Elastase and the pathobiology of unexplained pulmonary hypertension

Our laboratory has focused on the increased activity of an endogenous vascular elastase in the pathobiology of pulmonary hypertension and on the mechanisms by which it is upregulated and by which it orchestrates abnormal remodeling of the vessel wall, specifically the induction of growth factors, the induction of the glycoprotein tenascin, which amplifies the proliferative response, and fibronectin, which is critical to the process of smooth muscle migration in the context of neointimal formation. We explore strategies by which targetting these processes might arrest progression or induce regression of pulmonary vascular disease associated with unexplained pulmonary hypertension.

The smooth muscle cell: sinner or saint in restenosis and the acute coronary syndromes?

Proliferation of arterial smooth muscle cells has held center stage as the culprit in restenosis for almost two decades. Many strategies for combating restenosis target smooth muscle replication. However, none have proven beneficial in clinical trials. Indeed, inhibition of smooth muscle proliferation in human patients might produce the undesired effect of destabilizing vulnerable atherosclerotic plaques because these cells furnish the collagen responsible for the biomechanical strength of the plaque. Actually, in some cases the benefit of angioplasty may depend on stimulating smooth muscle replication and collagen elaboration, converting an "unstable" to a more stable plaque. Moreover, recent clinical and experimental evidence suggests that restenosis depends less on neointimal hyperplasia than on constrictive remodeling (i.e., advential scarring, producing a smaller lumen), a process independent of smooth muscle replication. The recognition that plaques vulnerable to disruption often do not produce flow-limiting stenoses highlights a need for reassessment of the strategies to treat or prevent the acute coronary syndromes. We should strive to treat aggressively risk factors such as hyperlipidemia whose control appears to stabilize plaques. Trials are even underway comparing such risk factor management with coronary artery intervention. If we could identify potentially unstable atheroma before they are evident, clinically, we might even contemplate angioplasty of nonsignificant stenoses to induce smooth muscle cell proliferation and reinforce the plaque's fibrous cap. This proposal may seem preposterous, yet we perform "primary" angioplasty every day in patients with an acute myocardial infarction whose "culprit" lesions underlying the thrombus are often not critical. Our knowledge of the biology of restenosis has lagged behind our practice of coronary intervention. Advances in understanding the biology of the complications of interventional therapy, hand in hand with technical advances, should help us to devise more rational and enduring approaches to benefiting our patients.

Mediators of restenosis

The multitude of actions and interacting components involved in inciting and sustaining myointimal hyperplasia and restenosis effectively precludes the use of a single type of intervention. No pharmacologic approach has been conclusively shown to prevent coronary restenosis after balloon angioplasty or graft restenosis after peripheral arterial bypass. Although no human studies have been performed to prevent restenosis with gene therapy, the animal data are compelling, and the local delivery of various inhibitory agents may represent a novel way of preventing restenosis in vascular beds subjected to endovascular or traditional open procedures. Until these modalities are proved effective, the treatment of vascular stenosis due to internal hyperplasia remains within the domain of the surgeon.

Pathophysiology of restenosis: interaction of thrombosis, hyperplasia, and/or remodeling

In response to arterial injury, a series of intravascular changes take place that lead to restenosis: thrombosis, neointimal hyperplasia, and remodeling of the vessel. Neointima formation involves thrombosis, recruitment (migration), and recruitment/cell proliferation. To determine the source of neointimal cells that accumulate at the site of injury, pig models of stented and catheterized arteries were examined. The phases of neointima formation can each be seen in the pig in which neointimal cells come from nearby arterial tissue. The pig model was also employed to assess the effect of different degrees of force exerted by self-expanding stents on the arterial wall. In this model, the luminal area increased in response to chronic stent force. Slow expansion may help prevent neointimal hyperplasia and maintain luminal patency without causing damage to the artery.

Fibromuscular dysplasia of the internal carotid artery in a child with alpha-1-antitrypsin deficiency

Fibromuscular dysplasia (FMD) is a non-inflammatory segmental arteriopathy of unknown origin. Most often the renal arteries are affected, however, also mesenteric, lumbar, vertebral, or carotid arteries may be involved. FMD has frequently been reported as a cause of stroke in adults, but very rarely in children. We report the case of an 11-year-old boy who presented with an ischaemic infarction in the anterior part of the territory of the left middle cerebral artery. Angiography demonstrated a 'string of beads' lesion suggestive of FMD causing occlusion at the origin of the middle artery. Laboratory analyses revealed the protease inhibitor (Pi) phenotype SZ (PiSZ) of alpha-1-antitrypsin deficiency as well as decreased antioxidants and signs of enhanced lipid peroxidation. Such an imbalance may be associated with diminished resistance to oxidation, possibly causing direct cellular and tissue injury. Whether alpha-1-antitrypsin deficiency and an impaired status of antioxidants, as seen in our patient, might play a role in the pathogenesis of FMD is presently unclear.

Time course of coronary endothelial dysfunction in acute untreated rejection after heterotopic heart transplantation

BACKGROUND

Endothelial dysfunction is one of the early events leading to atherosclerosis. It occurs early after orthotopic heart transplantation and precedes the appearance of accelerated graft coronary artery disease believed to stem from chronic rejection of the endothelium. Acute rejection may contribute to the development of graft vasculopathy.

METHODS

To assess the time course and specific mechanisms of coronary endothelial dysfunction in acute untreated rejection, a swine model of retroperitoneal heterotopic heart transplantation was used. Large white swine (age 10 +/- 2 weeks, weight 25 +/- 5 kg) were serum-typed for class I antigen of the swine leukocyte antigen system and selected to ensure a similar degree of incompatibility. Donor hearts were preserved with normothermic blood cardioplegia and regional hypothermia; the mean ischemic time was 64 +/- 15 minutes. Myocardial contractility decreased from day 5 (normal) to day 14 (weak), but electrical activity was preserved. All coronary arteries were patent, and International Society for Heart and Lung Transplantation grade 4 rejection was present in all hearts beyond 5 days. The endothelial function of epicardial coronary arterial rings of native and transplanted hearts was studied in organ chambers filled with modified Krebs-Ringer bicarbonate solution and compared 1, 5, 9, and 14 days after transplantation.

RESULTS

Maximal endothelium-independent relaxations were unaffected at all stages. Endothelium-dependent relaxations to serotonin and alpha 2-adrenergic agonist UK 14304 (which activate receptors coupled to Gi-proteins) and to sodium fluoride (a direct G-protein activator) deteriorated progressively over time. At 14 days maximal relaxations to the calcium ionophore A23187, adenosine diphosphate, and bradykinin were also reduced, but to a lesser degree than those to serotonin and sodium fluoride. Histomorphometric studies of the allograft coronary artery rings showed progressive intimal hyperplasia from day 5 to day 14, with an increase in the incidence from 29% +/- 8.3% to 61.5% +/- 12%.

CONCLUSIONS

These studies show that endothelial dysfunction in untreated acute rejection after heart transplantation develops beyond 5 days and initially involves G-proteins; the dysfunction worsens over time to finally affect all endothelial mechanisms and vascular smooth muscle. The progression of the associated intimal hyperplasia parallels the alteration in endothelial function, suggesting a permissive role of the dysfunction in the development of this acute form of coronary graft vasculopathy.

[Natural history of renal artery stenosis]

The time delay necessary for the appearance of an atherosclerotic renal artery stenosis from the initial process of atherogenesis is not well known and is probably influenced by genetic factors and the classical risk factors (i.e. cholesterol, blood pressure levels...). The pathophysiology of fibromuscular dysplasic renal artery stenoses is even less known. Whatever the cause of a renal artery stenosis, blood pressure increases when the stenosis increases and becomes "significant" with a parallelism between the degree of the stenosis and the severity of hypertension. Renal artery stenoses can progress with time and lead to a complete occlusion of the involved renal artery. The progressive obstruction of the renal artery can lead to malignant hypertension and can also induce a gradual irreversible ischaemic renal damage leading to end-stage renal failure.

Fibromuscular dysplasia in intramuscular arteries of Japanese quail (Coturnix coturnix japonica)

Fibromuscular dysplasia (FMD) was found in the intramuscular arteries of both commercial (normal) and mutant (LWC) strains of Japanese quail. The mutant strain LWC is afflicted with an inherited muscular dystrophy exhibiting myotonia. The arterial lesions were classified as medial fibroplasia or medial hyperplasia, both being subtypes of medial FMD. Some lesions showed extensive proliferation of medial smooth muscle into the vascular lumen, resulting in partial occlusion of the affected blood vessel. FMD occurred more frequently in the mutant LWC quail than in the commercial strain. Ischaemic changes were absent in the associated muscle structures in both strains. The significance of FMD in relation to the skeletal muscle changes in the mutant LWC strain remains unclear.

Role of endothelium in thrombosis and hemostasis

Vascular endothelium is strategically located at the interface between tissue and blood. It is pivotal for protecting against vascular injury and maintaining blood fluidity. Normal endothelium releases prostacyclin and nitric oxide, potent inhibitors of platelet and monocyte activation and vasodilators. Their syntheses are governed by isoforms of enzymes. Normal endothelial surface expresses ecto-adenosine diphosphatase, which degrades adenosine diphosphate and inhibits platelet aggregation; thrombomodulin, which serves as a binding site for thrombin to activate protein C; and heparin-like molecules, which serve as a cofactor for antithrombin III. Normal endothelium secretes tissue plasminogen activator, which activates the fibrinolysis system. Endothelium produces and secretes von Willebrand factor, which mediates platelet adhesion and shear-stress-induced aggregation. Injury to endothelium is accompanied by loss of protective molecules and expression of adhesive molecules, procoagulant activities, and mitogenic factors, leading to development of thrombosis, smooth muscle cell migration, and proliferation and atherosclerosis.

The vascular biology of nitric oxide and its role in atherogenesis

Nitric oxide (NO), the biologically active component of endothelium-derived relaxing factor, has critical roles in the maintenance of vascular homeostasis. Decreased endothelial NO production, as a result of endothelial dysfunction, occurs in the early phases of atherosclerosis. NO appears to inhibit atherogenesis by inhibiting leukocyte and platelet activation and by inhibiting smooth muscle cell proliferation. Endothelial denudation is a prominent feature of vascular injury associated with percutaneous angioplasty, and decreased NO production appears to contribute to the restenosis process. Manipulation of the NO/cGMP signal transduction system may provide novel therapeutic approaches for limiting atherogenesis and neointimal proliferation in the future.

Renal artery velocity mapping with MR imaging

An MR phase imaging sequence with a very short echo time was used to assess blood velocity and flow at the renal artery bifurcation. Cardiac-gated MR imaging data were obtained in six healthy subjects in sagittal planes adjacent to the abdominal aorta and transverse planes above and below the renal artery bifurcation. Average renal artery flow rate was 23.8 +/- 9 mL/sec. A strong individual variability was found for the velocity profiles in the abdominal aorta during end-systolic regurgitation. Flow rate was also determined in three patients with reduced renal artery blood flow. Two patients received therapy with percutaneous transluminal angioplasty. The successful outcome was documented with MR imaging. A reliable assessment of renal artery flow with MR phase imaging is feasible. Measurement of the velocity profiles yields valuable insights in the complicated flow regime at the renal artery bifurcation.

Structural cardiovascular alterations and blood pressure variability in human hypertension

AIM

To evaluate the cardiovascular risk of hypertensive patients in relation to left ventricular hypertrophy, arteriolar hypertrophy and blood pressure variability, and the effects of antihypertensive treatment.

LEFT VENTRICULAR HYPERTROPHY

In hypertensive subjects with marked left ventricular hypertrophy, cardiovascular problems are about three times more frequent than in hypertensives who do not have left ventricular hypertrophy. The evidence suggests, however, that a moderate degree of left ventricular hypertrophy may be compensatory and that regression of mild hypertrophy should not necessarily be pursued.

ARTERIOLAR HYPERTROPHY

An increased wall to lumen ratio leads to an increase in vascular resistance and thus promotes hypertension. Regression of this alteration with antihypertensive treatment appears to be both beneficial and achievable, although it is not clear whether all antihypertensive agents have the same effect. Moreover, there are methodological problems in determining whether a regression has actually been achieved.

BLOOD PRESSURE VARIABILITY

There is evidence to suggest that end-organ damage is more frequent and more marked in hypertensives with greater 24 h blood pressure variability. It appears that antihypertensive treatment does not easily reduce this variability, although the intermittent measurements taken by automatic monitoring devices do not fully reflect patterns of blood pressure variation. It may be that hypertensives with a greater degree of blood pressure variability can obtain a reduction in the magnitude of this variability with antihypertensive treatment.

The heart and vascular changes in hypertension

AIM

To review present knowledge on the causes of cardiovascular changes in hypertension and on the effects of antihypertensive treatment.

BACKGROUND

The clinical manifestations of hypertensive heart disease have changed considerably in recent decades, from predominantly cardiac failure to predominantly left ventricular hypertrophy, which is an independent risk factor for all cardiovascular events. This change parallels the recent development of ultrasonic devices which make it possible to investigate the vessels as well as the heart. These devices have shown that there are different types of cardiac remodeling, which are associated with different hemodynamic profiles.

TREATMENT OF CARDIOVASCULAR REMODELING

Recent studies have shown that antihypertensive treatment, both pharmacological and non-pharmacological, can significantly reduce left ventricular hypertrophy in hypertensive patients without jeopardizing the hemodynamic balance. However, hypertensive vessel disease has been less extensively investigated, with many studies concentrating on the carotid arteries. There appears to be a correlation between cardiac and carotid artery changes but so far there is no information on the effects of the antihypertensive treatment on the carotid alterations.

Large artery function and alterations in hypertension

HYPERTENSION AND ARTERIAL HEMODYNAMICS: One of the characteristics of hypertension is an impairment in arterial hemodynamics. Any definition of hypertension has to take account of oscillatory fluctuations during the cardiac cycle, that is, fluctuations in systolic and diastolic blood pressure around mean arterial pressure. These fluctuations are determined by ventricular ejection, arterial distensibility and the timing of arterial wave reflections. EFFECTS OF AGING ON LARGE ARTERIES: Larger arteries stiffen progressively with age, due to medial and intimal thickening. This alteration can be described as a decrease in arterial distensibility (Di = delta D/delta P x D, where D is the diameter of the artery and P is the blood pressure). The most obvious consequence of arterial stiffening is an increase in the amplitude of pulse pressure, caused by an increase in systolic pressure and a decrease in diastolic pressure. Two mechanisms underlie this increase in pulse pressure: a higher incident pressure wave generated by the left ventricle into a stiffened aorta and an increase in the velocity of the pressure wave traveling forward and back in the arterial tree. In young subjects, the reflected wave causes an increase in the early diastolic wave, but in older people the reflected wave is summed with a late systolic wave, causing a dramatic increase in central systolic pressure. These phenomena affect left ventricular function adversely, increasing myocardial oxygen consumption and tending to decrease coronary blood flow. Furthermore, the increased systolic blood pressure induces left ventricular hypertrophy. EFFECTS OF ANTIHYPERTENSIVE DRUGS: Although all classes of antihypertensive drugs can reduce blood pressure, only some can decrease arterial distensibility. Angiotensin converting enzyme inhibitors and calcium antagonists have been shown to decrease the stiffness of conduit arteries and dilate peripheral arteries. This may account for the superiority of these drugs in regressing left ventricular hypertrophy.

Postoperative follow-up of fibromuscular subaortic stenosis

OBJECTIVES

This study attempted to determine whether early subaortic resection at lower levels of obstruction reduces the rate of recurrence of subaortic stenosis or reduces secondary damage to the aortic valve, or both.

BACKGROUND

Fibromuscular subaortic stenosis is a progressive condition, and at present it is unclear whether early operation reduces the recurrence rate along with decreasing the incidence of aortic insufficiency.

METHODS

Thirty-seven patients with fibromuscular subaortic stenosis and no other significant cardiac abnormality who underwent open subaortic resection were evaluated. The preoperative, early and late postoperative catheterization or echocardiographic findings as well as the operative reports were reviewed. The median age at operation was 6.4 years (range 1.1 to 17.3). The entire group has been followed up postoperatively for a median of 5.2 years (range 1.1 to 11). Mean systolic gradients across the left ventricular outflow tract were used for the purpose of this study.

RESULTS

There was a significant correlation between the preoperative mean systolic gradient and the incidence of preoperative aortic regurgitation and late postoperative aortic valve thickening as well as the incidence and degree of late postoperative aortic regurgitation. Late postoperative gradient and degree of aortic regurgitation correlated significantly with the follow-up interval. Aortic regurgitation was progressive in some patients despite subaortic resection. A preoperative mean gradient > 30 mm Hg provided a reasonable cutoff for the likelihood postoperatively of needing a reoperation, having a postoperative shelf, a thickened aortic valve, moderate aortic regurgitation or a gradient of > 10 mm Hg.

CONCLUSIONS

Our results suggest that although early subaortic resection may not reduce the rate of recurrence of fixed subaortic stenosis, it is likely to reduce acquired damage to the aortic valve.

Complex branch renovascular disease: management options and late results

PURPOSE

The purpose of this report is to review management options and late results of complex renovascular disease managed over the last 22 years.

METHODS

Complex branch renal artery disease in 84 kidneys was repaired during 75 operations performed in 68 consecutive patients. There were 61 females (90%) and 7 males (10%) whose predominant pathologic diagnosis was fibromuscular dysplasia manifesting as either renovascular hypertension or aneurysmal degeneration. These patients underwent 15 in situ, 52 ex vivo, and 8 combined reconstructions. In situ repair primarily with use of the bifurcated internal iliac artery autograft was used for primary lesions of the proximal renal artery bifurcation (two branches). Ex vivo repairs, primarily with use of the multibranch internal iliac autograft and hypothermic perfusion preservation, were used for all other patterns of distal renal artery branch disease and reoperative problems.

RESULTS

Renovascular reconstruction was successful in salvaging 83 of 84 kidneys (98.8%) in 67 of 68 patients. There were no operative deaths. Two reconstructions thrombosed in the early postoperative period. One was due to severe aortic disease, the other to branch artery dissection after a failed balloon angioplasty. Both patients continued to have hypertension. Before hospital discharge 65 patients had 81 renal revascularizations proven patent by arteriography. Their renal function was assessed and blood pressure was determined in a follow-up extending to 20 years (mean 7.5 years, median 7.9 years). Late arteriograms were obtained in 30 patients (46%) an average of 52 months after operation (range 6 months to 18 years). They demonstrate stable renal artery repair with no evidence of late graft failure in each. Hypertension was cured or improved in 51 of 53 patients (96%) with a proven patent reconstruction. Aneurysms were successfully repaired in 11 patients. Renal function was improved in four patients with ex vivo repairs, unchanged in 59 patients (15 in situ, 44 ex vivo), and persistently worse in only three patients, all of whom had in situ repairs.

CONCLUSION

The branched arterial autograft allows the restoration of normal renal arterial anatomy and function when inserted to replace complex distal renovascular disease. This provides a durable repair, essential for younger patients affected by this pattern of disease who anticipate a normal life span after renovascular repair. Successful long-term correction of diastolic hypertension and aneurysmal disease was accomplished without significant morbidity.

Pseudohypertension in a child with Williams syndrome

Pseudohypertension has often been reported in elderly subjects, but is an unusual phenomenon in children. We report the case of a 5-year-old child who presented with features of Williams syndrome (characterized by elfin facies, supravalvar aortic stenosis, and peripheral pulmonary artery stenosis). Repeated blood pressure recordings made with appropriately sized blood pressure cuffs were very high, while simultaneous intraarterial blood pressure was normal, confirming the presence of pseudohypertension. This was shown to be caused by excessively thickened arterial vessels.

Effects of a high-cholesterol diet on arterial wall thickness and vascular reactivity in young rabbits

Cholesterol enrichment of arteries may induce biochemical and structural abnormalities in vascular smooth muscle resulting in increased arterial contractile sensitivity. We studied the effects of a high-cholesterol diet on arterial structural properties and vascular reactivity in young rabbits. In vivo measurements of aortic intimal-plus-medial thickness using high resolution ultrasound imaging were obtained before and after 3 weeks of a high-cholesterol diet in 12 rabbits (group 2) and compared to data from 12 animals a cholesterol-free diet fed (group 1). Six rabbits (group 3) were studied before and after a 3-week, high-cholesterol diet and after a subsequent 13-week, cholesterol-free recovery diet. Blood pressure responsiveness to noradrenaline was evaluated before and at the end of each diet period. In groups 2 and 3, high dietary cholesterol caused an increase in intimal-plus-medial thickness from 0.31 mm and 0.33 mm to 0.88 mm and 0.89 mm, respectively (p less than 0.001). Plasma cholesterol concentration rose from 0.9 +/- 0.26 mmol/l to 36.7 +/- 8.56 mmol/l. There was no change in group 1. In group 3, intimal-plus-medial thickness remained increased (1.01 mm) following the cholesterol-free recovery diet despite normal plasma cholesterol. Blood pressure responsiveness to noradrenaline was markedly increased after the high-cholesterol diet (p less than 0.001) in groups 2 and 3 and after the cholesterol-free recovery diet in group 3 (p less than 0.001), and was directly related to intimal-plus-medial thickness (r = 0.84; p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical spectrum of symptomatic external iliac fibromuscular dysplasia

External iliac fibromuscular dysplasia is a rare and usually asymptomatic disorder. We report eight symptomatic patients seen over a 15-year period and review pathophysiologic mechanisms accounting for the three following distinct lower extremity ischemic sequelae: (1) Emboli--episodic focal digital ischemia (blue toe) was seen in three patients. Resection and primary anastomosis of focal iliac ulcerative fibromuscular dysplasia (one patient) or resection and replacement (two patients) removed the embolic source and relieved the symptoms. (2) Chronic ischemia--gradual onset of full leg claudication in four patients was treated by operative graduated intraluminal dilation in three patients and prosthetic bypass in one. Arteriography subsequently showed a remodeled lumen in the three patients who underwent dilation. (3) Dissection--acute onset leg ischemia resulted from presumed dissection of the external iliac segment. After 4 months of conservative management of antiplatelet agents and exercise, symptoms resolved completely, and arteriogram showed spontaneous restoration of a normal lumen in the dissected segment. The clinical presentation of fibromuscular dysplasia may mimic other arterial processes such as atherosclerosis. Diagnosis is made only by arteriography with specific magnification views of the external iliac arteries and careful surveillance of the renal arteries. Appropriate treatment should be tailored to the clinical presenting symptom. For microembolic disease, resection and replacement are required. For chronic ischemia, intraluminal dilation is generally sufficient and durable and has proved to be a simpler and acceptable alternative to replacement or bypass. In acute dissection, surgical intervention may be deferred if the limb is viable to allow spontaneous healing and remodeling. Persistent symptoms may be the only indication for intervention in this ischemic manifestation of external iliac fibromuscular dysplasia.

Morphologic characteristics and functional significance of focal fibromuscular dysplasia of small coronary arteries

Focal fibromuscular dysplasia of small coronary arteries is not so rare as it is unrecognized. Although sometimes occurring as an isolated abnormality, it more often accompanies a variety of other lesions including inflammation or infiltration. In this review based on personal study of over 1,000 human hearts, the 3 topics include a description of the morphologic characteristics of the lesion, a discussion of its functional consequences affecting coronary flow, and an iteration of theoretical explanations for its development. The typical lesion is focal in distribution, is comprised of both fibrous and smooth muscle elements, and the histologic organization is one of dysplastic array. Included among the subjects discussed in functional consequences are coronary spasm, coronary reserve, chest pain, electrical instability of the heart, and comments on the role of focal fibromuscular dysplasia of small coronary arteries in hypertension, myocardial hypertrophy and heart failure. Theories as to its development include primary faults of smooth muscle or collagen, and focal abnormalities of clotting or neurovascular relation, but it is likely that the cause is multifactorial.