Simulation of dilated heart failure with continuous flow circulatory support

Lumped parameter models have been employed for decades to simulate important hemodynamic couplings between a left ventricular assist device (LVAD) and the native circulation. However, these studies seldom consider the pathological descending limb of the Frank-Starling response of the overloaded ventricle. This study introduces a dilated heart failure model featuring a unimodal end systolic pressure-volume relationship (ESPVR) to address this critical shortcoming. The resulting hemodynamic response to mechanical circulatory support are illustrated through numerical simulations of a rotodynamic, continuous flow ventricular assist device (cfVAD) coupled to systemic and pulmonary circulations with baroreflex control. The model further incorporated septal interaction to capture the influence of left ventricular (LV) unloading on right ventricular function. Four heart failure conditions were simulated (LV and bi-ventricular failure with/ without pulmonary hypertension) in addition to normal baseline. Several metrics of LV function, including cardiac output and stroke work, exhibited a unimodal response whereby initial unloading improved function, and further unloading depleted preload reserve thereby reducing ventricular output. The concept of extremal loading was introduced to reflect the loading condition in which the intrinsic LV stroke work is maximized. Simulation of bi-ventricular failure with pulmonary hypertension revealed inadequacy of LV support alone. These simulations motivate the implementation of an extremum tracking feedback controller to potentially optimize ventricular recovery. © 2014 Wang et al

Multimodality imaging: Bird’s eye view from The European Society of Cardiology Congress 2015 London, August 29-September 2, 2015

Cardiolog

Echocardiographic prediction of outcome after cardiac resynchronization therapy: conventional methods and recent developments

Echocardiography plays an important role in patient assessment before cardiac resynchronization therapy (CRT) and can monitor many of its mechanical effects in heart failure patients. Encouraged by the highly variable individual response observed in the major CRT trials, echocardiography-based measurements of mechanical dyssynchrony have been extensively investigated with the aim of improving response prediction and CRT delivery. Despite recent setbacks, these techniques have continued to develop in order to overcome some of their initial flaws and limitations. This review discusses the concepts and rationale of the available echocardiographic techniques, highlighting newer quantification methods and discussing some of the unsolved issues that need to be addressed

Biochemical indicators of LV function during mechanical ventilatory support in critically ill adults

Introduction: The role of cardiac function is emerging as a poorly explored but potentially significant factor in ventilator dependence. Measuring LV function in the ICU is difficult. Therefore, surrogate biochemical markers were evaluated to determine if they correlate with standard measures and whether these surrogates can be used to predict duration of MVS especially in the absence of PA catheter. Methods: Blood samples for plasma norepmephnne levels (PNL) and atrial natnureuc peptade (ANP) were collected while hemodynamic parameters were observed using standard methods on the day following the initiation of mechanical ventilatory support. Results: PNL was significantly correlated with systemic vascular resistance (r - .57, p 900 pg/L did so. Conclusions: Biochemical indicators such as PNL and ANP may be useful in categorizing hemodynamic status in mechanically ventilated adults when a PA catheter IB not in place

Noninvasrve estimation of paop during mechanical ventilatory support in critically ill adults

Introduction: At a time when there is renewed controversy about the use of flow-directed balloon-tipped pulmonary artery catheters and increasing hesitation in their use, the ability to estimate the PAOP nomnvasively is welcome. Methods: Twenty mechanically ventilated, critically ill adults with flowdirected, balloon-tipped pulmonary artery catheters were recruited to evaluate a nomnvasive device (VenCor, CVP Diagnostics, Laguna Beach CA) estimates PAOP based on the pulse pressure response to Valsalva as measured by finger plethysmography. Results: Twenty subjects (8 men, 12 women) ranging in age from 49 to 89 years (median- 61 ), had first day APACHE III acute physiology scores that ranged from 24 to 92 (median= 52 ). The PAOP measures ranged from 9 to 24 mm Hg. There is no significant difference (paired t - -0.91, df = 19, p>.05) between the two measures and they are significantly correlated (r=.90, p<.05) with each other. Conclusions: The VeriCor provides the means to estimate PAOP noninvasively

Impact of left ventricular function on duration of mechanical ventilatory support

Introduction: The primary focus on predicting ability to wean from mechanical ventilatory support (MVS) has been on ventilatory capacity, lung pathology, diaphragmatic strength and nutrition. While this focus has not been incorrect, results have been disappointing. Clinicians continue to be challenged by patients requiring prolonged MVS. Left ventricular (LV) function is emerging as a poorly explored but potentially significant factor impacting ventilator dependence. Methods: A prospective, comparative design was used to follow 53 critically ill adults requiring MVS until completely weaned up to 4 weeks following initiation of MVS. Subjects were male (n=27, 51%), white (n=50, 94%) and aged 21 to 89 years (mean=63.9, SD=12.9). LV function was measured weekly using surrogate indicators of preload [pulmonary artery occlusion pressure (PAOP) and atrial natriuretic peptide levels (ANP)] and afterload (plasma norepinephrine). Cox proportional hazards regression was used to develop predictive models of MVS duration, treating the longitudinally measured indicators of LV function as time-dependent covariates. Hypotheses were tested using likelihood-ratio statistics. Results: Most subjects (n=40, 75.5%) exhibited compromised LV function based on either PAOP (mean= 16.6 mmHg, SD=5.2) or plasma norepinephrine (median=957pg/mL, SQR=562) levels at MVS initiation. Within 4 weeks, 69.8% (n=37) had weaned completely from MVS. Examination of the surrogate indicators of LV function revealed that subjects having a relative decrease in plasma norepinephrine levels since MVS initiation [χ2(1)=2.73, p<.05] and having lower absolute plasma norepinephrine levels [χ2(1)=3.65, p<.05] were more likely to wean; however, neither absolute or relative change since MVS initiation in either PAOP or ANP predicted MVS duration. Conclusions: These findings suggest LV function may play a role in ventilator dependence and that decreasing afterload may shorten duration of MVS

Elevated Troponin-T levels in patients requiring prolonged mechanical ventdlatory support (MVS)

Introduction: Identifying non-pulmonary determinants is essential in liberating those ventilator-dependent patients, who despite demonstrating good pulmonary mechanics, are unable to resume unassisted, spontaneous ventilation. Prior research suggests heart function is one of these non-pulmonary determinants. Methods: As part of a larger study, blood was obtained from 19 subjects (10 men, 9 women)on Day 1 of MVS. They ranged in age from 21 to 89 years (mean=62.5). There were 11 medical and 8 surgical patients. Myocardial injury was evaluated using Troponin-T level (TnT). Results: Of 19 subjects, 6 had elevated TnT. Three of those with elevated TnT (>0.10 μg/L) had CK-MB and ECG evidence of MI, 3 did not. There was a significant difference in the duration of MVS between those who had elevated TnT (mean-18 days, median=20 days) and those who did not (mean=4 days, median = 3 days) and survival distribution functions as demonstrated by Kaplan Meier survival function plot [Generalized Savage log-rank test=6.55, df=1, p<.05]. Conclusions: Clinically recognized as well as unrecognized myocardial injury (ischemia or infarction) is related to prolonged MVS

Association of intraventricular mechanical dyssynchrony with response to cardiac resynchronization therapy in heart failure patients with a narrow QRS complex

Aims Current criteria for cardiac resynchronization therapy (CRT) are restricted to patients with a wide QRS complex (&gt;120 ms). Overall, only 30 of heart failure patients demonstrate a wide QRS complex, leaving the majority of heart failure patients without this treatment option. However, patients with a narrow QRS complex exhibit left ventricular (LV) mechanical dyssynchrony, as assessed with echocardiography. To further elucidate the possible beneficial effect of CRT in heart failure patients with a narrow QRS complex, this two-centre, non-randomized observational study focused on different echocardiographic parameters of LV mechanical dyssynchrony reflecting atrioventricular, interventricular and intraventricular dyssynchrony, and the response to CRT in these patients. Methods and results A total of 123 consecutive heart failure patients with a narrow QRS complex (&lt;120 ms) undergoing CRT was included at two centres. Several widely accepted measures of mechanical dyssynchrony were evaluated: LV filling ratio (LVFT/RR), LV pre-ejection time (LPEI), interventricular mechanical dyssynchrony (IVMD), opposing wall delay (OWD), and anteroseptal posterior wall delay with speckle tracking (ASPWD). Response to CRT was defined as a reduction ≥15 in left ventricular end-systolic volume at 6 months follow-up. Measures of dyssynchrony can frequently be observed in patients with a narrow QRS complex. Nonetheless, for LVFT/RR, LPEI, and IVMD, presence of predefined significant dyssynchrony is &lt;20. Significant intraventricular dyssynchrony is more widely observed in these patients. With receiver operator characteristic curve analyses, both OWD and ASPWD demonstrated usefulness in predicting response to CRT in narrow QRS patients with a cut-off value of 75 and 107 ms, respectively. Conclusion Mechanical dyssynchrony can be widely observed in heart failure patients with a narrow QRS complex. In particular, intraventricular measures of mechanical dyssynchrony may be useful in predicting LV reverse remodelling at 6 months follow-up in heart failure patients with a narrow QRS complex, but with more stringent cut-off values than currently used in 'wide' QRS patients. © 2010 The Author