Cardiac Helical Function


 Background. The aim of this study was to investigate: a) the starts and ends of the myocardial band; b) the slippage between the band segments, when performing both torsion and ventricular detorsion, implies that there should be an antifriction mechanism that avoids dissipating the energy; c) the electrical activation of the endocardial and epicardial bands and secondarily understand ventricular twist and the mechanism of active suction during the diastolic isovolumic phase. Methods. They were used: a) Ten young-bovine hearts (800-1000 g) and seven human hearts (one embrión, 4 g; one 10 years, 250 g and five adult, 300 g/average); b) five patients with no structural cardiac abnormalities and normal QRS complexes underwent three-dimensional endoepicardial electroanatomic mapping. Results. We have found in all the bovine and human hearts studied a nucleus (fulcrum) underlying the right trigone, whose osseus, chondroid or tendinous histological structure depends on the specimen analyzed. All the hearts studied presented myocardial attachment to the rigid structure of the fulcrum. Hyaluronic acid was found in the cleavage planes between the myocardial bundles.Endo-epicardial mapping demonstrates an electrical activation sequence in the area of the apex loop in agreement with the synchronic contraction of the descending and ascending band segments, consistent with the mechanism of ventricular twist. The late activation of the ascending band segment is consistent with its persistent contraction during the initial period of the isovolumic diastolic phase (the basis of the suction mechanism). Conclusions. The finding of the fulcrum gives support to the spiral myocardial band being the point of fixation that allows the helicoidal torsion. The hyaluronic acid would act as a lubricant and provide great resistance to mechanical pressures. This study explains the ventricular twist and the active suction mechanism during the isovolumic diastolic and early ventricular filling phases.Trial. This work does not correspond to a trial


Introduction
The function of the heart corresponds to a mechanical dimension that should be addressed in terms of its structure, which is where we nd the origin of the idea that led our research to explain its organicfunctional integrity. If we stop in classical descriptions of the heart we realize that anatomical attention was focused on its external and internal surfaces, granting scant importance to the intimate muscle conformation. (1) This was believed to be of a homogeneous solid nature with global uniform contraction, not considering that its mechanical capacity demanded a reinterpretation of its spatial anatomy and motions, leading us into other topics of its functioning that were completely disregarded by cardiology.
The anatomy of the heart was traditionally thought to be formed by spiraling muscle bundles, but these were never described in association with their physiology. Was Torrent Guasp who in 1970 (2) initiated the description and interpretation of the myocardial muscle band, starting point to understand its motions. This was demonstrated in multiple dissections showing that the ventricular myocardium is made up of a group of muscle bers coiled unto themselves, resembling a rope, attened laterally as a band, which by giving two spiral twists describes a helix that limits the two ventricles and de nes their performance (Fig. 1).
An explanation for this muscle homogenization with an intricate anatomical arrangement that hides the myocardial band, implies considering that its structural solidity is required in birds and mammals so that blood is ejected at high speed in a limited time span by an organ that must serve two circulations (systemic and pulmonary).
The anatomical evolutionary state of the heart agrees with ventricular mechanics but lacked the understanding of an electrical propagation that could accurately explain the physiology. The studies on this topic aim to show the integrity of an essential cardiac structure-function. (3)(4)(5)(6) The left ventricular endocardial and epicardial electrical activation performed in patients with three-dimensional electroanatomical mapping (TEM) allowed considering this fundamental topic to analyze it.
This pathway leading from structure to function induced to research on topics poorly explained by their mechanical organization (6)(7)(8), but which should be considered complementary among them and essential for the physiology of the heart, to know: 1) Anatomical and histological investigation of the segmental sequence of the myocardial band.
2) Support and insertion of the myocardial band.
3) How is ventricular torsion produced? 4) Is there a histology that explains the phenomenon of friction between the layers of the myocardium? Is there an organic lubricating source? 5) How is active protodiastolic ventricular suction produced? 6) Is it possible to consider in the heart a coupling phase between systole and diastole where cardiac suction takes place? Which is the energy mechanism in the active suction phase?

Material And Methods
The methods used in this study to explain the hypothesis of the anatomo-functional integrity of the heart were: 1) Cardiac dissection in bovids (ten young-bovine hearts (800-1000 g) and seven human hearts (one embrión, 4 g; one 10 years, 250 g and ve adult, 300 g/average).
2) Histological and histochemical analysis of anatomical samples.
3) Left ventricular endocardial and epicardial electrical activation in humans by means of TEM ( ve adult patients). The left ventricular endo and epicardial electrical activation sequence was studied with a navigation system and Carto mapping, enabling three-dimensional anatomical representation, with activation and electrical propagation maps. Isochronic and activation sequence maps were performed, correlating them with surface ECG.
Since the left ventricular muscle structure is composed of an endocardial and an epicardial portion, or descending and ascending segments, respectively, in the anatomical classi cation of Torrent Guasp (Figura 1), two access routes were used to perform the mapping. The endocardial access was achieved by conventional atrial transeptal puncture and the epicardial access by percutaneous approach in the pericardial cavity with an ablation catheter. Endocardial and epicardial mapping were immediately and consecutively performed. In addition, the electrical activation propagation times of the muscle band were measured in milliseconds (ms). The study was performed at Hospital Presidente Perón (Buenos Aires, Argentina) and included patients who had signed an informed consent previously approved by the Institutional Ethics Committee. All patients were in sinus rhythm, with normal QRS and no veri able cardiac disease by Doppler echocardiography and in resting and stress gamma camera studies. 4) Echocardiography to corroborate previous studies and the usefulness of these knowledge in clinical practice.

Results
Myocardic Architecture. Torrent Guasp demonstrated through multiple dissections in hearts of different species, including the human, that the ventricular myocardium is made up of a helical band (Figs. 1 and 2). (8) This study approach correlates with a cardiac structure presenting the remarkable characteristic of being adriving-suction pump with the size equivalent to a human st and 22 an average weight of 270 grams, which ejects 4-6 liters/minute at a speed of up to 300 cm/s, consuming only 10 watts, and working without interruption for 80 years without maintenance, almost without noise, and no smoke. Its work is equivalent to the daily withdrawal of 1 ton of water 1 m deep with a mechanical e ciency (work/energy relationship) of 50%, not achieved by man-made machines which only attain 30% e cacy. This allows ejecting 70% of the left ventricular volume with only 12% shortening of its contractile unit, the sarcomere. (9) In view of the criticism or indifference met by the helical myocardial band, its dissection nds a structure with de ned planes where the successive and related physiological heart motions of narrowing, shortening-twisting, lengthening-untwisting and expansion take place depending on the propagation of the electrical stimulus along its muscle pathways. It should be recalled that the myocardium constitutes a spiraling continuum in its bers responding to the helical pattern in its muscle bundles. This arrangement indicates the need of generating a mechanical work that dissipates little energy. Therefore, the ber layers very gradually shift their orientation, with more or less acute angles, to avoid that abrupt changes in the spatial organization dissipate the necessary work for cardiac function. (10) This situation generates a tangle of bers that allows the band to behave as a continuous transmission chain with the epicardial bers taking an oblique direction, the intermediate bers a transverse course and the endocardial bers also an oblique direction, but contrary to that of the epicardial plane. The endocardial and epicardial plane access angle is approximately 60 degrees in relation to the transverse bers. Fiber orientation de nes function and thus the ejection fraction is 60% when the normal helical bers contract and falls to nearly 30% if only the transverse bers shorten, reaching 15-20% if only the subendocardial longitudinal bers are deformed. This occurs when the left ventricle dilates in cardiac remodeling and the bers miss their oblique orientation, loosing muscular and mechanical e ciency. (11) In the progression from the ventricular base to the apex, the number of horizontal bers decreases in relation to the oblique bers, showing that the heart is organized as a continuous muscle helix (Fig. 3).
Myocardial muscle bundles and bands, which derive from phylogenetic development, essentially shape a master axis of precise dynamic requirement. The spatial muscle structure adopted by the myocardial muscle band has a double function: a) to limit the ventricular chambers and b) to ful ll the suction and driving action in its role of cardiac pump.
Segmentation of the myocardial band. Figure 4 shows the unfolded muscle band. Being able to unfold the myocardium with a similar thickness in all its extension proves that the band is real and not a "heuristic" or biased construction In its course, the myocardial band adopts a helical con guration that de nes the two ventricular chambers. The myocardial band is characterized by a descending and an ascending band. The former includes the right, left and descending segments, while the latter is formed by the remaining ascending segment (Fig. 1).
The myocardial band describes two spiral turns with the insertion of its initial end along the line extending from the pulmonary artery to the ori ce of the tricuspid valve, called the pulmo-tricuspid cord, in front of the aorta, while its nal end attaches below the aortic root. Both ends are xed by an osseous, chondroid or tendinous nucleus, depending on the different species (animal or human) used in the studies. This nucleus, which we have called cardiac fulcrum (1,11), is the only perceptible edge where the muscle band bers originate and end (Figs. 5 and 6). These insertions must be understood as the supporting point of the myocardial band to ful ll its hemodynamic function (Fig. 7). In our investigations we have not found insertion of cardiomyociytes in the collagen matrix of the trigones (Fig. 8).
In the band we can distinguish the basal and apical loops. The basal loop extends from the base of the pulmonary artery to the central band twist. On the other hand, the apical loop courses from this point of in exion to the base of the aorta. In turn, each loop consists of two segments. The basal loop consists of the right and left segments and the apical loop of the descending and ascending segments (Fig. 1). In the general loop con guration, the basal loop envelops the apical loop, so that the right ventricular chamber presents as an open slit in the muscle mass thickness forming both ventricles). The segments, in turn, are de ned by anatomical structures (Fig. 2).
These concepts indicate that the right ventricular free wall is formed by one loop (basal) and the left ventricular free wall by both loops (basal and apical). The fundamental point for cardiac mechanics is that the base and apical muscle bers course in different directions. This disparity nds correlation with the ber trajectories and the helical pattern of the muscle band limiting the ventricles.
Histological analysis of the myocardial band. The myocardium is a syncytial muscle with lateral bridges between its muscle bers and a laminar histological arrangement of the muscle bundles. Due to its histological arrangement, the myocardium (syncythyum) behaves like a auxetic biological material; in other words, it contracts simultaneously in 2 directions (longitudinal and circunferential) and thickens in a third direction (radial, towards the ventricular centroid). The histological analysis sequence of the unfolded myocardial band ( Fig. 9) demonstrates its linear orientation according to the segmental continuity of its spatial organization when the band is coiled, both in its internal and external surfaces. These orientations are identical in both surfaces (internal and external).
It can be seen that the myocardial structure is not a lattice (crisscross of myocardial bers) but a band.
The lattice concept used was developed due to the band folding resulting in overlapping segments, which are functionally independent and with friction between their surfaces. (12) This arrangement is essential to achieve myocardial torsion, a fundamental action of cardiac mechanics that would be impossible with the lattice structure.
No segment of the band histological sequence explored in our investigations presents a lattice organization. As the external surface of the distal descending segment ( Fig. 9, lower panel) twists to become the ascending segment, the cardiomyocytes generate in the planimetric histological sections a different architecture in their orientation from that of the internal surface, only site (cardiac apex) where this situations occurs. The rest of the orientation is always parallel. In the apex, the spiral course of the myocardial bers, which shift from the periphery towards the center, determine a torsion where the subepicardial bers become subendocardial, overlapping like the tiles of a roof, as evidenced in this image (Fig. 3). As previously expressed, the opposite orientation and rotational movement of the left ventricular bers, both at the basal and distal apical segment levels, explain myocardial band model.
The interventricular septum consists of a ventral and a dorsal part. The rst portion consists of the left descending segment, the intraseptal band ( nal segment of the muscle band) and the anterior septal band. The rst two belong to the left ventricle and the remaining one to the right ventricle. The posterior region of the septum is composed of the left descending segment (corresponding to the left ventricle) and the posterior septal band (corresponding to the right ventricle).
The spatial arrangement and the rotational motion of the ventricular bers, conform the architectural plan of the muscle band. Up to this moment, a classic interpretation has been made of blood circulation through the different heart chambers, which does not correlate with its muscle dynamics. And this is, ultimately, the engine for the circulation established by the myocardial band, which also de nes with its muscle structure, the limits of the chambers through which blood ows. This spatial arrangement of the muscle band, mainly at the level of descending and ascending segments, is the one that grants the ventricular chambers the shortening-twisting and lengthening-untwisting motions which are essential for cardiac function.
Muscle friction. The opposing sliding motion of the left ventricular internal segments in relation to the external segments to achieve the mechanism of ventricular torsion, generates an inevitable friction between them (Fig. 10). This would entail a high energy cost if the heart did not have a spongy system, with the participation of Thebesian and Langer venous conduits that act as a lubricating antifriction system: this is the hyaluronic acid, which ows across the myocardial thickness (Fig. 11). (13)(14)(15) Cardiac electric activation. As electroanatomical mapping corresponded to the left ventricle, the activation wave previously generated in the right ventricle was not obtained. Electroanatomical mapping took an average of 20 minutes. There were no complications related to the procedure itself or any of the approaches. Figures 12 to 14 show the projection of the endocardial an epicardial electric activation. In all the Figures the right projection is observed in the left panel and the left anterior oblique projection is simultaneously observed in the right panel. The zones activated at each moment are detailed in red. On the lateral part, the activation of the descending and ascending muscle bands that make up the muscle structure of the ventricular band in the rope model is represented. In it, the area depolarized at that moment is represented in red and those that were previously activated and are in the refractory period are represented in blue. Below the rope model, the average electrical propagation time along the muscle band can be seen measured in ms at the analyzed site.
Activation of the left ventricle occurs 12.4 ms ± 1.816 ms after its onset in the interventricular septum ( Fig. 12A). At that moment it also spreads to an epicardial area -ascending bands-evidencing a radial activation at a point we call "band crossover" that occurs on average 25.8 ms ± 1.483 ms after septal stimulation (Fig. 12B ) and at 38.2 ms ± 2.135 ms from cardiac activation onset. Synchronously, following the anatomical arrang ement of the descending band, the activation moves axially towards the ventricular apex reaching it at an average of 58 ms ± 2.0 ms (Figs. 13A and B). At the band "crossover" the activation loses its unidirectional character and becomes slightly more complex. Three simultaneous wave fronts are generated: 1) the distal activation of the descending band towards the apical loop; 2) the depolarization of the ascending band from the crossover towards the apex and 3) the activation of this band from the crossover towards the end of the muscle band in the aorta. Figures 13B, 14 A and B show the continuation and completion of this process. Intraventricular activation ends long before the termination of the QRS (Fig. 14A). The rest of the QRS corresponds to the late activation of the distal portion of the ascending band, which justi es the persistence of its contraction during the diastolic isovolumic phase, constituting the basis of the ventricular suction mechanism (Fig. 14B). A synthesis of the stimulation found in this study is shown with the rope model in Fig. 15 (upper panel).
According to Torrent Guasp, longitudinal diffusion of stimuli along the ventricular myocardial band explained the performance of the heart (Fig. 15, upper panel). However, this sequential "peristaltic" activation does not correlate with some currently well-known fundamental phenomena, as clockwise and counterclockwise twisting at the left ventricular apex and base, which are mainly responsible for its mechanical e ciency (Fig. 15, lower panel). Our research modi es these concepts since stimulus propagation is simultaneously axial and radial. A relationship must be found between activation and the mechanical result. The explanation is given by the simultaneous axial and radial electrical conduction pathways when they reach the band crossover, and is also supported by the spatial arrangement of the bers, the subendocardial ones being located on the right side and the subepicardial ones on its left side.
Stimulus propagation and left ventricular twisting. As noted, left ventricular activation begins in the endocardial descending band, which is almost simultaneously depolarized axially and radially. At the crossover point of both bands, the activation spreads from the endocardium to the epicardium (radial propagation), that is, from the descending to the ascending band.
From this point onwards, the ascending band depolarizes in two senses: towards the apex and towards the base, at the same time that the descending band completes its activation towards the apex (Fig. 14). Thus, two essential phenomena occur: 1) As the apical loop depolarizes from the band crossover in two simultaneous wave fronts (from the descending and from the ascending bands) it generates their synchronized contraction.
2) The activation of the ascending band propagates from the band crossover in two opposing directions: towards the apex and towards the base (Fig. 14). The resulting mechanical contraction will also have a divergent direction, giving origin to the apical and basal clockwise and counterclockwise rotations, respectively.
The contractile behavior like a auxetic biological material (contracts simultaneously in direction longitudinal and circunferential), together with the helical anatomical arrangement of the myocardial bers around the ventricular cavity, results in thickening radial myocardial and left ventricular wringing, which is a combination of twisting and reduction of the longitudinal axis. This muscular action results in a squeezing of the left ventricle. Thickening occurs towards the ventricuar centroid only, and is not accompanied by external thickening towards the pericardium. Furthermore, there is a decrease in cardiac diameter, as would be seen in a M-mode section of the LV in the paraesternal long axis plane; in such circunstances, the external cardiac diameter would be smaller in telesistole than in telediastole, despite myocardial thickening. This is due to the helical arrangement of the myocardial bers, which contribute to the thickening of the myocardium.
Active suction in the diastolic isovolumic phase. A fundamental issue we investigated, which did not have electrophysiological evidence, was to consider ventricular lling as an active phenomenon generated by a myocardial contraction that tends to lengthen the left ventricular apex-base distance after the ejective phase, thus producing a suction effect similar to a "suction cup". This mechanism is explained by the persistence of the ascending segment contraction during the isovolumic diastolic phase. (16)(17)(18)(19)(20)(21)(22) We have found that the endocardium is completely depolarized during the rst part of the QRS. If according to our studies the depolarization of the ascending segment starts 25.8 ms on average after that of the descending segment and its contraction persists for the same period of time, the condition of ventricular contraction will last approximately 400 ms. On the other hand, as ventricular systole lasts about 300 ms, the remaining 100 ms correspond to the diastolic isovolumic phase (erroneously called isovolumic relaxation, because as we see there is ventricular contraction). Brie y, during the initial part of this phase the ascending segment remains contracted as a result of the depolarization that occurred during the QRS.
The nal part of the QRS corresponds in our investigation to the activation of the ascending segment. In this way, during the diastolic isovolumic phase, the contraction necessary to generate suction ("suction cup effect") occurs. With the onset of untwisting during the diastolic isovolumic phase the ascending segment progressively lengthens, generating negative intraventricular pressure with this segment still contracted (active process) as an energy residue of the twisting process.
This suction phase between systole and diastole lasts around 100 ms and is active during muscle contraction with an intraventricular pressure drop below zero (Fig. 16). The difference in the duration of mean systolic strain between the systolic and postsystolic phase in the echocardiographic work of Mora Llabata et al. is 88 ± 7.1 ms, a value analogous to those found in our research in relation to the duration of the ascending segment activation in the suction phase. (23,24) We have measured the left intraventricular pressure curve in patients who underwent cardiac resynchronization therapy in order to show the improvement at the level of the suction mechanism in the diastolic isovolumic phase.
With the resynchronizer catheter positioned in the left ventricular endocardium (according to our research in the area of band "crossover") normal electrical activation is restored, achieving normalization of the segments' mechanical sequence and the restoration of the suction mechanism with the drop in left ventricular diastolic pressure. (25) In Fig. 17A, the curve corresponds to the left intraventricular pressure in a patient with LBBB in which the resynchronizer has been turned off. In Fig. 17B, in the same patient, the function of the device has been restored. It can be seen on the intraventricular pressure scale, to the right of each panel (in mmHg), that the diastolic pressure has decreased from 13 to 0 mmHg with ventricular resynchronization. The increase in systolic pressure by 10 mmHg has also been observed.
Echocardiography. Echocardiography has the ability to provide noninvasive understanding about the complex mechanism of myocardial contraction. For over 15 years the speckle tracking technique has been used to assess strain or myocardial deformation. This tool of two-dimensional (2D) ultrasound provides a regional qualitative analysis of left ventricular function, con rming the relationship between the cardiac anatomy of the helical muscle band and diverse echocardiographic ndings. According to Ballester et al.(6) the different segments of the basal and apical loops of Torrent Guasp's myocardial band correlate with 2D ultrasound ndings.
The left ventricular eyection fraction (LVEF) results from the combined action of longitudinal and circumferential myocardic contraction. The distinctive helical structure of obliquely oriented myocardial bers results in systolic rotation of the base and apex of the left ventricle (LV) in opposite directions around its longitudinal axis (the algebraic subtraction of this rotation causes twisting of the heart muscle) and the simultaneous shortening of the LV as the base is displaced towards the apex, all of which results in ventricular wringing. The combination of these events determines ventricular radial thickening and LVEF. Speckle tracking echocardiography allows us to study the muscular behavior of the myocardium by calculating Lagangrian strain. Strain is negative when de original distance between 2 points decreases, as occurs in myocardial muscle contraction (longitudinal and circunferential contraction) and is positive when the distance between them increases, as occurs in muscle thickening (radial thickening). Its accuracy has been validated with sonomicrometry and especially with nuclear magnetic resonance, respectively. 1) The myocardial muscle mass is more important at the mid-basal level where the basal and apical loop bers join. This explains that the maximum strain amplitude obtained by radial strain occurs at this level (basal radial strain + 44 ± 18% vs. apical strain + 23 ± 16.5%).
2) The descending bers adopt a progressively more oblique arrangement until they reach the apex.
Effectively, as expected, longitudinal strain is markedly greater at the ventricular apex due to this oblique change in the spatial arrangement (apical longitudinal strain − 21.9% ± 2.4 vs. basal longitudinal strain − 19.6% ± 2.4).

4)
To calculate the twist, the echocardiograph algorithm performs an algebraic sum (it adds the positive value of apical rotation to the negative one of basal rotation) In our experience, the value in normal subjects is around + 19 ± 9 º, always with predominant apical rotation 5) Post-systolic longitudinal strain, which indicates the activity during relaxation, is basically produced in septal segments and in the anterior basal region corresponding to the anatomical location of the ascending segment. (23) The twist of an elastic and non-compressible material, such as the myocardium, involves a longitudinal shortening. In the case of the LV, the base and the apex rotate in opposite directions around the longitudinal axis of the LV at the same time as the base moves closer to the apex, which occurs due to the helical arrangement of the myocardial bers. New parameters, possibly more adjusted to the current knowledge of physiology described, have been incorporated into our recent experience, including twist movements and the longitudinal shortening motions that are simultaneously developed during ventricular systole. (24) These are: a) the torsion index (twist/mitral annulus translational motion); and b) strain index (twist/left ventricular global longitudinal strain). Both parameters translate the active motions that are produced during systole "squeezing" the left ventricle, with a value of 13.1 ± 4 °/cm for the torsion index and 0.96 ± 0.36°/% for the strain index in the healthy population studied.
The "combined strain parameter" has also been postulated to assess left ventricular function. It includes the "strain product (twist × longitudinal strain)", which is probably better to evaluate contractility, and the previously described "strain index (twist/global longitudinal strain), which would establish the type of predominant disease. Thus, a normal "strain product" (-387 ± 137 ° x %) would translate into a preserved left ventricular global function, either by normality of both parameters or by the compensation provided between them ("pseudonormal" product). A reduced "strain product" could be due to the decrease of longitudinal strain, twist, or both, and would be characterized by the "strain index" (high, low or normal, respectively). Then, this "combined strain parameter" could help to better differentiate the disorder and in addition monitor the myocardial impairment derived from treatments or secondary to different cardiac diseases.
There are previous reports in the literature which have used the strain product (twist × longitudinal strain) as the best predictor of future cardiotoxicity by anthracyclines, due to a more global assessment of subendocardial and subepicardial bers.
The incorporation of strain parameters have allowed the recent classi cation of heart failure according to left ventricular mechanical function disorders. After observing speci c anomalous models of ventricular mechanics in different subgroups of heart failure patients, an alternative approximation has been proposed to characterize it. Thus, cardiac failure can be classi ed into two big subgroups: 1) dominant longitudinal dysfunction; 2) transmural dysfunction (longitudinal and circumferential). This classi cation is based on the double helix oblique orientation of left ventricular myocardial bers. Probably, the integration of pump and myocardial function parameters need to be jointly valued for a more accurate assessment of ventricular systolic function.
Future studies should assess whether, during longitudinal follow-up of patients, values of myocardial torsion have prognostic value in terms of predicting ventricular failure. On the other hand, in processes that affect the entire myocardium from the early stages onwards, and not just the subendocardium, myocardial torsion could provide extra information if both components are evaluated together.
In each different pathology, rotation, twisting and untwisting, are affected in different ways depending on myocardial torsion and the distribution of the most involved bers, with clearly manifested characteristics in ventricular hypertrophy, diabetes, amyloidosis and heart valve and pericardial diseases.
With a special technique known as Diffusion Tensor Magnetic Resonance Imaging with Multiresolution Tractography in a objective analysis, F Poveda et al (3) in 2013 reveals a continuous helical myocardial ber arrangement of both right and left ventricles, supporting the anatomical model of the helical ventricular myocardial band described by F. Torrent-Guasp and con rmed in our disecctions.
In the multislice coronary angiotomography studies, we have found that the analysis of the region described as cardiac fulcrum in the dissections performed, have an intensity in Houns eld units above 110 UH, while the adjacent muscle has units below 80 UH. In the patient of Fig. 18, the area described as fulcrum has an average of 132 ± 4.5 HU and the adjacent areas of myocardial muscle between 47.96 ± 12.5 and 77.59 ± 21.64.

Discussion
Regarding the argued di culty to dissect the myocardium, which is more apparent than real, we should consider that once the myocardial band originated as a loop in the arterial semicircle of amphibians and reptiles to adapt to the physiological demands of aerial life, the muscle bundles became rmly attached to their contact surfaces, hampering the necessary cleavage planes necessary for their anatomical dissection. The evolutionary goal was to develop a su ciently solid hemodynamic structure with the strength to generate the suction and pumping of the blood volume that supplied the whole organism. Thus, every attempt to dissect an anatomical segment from the rest of the myocardium, avoiding the real cardiac arrangement, always turns into an obstacle due to the structural plan of the axes where the orientation of the myocardial band courses. Its spatial helical arrangement is in agreement with the mechanical function evidenced by the different segments that compose it. No segment of the band's sequential histology, explored in our investigations, presents a mesh arrangement The myocardial band cannot be anatomically suspended and free in the thoracic cavity because it would be impossible to eject blood at a speed of 300 cm/s. Therefore, there must be a point of attachment, which was identi ed as the cardiac fulcrum (supporting point of leverage). In this supporting site, the muscle bers are inevitably forced to "intertwine" with the connective, chondroid or osseous fulcrum, and our anatomical and histological investigations have shown that this insertion attaches both the origin and end of the myocardial band. (18) This structural composition keeps correspondence with the activation of the myocardial band. The stimulus runs by its muscle pathways, but in order to ful ll the function proposed by its helical arrangement, it is essential for it to simultaneously activate the left ventricular descending and ascending segments. The transmission of the stimulus between them generates the necessary ventricular torsion (a situation similar to "wringing a towel") that enables the ejection of the blood content in a limited time span with the necessary force to adequately supply the whole body.
The circulatory duct of annelids works with a peristaltic mechanism in its contractile progression. The impulse along its length preserves a pattern of axial transmission, but after the cardiac duct twists in birds and mammals, radial transmission of the impulse is added, allowing the helical motion indispensable to produce the successive twisting-shortening motions during systole and untwistinglengthening in the subsequent suction phase.
The ventricular narrowing phase at the beginning of systole is shaped by the contraction of the basal loop right and left segments. The overlapping shortening phase due to the descent of the base while twisting occurs, is produced longitudinally, as the ring contracts before the apex. The fact that the apex remains xed is due to the movement of the base, descending in systole and ascending in diastole. This is better explained because the ascending band, rigid at the beginning of diastole, acts as a tight tutor keeping the apex immobile. The pressure generated to eject the highest amount of blood at the onset of ejection during an interval lasting 20% of the systolic phase is feasible due to the twisting motion. This action is achieved because the electrical stimulation propagates towards the descending band (axial propagation) and simultaneously to the ascending band (radial propagation). Although the electrical conduction progresses along the myocardial band, radial propagation towards the ascending band plays an essential role in ventricular twisting by allowing opposing forces on its longitudinal axis to generate the necessary intraventricular pressure to achieve abrupt blood ejection. Thus, a twisting mechanism similar to "wringing a towel" would be produced.
The following suction phase of the heart is not feasible due to the small difference with peripheral pressure. Neither can it be passive. The untwisting of the heart in the rst 100 ms of diastole (isovolumic diastolic phase) generates the negative intraventricular force to draw blood into the left ventricle, even in the absence of the right ventricle, as shown in experimental animals. (22) This suction phase ("suction cup" mechanism) is active with energy expenditure, and implies that the heart cycle consists of three stages: systole, suction and diastole.
Diastolic activation explains the insertion of a suction active coupling phase between systole and diastole, with muscle contraction, energy consumption, and a marked drop of intraventricular pressure. This effect draws blood into the ventricular chamber through a pressure difference with respect to the external pressure, and is responsible that in only 20% of the total lling time it should achieve 70% of the total lling volume.
The new echocardiographic proposed parameters integrate values of longitudinal shortening and twisting and provided reference strain values obtained in a population of healthy subjects allowing a complete physiological assessment of cardiac systolic function, and could be used for the early detection and characterization of its alteration. There is a consensus that future clinical practice should adopt a combined approach in which changes in LV rotational mechanics and longitudinal shortening are considered and interpreted together. Likewise, the integration of complementary parameters of pumping and myocardial function should be considered for a more accurate evaluation of LV systolic function.

Limitations
It is very di cut in our enviroments to get human hearts for dissection. All this research is necessary to replicate with a greater number of hearts and patients. Left an right trígones (adult human heart). There is no inclusion of cardiomyocytes.

Figure 9
Page 24/32 Segment sequence from the myocardial band histological analysis (bovine heart).       Coronary Angiotomography. The fulcrum is indicated in a green circle (human tomography).