01 December 2017 (online)
“sed levius fit patientia quidquid corrigere est nefas”
(Horace, Hor. Carm. 1.24.)
“Patience makes lighter what sorrow may not heal.” Seen from a cardiac perspective, this could be the motto of the right ventricle. It does not complain if it is stressed by volume or by resistance or by both but patiently enwraps its hyperactive left- and backward partner. Not surprisingly, as in everyday life, the silent and modest one tends to be ignored with the public attention being focused on the ever-present poser. And, again, as in human beings, origin and education influence the individual development of the two ventricles, eventually leading to two totally different personalities.
The right ventricle, which for once will have our undivided attention in this issue, is described as being the more primitive one. Comparative biology shows that the univentricular hearts of amphibia and reptiles show more similarities to what in birds and mammals has become the right ventricle than to the left one. Apart from the characteristic trabeculated structure, this can be exemplified by its extraordinary capability to be relatively independent of a true coronary arterial blood supply. In pulmonary atresia with intact ventricular septum, one may encounter what is called a “right ventricular-dependent” coronary circulation in which myocardial sinusoids provide right ventricular nourishment by internal surface enlargement, at the same time establishing sparse connections to the left coronary system with the right one being practically absent. In phylogenetic analogy, alligators cannot die from heart attacks because they have no coronaries which could become occluded.
Teleologically arguing, this patience is only possible because the recipient of the right ventricular output, the pulmonary arterial vascular bed, has an amazing compliance with low impedance levels. Thus, the right ventricle is able to achieve the same workload in volume per minute as the left one (the prerequisite of a biventricular circulation) with only about a sixth of the muscle mass. Its morphological characteristics allow it to accommodate increases in preload, whereas it adjusts relatively poorly to afterload changes, i.e., increased pulmonary arterial resistance: A gentle pressure on the liver will instantaneously raise cardiac output in the setting of volume depletion, whereas it is almost impossible to resuscitate a patient with pulmonary embolism. An atrial switch procedure for transposition of the great arteries, such as a Mustard or a Senning operation, will work beautifully in the beginning. When life becomes more stressful after a few decades and systemic impedance reaches heights unknown so far, the trouble starts for the hitherto silently working right chamber.
With the relative frequency of conotruncal abnormalities and other congenital afflictions of predominantly right-sided development, the right heart has always been familiar to the pediatric cardiologists. The predominant malformation, Tetralogy of Fallot, has, despite its relative complexity, also been among the first ones to become surgically corrected, which, in turn, has taught us a lot. Here, the right chamber has to keep up with increased afterload postnatally and cannot undergo the normal transformation to a low-pressure unit. Again, this works quite well for some time, because things do not change from prenatal life in which the right ventricle has been the workhorse for about 9 months anyway, generating most of the combined cardiac output. It finally becomes comforted by the surgeon whose main attention should focus on the right ventricular outflow tract reconstruction. Often, this will lead to a certain degree of pulmonary valve insufficiency, shifting right ventricular challenge from increased resistance to volume load for which it should in theory be better prepared. The necessary upkeep of right ventricular hypertrophy (one of the four things defined to be wrong by Etienne-Louis Arthur Fallot in 1888) may also lead to a “restrictive” physiology, a certain rigidity, which limits regurgitation volume. With its extraordinary patience, the right ventricle will, again, cope with these changes for a long time. The debate when to reoperate for pulmonary valve replacement is almost as old as cardiac surgery itself. Pediatricians, being protective people by nature, tend to postpone this operation pointing out the apparent well-being of the still growing child. This has led, and will continue to lead, to belated transferral, leaving the patient with a damaged ventricle even after a technically perfect repair. One of the problems in gathering sufficient data to better define right ventricular pathologies is its odd wrap-around shape, which impedes measurements and imaging. Refinements of modern technologies have started to shed more light on these puzzles.
It may be regarded as exaggerated to state that in adult cardiology there has been a relative lack of awareness of the right heart until recently. On the other hand, a story similar to that of the time point for pulmonary valve replacement in Fallot can be told for surgical treatment of tricuspid valve insufficiency. With the proverbial patience of Job, the right ventricle puts up for a very long time with all the nuisance its left counterpart and its rotten blood supply may have come up with, for instance mitral valve insufficiency caused by ischemic left ventricular remodeling. When a patient finally gets referred for valve repair in biventricular failure, the tricuspid valve needs a lot of caressing, and surgery in this setting has always been associated with rather dire results and therefore not been very popular. It is deliberately provocative to claim that with the growing interventional possibilities, the cardiologists have suddenly started to treat these patients earlier, not surprisingly with quite convincing results—not simply because of a superiority of these techniques and their limited invasiveness but also because of improved timeliness. This should now not lead to a continued postponement of surgical referral but, conversely, to earlier interdisciplinary discussions and improved selection, also and especially of open surgical candidates.
Cardiac surgeons are not necessarily renowned for being particularly patient and may therefore already have lost patience with this article on patience. Suffice it to say that there would be many more right heart aspects to ponder about. For the time being, let us end with Ambrose Bierce's ironic definition of our subject in his Devil's Dictionary:
“Patience, n. A minor form of despair, disguised as a virtue.”