How His bundle pacing prevents and reverses heart failure induced by right ventricular pacing.

Ideal heart performance demands vigorous systolic contractions and rapid diastolic relaxation. These sequential events are precisely timed and interdependent and require the rapid synchronous electrical stimulation provided by the His-Purkinje system. Right ventricular (RV) pacing creates slow asynchronous electrical stimulation that disrupts the timing of the cardiac cycle and results in left ventricular (LV) mechanical asynchrony. Long-term mechanical asynchrony produces LV dysfunction, remodeling, and clinical heart failure. His bundle pacing preserves synchronous electrical and mechanical LV function, prevents or reverses RV pacemaker-induced remodeling, and reduces heart failure.

Surgical ventricular restoration: where do we go from here?

The surgical treatment for ischemic heart failure (STICH) trial concluded that the addition of surgical ventricular restoration (SVR) to coronary bypass grafting did not lead to improved survival in patients with dilated ischemic cardiomyopathy. Observational studies at multiple centers over the last 15 years have shown consistent improvement in global ventricular function and approximately 70 % long-term survival. The causes of this discrepancy are reviewed here and likely relate to how the STICH trial was conducted. Recent subset analyses from the STICH investigators have provided some additional data relating ventricular volumes to outcomes. However, including patients with unsuitable entry criteria and operations confounds the data. We recommend an analysis of the STICH data based on the trial's initial design in order to determine if there are patients who may benefit by SVR.

Two- and three-dimensional speckle tracking echocardiography: clinical applications and future directions.

Two-dimensional speckle tracking echocardiography (2D STE) is a novel technique of cardiac imaging for quantifying complex cardiac motion based on frame-to-frame tracking of ultrasonic speckles in gray scale 2D images. Two-dimensional STE is a relatively angle independent technology that can measure global and regional strain, strain rate, displacement, and velocity in longitudinal, radial, and circumferential directions. It can also quantify rotational movements such as rotation, twist, and torsion of the myocardium. Two-dimensional STE has been validated against hemodynamics, tissue Doppler, tagged magnetic resonance imaging, and sonomicrometry studies. Two-dimensional STE has been found clinically useful in the assessment of cardiac systolic and diastolic function as well as providing new insights in deciphering cardiac physiology and mechanics in cardiomyopathies, and identifying early subclinical changes in various pathologies. A large number of studies have evaluated the role of 2D STE in predicting response to cardiac resynchronization therapy in patients with severe heart failure. However, the clinical utility of 2D STE in the above mentioned conditions remains controversial because of conflicting reports from different studies. Emerging areas of application include prediction of rejection in heart transplant patients, early detection of cardiotoxicity in patients receiving chemotherapy for cancer, and effect of intracoronary injection of bone marrow stem cells on left ventricular function in patients with acute myocardial infarction. The emerging technique of three-dimensional STE may further extend its clinical usefulness.

Ventricular torsion and untwisting: further insights into mechanics and timing interdependence: a viewpoint.

Ventricular torsion and untwisting are essential for normal ventricular function and their mechanisms are related to the temporal responses of the helical and circular muscle fibers that comprise cardiac architecture. Explanation of the presystolic isovolumic contraction (IVC) period is essential for analysis of these interactions. Structural and imaging studies by magnetic resonance, speckle tracking, velocity vector encoding, and sonomicrometer crystals are described to define why and how different muscular components contract asynchronously. Mechanical and functional relationships are described for pre-systolic IVC, torsion, postejection isovolumic interval, and rapid and slow filling. Circular fibers dominate to cause pre- and posttwisting global counterclockwise and clockwise movement, and helical fibers govern torsion whereby the base rotates clockwise and apex counterclockwise; untwisting cannot begin until torsion is completed. Prolonged torsion extends into the postejection isovolumic interval and delays untwisting, and is caused by prolonged contraction of the right-handed helical arm or descending segment of the helical ventricular myocardial band that narrows the ∼80 ms "timing hiatus" between end of shortening of the descending and the ascending segment or left-handed arm of the helical muscle. Longer torsion duration by this mechanism becomes the common theme for unbalanced torsion and untwisting in diastolic dysfunction, physiological, structural, and electrical disease processes, whose management may be guided by changing the interconnected reasons for these adverse mechanical and timing factors.

Cardiac mechanics revisited: the relationship of cardiac architecture to ventricular function.

The keynote to understanding cardiac function is recognizing the underlying architecture responsible for the contractile mechanisms that produce the narrowing, shortening, lengthening, widening, and twisting disclosed by echocardiographic and magnetic resonance technology. Despite background knowledge of a spiral clockwise and counterclockwise arrangement of muscle fibers, issues about the exact architecture, interrelationships, and function of the different sets of muscle fibers remain to be resolved. This report (1) details observed patterns of cardiac dynamic directional and twisting motions via multiple imaging sources; (2) summarizes the deficiencies of correlations between ventricular function and known ventricular muscle architecture; (3) correlates known cardiac motions with the functional anatomy within the helical ventricular myocardial band; and (4) defines an innovative muscular systolic mechanism that challenges the previously described concept of "isovolumic relaxation." This new knowledge may open new doors to treating heart failure due to diastolic dysfunction.

Reconstruction of myocardial tissue motion and strain fields from displacement-encoded MR imaging.

A quantitative analysis of myocardial mechanics is fundamental to understanding cardiac function, diagnosis of heart disease, and assessment of therapeutic intervention. Displacement encoding with stimulated-echo (DENSE) magnetic resonance imaging (MRI) technique was developed to track the three-dimensional (3D) displacement vector of discrete material grid points in the myocardial tissue. Despite the wealth of information gained from DENSE images, the current software only provides two-dimensional in-plane deformation. The objective of this study is to introduce a postprocessing method to reconstruct and visualize continuous dynamic 3D displacement and strain fields in the ventricular wall from DENSE data. An anatomically accurate hexagonal finite-element model of the left ventricle (LV) is reconstructed by fitting a prolate spheroidal primitive to contour points of the epi- and endocardial surfaces. The continuous displacement field in the model is described mathematically based on the discrete DENSE vectors using a minimization method with smoothness regularization. Based on the displacement, heart motion and myocardial stretch (or strain) are analyzed. Illustratory computations were conducted with DENSE data of three infarcted and one normal sheep ventricles. The full 3D results show stronger overall axial shortening, wall thickening, and twisting of the normal LV compared with the infarcted hearts. Local myocardial stretches show a dyskinetic LV in the apical region, dilation of apex in systole, and a compensatory increase in strain in the healthy basal region as a compensatory mechanism. We conclude that the proposed postprocessing method significantly extends the utility of DENSE MRI, which may provide a patient-specific 3D model of cardiac mechanics.

WITHDRAWN: Influences of Perfusion Pressure and Pulsatile Flow on Cerebral Flow Reserve and Oxygenation in the Isolated Perfused Swine Brain under Normothermia.

This article has been removed at the request of the Editor-in-Chief. Please see Elsevier Policy on Article Withdrawal: (http://www.elsevier.com/locate/withdrawalpolicy).

Surgical restoration of the postinfarction dilated ventricle.

Surgical restoration of the failing heart is related to rebuilding cardiac architecture and linked to: (a) understanding that the structure of the failing dilated heart involves changing the normal elliptic shape toward a dilated spherical form; (b) recognizing the anatomic fiber orientation framework and its functional implications; (c) establishing imaging measurement guidelines to determine indications for surgical intervention that focus upon volume and remote muscle evaluation rather than ejection fraction; and (d) summarizing left ventricular restoration results whereby rebuilding normal elliptic configuration improves function, reduces ventricular arrhythmias, alleviates mechanical dyssynchrony, and causes progressive improvement that extends long-term prognosis.

A new look at diastole.

The isovolumic period following systolic ejection is associated with untwisting of the apex that follows systolic torsion of the left ventricle, with simultaneous generation of negative pressures in the left ventricle. Previous studies have described this period as isovolumic relaxation, and have regarded the untwisting as entirely caused by restoring elastic forces. However, evidence from several sources indicates that some ventricular muscle is still contracting during this period, and that this muscle is subepicardial muscle or the ascending spiral segment of the ventricular myocardial band that extends from the apex up along the left ventricular epicardium and the right ventricular side of the septum to the root of the aorta. It is possible that diastolic dysfunction is due to defective incoordination of muscle contraction between the ascending and descending segments of this band rather than to defective passive restoring forces.

Mitral regurgitation: anatomy is destiny.

Mitral regurgitation (MR) occurs when any of the valve and ventricular mitral apparatus components are disturbed. As MR progresses, left ventricular remodelling occurs, ultimately causing heart failure when the enlarging left ventricle (LV) loses its conical shape and becomes globular. Heart failure and lethal ventricular arrhythmias may develop if the left ventricular end-systolic volume index exceeds 55 ml/m2. These adverse changes persist despite satisfactory correction of the annular component of MR. Our goal was to describe this process and summarize evolving interventions that reduce the volume of the left ventricle and rebuild its elliptical shape. This 'valve/ventricle' approach addresses the spherical ventricular culprit and offsets the limits of treating MR by correcting only its annular component.

What Is the Heart? Anatomy, Function, Pathophysiology, and Misconceptions.

Cardiac dynamics are traditionally linked to a left ventricle, right ventricle, and septum morphology, a topography that differs from the heart's five-century-old anatomic description of containing a helix and circumferential wrap architectural configuration. Torrent Guasp's helical ventricular myocardial band (HVMB) defines this anatomy and its structure, and explains why the heart's six dynamic actions of narrowing, shortening, lengthening, widening, twisting, and uncoiling happen. The described structural findings will raise questions about deductions guiding "accepted cardiac mechanics", and their functional aspects will challenge and overturn them. These suppositions include the LV, RV, and septum description, timing of mitral valve opening, isovolumic relaxation period, reasons for torsion/twisting, untwisting, reasons for longitudinal and circumferential strain, echocardiographic sub segmentation, resynchronization, RV function dynamics, diastolic dysfunction's cause, and unrecognized septum impairment. Torrent Guasp's revolutionary contributions may alter future understanding of the diagnosis and treatment of cardiac disease.

An experimental and clinical evaluation of a novel central venous catheter with integrated oximetry for pediatric patients undergoing cardiac surgery.

BACKGROUND: Central venous oxygen saturation (ScvO2) accurately reflects cardiocirculatory function, but is not always feasible in pediatric patients. Using an experimental and clinical approach, we determined the accuracy of a novel pediatric central venous catheter with integrated fiberoptic oximetry, correlated ScvO2 to periprocedural vital variables, and tested its feasibility in pediatric cardiac surgery patients. METHODS: In five anesthetized pigs, hemodynamics (cardiac index [CI], heart rate; mean arterial blood [MAP]; mean pulmonary artery [MPAP], central venous pressure [CVP]), fiberoptic ScvO2 (ScvO2-cath), and blood gas oximetry (ScvO2-blood) were measured during stable baseline conditions, preload reduction (caval occlusion), and dopamine infusion (5 mcg x kg(-1) x min(-1)). In 16 pediatric patients undergoing cardiac surgery (median age 8.4 mo; weight 8.0 kg), central venous oximetry catheters were placed percutaneously, and ScvO2-cath and hemodynamics recorded at several time-points during and until 24 h after surgery. Oximetry and hemodynamic data were compared by correlation (Pr) and the Bland-Altman analysis. RESULTS: There were no catheter-related complications. ScvO2-cath and ScvO2-blood measurements correlated significantly (P < 0.001) in both the experimental (Pr = 0.96) and clinical protocol (Pr = 0.94). A similar bias and precision over all time-points was detected in both protocols (Exp-bias: +0.03% +/- 4.11%; Clinical-bias: -0.03% +/- 4.41%). ScvO2-cath correlated (P < 0.001) with CI (Pr = 0.87), MAP (Pr = 0.59), MPAP (Pr = 0.44), and CVP (Pr = 0.38) and estimated CI better than MAP (Pr = 0.61), MPAP (Pr = 0.38), CVP (Pr = 0.35), or heart rate (Pr = 0.25). CONCLUSION: Integrated central venous oximetry catheters provide accurate continuous ScvO2 monitoring in pediatric patients undergoing cardiac surgery. ScvO2 fiberoptic oximetry correlates better with changes in CI as compared to routine hemodynamic variables.

Pathophysiologic implications of the helical ventricular myocardial band: considerations for right ventricular restoration.

This chapter describes the structure/function relationships of the right ventricle (RV), and shows how the geometry of the helical ventricular myocardial band model defines spatial geometry of the free wall and septum that underlie dynamic action. Myocardial fiber orientation is the keynote to performance in health and disease. The transverse geometry of the RV free wall allows constriction (bellows-type motion), whereas oblique septal fiber orientation and midline septal position is essential for ventricular twisting, the vital mechanism for RV ejection against increased pulmonary vascular resistance. Therefore, the septum is considered "the lion or motor of RV performance." Distortion of such normal structure/function relationships underlies the pathophysiologic mechanisms of RV failure. Operative methods that restore normal myocardial fiber orientation are described to outline evolving surgical techniques for the surgical treatment of RV failure.

Sudden cardiac death: directing the scope of resuscitation towards the heart and brain.

BACKGROUND: The fundamental goal of cardiopulmonary resuscitation (CPR) is recovery of the heart and the brain. This is best achieved by (1) immediate CPR for coronary and cerebral perfusion, (2) correction of the cause of cardiac arrest, and (3) controlled cardioplegic cardiac reperfusion. Failure of such an integrated therapy may cause permanent brain damage despite cardiac resuscitation. METHODS: This strategy was applied at four centers to 34 sudden cardiac death patients (a) after acute myocardial infarction (n = 20), (b) "intraoperatively" following successful discontinuation of cardiopulmonary bypass (n = 4), and (c) "postoperatively" in the surgical ICU (n = 10). In each witnessed arrest the patient failed to respond to conventional CPR with ACLS interventions, including defibrillation. The cardiac arrest interval was 72 +/- 43 min (20-150 min). Compression and drugs maintained a BP > 60 mmHg to avoid cerebral hypoperfusion. Operating room (OR) transfer was delayed until the blood pressure was monitored. In four patients femoral bypass maintained perfusion while an angiographic diagnosis was made. RESULTS: Management principles included no repeat defibrillation attempts after 10 min of unsuccessful CPR, catheter-monitored peak BP > 60 mmHg during diagnosis and transit to the operating room, left ventricular venting during cardiopulmonary bypass and 20 min global and graft substrate enriched blood cardioplegic reperfusion. Survival was 79.4% with two neurological complications (5.8%). CONCLUSIONS: Recovery without adverse neurological outcomes is possible in a large number of cardiac arrest victims following prolonged manual CPR. Therapy is directed toward maintaining a monitored peak BP above 60 mmHg, determining the nature of the cardiac cause, and correcting it with controlled reperfusion to preserve function.

The ventricular septum: the lion of right ventricular function, and its impact on right ventricular restoration.

OBJECTIVE: To evaluate the structure-function relationships of the right ventricle (RV) and septum and determine if the helical ventricular band model would define fiber orientation for maximal force response. Implications were made for right ventricular function. METHODS: The right ventricular free wall and biventricular septum were studied by inserting sonomicrometer crystals at different angulations to determine the maximum response of fiber shortening. These reactions were compared to the lateral left ventricular (LV) wall and further tested by use of positive and negative inotropic drug infusions. RESULTS: The maximum contraction of the free wall was achieved by placing crystals in the transverse orientation angulations, whereas oblique orientation allowed the maximal septal response. Fiber orientation angulation was the same for the LV free wall and septum. These angulations correlate with the MRI-related twisting actions of septal motion needed for ejection and suction for rapid filling. These findings have important impact, because they imply that the septum is 'lion of right ventricular function,' since septal twisting is essential when pulmonary vascular resistance is increased. The incidence of postoperative right heart failure due to septal dyssyncrony, with loss of septal twisting action from inadequate myocardial protection, is explored relative to RV free wall and septum function. Furthermore, early studies of right ventricular restoration in patients with RV dysplasia and RV failure after chronic pulmonary insufficiency following repair of Tetralogy of Fallot are described, with predominant attention directed toward rebuilding normal septal architecture and function. CONCLUSIONS: This experimental and clinical overview indicates that the septum is 'the lion of right ventricular function,' and implies that the use of this knowledge can become an important guideline for planning novel surgical geometric interventions after RV failure.