Reduced coronary flow reserve during exercise in cardiac transplant recipients

Endothelial dysfunction in conduit arteries and in microcirculation. Novel therapeutic approaches

The vascular endothelium not only is a single monolayer of cells between the vessel lumen and the intimal wall, but also plays an important role by controlling vascular function and structure mainly via the production of nitric oxide (NO). The so called "cardiovascular risk factors" are associated with endothelial dysfunction, that reduces NO bioavailability, increases oxidative stress, and promotes inflammation contributing therefore to the development of atherosclerosis. The significant role of endothelial dysfunction in the development of atherosclerosis emphasizes the need for efficient therapeutic interventions. During the last years statins, angiotensin-converting enzyme inhibitors, angiotensin-receptor antagonists, antioxidants, beta-blockers and insulin sensitizers have been evaluated for their ability to restore endothelial function (Briasoulis et al., 2012). As there is not a straightforward relationship between therapeutic interventions and improvement of endothelial function but rather a complicated interrelationship between multiple cellular and sub-cellular targets, research has been focused on the understanding of the underlying mechanisms. Moreover, the development of novel diagnostic invasive and non-invasive methods has allowed the early detection of endothelial dysfunction expanding the role of therapeutic interventions and our knowledge. In the current review we present the available data concerning the contribution of endothelial dysfunction to atherogenesis and review the methods that assess endothelial function with a view to understand the multiple targets of therapeutic interventions. Finally we focus on the classic and novel therapeutic approaches aiming to improve endothelial dysfunction and the underlying mechanisms.

Methods for evaluating endothelial function: a position statement from the European Society of Cardiology Working Group on Peripheral Circulation

The endothelium holds a pivotal role in cardiovascular health and disease. Assessment of its function was until recently limited to experimental designs due to its location. The advent of novel techniques has facilitated testing on a more detailed basis, with focus on distinct pathways. This review presents available in-vivo and ex-vivo methods for evaluating endothelial function with special focus on more recent ones. The diagnostic modalities covered include assessment of epicardial and microvascular coronary endothelial function, local vasodilation by venous occlusion plethysmography and flow-mediated dilatation, arterial pulse wave analysis and pulse amplitude tonometry, microvascular blood flow by laser Doppler flowmetry, biochemical markers and bioassays, measurement of endothelial-derived microparticles and progenitor cells, and glycocalyx measurements. Insights and practical information on the theoretical basis, methodological aspects, and clinical application in various disease states are discussed. The ability of these methods to detect endothelial dysfunction before overt cardiovascular disease manifests make them attractive clinical tools for prevention and rehabilitation.

Coronary flow reserve in hypertrophic cardiomyopathy: relation with microvascular dysfunction and pathophysiological characteristics

BACKGROUND.: The decrease in coronary flow reserve (CFR) in hypertrophic cardiomyopathy (HCM) predisposes to myocardial ischaemia, systolic dysfunction and cardiac death. In this study we investigate to which extent haemodynamic, echocardiographic, and histological parameters contribute to the reduction of CFR. METHODS.: In ten HCM patients (mean age 44+/-14 years) and eight heart transplant (HTX) patients (mean age 51+/-6 years) CFR was calculated in the left anterior descending coronary artery. In all subjects haemodynamic, echocardiographic and histological parameters were assessed. The relationship between these variables and CFR was determined using linear regression analysis. RESULTS.: CFR was reduced in HCM compared with HTX patients (1.6+/-0.7 vs. 2.7+/-0.8, p<0.01). An increase in septal thickness (p<0.005), indexed left ventricular (LV) mass (p<0.005), LV end-diastolic pressure (p<0.001), LV outflow tract gradient (p<0.05) and a decrease in arteriolar lumen size (p<0.05) were all related to a reduction in CFR. CONCLUSION.: In HCM patients haemodynamic (LV end-diastolic pressure, LV outflow tract gradient), echocardiographic (indexed LV mass) and histological (% luminal area of the arterioles) changes are responsible for a decrease in CFR. (Neth Heart J 2007;15:209-15.).

Features of cardiac allograft coronary endothelial dysfunction

The aim of the study was to evaluate the features and mechanism of cardiac allograft coronary endothelial dysfunction. Coronary blood flow and epicardial coronary artery diameter response to intracoronary acetylcholine and N(G)-monomethyl-l-arginine were assessed in 19 cyclosporine-treated heart transplant recipients with normal coronary angiograms (3.8 +/- 2.3 years after transplantation) and compared with 19 age-, gender-, and cardiovascular risk factor-matched nontransplantation control patients with normal coronary angiograms. Heart transplant recipients had more epicardial vasoconstriction in response to intracoronary acetylcholine (mean -16 +/- 19% [SD] vs 4 +/- 10%; p = 0.036). Microvascular endothelial function was similar between groups. Coronary flow reserve in response to adenosine was higher in the transplant group (3.6 +/- 0.8 vs 3.1 +/- 0.7; p = 0.04). The effect of N(G)-monomethyl-l-arginine (64 micromol/min) on coronary blood flow (-16 +/- 21% vs -37 +/- 19%; p = 0.018), coronary artery diameter (-10 +/- 13% vs -21 +/- 11%; p = 0.04), and coronary vascular resistance (34 +/- 40% vs 73 +/- 63%; p = 0.047) was significantly attenuated in the transplant group compared with controls. In conclusion, cardiac allograft epicardial coronary endothelial function was abnormal and may be related to an impaired endogenous NO synthetase pathway and reduced endothelial nitric oxide production in transplant recipients.

Serial measurements of peripheral vascular reactivity and exercise capacity in congestive heart failure and after heart transplantation

BACKGROUND

The regulation of nutritive blood flow to skeletal muscles during exercise seems to make an important contribution to exercise capacity. In congestive heart failure (CHF) this regulation seems to be impaired, with attenuated peripheral vasodilatory capacity. The results regarding improvement of peripheral vasoreactivity after heart transplantation (HTx) are conflicting, and the contribution of impaired peripheral vasoreactivity to the observed reduced exercise capacity among heart transplant recipients (HTR) has not been well elucidated. We therefore assessed the reversibility of impaired vasoreactivity in forearm and calf after HTx with relationship to exercise capacity.

METHODS AND RESULTS

The vasoreactivity of both forearm and calf was studied with venous occlusion plethysmography and related to exercise capacity in 64 patients with CHF and in 22 controls. Of these patients, 29 patients underwent HTx, and the same measurements were performed 10 days, 6 months and 1 year after HTx, and in a group of 15 HTR who had undergone HTx several years ago. Our main findings were (1) impaired resting blood flow in patients with CHF improved after HTx and even surpassed levels of controls; (2) peak forearm blood flow remained attenuated early after HTx, but normalized during the first year postoperatively; (3) both forearm and calf minimal resistance remained elevated after HTx; (4) vascular reactivity displays regional variations in forearm and calf both during CHF and after HTx; and (5) peripheral vascular reactivity relate to exercise performance in both patients with CHF and HTR, but the relationship seemed more pronounced in CHF.

CONCLUSION

With impaired vasoreactivity related to limited exercise capacity in CHF, improvement is evident after HTx, but both forearm and calf minimal resistance remains elevated. These findings suggest increased vasoconstrictor drive to both exercising and non-exercising muscles, possibly contributing to persistent physical limitation after HTx.

Angiographic presentation of coronary artery spasm in heart transplant recipients

We describe the angiographic characteristics of coronary artery spasm observed in 12 out of 247 (4.9%) patients who underwent 808 coronary angiographies after heart transplantation. Coronary artery spasm was diagnosed when localized and reversible narrowing of the coronary lumen was identified. After coronary artery spasm identification all patients were followed-up clinically for a mean period of 5.1 years. Coronary artery spasm was documented 1-3 years after heart transplant. Coronary artery spasm affected 1 main coronary artery in 10 patients and 2 in 2 patients; in 3 patients 1 or more secondary branches were also affected. The right coronary artery was affected by coronary artery spasm in 8 patients and the anterior descending coronary artery in 6 patients. In 6 patients coronary artery spasm was mechanically induced by the catheter tip. The degree of luminal narrowing due to coronary artery spasm ranged from mild to almost complete occlusion. Coronary artery spasm appeared as a single tubular smooth and concentric stenosis in 8 patients, was discrete in 2 patients and multiple on the same vessel in 2 patients. In 1 patient coronary artery spasm was erroneously interpreted as an organic lesion and percutaneous transluminal coronary angioplasty was planned. During follow-up 3 patients out of 4 who had shown multiple coronary artery spasm died and 2 patients developed critical organic stenosis. In conclusion coronary artery spasm after heart transplant is less rare than commonly believed. Although it usually has a peculiar appearance, it can be misinterpreted as an organic lesion. Multiple coronary artery spasm appears to carry a poor prognosis.

Incidence, progression and functional significance of cardiac allograft vasculopathy after heart transplantation

BACKGROUND

Cardiac allograft vasculopathy after heart transplantation leads to an accelerated form of atherosclerosis with marked and often diffuse vessel wall changes that limit long-term survival. Previous studies showed contradictory results relating vessel wall changes to endothelial vasodilator response.

METHODS

A total of 30 cardiac transplant recipients were studied 3, 12, and 24 months after heart transplantation. Coronary angiography was performed at rest, during supine bicycle ergometry, and after 1.6 mg sublingual nitroglycerin. Coronary cross-sectional area (biplane coronary angiography) and coronary artery wall changes (intravascular ultrasound) were assessed and extent of intimal changes correlated to vasodilator responses to nitroglycerine and bicycle ergometry.

RESULTS

Intravascular ultrasound showed significant intimal thickening in 43, 64, and 58% of patients at 3, 12, and 24 months. Intimal thickening 3 months after transplantation was related to donor age (r=0.70, P<0.01) but did not predict progression of disease that manifested itself angiographically as a decrease in coronary cross-sectional area at 12 and 24 months (P<0.005) and significant coronary stenosis in 12% of patients after 24 months. Endothelium-independent vasodilatation after nitroglycerin (33+/-15, 44+/-20, and 43+/-24%) was normal. Endothelium-dependent, flow-induced vasodilatation during exercise was decreased (14+/-11, 18+/-14, and 16+/-17%) but did not correlate to intimal changes assessed by ultrasound.

CONCLUSIONS

The study confirms the high incidence of intimal thickening after heart transplantation as assessed by intravascular ultrasound. Impaired exercise-induced vasodilatation suggests diminished bioavailability of endothelium-derived nitric oxide to physiological stimulation but the lack of relationship between coronary wall changes and this functional impairment suggests intermittent and presumably reversible endothelial injury in graft atherosclerosis.

Effect of plasma insulin level on myocardial blood flow and its mechanism of action

Considerable evidence suggests that coronary endothelium regulates myocardial blood flow and metabolism by elaborating vasoactive substances. The physiologic signals mediating this process are uncertain. To test the hypothesis that the process is influenced by physiologic variation in local insulin concentration, we examined the effect of direct intracoronary insulin infusion on myocardial blood flow and oxidative substrate metabolism in 10 patients with coronary heart disease. Ten men (aged 51 to 68 years) who were fasting received a 60-minute intracoronary infusion of insulin at a rate (10 mU/min) sufficient to raise coronary venous plasma insulin from 12+/-4 to 133+/-17 mU/ml without increasing the systemic insulin level. Local coronary hyperinsulinemia increased coronary sinus blood flow in every subject, from 50+/-4 to 61+/-6 ml/min (p<0.01). Insulin also increased myocardial uptake of glucose (from 6+/-1 to 17+/-6 mmol/min) and lactate (from 8+/-2 to 12+/-5 mmol/min), resulting in approximately 30% increase in total oxidative substrate uptake, but without increasing myocardial oxygen consumption (7.0+/-0.7 vs. 7.1+/-0.8 ml/min). Thus, physiologic elevation in the local plasma insulin concentration increases coronary blood flow in the absence of any increase in myocardial oxygen demand or consumption, suggesting a primary reduction in coronary tone, while simultaneously restraining the oxidation of imported substrates. These observations are consistent with insulin-mediated elaboration of vasoactive and/or paracrine factors within the coronary circulation.

Progressive deterioration of coronary flow reserve after heart transplantation

BACKGROUND

The purpose of this study was to determine coronary flow reserve in cardiac allograft recipients early (0 to 3 years) and late (3 to 7 years) after heart transplantation.

METHODS AND RESULTS

With the use of a Doppler tipped guide wire, coronary flow reserve (ratio of hyperemic to baseline coronary flow velocity) was measured in 82 patients before and after intracoronary adenosine. Forty-five patients were early (< or =3 years) after transplantation, 24 were late, and 13 were control patients with single-vessel coronary artery disease. Coronary flow reserve in the early transplantation patients was similar to that in the control group (2.9+/-0.2 vs 3.0 +/-0.6, p=not significant) but was reduced in the late transplantation group (2.2+/-0.5 vs 3.0+/-0.6, p < 0.001). There were differences in coronary flow reserve between the early and late transplantation patient groups (3.0+/-0.6 vs 2.2+/-0.5, p < 0.001 ) despite equally elevated mean arterial pressure, mean heart rate, mean pulmonary capillary wedge pressure, and mean left ventricular mass in the two groups. Coronary flow reserve in patients with angiographic allograft arteriopathy (n=19) was reduced when compared with coronary flow reserve of patients with normal vessels (n=50) (1.9+/-0.3 vs 3.1+/-0.6, p < 0.001).

CONCLUSIONS

There is progressive deterioration of coronary flow reserve over time after transplantation. Dysfunction of the coronary microcirculation rather than determinants of myocardial oxygen consumption contributes to this reduction.

Role of dobutamine stress echocardiography in heart transplant patients

The objective of this focused review is to describe the rationale, methods, and potential clinical applications of dobutamine stress echocardiography (DSE) in heart transplant recipients. More than 500 studies in 150 heart transplant patients who underwent this procedure (1991-96) are reviewed. Relevant studies from the medical literature that have assessed the utility of DSE in the diagnosis of transplant coronary artery disease (TCAD) are discussed, the predictive ability of DSE for development of TCAD is determined, and the prognostic value of this test in the heart transplant population is evaluated. The protocol of DSE used in the laboratory for this study is presented and discussed with reference to other major studies that have determined the sensitivity, specificity, and positive and negative predictive accuracies. Since many noninvasive cardiac tests have not been consistently optimal to detect TCAD, a substantial number of patients undergo routine surveillance with coronary angiography to define the presence and magnitude of TCAD. Recent studies with DSE have shown it to be valuable in the noninvasive diagnosis of TCAD and to have an accuracy unmatched by other widely used imaging modalities. Other important evolving indications for DSE in heart transplant patients, such as prediction of prognosis and occurrence of cardiac events, are briefly discussed. Based on this study and the currently available literature, DSE appears to be a highly reproducible noninvasive test which can be serially employed in the routine surveillance of coronary artery disease in heart transplant patients.