Responses to changes in filling and contractility of indices of human left ventricular mechanical performance

Aortic acceleration as a noninvasive index of left ventricular contractility in the mouse

The maximum value of the first derivative of the invasively measured left ventricular (LV) pressure (+ dP/dtmax or P') is often used to quantify LV contractility, which in mice is limited to a single terminal study. Thus, determination of P' in mouse longitudinal/serial studies requires a group of mice at each desired time point resulting in "pseudo" serial measurements. Alternatively, a noninvasive surrogate for P' will allow for repeated measurements on the same group of mice, thereby minimizing physiological variability and requiring fewer animals. In this study we evaluated aortic acceleration and other parameters of aortic flow velocity as noninvasive indices of LV contractility in mice. We simultaneously measured LV pressure invasively with an intravascular pressure catheter and aortic flow velocity noninvasively with a pulsed Doppler probe in mice, at baseline and after the administration of the positive inotrope, dobutamine. Regression analysis of P' versus peak aortic velocity (vp), peak velocity squared/rise time (vp2/T), peak (+ dvp/dt or v'p) and mean (+ dvm/dt or v'm) aortic acceleration showed a high degree of association (P' versus: vp, r2 = 0.77; vp2/T, r2 = 0.86; v'p, r2 = 0.80; and v'm, r2 = 0.89). The results suggest that mean or peak aortic acceleration or the other parameters may be used as a noninvasive index of LV contractility.

The Effect of Lower Body Positive Pressure on Left Ventricular Ejection Duration in Patients With Heart Failure

Lower body positive pressure (LBPP) treadmill activity might benefit patients with heart failure (HF). To determine the short-term effects of LBPP on left ventricular (LV) function in HF patients, LV ejection duration (ED), a measure of systolic function was prospectively assessed in 30 men with stable HF with LV ejection fraction ≤ 40% and 50 healthy men (N). Baseline measurements (100% body weight), including blood pressure (BP), heart rate (HR) and LVED, obtained via radial artery applanation tonometry, were recorded after 2 minutes of standing on weight support treadmill and after LBPP achieving reductions of 25%, 50%, and 75% of body weight in random sequence. Baseline, HR, and LVED (251 ± 5 vs 264 ± 4 ms; P = .035) were lower in the HF group. The LBPP lowered HR more (14% vs 6%, P = .009) and increased LVED more (15% ± 7% vs 10% ± 6%; P = .004) in N versus HF. Neither group had changes (Δ) in BP. On generalized linear regression, the 2 groups showed different responses (P < .001). Multivariate analysis showed %ΔHR (P < .001) and HF (P = .026) were predictive of ΔED (r² = 0.44; P < .001). In conclusion, progressive LBPP increases LVED in a step-wise manner in N and HF patients independent of HR lowering. The ΔLVED is less marked in patients with HF.

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

Whatever Happened to Measuring Ventricular Contractility in Heart Failure?

Attempts have been made to assess and measure ventricular contractility in patients and whether it can be used to identify heart failure. Due to the assumption that if the contractility of all the muscle fibres in a heart were lower, could it be called heart failure? Early attempts involved the assumption of a model of muscle that had a contractile unit in series with an elastic element, but this was found to be incorrect. Further attempts applied the series elastic model but this model also proved challenging. However, one method has assessed changes in contractility in a given patient, in response to an intervention, but could not compare contractility in a patient with heart failure with a normal person. End-systolic pressure-volume (ESPV) is regarded as a more correct index of contractility and this method was used to confirm changes in contractility from beat to beat during AF, showing results that end-systolic volume varied and indicating a shift of ESPV from beat to beat. This review will discuss the difficulty in measurement, the complicated nature of myocardial fibre orientation and hypertrophy, and whether myocardial contractility failure precipitates increased global heart failure.

Heart failure: when form fails to follow function

Cardiac performance is normally determined by architectural, cellular, and molecular structures that determine the heart's form, and by physiological and biochemical mechanisms that regulate the function of these structures. Impaired adaptation of form to function in failing hearts contributes to two syndromes initially called systolic heart failure (SHF) and diastolic heart failure (DHF). In SHF, characterized by high end-diastolic volume (EDV), the left ventricle (LV) cannot eject a normal stroke volume (SV); in DHF, with normal or low EDV, the LV cannot accept a normal venous return. These syndromes are now generally defined in terms of ejection fraction (EF): SHF became 'heart failure with reduced ejection fraction' (HFrEF) while DHF became 'heart failure with normal or preserved ejection fraction' (HFnEF or HFpEF). However, EF is a chimeric index because it is the ratio between SV--which measures function, and EDV--which measures form. In SHF the LV dilates when sarcomere addition in series increases cardiac myocyte length, whereas sarcomere addition in parallel can cause concentric hypertrophy in DHF by increasing myocyte thickness. Although dilatation in SHF allows the LV to accept a greater venous return, it increases the energy cost of ejection and initiates a vicious cycle that contributes to progressive dilatation. In contrast, concentric hypertrophy in DHF facilitates ejection but impairs filling and can cause heart muscle to deteriorate. Differences in the molecular signals that initiate dilatation and concentric hypertrophy can explain why many drugs that improve prognosis in SHF have little if any benefit in DHF.

The NO stimulator, Catestatin, improves the Frank-Starling response in normotensive and hypertensive rat hearts

The myocardial response to mechanical stretch (Frank-Starling law) is an important physiological cardiac determinant. Modulated by many endogenous substances, it is impaired in the presence of cardiovascular pathologies and during senescence. Catestatin (CST:hCgA352-372), a 21-amino-acid derivate of Chromogranin A (CgA), displays hypotensive/vasodilatory properties and counteracts excessive systemic and/or intra-cardiac excitatory stimuli (e.g., catecholamines and endothelin-1). CST, produced also by the myocardium, affects the heart by modulating inotropy, lusitropy and the coronary tone through a Nitric Oxide (NO)-dependent mechanism. This study evaluated the putative influence elicited by CST on the Frank-Starling response of normotensive Wistar-Kyoto (WKY) and hypertensive (SHR) hearts by using isolated and Langendorff perfused cardiac preparations. Functional changes were evaluated on aged (18-month-old) WKY rats and SHR which mimic human chronic heart failure (HF). Comparison to WKY rats, SHR showed a reduced Frank-Starling response. In both rat strains, CST administration improved myocardial mechanical response to increased end-diastolic pressures. This effect was mediated by EE/IP3K/NOS/NO/cGMP/PKG, as revealed by specific inhibitors. CST-dependent positive Frank-Starling response is paralleled by an increment in protein S-Nitrosylation. Our data suggested CST as a NO-dependent physiological modulator of the stretch-induced intrinsic regulation of the heart. This may be of particular importance in the aged hypertrophic heart, whose function is impaired because of a reduced systolic performance accompanied by delayed relaxation and increased diastolic stiffness.

Effect of myocardial contractility on hemodynamic end points under concomitant microvascular disease in a porcine model

In this study, coronary diagnostic parameters, pressure drop coefficient (CDP: ratio of trans-stenotic pressure drop to distal dynamic pressure), and lesion flow coefficient (LFC: ratio of % area stenosis (%AS) to the CDP at throat region), were evaluated to distinguish levels of %AS under varying contractility conditions, in the presence of microvascular disease (MVD). In 10 pigs, %AS and MVD were created using angioplasty balloons and 90-μm microspheres, respectively. Simultaneous measurements of pressure drop, left ventricular pressure (p), and velocity were obtained. Contractility was calculated as (dp/dt)max, categorized into low contractility <900 mmHg/s and high contractility >900 mmHg/s, and in each group, compared between %AS <50 and >50 using analysis of variance. In the presence of MVD, between the %AS <50 and >50 groups, values of CDP (71 ± 1.4 and 121 ± 1.3) and LFC (0.10 ± 0.04 and 0.19 ± 0.04) were significantly different (P < 0.05), under low-contractility conditions. A similar %AS trend was observed under high-contractility conditions (CDP: 18 ± 1.4 and 91 ± 1.4; LFC: 0.08 ± 0.04 and 0.25 ± 0.04). Under MVD conditions, similar to fractional flow reserve, CDP and LFC were not influenced by contractility.

Arterial dP/dtmax accurately reflects left ventricular contractility during shock when adequate vascular filling is achieved

Background

Peak first derivative of femoral artery pressure (arterial dP/dt_max) derived from fluid-filled catheter remains questionable to assess left ventricular (LV) contractility during shock. The aim of this study was to test if arterial dP/dt_max is reliable for assessing LV contractility during various hemodynamic conditions such as endotoxin-induced shock and catecholamine infusion.

Methods

Ventricular pressure-volume data obtained with a conductance catheter and invasive arterial pressure obtained with a fluid-filled catheter were continuously recorded in 6 anaesthetized and mechanically ventilated pigs. After a stabilization period, endotoxin was infused to induce shock. Catecholamines were transiently administrated during shock. Arterial dP/dt_max was compared to end-systolic elastance (Ees), the gold standard method for assessing LV contractility.

Results

Endotoxin-induced shock and catecholamine infusion lead to significant variations in LV contractility. Overall, significant correlation (r = 0.51; p < 0.001) but low agreement between the two methods were observed. However, a far better correlation with a good agreement were observed when positive-pressure ventilation induced an arterial pulse pressure variation (PPV) ≤ 11% (r = 0.77; p < 0.001).

Conclusion

While arterial dP/dt_max and Ees were significantly correlated during various hemodynamic conditions, arterial dP/dt_max was more accurate for assessing LV contractility when adequate vascular filling, defined as PPV ≤ 11%, was achieved.

Mechanical restitution curves: a possible load independent assessment of contractile function

OBJECTIVE

The time constant of mechanical restitution (T((MRC))), proposed to reflect changes in calcium release and uptake, has been shown to increase in left ventricular (LV) failure, and might have a potential as an index of contractile function. However, in vivo studies of the effect on T((MRC)) of changing loading conditions in the normal and failing heart have not been reported. Consequently, in this study, we tested the hypothesis that the increase in T((MRC)) in vivo is independent of preload and afterload.

METHODS

Left ventricular pressure-volume loops were assessed at baseline in eight open chest pigs using the combined pressure-volume conductance catheter technique during right atrial pacing at 120b/min. Mechanical restitution curves (MRC) were constructed during four different loading conditions in all eight animals: uninfluenced load, reduced preload (balloon catheter in v. cava inferior), increased afterload (balloon catheter in descending aorta), and increased preload combined with reduced afterload (aortocaval shunting). Acute LV failure was then induced by microembolization through the left main coronary artery, and the experimental protocol was repeated. Contractile response was defined as the maximal first derivative of pressure (dP/dt(max)), and T((MRC)) was calculated using a least square approximation algorithm.

RESULTS

Hemodynamic data 30min after microembolization showed decreased mean arterial pressure (98+/-14-67+/-10mmHg, (mean+/-SD) P<0.0001) and dP/dt(max) (1482+/-193-1001+/-125mmHg/s, P=0.001). Stroke volume decreased from 30+/-5 to 20+/-5ml (P<0.0001) compared to baseline, and preload recruitable stroke work decreased from 52+/-7 to 31+/-10mmHg (P=0.002). T((MRC)) increased in all eight animals after induction of LV failure at all loading conditions. There was no difference between the different loading conditions at baseline, nor at LV heart failure, but T((MRC)) increased significantly after the induction of heart failure (ANOVA, two ways).

CONCLUSIONS

We have shown that the left ventricular T((MRC)) increases after developed heart failure. The increase in T((MRC)) was independent on loading conditions and thus have a potential for a contractility index.

Interval-force relation is unaffected by the presence of cardiomyopathy or coronary artery disease in patients with atrial fibrillation

BACKGROUND

We tested the hypothesis that cycle length-dependent cardiac contractility in atrial fibrillation is primarily governed by the negative interval-force relation in patients with normal and depressed systolic function.

METHODS AND RESULTS

We performed two-dimensional guided M-mode echocardiography in 41 patients (mean age, 69 +/- 4 years; range, 48 to 92 years; 19 men, 11 women). Twelve patients had objective evidence of left ventricular systolic dysfunction (CMP; mean ejection fraction, 37% +/- 7%) in the absence of coronary artery disease (CAD), 13 patients had documented CAD (mean ejection fraction, 43% +/- 6%), and 16 patients had normal resting left ventricular systolic function (mean ejection fraction, 58% +/- 7%). Simultaneous beat-to-beat blood pressure, end-systolic and end-diastolic dimension, circumferential velocity of fiber shortening (Vcf), and end-systolic wall stress (ESWS) were calculated for all patients. All three groups showed a significant linear relation between beat-to-beat Vcf and Vcf corrected for afterload (represented as the Vcf/ESWS ratio) and preceding cycle length. There was, however, no significant difference in the relation between either of these variables and cycle length among the three groups. There was also no difference in the rate of change in either Vcf or Vcf corrected for afterload (Vcf/ESWS ratio) from beat-to-beat among the three groups. Control patients with normal systolic function showed greater Vcf at any given cycle length compared with patients with CMP or CAD.

CONCLUSION

Our data show that, for each beat in atrial fibrillation, Vcf and Vcf/ESWS ratio are decreased after shorter cycle lengths and increased after long cycles, but there is no significant attenuation of this effect in patients with systolic dysfunction with or without coronary disease compared with controls. Thus, the negative interval-force relation, the predominant determinant of beat-to-beat variation in contractility in atrial fibrillation, is preserved in patients with CAD or reduced left ventricular systolic function.

Basal release of nitric oxide augments the Frank-Starling response in the isolated heart

BACKGROUND

The Frank-Starling response contributes to the regulation of cardiac output. The major underlying subcellular mechanism is a length-dependent change in myofilament responsiveness to Ca2+. Recent studies indicate that nitric oxide decreases myofilament responsiveness to Ca2+ and modulates myocardial relaxation and left ventricular (LV) diastolic function. We therefore investigated the interaction between nitric oxide and the Frank-Starling response.

METHODS AND RESULTS

Isolated ejecting guinea pig hearts (constant afterload and heart rate) were studied before and after interventions. Elevation of filling pressure from 10 to 20 cm H2O increased cardiac output, LV end-diastolic pressure (LVEDP), and peak LV pressure (LVPmax). In the presence of N(G)-monomethyl-L-arginine (L-NMMA, 10 micromol/L; n=10) or free hemoglobin (1 micromol/L; n=8), preload-induced increases in cardiac output were significantly attenuated but baseline cardiac output was unaffected. The effects of L-NMMA were inhibited in the presence of excess L-arginine (100 micromol/L; n=6). These changes were not attributable to alterations in coronary flow. Prostaglandin F2alpha (0.01 micromol/L; n=6), which reduced coronary flow, failed to alter the cardiac output response to preload elevation. The exogenous nitric oxide donor sodium nitroprusside (1 micromol/L; n=6) reduced cardiac output at the lowest preload but not at higher preloads. LVEDP was elevated after L-NMMA and hemoglobin but reduced after sodium nitroprusside.

CONCLUSIONS

Basal intracardiac production of nitric oxide significantly augments preload-induced rises in cardiac output in the isolated ejecting guinea pig heart. The mechanism appears to be unrelated to changes in coronary flow and may involve direct effects of nitric oxide on myocardial diastolic and/or systolic function.

Cardiac stimulus intensity and heartbeat detection: effects of tilt-induced changes in stroke volume

The effects of variations in stroke volume on the intensity of cardiac stimuli was examined in a series of three experiments that employed classical psychophysical methods to assess heartbeat detection. Stroke volume was manipulated by passive body tilt and recorded using impedance cardiography while subjects performed heartbeat detection tasks. The postural manipulation generated little or no change in contractility or momentum but did produce substantial changes in stroke volume. However, this potential source of variation in cardiac stimulus magnitude did not influence either the precision of heartbeat detection or the temporal location of heartbeat sensations. It is concluded that the intensity dimension of the heartbeat stimulus is not determined by stroke volume.

Analysis of left ventricular contractile behaviour during atrial fibrillation

OBJECTIVES

The purpose of this study was to explore the physiology underlying the beat-to-beat variations of ventricular function during atrial fibrillation (AF).

METHODS

Left ventricular pressure, and its first derivative (LVdP/dtmax, an index of contractility, and aortic blood velocity (and its integral AVI, an ejection index), were recorded using cathetermounted transducers in 15 patients with AF during cardiac catheterisation. Transfer function modelling was used to examine the influence of preceding intervals on LVdP/dtmax, and of LVdP/dtmax on AVI. The technique also allowed simulation of the behaviour of LVdP/dtmax in response to specific manipulations of interval.

RESULTS

The variations in LVdP/dtmax recorded from the AF patients were shown to be dependent on up to six preceding intervals; a maximum of 91% of the variation was explicable in this way. The influences of mechanical restitution (MR, the relationship between preceding interval and contractility), postextrasystolic potentiation (PESP, the inverse relationship between pre-preceding interval and contractility) and the decay of that potentiation were all demonstrated. These influences collectively appeared to be powerful determinants of AVI. Simulations of LVdP/dtmax, following single interval perturbations, were entirely consistent with these interval force effects.

CONCLUSIONS

The cardiac interval force relationship in man is an important determinant of the beat-to-beat variations of contractile and ejection function during AF: the beat-to-beat variations in contractile (or inotropic) function are independent of changes in ventricular filling or fibre-length.

Dynamic cardiomyoplasty in chronic left ventricular failure: an experimental model

Dynamic cardiomyoplasty continues to attract interest as a therapeutic option in the management of heart failure. In a large animal model of ischemic heart failure, we have compared dynamic cardiomyoplasty with both adynamic cardiomyoplasty and a control group. Heart failure was induced by coronary artery ligation in sheep, and under the same anesthetic dynamic cardiomyoplasty (n = 5), adynamic cardiomyoplasty (n = 4), or no further procedure was performed (n = 5). After recovery the animals were housed for a further 3 months. The dynamic cardiomyoplasty underwent a recognized muscle transformation protocol during this period. At terminal studies, the animals were hemodynamically assessed, both under baseline conditions and after colloid volume loading. The data at baseline were compared with unpaired t tests, and the function curves created by volume loading were compared by analysis of variance. Although the changes at baseline were small, there were highly significant improvements in the function curves in the dynamic cardiomyoplasty group when the stimulators were turned on compared with stimulators off (p = 0.005) for cardiac output; p = 0.035 for left ventricular end-diastolic pressure; p = 0.002 for pulmonary artery capillary wedge pressure; p = 0.004 for stroke volume; and p = 0.003 for cardiac power). There were also significant improvements in indices of cardiac performance when the dynamic cardiomyoplasty group was compared with both the control and adynamic cardiomyoplasty groups. We conclude that there is experimental evidence that cardiomyoplasty augments cardiac function in a model of chronic left ventricular failure.

Postextrasystolic potentiation and its contribution to the beat-to-beat variation of the pulse during atrial fibrillation

BACKGROUND

Beat-to-beat variations in the pulse during atrial fibrillation (AF) have conventionally been attributed to time-dependent changes in filling. We have explored the possibility that they are dependent on the intrinsic myocardial interval force relation.

METHODS AND RESULTS

Left ventricular (LV) contractility (maximum rate of rise of pressure, LV dP/dtmax) and ascending aortic blood velocity were measured during cardiac catheterization in 15 patients with AF. Beats preceded by an interval of less than 500 msec were excluded from analysis to reduce the confounding influence of incomplete mechanical restitution. The LV dP/dtmax was then related to the prepreceding interval. An inverse relation consistent with postextrasystolic potentiation was obtained in all 15 patients (Spearman's rank correlations, -0.56 to -0.86; p less than or equal to 0.0001). This relation was confirmed in three patients during pacing that overrode the AF and introduced single-interval variations into steady-state pacing. The ECG sequences from six of the AF patients were used to drive isometrically contracting guinea pig papillary muscle and human right ventricular tissue (n = 7); the same inverse relation was demonstrated. On a beat-by-beat basis, the maximum rate of rise of force in the isolated muscle correlated well with LV dP/dtmax in the patients (r = 0.50-0.86, p less than or equal to 0.0001). The relation of the integral of aortic velocity (AVI, proportional to stroke volume) to prepreceding interval was also inverse, whereas important correlations were demonstrated between LV dP/dtmax and AVI (Spearman's rank correlations, 0.27-0.95; p less than or equal to 0.0001).

CONCLUSIONS

This study demonstrates that postextrasystolic potentiation contributes to the characteristic beat-to-beat variation of the pulse in AF.