Alterations of endothelium-dependent and -independent regulation of coronary blood flow during heart failure

Coronary blood flow in heart failure: cause, consequence and bystander

Heart failure is a clinical syndrome where cardiac output is not sufficient to sustain adequate perfusion and normal bodily functions, initially during exercise and in more severe forms also at rest. The two most frequent forms are heart failure of ischemic origin and of non-ischemic origin. In heart failure of ischemic origin, reduced coronary blood flow is causal to cardiac contractile dysfunction, and this is true for stunned and hibernating myocardium, coronary microembolization, myocardial infarction and post-infarct remodeling, possibly also for the takotsubo syndrome. The most frequent form of non-ischemic heart failure is dilated cardiomyopathy, caused by genetic mutations, myocarditis, toxic agents or sustained tachyarrhythmias, where alterations in coronary blood flow result from and contribute to cardiac contractile dysfunction. Hypertrophic cardiomyopathy is caused by genetic mutations but can also result from increased pressure and volume overload (hypertension, valve disease). Heart failure with preserved ejection fraction is characterized by pronounced coronary microvascular dysfunction, the causal contribution of which is however not clear. The present review characterizes the alterations of coronary blood flow which are causes or consequences of heart failure in its different manifestations. Apart from any potentially accompanying coronary atherosclerosis, all heart failure entities share common features of impaired coronary blood flow, but to a different extent: enhanced extravascular compression, impaired nitric oxide-mediated, endothelium-dependent vasodilation and enhanced vasoconstriction to mediators of neurohumoral activation. Impaired coronary blood flow contributes to the progression of heart failure and is thus a valid target for established and novel treatment regimens.

Remodeling of left circumflex coronary arterial tree in pacing-induced heart failure

Congestive heart failure (CHF) is a very serious heart disease that manifests an imbalance between left ventricle supply and demand. Although the mechanical demand of the failing heart has been well characterized, the systematic remodeling of the entire coronary arterial tree that constitutes the supply of the myocardium is lacking. We hypothesize that the well-known increase in ventricle wall stress during CHF causes coronary vascular rarefaction to increase the vascular flow resistance, which in turn compromises the perfusion of the heart. Morphometric (diameters, length, and numbers) data of the swine left circumflex (LCx) arterial tree were measured in both CHF (n = 6) and control (n = 6) groups, from which a computer reconstruction of the entire LCx tree was implemented down to the capillary level to enable a hemodynamic analysis of coronary circulation. The vascular flow resistance was increased by ∼75% due to a significant decrease of vessel numbers (∼45%) and diameters in the first capillary segments (∼10%) of the LCx arterial tree after 3-4 wk of pacing. The structural remodeling significantly changed the wall shear stress in vessel segments of the entire LCx arterial tree of CHF animals. This study enhances our knowledge of coronary arterial tree remodeling in heart failure, which provides a deeper understanding of the deterioration of supply-demand relation in left ventricle.

Insulin resistance and exercise tolerance in heart failure patients: linkage to coronary flow reserve and peripheral vascular function

Background

Insulin resistance has been linked to exercise intolerance in heart failure patients. The aim of this study was to assess the potential role of coronary flow reserve (CFR), endothelial function and arterial stiffness in explaining this linkage.

Methods

39 patients with LVEF < 35% (median LV ejection fraction (LVEF) 31 (interquartile range (IQ) 26–34), 23/39 of ischemic origin) underwent echocardiography with measurement of CFR. Peak coronary flow velocity (CFV) was measured in the LAD and coronary flow reserve was calculated as the ratio between CFV at rest and during a 2 minutes adenosine infusion. All patients performed a maximal symptom limited exercise test with measurement of peak oxygen uptake (VO₂peak), digital measurement of endothelial function and arterial stiffness (augmentation index), dual X-ray absorptiometry scan (DEXA) for body composition and insulin sensitivity by a 2 hr hyperinsulinemic (40 mU/min/m²) isoglycemic clamp.

Results

Fat free mass adjusted insulin sensitivity was significantly correlated to VO₂peak (r = 0.43, p = 0.007). Median CFR was 1.77 (IQ 1.26-2.42) and was correlated to insulin sensitivity (r 0.43, p = 0.008). CFR (r = 0.48, p = 0.002), and arterial stiffness (r = −0.35, p = 0.04) were correlated to VO₂peak whereas endothelial function and LVEF were not (all p > 0.15). In multivariable linear regression adjusting for age, CFR remained independently associated with VO2peak (standardized coefficient (SC) 1.98, p = 0.05) whereas insulin sensitivity (SC 1.75, p = 0.09) and arterial stiffness (SC −1.17, p = 0.29) were no longer associated with VO2peak.

Conclusions

The study confirms that insulin resistance is associated with exercise intolerance in heart failure patients and suggests that this is partly through reduced CFR. This is the first study to our knowledge that shows an association between CFR and exercise capacity in heart failure patients and links the relationship between insulin resistance and exercise capacity to CFR.

Coronary flow reserve in idiopathic dilated cardiomyopathy: relation with left ventricular wall stress, natriuretic peptides, and endothelial dysfunction

Studies have demonstrated impaired coronary blood flow reserve (CBFR) in idiopathic dilated cardiomyopathy (IDCM). It was the aim of this study to examine the potential underlying mechanisms for CBFR reduction in patients with IDCM by Doppler ultrasound techniques. Forty-eight clinically stable patients with heart failure caused by IDCM (New York Heart Association classes 1-3) were evaluated by echocardiographic and Doppler techniques with the assessments of CBFR and brachial artery flow-mediated dilation (FMD). CBFR was estimated as the hyperemic (dipyridamole: 0.84 mg/kg in 10 minutes, intravenously) to resting coronary diastolic peak velocities ratio. N-terminal pro-brain natriuretic peptide (Nt-pro-BNP) plasma levels were measured at the time of the index echocardiogram. Left ventricular (LV) ejection fraction was 30% +/- 8%, and wall motion score index was 2.0 +/- 0.25. The best correlation with CBFR was found with LV wall thickness-to-cavity radius (r = 0.77, P < .0001). A strong correlation of log-transformed Nt-pro-BNP levels was observed with CBFR (r = -0.64; P < .0001). No significant correlation was documented between CBFR and FMD. The stepwise regression model showed that LV wall thickness-to-cavity radius was the strongest independent predictor of CBFR followed by New York Heart Association class and log-transformed Nt-pro-BNP leading to a cumulative R value of 0.82 (P < .0001). The results of the study indicate that by measuring variables related to LV end-diastolic wall stress, such as LV wall thickness-to-cavity radius and plasma Nt-proBNP, it is possible to have information about CBFR in patients with heart failure secondary to IDCM.

NO and PGI(2) in coronary endothelial dysfunction in transgenic mice with dilated cardiomyopathy

OBJECTIVE

The aim of the present work was to analyze coronary endothelial function in the transgenic mouse model of dilated cardiomyopathy (Tgalphaq*44 mice).

METHODS

Coronary vasodilatation, both NO-dependent (induced by bradykinin) and PGI(2)-dependent (induced by acetylcholine), was assessed in the isolated hearts of Tgalphaq*44 and FVB mice. Cardiac function was analyzed in vivo (MRI).

RESULTS

In Tgalphaq*44 mice at the age of 2-4 months cardiac function was preserved and there were no alterations in endothelial function. By contrast, in Tgalphaq*44 mice at the age of 14-16 months cardiac function was significantly impaired and NO, but not PGI(2)-dependent coronary function was altered. Interestingly, the basal level of PGI(2) in coronary circulation increased fourfold as compared to FVB mice. Cardiac O(2) (-) production increased 1.5-fold and 3-fold in Tgalphaq*44 vs. FVB mice at the age of 2-6 and 14-16 months, respectively, and was inhibited by apocynin. Interestingly, inhibition of NADPH oxidase or NOS-3 normalized augmented PGI(2) production in Tgalphaq*44 mice. There was also an increased expression of gp91phox in Tgalphaq*44 vs. FVB hearts, without evident alterations in the expression of COX-1, COX-2, NOS-3 and PGI(2)-synthase.

CONCLUSIONS

In the mouse model of dilated cardiomyopathy, endothelial dysfunction in coronary circulation is present in the late but not the early stage of heart failure pathology and is characterized by a decrease in NO bioavailability and a compensatory increase in PGI(2). Both the decrease in NO activity and the increase in PGI(2) activity may result from excessive O(2) (-) production by cardiac NADPH oxidase in Tgalphaq*44 hearts.

Vasoconstrictive Response in the Vascular Beds of the Non-Exercising Forearm During Leg Exercise in Patients With Mild Chronic Heart Failure

BACKGROUND

Reduced exercise capacity may be related to decreased redistribution of blood flow from the non-exercising tissues to the exercising skeletal muscle in patients with mild chronic heart failure (CHF).

METHODS AND RESULTS

In the present study 14 patients with mild CHF and 10 healthy subjects (N) underwent symptom-limited multistage-ergometer exercise, during which forearm vascular resistance (FVR), cardiac index (CI), systemic vascular resistance index (SVRI), and oxygen uptake (VO(2)) were measured non-invasively using the plethysmograph, impedance, and respiratory gas analysis methods, respectively. The VO(2) and CI at peak exercise were lower (p<0.01 each), and SVRI and FVR at both rest and peak exercise were higher in the CHF group than in N. However, both the percent increase in FVR and percent decrease in SVRI from the resting state to peak exercise were lower in CHF than N, and both of them correlated with not only peak VO(2), but also the corresponding resting value of FVR and SVRI (p<0.01 each).

CONCLUSIONS

Redistribution of blood flow from the non-exercising tissues to the working skeletal muscles, which may participate in exercise capacity, can be blunted in CHF. The decreased vasoconstrictive response in the non-exercising tissues is intimately related to the increased resting vascular tone in CHF.

Alterations of alpha-adrenergic modulations of coronary microvascular tone in dogs with heart failure

BACKGROUND

It remains unclear whether coronary microvascular response to alpha-adrenergic activation alters in chronic heart failure (CHF).

METHODS AND RESULTS

We investigated the alpha-adrenergic receptor-mediated effects on coronary pressure-flow relationship (CPFR) in a tachycardia-induced canine heart failure model. The dogs studied were male (29 of 31) and the drugs were given intracoronary. The slope of CPFR during long diastole was evaluated as an index of coronary vascular resistance, during alpha1- or alpha2-adrenergic stimulation or inhibition under anesthesia in the baseline and failing state after 3 weeks of rapid ventricular pacing. Resting coronary blood flow and CPFR did not change in the failing state from the baseline state. Neither alpha1 nor alpha2 stimulation changed the slope of CPFR in the baseline state. However, in the failing state, alpha1 stimulation decreased the slope of CPFR by 23 +/- 5% (P < .05), whereas alpha2 stimulation increased it by 73 +/- 10% (P < .05), which was nearly abolished by pretreatment with NG-nitro-L-arginine methyl ester.

CONCLUSION

Alpha2-mediated vasodilatory action, presumably via endothelium-derived nitric oxide release, would be enhanced in the coronary microvascular bed, which may antagonize enhanced alpha1-induced vasoconstriction in CHF.

Impaired Vasoreactivity in End-Stage Heart Failure Patients on Intravenous Inotropic Support

BACKGROUND

Vasoreactivity is known to be impaired in heart failure patients; however, it has not been determined whether standard medical therapy for end-stage heart failure patients (ES-HF) ameliorates this impairment. Therefore, we sought to investigate flow-mediated dilation (FMD) responses in ES-HF with normal or near normal cardiac indices from continuous inotropic support.

METHODS AND RESULTS

Vascular ultrasound was used to assess FMD responses to isometric exercise and cuff occlusion in 15 ES-HF patients and 5 control subjects (C). ES-HF patients had significant hyperemic response to maximal exercise (P < .05), which was blunted relative to C (ES-HF; 84 +/- 21 mL/min versus C; 299 +/- 85 mL/min, P < .05). ES-HF patients did not show a significant hyperemic response to submaximal exercise. C had a significant increase in arterial diameter that exceeded ES-HF after both maximal (C; 8 +/- 1% versus. ES-HF; -0.9 +/- 0.86%, P < .05) and submaximal exercise (C; 6 +/- 1% versus ES-HF; 0.57 +/- 1%, P < .05). FMD responses at similar absolute workloads showed that both the mean hyperemic response and the change in arterial diameter were significantly greater in C. After cuff occlusion, the mean hyperemic response for ES-HF was again significantly blunted compared with C (ES-HF; 117 +/- 26% versus C; 352 +/- 86%, P < .05). After cuff occlusion, arterial diameter in C significantly increased in response to hyperemia, whereas ES-HF patients had a paradoxical vasoconstrictive response (C; 10.7 +/- 1.1% versus ES-HF; -5.3 +/- 1.5%, P < .05).

CONCLUSION

Peripheral vasoreactivity in response to either maximal exercise, submaximal exercise, or hyperemic stimuli is impaired in ES-HF patients with normal resting cardiac outputs.

Coronary Blood Flow Responses are Impaired Independent of NO and Endothelial Function in Conscious Dogs with Dilated Cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is characterized by nitric oxide (NO) deficiency and endothelial dysfunction. Whether endothelium-independent vasodilation is preserved, particularly in the coronary circulation, remains controversial.

METHODS AND RESULTS

We studied systemic and coronary flow responses to the endothelium-dependent agonist, acetylcholine, the cGMP-dependent NO-donor, nitroglycerin, the predominantly endothelium-independent agonist, adenosine, the beta-adrenergic cAMP-dependent agonist, isoproterenol, and the calcium channel antagonist, nicardipine, in conscious dogs with pacing-induced DCM. Systemic blood flow response was impaired to acetylcholine but preserved to other vasodilators in DCM. In contrast, coronary blood flow response was significantly ( P < .05) depressed to all agonists. (Peak coronary blood flow response, control versus DCM: acetylcholine: 221 +/- 14% versus 156 +/- 11%; nitroglycerin: 220 +/- 17% versus 138 +/- 9%; adenosine: 635 +/- 65% versus 376 +/- 56%; nicardipine: 338 +/- 59% versus 115 +/- 23%; isoproterenol: 219 +/- 18% versus 86 +/- 20%). The attenuation was independent of systemic hemodynamic differences.

CONCLUSION

In contrast to systemic responses, coronary blood flow responses in DCM are impaired dependent or independent of NO or second messenger mechanisms, implying either distal signaling defects or structural abnormalities in the coronary vasculature.

Reduced coronary vasodilator responses to amlodipine in pacing-induced heart failure in conscious dogs: role of nitric oxide

1. This study examined whether NO is involved in the in-vivo coronary vasodilator effects of amlodipine (a calcium channel blocker) and whether heart failure (HF) alters the coronary responses to amlodipine. 2. Nine conscious dogs were chronically instrumented to measure circumflex coronary blood flow (CBF) and coronary diameter (CD). Drugs were administered directly into the circumflex artery through an indwelling catheter to avoid systemic changes. HF was induced by right ventricular pacing (240 b.p.m., 3 weeks). 3. Compared with control (C), in HF, coronary responses to acetylcholine (1 - 10 ng kg(-1)) were reduced while responses to nitroglycerin (0.1 - 0.5 microg kg(-1)) were unchanged. In C, amlodipine (30 - 150 microg kg(-1)), increased dose-dependently CBF and CD. After LNA (a NO synthase inhibitor, 2 mg kg(-1)), amlodipine produced less increases in CBF and CD (+121+/-26 ml min(-1) and +76+/-35 microm versus +196+/-40 ml min(-1) and +153+/-39 microm respectively for 150 microg kg(-1) amlodipine alone, both P<0.05). In HF, the coronary responses to amlodipine were reduced (150 microg kg(-1) of amlodipine increased CBF and CD +121+/-23 ml min(-1) and +77+/-21 microm respectively, both P<0.05). After LNA, the CBF responses to amlodipine tended to be reduced (+94+/-19 ml min(-1) at 150 microg kg(-1)) but CD responses were significantly reduced (+41+/-16 microm, P<0.05). The supplementation with L-arginine did not enhance the coronary responses to amlodipine. 4. These results indicate that, in conscious dogs, NO participates in the coronary responses to amlodipine and in HF, the coronary responses to amlodipine are reduced, which is related to a reduced NO production.