shutting down the LVAD caused rapid reversal of collapse. In conclusion, rotary LVAD suction causes unfavorable conditions for effective unloading. The use of pump interventions appears a promising tool to detect suction and to avoid the associated hemodynamic depression.
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ABSTRACT: PURPOSE OF REVIEW: To summarize the available evidence concerning the occurrence and treatment of ventricular arrhythmias in patients supported with long-term ventricular assist devices (VADs). RECENT FINDINGS: Approximately one-third of left ventricular assist device-supported patients experience significant ventricular arrhythmias, with higher rates in certain patient subsets. Ventricular arrhythmias are associated with both increased mortality and morbidity in VAD-supported patients. Mechanical factors, myocardial fibrosis and alterations in cardiac myocyte physiology because of myocardial unloading are contributors to ventricular arrhythmias in this population. In the absence of definitive trials, current evidence supports implanted cardioverter defibrillators (ICDs) in long-term VAD patients to mitigate the risks associated with ventricular arrhythmias. Though antiarrhythmic therapies have limited efficacy, amelioration of inflow cannula contact with the endocardium and suction events or ablation of specific anatomic origins of ventricular arrhythmias, when present, are also efficacious in VAD-supported hearts. SUMMARY: As the application of long-term VAD support continues to grow, it will be increasingly important to clarify and target the mechanisms contributing to ventricular arrhythmias in this population. Prospective trials assessing the benefits of de-novo ICD placement, ablative strategies and other prophylactic and therapeutic interventions will be increasingly important to further improve the survival and quality of life among VAD-supported patients.Current opinion in cardiology 04/2013; · 2.66 Impact Factor
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ABSTRACT: OBJECTIVE: Studies have shown that pump output by continuous-flow left ventricular assist devices (LVADs) increases with graded exercise testing. However, data on pump behavior during activities of daily living and sleep, where cardiac output requirements vary markedly, are lacking. We sought to determine pump parameters and activity levels in stable patients receiving outpatient LVAD therapy. METHODS AND RESULTS: Eleven outpatients (mean age 51 ± 14 years, 9 male) with centrifugal continuous-flow LVADs underwent monitoring of LVAD flow, heart rate (HR), energy expenditure, and physical activity over 1 week in an outpatient setting. Physical activity was recorded with the use of a combined pedometer, accelerometer, and calorimeter Sensewear armband. Pump, HR, and physical activity parameters were time matched for correlation analysis. Outpatients had an average pump flow of 5.67 ± 1.27 L/min and engaged predominately in low levels of physical activity (mean daily step count 3,249/day). Across the entire cohort, pump flow exhibited strong univariate relationships with patients' energy expenditure (r = 0.73), step count (r = 0.69), HR (r = 0.73), sleep (r = -0.89), and skin temperature (r = -0.85; P < .0001 for all). Multivariate analysis suggested that pump output was predominantly affected by recumbent position, energy expenditure and skin temperature (r2 = 0.84; P < .0001). Pump flow and power consumption were significantly lower during sleep than during wake periods (5.48 ± 1.31 L/min vs 5.80 ± 1.26 L/min; P < .001). CONCLUSIONS: Pump output from continuous-flow LVADs is adaptive to changes in activities of daily living. Circadian variation in pump flow is mostly explained by recumbency and activity levels. Despite adequate pump flow, many LVAD patients continue to live sedentary lifestyles.Journal of cardiac failure 03/2013; 19(3):169-175. · 3.25 Impact Factor
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ABSTRACT: In recent times, the problem of noninvasive suction detection for implantable rotary blood pumps has attracted substantial research interest. Here, we compare the performance of various suction indices for different types of suction and non-suction events based on pump speed irregularity. A total of 171 different indices that consist of previously proposed as well as newly introduced suction indices are tested using regularized logistic regression. These indices can be classified as amplitude based (derived from the mean, maximum, and minimum values of a cycle), duration based (derived from the duration of a cycle), gradient based (derived from the first order as well as higher order differences) and frequency based (derived from the power spectral density). The non-suction event data consists of ventricular ejection with or without arrhythmia and intermittent and continuous non-opening of the aortic valve. The suction event data consists of partial ventricular collapse that occurs intermittently as well as continuously with or without arrhythmia. In addition, we also attempted to minimize the usage of multiple indices by applying the sequential forward floating selection method to find which combination of indices gives the best performance. In general, the amplitude-based and gradient-based indices performed quite well while the duration-based and frequency-based indices performed poorly. By having only two indices ([i] the maximum gradient change in positive slope; and [ii] the standard deviation of the maximum value in a cycle), we were able to achieve a sensitivity of 98.9% and a specificity of 99.7%.Artificial Organs 05/2013; · 1.96 Impact Factor