The Structure and Function of the Helical Heart and Its Buttress Wrapping. IV. Concepts of Dynamic Function From the Normal Macroscopic Helical Structure

The Structure and Function of the Helical Heart and Its Buttress Wrapping. IV. Concepts of Dynamic Function From the Normal Macroscopic Helical Structure Gerald D. Buckberg) Carmine Clemente) James L. Cox) H. Cecil Coghlan) Manuel Castella) Francisco Torrent-Guasp) and Morteza Gharib Torrent-Guasp's model of the helical heart is presented, which includes the cardiac muscular structures that produce 2 simple loops and that start at the pulmonary artery and end in the aorta. These components include a horizontal basal loop that surrounds the right and left ventricles, changes direction through a spiral fold in the ventricular band to cause a ventricular helix produced by now obliquely oriented fibers, forming a descending and ascending segment of the apical loop with an apical vortex. These anatomic concepts are successively activated to produce a sequence of narrowing by the basal loop, shortening by the descending segment, lengthening by the ascending segment, and widening in the cardiac cycle that causes ventricular ejection to empty and suction to fill. The factors responsible for internal torsional movements for cardiac output and suction are defined, together with mechanisms responsible for electromechanical activity produced during sequential changes in contraction and relaxation properties. These interactions of mechanical structure and function are defined in relation to pressure-related cardiac events observed from aortic, left ventricular, and left atrial recordings. Copyright © 2001 by W.B. Saunders Company Key words: Fiber architecture, isovolumetric contraction, double helical coil, myocardial band, excitation-contraction.

T

he novel contributions of Torrent-Guasp de-

fine the macroscopic architecture of the myocardium, as shown in the Handbook qf Physiology in 1979, I as an interaction between an external wrapping of a basal loop to form a stiff outer shell, and an internal double helix with a vortex at its apex. 2,3 These underlying concepts are summarized and then synthesized with dynamic functional components. The structural configuration of the myocardial band includes a circumferential basal loop, to surround the left and right ventricles that then

From the Departments of Surgery and Neurobiology, University of California at Los Angeles, Los Angeles; the California Institute of Technology, Pasadena, CA; The International Medicine Group, Washington, DC; and the Department of Cardiology, University ofAlabama at Birmingham, Birmingham, AL. Address reprint requests to Gerald D. Buckberg, MD, Department of Surgery, UCLA Medical Center, 2-258 CHS, Los Angeles, CA 90095-1711. Copyright © 2001 by WB. Saunders Company 1043-0679/01/1304-0004$35.00/0 doi: 10.1 053/stcs.2001.29956

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become an oblique double helix to form the apical loop. The apical vortex similarly includes two components within this spatial orientation. First, the descending segment proceeds from base to apex. After the turn in the helix, there is an ascending segment that originates at the apical tip and extends toward the aortic valve. The reciprocal spiral nature of apical components is firmly established by air insufflation studies by Lunkenheimer et a1. 4 Sequential contrast scan tomography sections the ventricle transversely to allow evaluation of each spiral component, and to define development of characteristic clockwise versus counterclockwise reciprocal spiral rotation between the descending and ascending segments within the apical loop. These geometric changes are visualized passively in nonviable hearts, and must become dynamically activated for function. This anatomic spiral configuration is also clarified histologically during transverse section morphology by Greenbaum et a1. 5 A fundamental component is the anisotropic fiber orientation proceeding from apex to base in opposite direc-

Seminars in Thoracic and Cardiovascular Surgery, Vol 13, No 4 (October), 2001:

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Figure 1. The intact heart, showing the basal loop and helical loop. The rope model, beneath the heart model, defines the underlying architectural pattern, with three segments. These include (1) the point of origin and finish at the aorta and pulmonary artery, (2) the circumferential wrap around the basal loop with RS and LS, and (3) the helix that includes the descending segment and ascending segment of the apical loop.

tions in the descending and ascending segments that produces the shape contour needed for electric activation and then subsequent contraction for both ejection and filling. 6. s The architecture for these underlying anatomic elements of the myocardial band proceed initially in a sequential manner from right to left segments of the basal loop, and then continue in a more oblique way within the descending segment in the apical loop. The oblique sequence of fiber formation undergoes a helical turn at the apex to finish at the aorta and reflect the basal wrap and helical coils of a rope (Fig 1). The

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anatomic blueprint of underlying nonfunctional structure is characterized by the morphologic dissections of Torrent-Guasp, 1·3 and through the air insufflation studies that allow gentle muscular separation of the 100ps.4 These noninvasive studies establish configuration and simultaneously offset concerns of conceptual artificial cleavage planes that are developed during manual dissection of ventricular folds. The insufflated air follows the muscular fibers and dissects between planes to reveal natural fiber formation. The functional counterpart of this myocardial band fiber orientation becomes established by recordings of the contraction sequence of movement within the myocardial band by Fourier analysis in nuclear medicine studies. 9 The repetitive sequence of traveling wave contractile activity is then used to establish the mechanical functional component, evident by surface visualization of the beating heart, and brought together more completely by interaction of the sequential band contraction components through magnetic resonance imaging (MRI) studies, evaluation of excitation-contraction coupling, and integration of these observations with conventional pressure recordings, and sonomicrometer recordings that underlie basic physiologic considerations. Figure 2 describes these underlying anatomic components that separate the rolled, intact heart into an unscrolled muscular band with a transverse basal loop, and an obliquely oriented apical loop composed of a descending and ascending segment. This article defines the mechanics of cardiac sequential function during traveling wave progress of sequential contraction along the myocardial band. These changes are correlated with contractile alterations by (I) visual inspection of the heart in the operating room, (2) internal structure-function relationships evaluated by MRI analysis, and (3) sonomicrometer recordings of sequential function. Our intent is to define how the resultant actions of narrowing, shortening, lengthening, and widening relate to the function activation of the fibers within the myocardial band.

Dynamic Function The visible function of the beating heart includes two longitudinal movements, shortening and lengthening, and two transverse movements, narrowing and widening. These actions shown in Figure 3

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Figure 2. (A) The ventricular myocardial band. The basal loop has been represented in white, with the RS and the LS, and the apical loop, in black, with the descending segment and the ascending segment. (B) The descending segment and the ascending segment as they are in repose. (C) The contraction of the descending segment originates the counterclockwise rotation (torsion) of the ventricular base (upper arrow) and the clockwise rotation of the apex (lower arrow) and, as a consequence, inevitably the ventricular base descends, shortening movement of the ventricular mass. (D) The contraction of the ascending segment originates the clockwise rotation (untorsion) of the ventricular base (upper arrow) and the counterclockwise rotation of the apex (lower arrow) and, as a consequence, inevitably the ventricular base ascents, lengthening movement of the ventricular mass.

are seen by echocardiography, and MRI film from the cardiac surface,lo in this sequence: (l) narrowing movement, a decrease in the transverse diameter of the base, caused by the contraction of both segments of the basal loop (Figs 3A and B); (2) shortening movement, a decrease in the longitudinal axis caused by the initial descending segment contraction, and shortly thereafter ascending segment contraction (Fig 3C); (3) lengthening movement, an increase in the longitudinal axis caused by the contraction of the ascendant segment, after descending segment contraction stops (Fig 3D); (4) widening movement, an increase in the transverse diameter of the base, from stretching of the ventricular walls during rapid filling, and slow ventricular stretch with relaxation and passive filling (Fig 3E).

This contractile sequence requires progression of the contractility wave along the successive four segments of the myocardial band so that the basal segment contracts (narrows), before the two apical segments shorten, and then lengthen by the ascending segment, and finally widen. The mechanical activity proceeds from the basal loop (right ventricle to left ventricle), to the apical loop (descending to ascending segments), or right- to left- to descending- to ascending segments. This progress was shown initially by Roy and Adami II in 1890, and then corroborated by Armour and Randall 12 in 1970 with strain gauges, and now by nuclear medicine studies by Flotats et aI,9 who confirm a sequential contraction, progressing from the right ventricular (RV) basal loop

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Figure 3. The four cardiac movements. (A and B) Narrowing by contraction of th e basal loop, (C) shortening by contraction of the descending segment of the apicaiioop, (D) lengthening by contraction of the ascend ing segment of the a pical loop, and (E) relaxation without contraction. This is the normal sequence of progressive systole with peristaltic contraction of each segme nt of the myocardial band.

segme nt to the left ventricular (LV) basal loop, and to the descending and asce nding segments of the apical loop.

The Problem of the Ventricular Dilation Traditionally, ejection of blood follows ventricular constriction because narrowing the ventricle initiates the raise in intraventricular pressure that will open the aortic valve after the ventricle thickens. This mechanism of heart mechanics

does not explain suction of blood from the atria when the mitral valve opens. The left ventricular cavit ies fill in a rapid powerfu l manner (0.15 s), accounting for 50% of diastolic inflow during the first 20% of the time interval between mitral valve opening and subsequent clos ure during isovolumic (isometric) systolic contraction. The ra pid filling int erval cannot b e achieved by passive flow from a pressure gradi ent becaus e the normal difference between atrial and left ve ntricular pressures is approximat ely 5 mm Hg.

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Consequently, suction is needed and requires a forceful muscular contraction to allow the cavity to develop a structural change to allow the filling of its chambers after the mitral valve opens. This elongation must occur at a time when its blood volume is fixed during the isovolumetric phase after ejection. There are two phases of dilatation, which include an active phase of muscular contraction causing suction, and a passive phase of widening during the diastolic interval after the ascending segment stops its contraction.

The Mechanism Through Which the Ventricles Perform Their Narrowing, Shortening, Lengthening, and Widening Movements Narrowing of the Ventricles A new cycle begins in the relaxed heart at the completion of diastolic filling (Fig 3). Narrowing occurs because the apical loop becomes embraced by sequential contraction of first the right segment (RS) and then the left segment (LS) of the basal loop. The consequence is a rigid muscular shell that surrounds the apical loop, which contains the subsequently successive, contracting descending and ascending segments. The direction of fibers is transverse in the stiff outer shell of the basal loop, so that the circumferential contraction slightly reduces the left ventricular diameter and causes a slight "cocking" of the basal loop in a clockwise direction before apical twisting, as described in 1961 by Coghlan et al. 13 The isovolumetric contractile phase is initiated by the basal loop, whose horizontal fibers act as a buttress to avoid spreading of the oblique apical loop fibers during their subsequent contraction.

Shortening of the Ventricles The internal configuration of the ventricular mass is shown in Figure 2A, which separates the basal loop (in white), composed of the right and left segment, which surrounds the apical loop (in black). The descending segment, and ascending segment, components of the apical loop, cross each other to produce the right angle or X-shaped formation within the septum, as described by Mall l4 in 1911. The initial contraction of the basal loop (Fig 3A and 3B) is followed immediately by contrac-

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tion of the descending segment of the apical loop, which simultaneously produces two contrary rotations (Fig 2C). One is counterclockwise at the base, and the other is clockwise at the apex. This writhing, or torsion, initiates shortening of the ventricular cavities. In the helical heart with contractile progression down the descending segment, there is sequential torsion, or twisting, to shorten the slope and make the long axis more longitudinal, while simultaneously thickening the muscles to compress the intraventricular contents. The apical loop muscle mass then undergoes a turn, or vortex at the apex, to become the ascending segment, where segmental torsion is directed in a manner reciprocal to the descending segment. These contractile changes begin shortly after descending contraction (Fig 4), contribute to shortening as a counter rotating force shown by implanted crystals,6,8 and will be considered more extensively under the section "Lengthening of the Ventricles." A major force of twisting while shortening during apical descending segment contraction is the wide basal loop that is connected to the apical loop by the fold in the myocardial band; the overriding trajectory is counterclockwise rotation during its contraction (Figs 2 and 5). This directional wringing motion continues, even though the narrower apex turns clockwise, because the guiding momentum is the wider axis of the turn of the upper connection of the basal aspect of the descending segment to the basal loop that maintains the apical counterclockwise turn. The similarity to this trajectory of force is when a train moves forward in one direction (corresponding to the bulk of the descending segment rotating counterclockwise) with the passengers at the apex running backward (corresponding to clockwise twisting backward). The consequent apical rotation is always counterclockwise. The sequence is the apex moves counterclockwise during the descending loop contraction as it is turned by the counterclockwise motion of the descending segment. 15 During the later phase of ascending segment contraction, the apex then moves normally in a counterclockwise direction, as the torsion reverses and wringing of the ascending segment goes from apex to base in a clockwise direction (Figs 2 and 5). Consequently, the sequential twisting of both the descending and ascending apical loop segments reflect the

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Figure 4. (A) The model (upper tracing) and intact ventricle (lower tracing) with position of sonomicrometer crystals. The descending segment is deep, with hatched lines, whereas the ascending segment is superficial (solid line). (B) The simultaneous recording of descending segment and ascending segment contractions, left ventricular pressure by Millar catheter (Millar Instruments Inc, Houston, TX), and dP/dt from the pressure tracing. Note the delayed start of ascending segment contraction (first dotted line), and its termination after descending segment stopped (second dotted line). The longitudinal lines show the start contraction of descending segment, the start contraction of ascending segment, the stop contraction of descending segment, and the stop contraction of ascending segment.

torsion of the band described by Borelli 16 in 1681. However, these segments twist in opposite directions, and on themselves within the helix. The tip contains an apical vortex that is a movable or rotational point, where the musculature appears visually fixed.

Lengthening of the Ventricles The movement of lengthening follows internal and external factors. The sequential contraction of the ascending segment (Fig 2D) immediately follows the initiation of descending loop contrac-

tion, and continues after descending contraction stops (Fig 4). The descending segment remains somewhat stiffened within its muscular walls, but less so than the newly contracting ascending segment, and thereby configures a pronounced Sshape (Fig 2C) from tension (Fig 2D) of its muscular fascicles. The residual stiffening allows the descending segment to become a fulcrum or guide around which the ascending segment contracts. There is progressive active contraction of the ascending segment with a change in the slope to become more vertical. The isovolumetric rise

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or lengthening occurs afler the active contraction of the descending segment stops, and corresponds to less opposition to the reciprocal direction twisting of the ascending segment. The contractile phase of lengthening differs from the current concept of isovolumetric relaxation (IVR), so that this interval is a late isovolumetric contraction (lYC) and alters the conventional concept of r ecoil from potential energy.6.8 Torrent-Guasp suggests the progressive sequence may reflect a m echanism of contraction similar to the paraventricular musculature of snakes when they rise to attack. 17 .18 The analogy to the snake may b e misleading because the snake is longitudinal; the heart has a helical structure and the sequential contracting muscle segments wrap around themselves. When the active contraction of the descending segment is

Figure 5. External rotation of the ext ernal base and apex, seen by vision and MRI during isovolumetric phase of basal loop contraction (narrowing the transverse diameter). The contrac tion of the descending loop shortens the ventricle, while both the base and apex rotat e counterclockwise. The contractile descending segment is behind the overlying ascending segment. The clock shows the traj ectory of rotation. Contraction of the apical loop produces external counterclockwise rotation, lengthening the ventricle and starting the rapid filling phase . When the ventricular band relaxes, the passive filling is achieved withou t active contraction of the basal or apical loops.

stopped, its rigidity persists, and active ascending segm e nt contraction and coincident thickening produces a quick and powerful ascent or lengthe ning movement of the ventricle toward the base that is accompanied by a clockwise motion of the ventricular base, and a counterclockwise movem ent of the apex (Figs 2C and 2D). Two explanations for the mechanisms of shortening and lengthening of the ventricles include first, the conventional concept of twisting (or torsion) of the descending segment to ejection (as described by Borelli 16 in 1681), and then successive un torsion (recoil or r e lease of torsion)9 to le ngthen. This conce pt of twisting and untwisting is consistently described in each MRI study of endocardial and epicardial segments,6.8.19 and is favored by Torrent-Guasp. Through this concept , the heart does not either shorten or

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Figure 6. MUGA scan view. Apical loop contraction starting at septum. (A) Descending segment contraction develops, shown in cloverleaf region now appearing in the center of previously noncontractile area of apical loop, causing shortening of the ventricles. This correlates with left ventricular ejection phase. (B) Contraction progresses into ascending segment, which raises to lengthen the ventricle. The wave of active contractile sequence now appears in the previously motionless layer above the descending segment. Simultaneously, there is the beginning of withdrawal of color from the descending segment, as the peristaltic wave enters the ascending segment. The maintained color of the cloverleaf segment reflects residual, reduced descending segment contraction, to maintain descending segment stiffening and allow cavitary lengthening during ascending segment contraction.

lengthen along its longitudinal axis through respectively segmental descending (drawing down) or ascending (stiffening up) movements, but through rotational movements on itself, torsion and untorsion, twisting and untwisting around that longitudinal axis, as shown in Figures 2C and 2D. Application of the torsion-un torsion concept indicates that twisting movement implicates shortening, the untwisting movement implies always a lengthening and enlarge ment of a material object. Cardiac application of this mechanicallaw explains how the ventricular cavities can suddenly and powerfully decrease and increase their volume for ejection and suction of blood. The alternat e hypothesis for lengthening is a progressive torsion t hroughou t the apical loop, initially in one direction (descending limb) , and after the apical vortex in a reciprocal direction in the ascending segment. This concept is introduced by Buckberg and Coghlan. The multiple gated acquisition (MUGA) scan, wit h Fourier

analysis reported by Flotats et al 9 confirmed that there is an active contraction in the ascending segment when it lengthens (ie, torsion) (Figs 6A and 6B). The onset is promptly after the descending contraction, and during its contraction, as seen on sonomicrome ter recordings (Fig 4). When this occurs, the contraction of the descending segment persists. There is a continuance of the ascending contraction, after the active contraction of the descending segment stops to account for lengthening from reciprocal torsion in the ascending segment. The descending segment remains rigid, despite the absence of active contraction, so that a thickened, stiffened muscle allows the descending segme nt to become a fulcrum, but one which contains less tensile force than the newly contracting ascending segment that wraps around the descending segment that is a guide to lengthening. Under these circumstances, the prior concept of untorsion reflects loosening, or loss of twisting (untwisting), in the ascending segme nt, and this does not occur. Con-

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sequently, the concept of un torsion relates to relaxation that occurs ajter the systolic phase, and characterizes the noncontractile phase during diastole. This novel concept, torsion in an opposite direction during contraction of the ascending segment, produces a writhing of that segment, in the same manner that Mall,14 Borelli,16 and Lower 2o described for the descending segment to eject. Now, however, the result is lengthening of the ascending segment caused by its shortening, thickening, but also its elongation, as seen in Figure 2. The helical model, thereby brings into focus the same mechanism for shortening and longitudinal lengthening that had previously been hidden through inability of anatomists to dissect and define the apical helix whereby there is successive and sequential peristaltic contractile motion, starting in the descending segment (from base to apex) and then in the ascending segment (from apex to base) in a reciprocal direction. In one sense, the reciprocal twisting of the ascending segment in an opposite direction "resurrects" Borelli's concepts of reciprocal torsion, through the novel recognition by TorrentGuasp of the ascending segment of the apical loop. These shortening and lengthening motions are confirmed through MRI tagging by Lorenz et aFl and by Moore et aI.22 The segmental basal loop motion reflects a female screw bolt when coiling down and up on its helical male screw. The basal loop descends and ascends, in a coillike manner, embracing the apical loop when twisting in one direction, this is followed by twisting in another direction, after the vortex to reflect the reciprocal clockwise and counterclockwise consequences of oblique muscle counterforces during descending segment and ascending segment contractions (Figs 2C and 2D).6,8 These activities produce a shortening movement of the base by clockwise and counterclockwise twisting its longitudinal axis, which reverses when the basal and apical cores are twisted in opposite directions. Any material object in a helical formation can become twisted in one direction, and after the vortex, spirals to twist in another direction. It will therefore undergo shortening and lengthening depending on the length and resulting radius within the helix of the involved segment. 6,23 Applying this mechanical law to the heart, the api-

cal loop suddenly and powerfully decreases and increases the volume of the ventricular cavities, inducing a corresponding ejection and suction of blood. The lengthening movement of the ventricles is caused by contraction, producing twisting, together with thickening and a more longitudinal course or torque. The concept of stretching, like a spring, is recognized, but the shortening is caused by contraction, and not the recoil from stored potential energy, as has been suggested to explain the elastic elements responsible for restoring forces. 24 The ascending segment is longer, has more radius, and undergoes the same change of twisting in the opposite direction. The relaxed ascending segment becomes elongated during the initiation of descending segment contraction. The ascending segment will contract and compresses or thickens from this more transverse position. This contraction-related shortening will allow the ascending segment to at first compress the descending segment and then lengthen (Fig 2) and become more longitudinal in its orientation when it is no longer opposed by descending segment contraction.

Internal and External Consequences of Sequential Shortening and Lengthening The concept of ascending segment lengthening caused by contraction becomes confusing because the thickening muscle is known to shorten. The explanation must therefore define changes that are observed from the external appearance of motion, yet result from internal activity within the apical loop. The central theme of muscle contraction is twisting, which will produce a torque or angular force that apex and base see in respect to each other. The motion reflected to the external observer is the same as twisting, but in a relative sense reflects the torque. This relationship is seen from both the internal changes of the descending and ascending limb shown in Figure 2, and the exterior motion shown in Figure 5, which appears on both external visualization and MRI recordings that define both deformation on tagged images, and ejection and suction flow dynamICS. Insight into these dynamics come from finite muscle analysis studies, using a helix fiber angle, that show the inner LV shell contracts at a 60° angle from epicardium to endocardium during ejection, then the outer shell contracts in an

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Figure 7. Figure 2 is repeated, with coils in the descending segment and ascending segment. (B) Note that the basal loop narrows while the coils in the apical loop are relaxed (ie, no contraction). (C) There is contraction of the descending segment from base to apex with shortening of the loop, thickening, and longitudinal directional motion of the descending segment. Note the elongation of the ascending loop segment during descending segment contraction in comparison with B. (D) The sequential contraction goes around the apical helix into the ascending segment that now contracts from apex to base. Again, there is thickening, shortening, and elongation of the segment to directionally rise, despite a shorter longitudinal length. There remains residual active but diminished contraction in the descending segment, to allow its rigidity and thereby allow elongation by ascending segment contraction.

opposite 60° direction in the latter part of systole. 25 A similar angular direction is seen in the rope described in Figure I, which defines the descending segment and ascending segment of the apical loop. The layers of muscle contain internal imbrications, as described by Mall l4 in 1911, by using the term shingles atop a roof This was described more completely by Streeter,26 who worked with Torrent-Guasp, to begin to define the imbrication angle. The overlapping fibers folIowa spiral figure-eight angle in the inner shell of the descending segment (starting from the endocardium) in an opposite, and comparable angle in the ascending segment, or epicardial region in the apical 100p.19 Figure 2 has been modified to show this shingle relationship in Figure 7 in the sense of coils that overlap each other within these segments. The coil within a coil organizational

pattern mirrors the internal coils within the reciprocal helical horns of ram-like animals (Fig 8).27,28 The sonomicrometer crystals were inserted in the pathway of the compressive di-

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Figure 8. Natural coils within coils of ram-like animal (eland). (A) Note the reciprocal coils of the horns, and (b) external spiral coils within each horn to provide stability during contact in battle with other animal.

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rection of these coils, twisting one on another, to gain maximum coaptation during contraction (Fig 4) . Note in Figur e 7 the similarity of coils in ascending segment and desce nding segment before beginning of contraction in the descending segment, and the compression of th ese coils in the d esce nding segment together with shortening and a more longitudinal direction of that segment. This torque develops from twisting. This writhing to compress intraventricular contents resembles the twisting of a rope described by Borelli 16 in 1681, to produce ejection. The rope contains a figure-eight vortex at the apex to connect a coi l that goes in an opposite direction to explain suction. Note also the stretching of the coils within the ascending

Figure 9. Chronologie sequence of contraction of both segme nts of the apical loop as recorded by sonomicrometer crystals. (A) The descending segment contracts first, to begin ej ection, wh ile the ascending segment is relaxed (first solid longitudinal line). (B) Shortly after descending segment contraction, the ascending segment starts to contract (hatched line), to reflect both segments contract ing in reciprocal directions for the res t of ejection. (C) When the descending segment reaches its maximal contraction (second solid line) th e asce nding segment continues contracting to raise the ventricle and start the isovolumetric contractile phase, which stops at the dotted line.

segment to produce a longe r initial length. In Fig ure 7C, contraction of the ascending segm e nt causes compression of these coils, together with a more longitudinal direction, or le ngth e ning. Insight into this lengthening is a lso seen in Figure 9, which charact e rizes the sonomicromet er tracings, and shows the stretching and slightly delayed ascending segment contraction and its persistence aft e r th e desce nding segm e nt contraction finishes. The torque is shown in Figure 7C under twisting in the opposite direction. Consequently, th e twisting of a rope, d escribed by Borelli 16 for ejection within the d esce nding segment, occurs also in the ascending segment to shorten. The r e is opposite di-

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rec tion twist caus ed by th e helix, which produces lengthening to pr e pare for suction. The uncovering of the a sce nding segment to complete the helical form of th e apical loop, in one way resurrects the torsion concept of Borelli of wringing of a towel downwa rd to eject, and now wringing of a towel in a r everse direction upward, to lengthen and fill.

Widening of the Ventricles There are two wide ning components, the first caused by muscle contraction and the second caused by contractile effects on ventricular volume. These are consequ e nces of reciprocal twisting to lengthen, rotat e, and widen as the ventricula r chamber fills. The asce nding segment, responsible for lengthening, also contains the thin aberrant fibers . These superficial thin fibers (Fig 10) come from th e anterior left ventricle, a nd contract with th e a scending segment whil e the ventricles are lengthening. They also cover subepicardially, the free wa ll of the right ventri-

Figure 10. Schematic reprodu ction of the ventricles in frontal view. Two groups of a berra nt fibers have been rem oved, showing, unde rn eat h, the autochthonous mu sculature of the ri ght ve n tricle. The aberrant fibers jump from the ante rior face of the left ventricle to cove r the free wa ll of th e rig ht ve ntricle and, aft er passing over the post erior face of th e ventricles (see a rrow on left), they a rrive a gain a t the anterior face of th e left ventricle (a r row on rig h t).

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cle, finishing at the pulmona ry a rt ery and tricuspid orifice rings, and along the perime ter of the ve ntricular base. This anatomic distribution allows them to pull, simult a neously, both ventricular walls to help open the ventricular cavities and produce a rotating action that is externally visible. Th e mitral valve opens during th e initiation of active or contractile phase of le ngthening,29-31 a nd high velocity filling occurs after lengthening has be en achieved. 32 The fun ctional change is ra pid widening movement of the ventricles caused by active suction of a trial blood into the left ventricular cavity, stemming from the predominant action of ascending segment lengthening. In contrast, the aberrant pa thways produce an external change because th e widening and narrowing movements of th e ventricular mass represe nt secondary events compared with those m entioned earlier relating to the inte rnal actions of desce nding segment and asce nding segme nt that change ventricular cavity volume. During relaxa tion, after ascending segme nt contraction, there is physical (or passive) wid ening of the left ve ntricular chamber from left ventricular filling from the left atrium that is caused by pressure, not asce nding segment contraction. The rotational effects of these aberrant fibers are clear on visual cardiac inspection, where they rotate to turn the left and right ventricles without contributing to the intracavitary left ventricular wall thickening that is primarily responsible for ej ection and suction. This disparity becomes most evident after myocardial infarction with occlusion of the left anterior desce nding artery, whe re those aberrant supe rfic ial fibers are salvaged by revascularization. Th e surgeon observes a h ealthy appearance on the cardiac surface, yet the re is loss of the unde rlying requirements of ej ection and suction produced b y the deeper fibers o f the descending segme nt and ascending se gm ent. Confirmation of the underlying segme ntal noncontraction (akin esia) is clear from ve ntriculogram, echocardiogra m, and MRI recordings.

The Chronologie Location in the Cardiac Cycle of the Decrease and Increase of the Volume of the Ventrieular Cavities Robb a nd Robb33 showed that the progression of the e lectric excitatory pathway in the ventricular myocardium takes place a long th e longitudinal

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axis of the fibers, so that the four segments of the ventricular band must successively enter into activity: right, left, descendent, and ascendant. The final result is a novel anatomic and physiologic correlation of excitation and contraction that follows the visible Purkinje network and the new macroscopic ventricular myocardial mass. Robb and Robb 34 describe that the Purkinje system, in its final distribution, becomes oriented in a line parallel to muscle fibers. The action current is distributed to each muscle individually, and where the wall is thin, as the apices, and pulmonary conus, the pathways are demonstrably shorter. The pathway to the deeper muscle is longer, and the negativity is later, as with the septum comprised by the apical loop. The intracellular matrix sheaths separating these muscles may become a critical factor, to correlate electric changes and single muscle bundle contraction. The sequence ofPurkinje fiber excitation front or wave follows a cable-like electric system that visually penetrates only in humans, to the endocardium (inner third). This is termed a specialized conduction system and carries impulses that spread in line with fiber orientation. Unfortunately, the precise sequential spread of impulses, followed by production of sequential contractions of muscles, has not yet been clearly defined. It is known from multisite recordings that there is a progressive delay in the appearance of the action potential, from its early origin at the SA node to the atrioventricular node, slightly later in the Purkinje system, and latest in ventricular muscle fibersY The impulse moves more rapidly in neural than muscular environments, and the conduction system is formed from primitive myosin for rapid movement. 36 The heart contains a somewhat thicker myosin in the atria (where excitationcontraction is more rapid than ventricular) and, finally, the thickest myosin is within the ventricles. Consequently, these differences in thickness of muscle elements and their connective tissue matrix pathway between the Purkinje fiber and myocyte can define excitation and contraction, as suggested by Robb and Robb. 33 ,34 Studies by Sodi-Pallares and Calder 37 and Cox 38 show that the right ventricle wall is activated before the left ventricular wall. The thinnest contractile fibers for ejection surround the right ventricle basal segment and then the left ventricle basal segments. Armour and Randall 12 observed that the basal loop of the left ventricle

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Figure 11. Diagram from Roy and Adami manuscript from 1890, showing method of recording contraction from the deep papillary muscles, and epicardial basal loop during normal heart function. The initial contraction always began at the epicardial segment of the basal loop, before papillary muscle contraction.

contracts before shortening of the apical loop that provides the contractile origin of the papillary muscles. Their observations follow precisely the report of Roy and Adami II in Cambridge in 1890, showing that the circumferential basal segments contracted before the apical loop contracts and shortens the papillary muscles (Fig 11). The circumferential surrounding fibers, which are called aberrant fibers, cover the underlying right and left segments of the basal loop that become progressively thicker to form the stiff outer shell during contraction. The papillary muscles are thicker and emerge from the descending segment of the apical loop, which defines the bulk of the myocardium descending, which includes the anterolateral left ventricle, the septum, and the papillary muscles. Armour and Randall l2 also observed a hiatus between the first point of excitation at the anterior papillary muscle and its later contraction

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Ao Figure 12. Sequence of contraction of the different segments of the myocardial band through the cardiac circle. (A) Contraction of the basal loop, (B) contraction of the descending segment and shortly after ascending segment, and (C) contraction of the ascending segment while the descending segment maintains its stiffness.

after the basal loop shortened. These observations may show why (1) the anterior papillary muscle is stimulated first, yet its thicker underlying contractile element formed by the apical loop undergoes delayed contraction; (2) the right ventricle and then the thicker left ventricle of the basal loop contracts sequentially, introducing the isovolumetric or isometric phase, with ballooning of the mitral and tricuspid valves into the left and right atria; and (3) the descending segment and then ascending segment of the apical loop contract progressively to at first shorten and then lengthen ventricular cavities. The apex is relatively fixed, and this results in initial retraction of the mitral valve during ejection from the papillary muscle shortening, then ventricular elongation with deformation and unwinding to create an avenue for suction. Recent Fourier analysis of a MUGA scan study shows the sequential contraction of (l) the right ventricular basal segment, (2) the left ventricular basal segment, (3) finally, the descending limb of the septum, and (4) shortly thereafter, the ascending limb of the septum to conform to the pattern of mechanical activity that follows the trajectory of the myocardial band. 9 These nuclear medicine observations are consistent with reports of Roy and Adami II in 1890, Armour and RandaljI2 in 1970, and the novel peristaltic excitation-contraction pathway described in the basal and apical loops to blend the specialized conduction system with macroscopic anatomy. The main purpose of the contraction of the basal loop is to act as a buttress making up that rigid cylinder that alternatively comes up and

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down, movements that follow the contractile action of the descending segment and ascending segment of the helicoid apical loop. The heart is called the motor if the blood circulation, the apical ventricular loop is called the cardiac motor. At the beginning of the cardiac cycle (during the so-called isovolumic or isometric phase) the ventricular cavities decrease in volume, shown in Figures 2 and 12. The consequence is an increase in intraventricular pressure during this phase, caused by a narrowing movement (Fig 3) initiated by the contraction of the RS and LS of the basal loop. Afterwards, that decrease of volume is continued as a result of the contraction of the descending segment of the apical loop, which gives rise to the shortening movement of the ventricles, with thickening, which induces the beginning of ejection of blood. The contraction of these three segments (right and left basal loop and descending segment of apical loop) corresponds to the ascending ramp of the intraventricular pressure curve (Figs 2 and 12). Recent sonomicrometer recordings confirm that the contraction of the ascending segment originates shortly after the contraction of the descending segment,6 and thereby also occurs during ejection (Fig 4). This observation is consistent with early evidence of ascending segment in nuclear medicine studies, where Fourier analysis confirms the sequential peristaltic development of contraction in the band (Fig 6). The descending contraction is dominant, and shortening continues. Conversely, lengthening occurs after the active contraction of the descending segment is complete. The consequence is the

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absence of active contractile opposition to ventricular ascent during the isovolumetric contractile phase that produces the elongation activity of the ascending segment. The sequence that correlates sequential descending and then ascending contractile actions with the sonomicrometer documentation is shown in Figure 9. The ventricular cavities increase in volume because of their lengthening and widening, as a result of the contraction of the ascending segment (ie, of the contraction of the intraseptal and the aberrant fibers). The reciprocal spiral contraction of the ascending segment produces ascent of the base. Elongation occurs after the cessation of contraction of the descending segment. The descending ramp of the intraventricular pressure curve from its highest point to the lowest point, and a fall of intraventricular pressure, occurs during this period of time. The result is lengthening of the cavities of the ventricles without a change in blood volume. The change in shape to lengthen the chamber is caused by ascending segment contraction, so the concept of isovolumetric relaxation (IVR) must be changed to isovolumetric contraction (IVe). The mitral valve leaflets separate during this isovolumetric phase of contraction,29-31 and this has been ascribed to alterations in geometry.3D The unopposed contraction and deformation of the ascending segment produces this mitral opening. Recent MRI studies confirm prior echocardiographic characterization that long axis wall motion precedes rapid transmitral blood flow 32 that is a suction of blood, or thc rapid ventricular filling phase that occurs when LV pressure falls below left atrial pressure (Figs 2 and 12). These observations clarify the role of the entire ventricular mass in the progress of cardiac activity, and focus on the critical importance of sequential contractile motion along the myocardial band.

ventricular cavities, the suction of blood cannot occur by dilatation alone. We introduce a novel interpretation of heart mechanics to address the longitudinal movements. Ventricular shortening and lengthening movements become integrated with torsion, and then reverse torsion, and thereby relate to both the ejection of blood to empty, as well as suction of blood to actively fill the cardiac chamber. These longitudinal activities synthesize with the sequential peristaltic contractile activities of the entire ventricular mass along the myocardial band, which courses from the pulmonary artery to the aorta, the basal loop acts as a buttress because the successive contractions of its right and left basal loop segments to form a stiff outer shell (cylinder) that descends to tightly embrace the apical loop (helical coil) that descends during contraction of the descending segment, and then ascends during contraction of the ascending segment. The consequence is changes in intraventricular pressure that correspond with ejection and suction of blood. Although these interpretations of heart mechanics seem firmly supported by the structural architecture of the ventricular myocardium, further studies are needed to explore the functional contractile dualism of the heart. The accumulated data may clarify new concepts of heart structure and mechanics that can change diagnosis and treatment.

References 1. Streeter DD: The cardiovascular system I, in American

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Discussion In the classic interpretation of heart mechanics, the transverse movements of the ventricular mass, its narrowing and widening, are considered the most important in the work of the heart. That conventional idea suggests that the heart performs its functions mainly by alternating constrictions and dilations. Although ejection of blood is easily explained from constriction of the

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