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E D I T O R ’ S P A G E

RV Form and FunctionA Piston Pump, Vortex Impeller, or Hydraulic Ram?

Partho P. Sengupta, MD, Jagat Narula, MD, PHD

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The iPIX by Saremi et al. (1) in this issue

of iJACC highlights the precision of currentimaging techniques in displaying the com-plex 3-dimensional structure of the right

entricle (RV). The investigators illustrate the in-ricacy of normal RV geometry, highlighting theistributions of anatomical folds, irregular trabe-ulations and, more importantly, the RV in-undibulum. These remarkable pictures only makene question more on the physiological relevancef the complex RV geometry. The separation of ahin-walled, highly compliant RV and a thick-alled, highly contractile left ventricle (LV) haseen justified to the evolutionary needs of airreathing and high metabolism (2). The separa-ion of the right and the left circulations ensureresence of lower blood pressures in the pulmo-ary circulation; in its absence the thin blood-gasarrier required for high oxygen demands woulde breached with the least amount of exertion.iven that the 2 chambers require being separate,

here has been little information, however, to jus-ify why the geometry of the 2 chambers need toe so different.

RV as a piston pump. Longitudinal shortening andbase-to-apex piston-like motion of the atrioventric-ular plane have been suggested to be a greatercontributor to RV stroke volume than short-axis orcircumferential shortening. A number of measure-ments have therefore been explored, including thetricuspid annular plane systolic excursion (TAPSE),RV free wall annular velocities, and longitudinalstrain of the RV free wall. However, RV function issustainable even in the absence of RV free wallactivity, which can be completely excised and re-placed by an inert prosthetic patch as long as LVfunction is preserved. These observations question

wFrom the Icahn School of Medicine at Mount Sinai, New York, New York.

the longitudinal traction of the tricuspid annulus asthe basis for the pyramid-shape of the RV. More-over, the conventional echocardiographic indexesbased on RV longitudinal contraction have beeninconsistent and show poor correlation with RVglobal ejection fraction, at least in a post-operativepopulation with congenital heart diseases.RV as a vortex impeller. We have previously dis-cussed the structure and function of the LV inrelation to the sequence of blood flow, which ischaracterized by the formation of an asymmetriclarger anterior directed vortex formation. However,the RV geometry theoretically allows for an easyintraventricular transit of blood which does notrequire sustained vortex formation (Fig. 1A). Onlytransient vortex rings develop below the tricuspidorifice, that dissipate quickly. The intraventricu-lar RV flow has been confirmed in vivo usingechocardiography contrast particle imaging ve-locimetry (Figs. 1B and 1C) and has only revealedthe formation of vortices transiently in the tricuspidinflow region that vanish rapidly during diastole.The average flow in the RV during systole anddiastole therefore appears largely streamlined.RV as a hydraulic ram. A hydraulic ram is an ancientyclical water pump that was invented in the 17thentury which is based on developing a pressureurge when fluid in motion is forced to stop (or changeirection) suddenly. The pressure built is then used to

ift water to a point higher (supply head) than wherehe water originally started (deliver head) with theeast energy expenditure (Fig. 2). Blood flowing intohe ram under low pressure leaves it under muchigher pressure. The idea of the cardiac chambersherefore working on a principle similar to that of theater ram was prevalent in the mid-20th century (3).In a hydraulic ram (Fig. 2) the water in the

rive pipe flows under gravity and picks up ki-etic energy until the waste valve suddenly closesue to increasing drag. The momentum of the

ater flow in the supply pipe against the now

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closed waste valve causes a pressure surge thatopens the delivery valve, and forces water to flowinto the delivery pipe. The delivery pipe leads toan air chamber that cushions the pressure devel-opment. The air contained in chamber is com-pressed, and then it expands and forces the waterfrom the chamber into the outflow tube. As theflow reverses, the delivery check valve closes. If allwater flow has stopped, the loaded waste valve re-opens, which allows the process to begin again.The direct analogy of the hydraulic ram withthe function of the LV is not feasible because ofthe presence of a dominant vortex-aided designof the LV. However, the potential of RV func-tion modeled on a hydraulic ram seems attractive.The most compelling aspect of the analogy is thedevelopment of a pulsatile flow from a continuousflow and the striking similarity between the pres-sure curve tracings obtained from the water ramand the ventricle.Role of LV in RV function. The left side of the heart

lays a major role in assisting RV ejection. Theeptum thickens equally in both the RV and LVirections besides shortening along its apex-to-base

ongitudinal axis and contributes �60% of theystolic contractile force of the RV (4); injectinglutaraldehyde into the septum similarly reducesV pressure development. In addition, the end-iastolic position of the septum may present as aorm of septal preload and influence septal motionuring systole. Echocardiographic analyses confirm

nterventricular septum (IVS) shift with an increasen RV preload and influence the maximal IVSeformation and RV function. Thus, ventricular

nterdependence creates a balance of forces at thenterventricular sulcus. The forces in the LV freeall are balanced across forces in the RV free wall

nd the interventricular septum. Thus changing 1all can directly affect all 3 walls.

The role of right atrium. The blood streams from theuperior and inferior vena cava produce a noncol-iding flow rotation and vortex in the right atriumRA). Due to the characteristic morphology of theA and its role as a receiving and dilating chamberuring ventricular systole, flow keeps continuouslyrriving into the RA even when the tricuspid valves closed. One could imagine that without this rolef the RA cavity, the shutting of the tricuspid valveould halt the whole column of venous blood, andgreat pressure wave would be generated from this

topping of blood flow. These large changes in

ressures waves in the absence of unyielding veins

Figure 1. 3- and 2-Dimensional Flow Across the RV and RV Outflow Tract

(A) The 3-dimensional (3D) helical flow is shown during systole; streamlinesare color-coded (blue to red) with the local blood kinetic energy. Right ven-tricle (RV) intracavity flow is computed by using numerical simulation of theequations governing blood motion inside an RV geometry obtained by 3Dechocardiography. The image was recreated for iJACC by Gianni Pedrizzettiand Jan Mangual. (B and C) Transesophageal contrast particle imagingvelocimetry has been performed in a patient with normal RV function. Aver-age flow in systole (B) and diastole (C) are shown with streamlines that arecolor coded (blue to red) with the local blood kinetic energy. In contrast tothe left ventricle where the intracavity flow is dominated by vortex forma-tion, dominant vortical flow structures are not seen in the average flow pro-file of the RV. Transient vortices are formed in the inflow region, whichrapidly dissipate in diastole. Since the flow obtained in this example is in a2-dimensional plane, it may underestimate the helical spin seen in the RVinfundibulum.

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could be large enough to damage the venous system.This safety action of dilating atria as a receivingchamber remains under valued.The role of RV inflow and body. When the hydraulicram model is invoked for the RV function, theseptum may be perceived as the air cushion, trans-ducing forces developed across the septum in theLV cavity for systolic RV ejection. Indeed, thestrong correlation between LV pressure and RVperformance, the impairment of RV function inisovolumic rabbit hearts with reduced LV free-wallcontractility, and the detrimental effects of surgicaltransection of the LV free wall on RV developedpressure, which returns to normal after repair of theLV wall, suggests that the RV derives substantialsupport during ejection from the LV work.

The timing and the direction of blood flow inthe LV and RV also deserve consideration. Thetricuspid valve opens before the mitral valve, giv-ing the RV an advantage in directing and loadingthe blood flow over the unloaded septum. Con-versely, the RV ejection exceeds the LV ejection,which could allow the fluid forces developedacross the LV side of septum to maximally influ-ence the RV ejection. The tilt in the direction ofthe tricuspid valve plane and the streaming offlow from the RA allows maximum impact of thepreload over the convex surface of the septum(Fig. 1B), while the trabeculae would provide in-creased surface area for preload distribution. Theseptum would be shifted and deformed (right to

Figure 2. Basic Working of a Hydraulic Ram and a Historical Re

The concept of hydraulic ram (left) was developed 200 years ago atile flow (see text for details). The right side shows a pressure tracthe outflow tube (Top). This historic tracing depicts the experimperformed a series of experiments to relate the work of a hydraCraig Skaggs.

left shift) with greater right heart preload. The f

thin RV free wall would accommodate increasingblood volume that primarily loads the septum, themotor and force-generating surface of the RV.

It is also quite intriguing to note that the largeranterior vortex developed in the LV cavity primarilyflogs the septum and anteroseptal region of the LVwall before being redirected into the LV outflow.This congruence in design, such that fluid forces inthe LV cavity are directed over the septum, influ-ences interventricular interactions. Indeed, experi-mental studies have shown that rapid removal andaddition of fluid into the LV causes immediatechanges in RV pressure and volume outflow (5).The role of RV outflow. And finally, it is tempting to

ypothesize what potentially could be the reason forhe RV to have a long outflow. Firstly, a long outflowould allow a larger surface area for maximal interac-ion between the LV and RV. Secondly, the entry oflood under pressure from the RV body into narrowedV outflow would allow development of flow accel-

ration for development of a propulsive jet. Thirdly,he flow across the RV outflow may allow develop-ent of a helical spin in the flow. The numericalodel (Fig. 1A) and 4-dimensional flow using mag-

etic resonance imaging have shown presence ofelical flow in the RV outflow and pulmonary arteries.resence of helical spin, just like a gun barrel, providesetter directional stability and minimizes flow separa-ion and turbulence.

In all, some of the historical models of cardiac

of Pressure Tracings Obtained Inside a Ram

ses the water hammer effect to convert a continuous to a pulsa-obtained from a water ram at the delivery pipe (Bottom) andl work of Professor Leon Manteuffel-Szoege (1904–1973), whoram to a beating heart (3). Figure illustration recreated by

cord

nd uingentaulic

unction discussed here may need to be revisited.

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Furthermore, collective evidence from imaging

Pedersen M, Löfman C, Wang T.How the python heart separates pul-

3

4. Damiano RJ, LaJL, Lowe JE, Santa

ods will eventually help piece together the func-

techniques and quantitative and numerical meth- tional significance of the intriguing RV chamber.

5

R E F E R E N C E S

1. Saremi F, Ho SY, Sanchez-QuintanaD. Morphological assessment of theRVOT: CT and CMR imaging. J AmColl Cardiol Img 2013;6:631–5.

2. Jensen B, Nielsen JM, Axelsson M,

monary and systemic blood pressuresand blood flows. J Exp Biol 2010;213:1611–7.

. Manteuffel-Szoege L. Energy sourcesof blood circulation and the mechanicalaction of the heart. Thorax 1960;15:47–53.

Follette P, Coxmore WP. Sign-

ificant left ventricular contributionto right ventricular systolic func-tion. Am J Physiol 1991;261:H1514 –24.

. Chow E, Farrar DJ. Right heart functionduring prosthetic left ventricular assis-tance in a porcine model of congestive

heart failure. J Thorac Cardiovasc Surg1992;104:569–78.