INTRODUCTION
Continued education has traditionally beenconsidered to be of great importance in RevistaEspañola de Cardiología. The "Editorial," "ReviewArticle," and "Update" sections are the usualmeans for transmitting to readers the opinionsand points of view of experts of known prestige inthe different aspects of cardiovascular disease. Inthe case of the Update section, over the years wehave attempted to select areas of obvious interestto a large part of our readers that, not being theobject of attention in more classical reviews, wouldotherwise be overlooked. Thus, the subjects we haveattempted to address in a cross-cutting manner inrecent years include: "Cardiovascular disease inwomen" (2006),1 "Non-coronary arterial disease" (2007),2 "Cardiovascular prevention" (2008),3 and "Cardiovascular translational medicine" (2009).4
The subject selected this year for in-depthevaluation, "The right heart and pulmonarycirculation," encompasses several aspects thatare undoubtedly attractive. The first is its evidentimplication in the practice of cardiologists of all hues,whether general or specialized, ranging from thosedevoted to clinical activity to basic researchers. Onthe other hand, after decades of highly predominantattention to the left chambers of the heart and thesystemic vessels, over the last 15 years we havebeen witnessing a progressive awareness of theimportance of right ventricle (RV) dysfunction indifferent heart diseases,5 both in those cases in whichthis chamber plays the leading role in the condition(as in arrhythmogenic right ventricular dysplasia or certain congenital heart diseases) and in those inwhich it accompanies conditions involving the leftheart chambers and valves, significantly modifyingthe clinical signs and prognosis. To paraphrase thetitle of a recent report, we now consider that "theleft heart will only be able to work as much as theright heart lets it."6 With respect to the pulmonarycirculation, the past decade has witnessed importantadvances based on a more complete knowledgeof the pathophysiology of the different forms ofpulmonary hypertension, which has been expressedin a classification that is of evident practical utility,as well as an improved diagnostic approach and,what is more important, the possibility of employingtreatments that are useful for the improvement ofthe symptoms and the prognosis of these patients.
Therefore, this Update arrives just in time to helpus learn about the latest findings, incorporate thediagnostic and therapeutic advances into our clinicalpractice and become aware of the uncertainties andgaps left by our current knowledge. The editors of Revista Española de Cardiología can state with pridethat among the authors who have agreed to contributetheir knowledge to this series of monographs are themajor world experts in this field. Approximately halfof the reports are written by authors living in theUnited States, and half were submitted by specialistsfrom different European countries.
REASONS FOR A SECULAR OVERSIGHT
As early as 1553, the Aragonese physicianMiguel Servet published his pioneering theories,scientifically confirmed by the work of Harvey inthe 17th century, concerning the existence of anindependent pulmonary circuit for the oxygenationof the blood, which is conducted and propelledinto the pulmonary circulation from the rightchambers of the heart. However, the importance ofthe function of the right heart continued to be thesubject of debate until the end of the 20th century.This chamber has traditionally been consideredto play a secondary role in the circulatory system,where it was thought to enhance the capacity of the pulmonary circulation more than to propel the flowof blood through the lungs. This belief was foundedon experimental works based on the ablation or thereplacement of the free RV wall in open-chestedanimals, in which this maneuver produced littleimpact on the cardiac output.7 This came to beconfirmed decades later with the viability of thosepatients with congenital heart disease in whom theRV was excluded from the pulmonary circulation bymeans of a cavopulmonary shunt like that created inthe Fontan procedure. The fact that the circulationis far from normal in both cases has been recognizedonly recently.8
On the other hand, the noninvasive study ofthe anatomy and function of the right chambershas classically been highly difficult, especially ifcompared with the easy accessibility of the leftventricle (LV) to evaluation using ultrasonographicand isotopic techniques. Moreover, the spatialconfiguration of the LV makes its easy to estimateits volume by means of models (such as the so-called ellipsoid of revolution) that make it possibleto accurately calculate its volume on the basis oftwo-dimensional measurements. This has facilitatedthe quantification of the contractile function of theventricle with measurements such as the LV ejectionfraction, which, although it has its limitations, hasenabled great advances in the classification and thestudy of patients with dysfunction of this chamber.In the case of the RV, the opposite occurs since,given its irregular shape, with entry route, apicalregion and exit route its volume is difficult to analyzeon the basis of 2-dimensional measurements.8 Thesituation is more or less the same when we considerthe physiological aspects: the study of LV function ismore accessible because its basic task is to generatehigh pressures (easy to estimate through the arterialpressure) by means of the contractility (estimableusing parameters such as the ejection fraction).In contrast, the function of the RV is basically tomaintain pulmonary flow (much more difficult tomeasure in practice) in a low-pressure system,6 andthe contractility of its free wall does not always reflectits function well because it varies widely dependingon the loading conditions.
THE RIGHT VENTRICLE AND PULMONARYCIRCULATION IN CURRENT CARDIOLOGY
Despite the reported difficulties, the growingknowledge of our anatomy and physiology of theRV and of the mechanisms that operate in thepresence of disease have brought us to grant theright heart the importance it warrants. Pulmonarycirculation, must combine a low pressure (to avoidthe formation of pulmonary edema through thethin and highly permeable membranes that permit gas exchange, with the capacity to absorb the entirecardiac output through a circulation characterizedby very low resistance. As a consequence, the pumpthat propels the circulation in this circuit mustbasically be capable of maintaining an elevatedcardiac output without generating high pressures.Thus, the RV presents anatomical characteristics(due to its shape, greater volume and the distributionof the muscle layers) and physiological features(asynchronous, "peristaltic"-like contraction) thatdiffer widely from those of the LV. Substantialdifferences between RV and LV have been reportedin the genes and in the molecular and cellularmechanisms that are observed under normalconditions and in the presence of disease, both inembryonic and fetal development and in the adultindividual. Suffice it to say that, in recent years,the most important journals related to this areahave devoted considerable space to reviewing theseconcepts.9-13 The first article of this series, whichthe readers will find immediately following thispresentation, focuses on a description of our basicknowledge of the right heart.14
On the other hand, the advances in cardiovascularimaging techniques have revolutionized the studyof the right cardiac chambers and the pulmonaryvasculature. While the three-dimensionalreconstruction of ultrasonographic images cansolve the problem of measuring the volume of theRV, magnetic resonance is the technique that isclearly becoming the "gold standard" in this fieldas it enables the accurate evaluation of anatomicaland physiological parameters of the circulation inthe right heart.8,15,16 We will devote a chapter of thisUpdate to the review of this technique.
However, the fact that perhaps has contributed themost to the present interest in the RV and pulmonarycirculation is the clinical confirmation of their impacton different heart diseases. Thus, the presence ofboth pulmonary hypertension and RV dysfunctionare common findings in "left" heart disease and actas powerful predictors of a poorer prognosis. Thediagnosis and clinical management of this situationare a challenge that will affect cardiologists in thecoming years17,18 and is the subject of a chapter of this series.
Other aspects of which the clinical cardiologistalso be aware are the incidence and the clinicalimpact of RV both in acute situations (such as RVinfarction, pulmonary thromboembolism and graftdysfunction following heart transplantation) and inchronic conditions, especially valve diseases, certaincongenital heart diseases and different forms ofchronic pulmonary hypertension.
The strategies for the prevention and treatment ofRV involvement in these situations will be of greatvalue when put into practice.12,13,17
Two articles of this series will be devoted toreviewing the "state of the art" in a field as timelyas that of pulmonary hypertension. The first focuseson the pathophysiological and diagnostic aspectsas well as the evaluation of the prognosis, while thesecond provides an update on the possibilities andlimitations of the different therapeutic measuresdeveloped over the past 15 years, beyond the recentlypublished norms and clinical practice guidelines.19,20
Given its incidence and clinical impact,thromboembolic disease warrants particularattention. The spectrum of clinical signs is very broadsince the development of pulmonary hypertensionand, in advanced phases, RV dysfunction accompanythe most severe acute forms. In discussing therecent publication of the European guidelines forpulmonary embolic disease,21 we will be able to offerthe comments of one of the highest authorities inthis field.
In contrast to those mentioned previously, thereare certain conditions in which RV is the primarysubstrate of the disease. These include types ofcardiomyopathy that predominantly affect thechambers of the right side of the heart, in whichthe genesis of potentially lethal arrhythmias isnot uncommon, and aggressive measures for theirprevention and treatment may be required. Wehave increasingly greater knowledge of the geneticaspects of these diseases, which are associated withanomalies in the genes that encode the desmosomalproteins. Other arrhythmogenic heart diseases thatinvolve the right-sided chambers also appear to havea genetic basis and will be dealt with in the samechapter.22,23
There are a number of connections betweencongenital heart diseases and conditions affectingthe chambers of the right side of the heart andthe pulmonary vasculatureThis subject will beapproached in two separate articles: the first refersto the different forms of structural involvement ofthe right heart in these heart diseases, their clinicalimplications and their treatment,24,25 whereas the second focuses on the subgroup of patients,frequently of adult age, with pulmonary hypertensionassociated with congenital shunts, a field in which thetraditional absence of effective therapeutic measureshas given way over the past decade to significantinnovations.26,27
The series of reviews will close with a chapterdevoted to the surgical possibilities in the treatmentof right heart disease, with a greater emphasis on thecontroversial subject of surgery of the tricuspid valvewhich, despite the fact that it has been carried out fordecades, has yet to be associated with an indicationthat is generally accepted among cardiac surgicalteams.28 Other currently performed interventions,such as the implantation of mechanical circulatory assist devices for situations of RV failure resistant toother measures, will also be discussed.
CONCLUSIONS
It is evident that we cannot ignore the basicaspects of the diagnosis and treatment of the diseasesaffecting what used to be referred to as the "minorcirculation," since the tools that are presentlyavailable enable their evaluation and management.We hope that enumerating the different aspectsencompassed in the conditions affecting the rightchambers of the heart and the pulmonary vessels,given their incidence and clinical importance, hasawakened reader interest. The objective of this seriesof Update chapters is to provide the cardiologistwith the knowledge necessary to confront theseaspects with confidence when they arise in his or herprofessional activity. Thus, we invite the readers of Revista Española de Cardiología to follow us monthafter month as we present this series, in which ourguides will be experts of known worldwide prestige.
If the publication of these articles contributes tocardiologists granting diseases of the right heart andthe pulmonary vasculature their proper importancein our daily practice, the effort will have had itsreward: among us, it will never again be a "minorcirculation."
Correspondence: Revista Española de Cardiología.
Sociedad Española de Cardiología.
Nuestra Señora de Guadalupe, 5-7. 28028 Madrid. España.
E-mail: rec@revespcardiol.org