Left Atrioventricular Junction Research Articles

Expression of Stem Cell Niche-Related Biomarkers at the Base of the Human Tricuspid Valve.

Stem cell niches have been thoroughly investigated in tissue with high regenerative capacity but not in tissues where cell turnover is slow, such as the human heart. The left AtrioVentricular junction (AVj), the base of the mitral valve, has previously been proposed as a niche region for cardiac progenitors in the adult human heart. In the present study, we explore the right side of the human heart, the base of the tricuspid valve, to investigate the potential of this region as a progenitor niche. Paired biopsies from explanted human hearts were collected from multi-organ donors (N = 12). The lateral side of the AVj, right atria (RA), and right ventricle (RV) were compared for the expression of stem cell niche-related biomarkers using RNA sequencing. Gene expression data indicated upregulation of genes related to embryonic development and extracellular matrix (ECM) composition in the proposed niche region, that is, the AVj. In addition, immunohistochemistry showed high expression of the fetal cardiac markers MDR1, SSEA4, and WT1 within the same region. Nuclear expression of HIF1α was detected suggesting hypoxia. Rare cells were found with the co-staining of the proliferation marker PCNA and Ki67 with cardiomyocyte nuclei marker PCM1 and cardiac Troponin T (cTnT), indicating proliferation of small cardiomyocytes. WT1+/cTnT+ and SSEA4+/cTnT+ cells were also found, suggesting cardiomyocyte-specific progenitors. The expression of the stem cell markers gradually decreased with distance from the tricuspid valve. No expression of these markers was observed in the RV tissue. In summary, the base of the tricuspid valve is an ECM-rich region containing cells with expression of several stem cell niche-associated markers. Co-expression of stem cell markers with cTnT indicates cardiomyocyte-specific progenitors. We previously reported similar data from the base of the mitral valve and thus propose that human adult cardiomyocyte progenitors reside around both atrioventricular valves.

Local Variation and Age-Related Change in Atrial and Ventricular Myocardial Contiguity at the Atrioventricular Junction in Human Hearts

Background: We explored the histologic patterns of and age-related changes in atrial and ventricular myocardial contiguity at the left and right atrioventricular (AV) junction that could be a target site for catheter ablation.Methods and Results: Twenty-three structurally normal adult hearts obtained at autopsy were studied. The 2 AV annuli were divided into 13 clinically recognized portions in which we measured distance between the atrial and ventricular myocardium at the AV junction. Overall, measured distance was less on the right than left side (mean [±SD] 0.74±0.59 vs. 1.15±0.78 mm, respectively), and distance increased gradually with age. The gap was smallest at the anterolateral portion on the right side and posterolateral portion on the left side. Three specific features were noted, namely extension of the ventricular myocardium (coarse trabeculae) towards the atrium on the right side of the AV junction, extension of the atrial myocardium onto the AV valve leaflets, and a collection of small myocardial cells, perhaps including specialized cells, in the right anterolateral portion. No concealed AV muscular connections were found.Conclusions: Contiguity and separation of the myocardium at the AV junction have specific patterns, and myocardial proximity is influenced by age. These histologic features of the AV junction may prove to be informative for catheter ablation of tachyarrhythmias related to the AV junction.

Prognostic value of fast semi-automated left atrial long-axis strain analysis in hypertrophic cardiomyopathy

BackgroundThe prognostic value of left atrial (LA) size and function in hypertrophic cardiomyopathy (HCM) is well recognized, but LA function is difficult to routinely analyze. Fast LA long-axis strain (LA-LAS) analysis is a novel technique to assess LA function on cine cardiovascular magnetic resonance (CMR). We aimed to assess the association between fast LA-LAS and adverse clinical outcomes in patients with HCM.Methods359 HCM patients and 100 healthy controls underwent routine CMR imaging. Fast LA-LAS was analyzed by automatically tracking the length between the midpoint of posterior LA wall and the left atrioventricular junction based on standard 2- and 4-chamber balanced steady-state free precession cine-CMR. Three strain parameters including reservoir strain (εs), conduit strain (εe), and active strain (εa) were assessed. The endpoint was set as composite adverse events including cardiovascular death, resuscitated cardiac arrest, sudden cardiac death aborted by appropriate implantable cardioverter-defibrillator discharge, and hospital admission related to heart failure.ResultsDuring an average follow-up of 40.9 months, 59 patients (19.7%) reached endpoints. LA strains were correlated with LA diameter, LA volume index (LAVI) and LA empty fraction (LAEF) (all p < 0.05). In the stepwise multivariate Cox regression analysis, εs and εe (hazard ratio, 0.94 and 0.89; p = 0.019 and 0.006, respectively) emerged as independent predictors of the composite adverse events. Fast LA εs and LA εe are stronger prognostic factors than LA size, LAVI and the presence of left ventricular late gadolinium enhancement.ConclusionsFast LA reservoir and conduit strains are independently associated with adverse outcomes in HCM.

High-resolution analysis with multiphase computed tomography of the left atrio-ventricular junction in mitral annular disjunction

Abstract Background Mitral annular disjunction (MAD) has been associated with myxomatous mitral valve disease (MMVD) but functional analyses of the mitral annulus (MA) and the entire left atrio-ventricular junction (LAVJ) are lacking from high-resolution imaging to understand MAD physiopathology. Purpose Using multiphase cardiac computed tomography imaging (4D-MCCTI), we aimed at characterizing the morphological changes of MA and LAVJ throughout the cardiac cycle. Methods Volume imaging data sets through time were obtained from 4D-MCCTI of 2 groups of 10 patients as defined by echocardiographic diagnosis of MMVD and/or MAD: MMVD+MAD+, MMVD+MAD− and 20 case-controls without mitral regurgitation (MMVD−). Data were implemented in a custom software for 3D semi-automated delineation of 18 points around MA perimeter. Coordinates of these points in each of the 10 time-phases within an RR interval were used for MA reconstruction and calculation of areas, perimeters, 360°-diameters and parameters of planar/vertical deformation. Subsequently, left ventricle (LV) and left atrium (LA) inner contours were delineated. Results Groups were similar for age, body surface area and LV ejection fraction. Compared to the 2 other groups, MA expansion in MMVD+MAD+ started early after end-diastole, following LA expansion, and reached a maximum at end-systole (ES): 3D-area ES: 13.9±4.0cm2/m2, 3D-perimeterE S: 10.4±1.6cm/m2 versus respectively 8.8±3.0cm2/m2, 7.9±1.4cm/m2 in MMVD+MAD− (p&amp;lt;0.001) and 6.1±1.3cm2/m2, 7.0±1.1cm/m2 in MVVD− (p&amp;lt;0.001). However throughout the cardiac cycle, MA perimeter reduction was not altered in MMVD+MAD+: −14.0±6.3%, compared to MMVD+MAD−: −10.1±5.6% and MMVD−: −8.7±2.3% (p=0.09). MA shape modification was different in MMVD+MAD+ group, MA becoming more elliptical during systole, whereas MA reached a minimal eccentricity index (EcI) at ES in both MMVD+MAD− and MMVD− groups: EcIES = 0.63±0.09 versus 0.52±0.15 and 0.49±0.13 (p=0.04), respectively (Figure). Surprisingly, vertical deformation of MA increased during early systole in MMVD+MAD+ group when MA became more planar in the MMVD+MAD− and MMVD− groups. Conclusions MA function was globally preserved in MAD but was desynchronized with respect to LV contraction. Eccentricity index of mitral annulus Funding Acknowledgement Type of funding source: None

High-resolution Four-dimensional Analysis with Multislice Computed Tomography of the Left Atrio-ventricular Junction in Mitral Annular Disjunction

High-resolution Four-dimensional Analysis with Multislice Computed Tomography of the Left Atrio-ventricular Junction in Mitral Annular Disjunction

How are the cardiomyocytes aggregated together within the walls of the left ventricular cone?

The manner of packing together of the cardiomyocytes within the walls of the cardiac ventricles has now been investigated for over half a millennium. In 1669, Lower dissected the ventricular mass, likening the arrangement to skeletal musculature, in the form of a myocardial band extending between the right and left atrioventricular junctions. Pettigrew subsequently showed obvious helical arrangements to be evident within the ventricular walls, but emphasised that the cardiomyocytes were attached to each other, and could not justifiably be compared with skeletal cardiomyocytes. Torrent-Guasp then reactivated the notion that the ventricular mass was formed of a solitary band. Unlike Lower, he dissected the band as extending between the pulmonary to the aortic roots. Multiple investigations conducted using gross dissection and histology, and more recently diffusion tensor magnetic resonance imaging and computed tomographic analysis, have shown an absence of any anatomical boundaries within the walls that might permit the mass uniformly to be dissected so as to reveal the band. A response to a recent letter to the Journal, nonetheless, claimed that the dissections had been validated by clinicians interpreting the findings so as to provide an explanation for ventricular cardiodynamics, arguing that the findings provided a suitable anatomical model for this purpose. Anatomical models, however, are of no value unless they are anatomically correct. In this review, therefore, we summarise the evidence showing that the cardiomyocytes making up the ventricular walls, rather than forming a ventricular myocardial band, are instead aggregated together to form a three-dimensional myocardial mesh.

Apoptosis and epicardial contributions act as complementary factors in remodeling of the atrioventricular canal myocardium and atrioventricular conduction patterns in the embryonic chick heart.

During heart development, it has been hypothesized that apoptosis of atrioventricular canal myocardium and replacement by fibrous tissue derived from the epicardium are imperative to develop a mature atrioventricular conduction. To test this, apoptosis was blocked using an established caspase inhibitor and epicardial growth was delayed using the experimental epicardial inhibition model, both in chick embryonic hearts. Chicken embryonic hearts were either treated with the peptide caspase inhibitor zVAD-fmk by intrapericardial injection in ovo (ED4) or underwent epicardial inhibition (ED2.5). Spontaneously beating embryonic hearts isolated (ED7-ED8) were then stained with voltage-sensitive dye Di-4-ANEPPS and imaged at 0.5-1 kHz. Apoptotic cells were quantified (ED5-ED7) by whole-mount LysoTracker Red and anti-active caspase 3 staining. zVAD-treated hearts showed a significantly increased proportion of immature (base to apex) activation patterns at ED8, including ventricular activation originating from the right atrioventricular junction, a pattern never observed in control hearts. zVAD-treated hearts showed decreased numbers of apoptotic cells in the atrioventricular canal myocardium at ED7. Hearts with delayed epicardial outgrowth showed also increased immature activation patterns at ED7.5 and ED8.5. However, the ventricular activation always originated from the left atrioventricular junction. Histological examination showed no changes in apoptosis rates, but a diminished presence of atrioventricular sulcus tissue compared with controls. Apoptosis in the atrioventricular canal myocardium and controlled replacement of this myocardium by epicardially derived HCN4-/Trop1- sulcus tissue are essential determinants of mature ventricular activation pattern. Disruption can lead to persistence of accessory atrioventricular connections, forming a morphological substrate for ventricular pre-excitation. Developmental Dynamics 247:1033-1042, 2018. © 2018 Wiley Periodicals, Inc.

Validation of a rapid semi-automated method to assess left atrial longitudinal phasic strains on cine cardiovascular magnetic resonance imaging

BackgroundAbnormal left atrial (LA) function is a marker of cardiac dysfunction and adverse cardiovascular outcome, but is difficult to assess, and hence not, routinely quantified. We aimed to determine the feasibility and effectiveness of a fast method to measure long-axis LA strain and strain rate (SR) with standard cardiovascular magnetic resonance (CMR) compared to conventional feature tracking (FT) derived longitudinal strain.MethodsWe studied 50 normal controls, 30 patients with hypertrophic cardiomyopathy, and 100 heart failure (HF) patients, including 40 with reduced ejection fraction (HFrEF), 30 mid-range ejection fraction (HFmrEF) and 30 preserved ejection fraction (HFpEF). LA longitudinal strain and SR parameters were derived by tracking the distance between the left atrioventricular junction and a user-defined point at the mid posterior LA wall on standard cine CMR two- and four-chamber views. LA performance was analyzed at three distinct cardiac phases: reservoir function (reservoir strain εs and strain rate SRs), conduit function (conduit strain εe and strain rate SRe) and booster pump function (booster strain εa and strain rate SRa).ResultsThere was good agreement between LA longitudinal strain and SR assessed using the fast and conventional FT-CMR approaches (r = 0.89 to 0.99, p < 0.001). The fast strain and SRs showed a better intra- and inter-observer reproducibility and a 55% reduction in evaluation time (85 ± 10 vs. 190 ± 12 s, p < 0.001) compared to FT-CMR. Fast LA measurements in normal controls were 35.3 ± 5.2% for εs, 18.1 ± 4.3% for εe, 17.2 ± 3.5% for εa, and 1.8 ± 0.4, − 2.0 ± 0.5, − 2.3 ± 0.6 s− 1 for the respective phasic SRs. Significantly reduced LA strains and SRs were observed in all patient groups compared to normal controls. Patients with HFpEF and HFmrEF had significantly smaller εs, SRs, εe and SRe than hypertrophic cardiomyopathy, and HFmrEF had significantly impaired LA reservoir and booster function compared to HFpEF. The fast LA strains and SRs were similar to FT-CMR for discriminating patients from controls (area under the curve (AUC) = 0.79 to 0.96 vs. 0.76 to 0.93, p = NS).ConclusionsNovel quantitative LA strain and SR derived from conventional cine CMR images are fast assessable parameters for LA phasic function analysis.

Influence of the short-axis cine acquisition protocol on the cardiac function evaluation: A reproducibility study

PurposeTo define the optimal cardiac short-axis cine acquisition protocol for the assessment of the left and rightventricular functions. Materials and methods20 volunteers were recruited and breath-hold CINE images were acquired on a Siemens Prisma 3T MRI. Four short-axis acquisition planes were defined from the 4-chamber view. AV Junctions: short-axis slices parallel to the plane that cuts through the external right and left atrioventricular junctions. Left AV Junctions: short-axis slices parallel to the plane that cuts through both left atrioventricular junctions. Septum: short-axis slices perpendicular to the septum with one cutting through the septum junction. LongAxis: short-axis slices perpendicular to the long axis with one cutting through the septum junction. Intra and inter reproducibility was assessed using Bland-Altman coefficient of variation (CV) and Lin’s concordance correlation coefficient (CCC). The influence of the protocol on the ejection fraction (EF) and stroke volume (SV) was quantified statistically using pair-wise CV and Pearson’s correlation coefficient R2. ResultsAll protocols led to high reproducibility for the LV EF (mean intra CV=3.83%, mean inter CV=4.81%, lowest CV=4.20% (AV junctions) and highest CV=5.24% (Left AV Junctions)). Reproducibility of the RV measurements was lower (mean intra CV=7.84%, mean inter CV=9.17%). Septum protocol led to significantly lower variability compared to the other 3 protocols for RV EF (CV=7.62% (Septum), CV=8.42% (Long Axis), CV=9.54% (Left AV Junctions) and CV=11.08% (AV Junctions) with Lin’s CCC varying from 0.4 (AV Junctions) to 0.69 (Septum) for inter-observer reproducibility). No differences in group average for clinical parameters was found for both LV and RV clinical measurements. However, patient-specific RV EF evaluation is dependent on the chosen protocol (CV=9.95%, R2=0.52). ConclusionBased on the results of the study cine mode short-axis acquisitions should be planned perpendicular to the septum in order to guarantee optimal RV and LV measurements.

Can a swallowed foreign body cause severe mitral valve regurgitation ?

Very rarely a foreign body in the esophagus may penetrate anteriorly to heart or aorta. Such foreign bodies may cause pericardial effusion and cardiac tamponade. To report that an accidentally swallowed foreign body in the esophagus may penetrate the heart and even cause severe mitral regurgitation. A 20 month old girl previously healthy presented to the emergency department with 3 days history of fever, respiratory distress, vomiting and poor feeding. The mother reported that her child had some choking event almost a week before, when the child was admitted to another hospital where diagnosis was made of myocarditis. Anti-failure medications prescribed. On examination she had palpable peripheral pulses, a pansystolic murmur on the cardiac apex, and hepatomegaly. EKG showed sinus tachycardia with left ventricular hypertrophy. Chest X-ray revealed normal cardiac size with lungs congestion and suspicion of possible foreign body. Echocardiography showed dilatation of the left atrium and of the pulmonary veins, severe mitral regurgitation with an echogenic structure in next to the posterior mitral valve leaflet with consensual moving. Chest CT scan revealed a high-density metallic foreign body inside the heart in correspondence of the left atrio-ventricular junction. The foreign body was removed surgically and proved to be a thin shiny metal bar, 2 cm in length. The mitral valve was completely damaged and was replaced by mechanical valve (Carbomedics 18 mm). The postoperative course was uneventful and patient was discharged home with anti-failure medications (frusemide, captopril) and warfarin. She remained asymptomatic one year after surgery. The process of diagnosing a foreign body in an infant or a toddler, eroding from the esophagus to the heart was very tricky. The diagnosis was suspected by the history of chocking. The x-ray of the chest showed an abnormal structure on the heart shadow, which was further underlined by the echocardiogram suggesting abnormal structure in the heart. Finally CT angio of heart confirmed a metallic foreign body in the left atrium. Happily, MRI was not done; it may have proved disastrous in such a case. The strategy regarding foreign body management either conservative or by its removal either by cardiac catheterization or surgery, depends on location, size of foreign body as well as on whether the patient is symptomatic and in danger to develop further complications. In our case, as the foreign body was in the left atrium and the patient was very critically ill, we opted to remove it by surgery. Moreover, it was thought that patient might need mitral valve repair but unfortunately the valve was so damaged that we opted for mitral valve replacement.

The spectrum of double-outlet right atrium including hearts with three atrioventricular valves

Double-outlet right atrium (DORA) is characterized by simultaneous right atrial emptying into both ventricles. Ventriculoatrial septal malalignment is the cardinal morphological feature. Three cases are presented to depict two major types of DORA-DORA with a malaligned atrial septum and DORA with a malaligned ventricular septum. We describe two subtypes of each form of DORA: DORA with a malaligned atrial septum presents with either a common atrioventricular (AV) junction (guarded by a common AV valve) or with a single AV junction (due to the absence of the left AV junction). DORA with a malaligned ventricular septum may be associated with a right ventricle (RV) that is adequate for biventricular repair or a severely hypoplastic RV not compatible with biventricular repair. DORA with a malaligned ventricular septum is closely related to typical straddling of the tricuspid valve. Peculiarly, DORA with a malaligned ventricular septum presents three AV valves at the AV junction and is associated with an abnormal disposition of the AV conduction axis. Clear understanding of the morphology of these lesions is important in preventing a surgical misadventure at the crux of the heart.

Morphology and Morphogenesis of Atrioventricular Septal Defect With Common Atrioventricular Junction

For many years, the lesions now often described as atrioventricular septal defects were considered to represent atrioventricular canal malformations or endocardial cushion defects. It was also long recognized that patients with the so-called ostium primum defect should be included in this category. The phenotypic feature of these hearts is the presence of a common atrioventricular junction, as opposed to separate right and left atrioventricular junctions. The presence of the common atrioventricular junction underscores the associated phenotypic features, such as the presence of a trifoliate left atrioventricular valve, which has no resemblance to a cleft mitral valve; unwedging of the subaortic outflow tract; and disproportion between the inlet and outlet dimensions of the left ventricle. These features are comparable in patients having the so-called partial, intermediate, and complete variants of the malformation. Anatomical differentiation depends on the morphology of the leaflets of the common atrioventricular valve that bridge the ventricular septum. If these bridging leaflets are fused one to the other, then there are dual orifices, rather than a common orifice, within the common atrioventricular junction. The relationships of the bridging leaflets to the septal structures determine the potential for shunting across the atrioventricular septal defect, which can occur at atrial and ventricular levels or exclusively at either atrial or ventricular level. Rarely, the atrioventricular septal defect may close spontaneously. Recent evidence from studies of cardiac development shows that rather than being an endocardial cushion defect, the malformation results from failure of ingrowth into the developing heart from the dorsal mesenchymal tissues.

Cardiac Anatomy for the Interventional Arrhythmologist: I.Terminology and Fluoroscopic Projections

Cardiac anatomy is complex and its understanding is essential for the interventional arrhythmologist. The first difficulty is the terminology used to describe the location of sites of mapping and ablation. For many years, electrophysiologists have named these positions following the conventional electrocardiographical vocabulary, or the terminology used by surgeons performing arrhythmic surgery. This traditional nomenclature, however, failed to take note of the crucial principle of considering the location of the heart in the human body as viewed in its erect position. In other words, it had failed to use an attitudinally appropriate terminology. Almost 10 years ago, a new attitudinal nomenclature was proposed for the right and left atrioventricular junctions. In this first of a series of reviews of cardiac anatomy as seen by the interventional arrhythmologist, we discuss the role of attitudinally appropriate terminology, and relate this to the projections used for cardiac fluoroscopy, fluorography, and angiography. Throughout our series of reviews, we will illustrate the value of The Visible Human Slice and Surface Server in facilitating the understanding of the fluoroscopic anatomy. (PACE 2010; 497-507).

Accessory Atrioventricular Myocardial Connections in the Developing Human Heart

Fetal and neonatal atrioventricular (AV) reentrant tachycardias can be life-threatening but resolve in most cases during the first year of life. The transient presence of accessory AV myocardial connections during annulus fibrosus development may explain this phenomenon. A total of 45 human embryonic, fetal, and neonatal sectioned hearts (4 to 36 weeks of development) were studied immunohistochemically. Accessory myocardial AV connections were quantified and categorized according to their specific location, and 3D reconstructions were made. Between 4 and 6 weeks of development, the atrial and ventricular myocardium was continuous at the primitive AV canal. At 6 to 10 weeks, numerous accessory myocardial AV connections were identified in the left (45%), right (35%), and septal (20%) regions of the AV junction. Most right-sided accessory connections comprised distinct myocardial strands, whereas left-sided connections consisted of larger myocardial continuities. At 10 to 20 weeks, all accessory AV connections comprised discrete myocardial strands and gradually decreased in number. The majority of accessory connections were located in the right AV junction (67%), predominantly in the lateral aspect (45%). Seventeen percent of the accessory connections were observed in the left AV junction, and 16% were observed in the septal region. 3D reconstructions of the developing AV nodal area at these stages demonstrated multiple AV node-related accessory connections. From 20 weeks until birth, and in neonatal hearts, no further accessory myocardial AV connections were observed. Isolation of the AV junction is a gradual and ongoing process, and right lateral accessory myocardial AV connections in particular are commonly found at later stages of normal human cardiac development. These transitory accessory connections may act as substrate for AV reentrant tachycardias in fetuses or neonates.

Ectopic nodal structures in a patient with atrial tachycardia originating from the mitral valve annulus

We report a case, which we believe to be rare, of adenosine-sensitive atrial tachycardia (AT) originating from the mitral valve annulus. The patient, a 73-year-old woman, died of unrelated cause 4 years after radiofrequency (RF) ablation therapy. Histologically, fibrous replacement of atrial musculature by mature collagenous tissue produced by the RF current was observed at the left inferior atrioventricular junction. In serial sections that included the coronary sinus, two distinct nodal structures containing small, pale myocytes within the fibrous tissue matrix were identified around the region of the ablation lesion. Our case appears to be a unique representation of tissue that was associated with the occurrence and maintenance of AT.

An Unusual Accessory Pathway: Anteroseptal to Ventricular Outflow Region Connection

Accessory pathways are typically located along the left or right atrioventricular junction. Distinct ventricular pre-excitation patterns determined by surface electrocardiography can provide reasonable pathway localization prior to invasive mapping and catheter ablation. We report an accessory pathway producing an unusual electrocardiographic appearance suggestive of ventricular outflow region pre-excitation. Pacing maneuvers and standard intracardiac recordings confirmed an atrial insertion immediately adjacent to the atrioventricular (AV) node and supported a ventricular insertion at the outflow tract region well away from the AV junction. The elimination of pathway conduction was achieved with radiofrequency (RF) energy at the atrial insertion after successful ice mapping excluded AV block at the target site. This is the second such pathway observed at our institution over a 20-year period.

Emerging patterns of cardiac conduction in the chick embryo: Waveform analysis with photodiode array‐based optical imaging

Major difficulties investigating the developing cardiac conduction system stem from that the embryonic heart is extremely small (< 2 mm) and cardiac activation is relatively rapid (< 8 msec). The objective of this study was to investigate the electrophysiology of the embryonic chick cardiac conduction system at periseptation stages with a photodiode array-based detection method of optical mapping capable of high spatial and temporal resolution. Previous work indicated that, in chicken embryos, a switch occurs in ventricular activation pattern from immature base-to-apex to mature apex-to-base pattern at the time of ventricular septation. It was our aim to map activation in more detail to identify the active pathway or pathways of atrioventricular conduction at these particular stages. Analysis of preseptated hearts (n = 10) showed that the latest atrial activation took place just above the site of the earliest ventricular activation at the ventral left ventricular base. Analysis of postseptated hearts (n = 11) showed apex-to-base conduction consistent with activation through the maturing His-Purkinje system. Evaluation of hearts during septation revealed a gradual transition of ventricular activation patterns rather than an abrupt "switch." External pacing of preseptated hearts revealed significant slowing of interventricular conduction compared with spontaneous beats (spontaneous, 61.7 cm/sec +/- 9 cm/sec vs. paced, 36.5 cm/sec +/- 10 cm/sec). The more detailed mapping revealed that, before septation, the pattern of activation of the ventricular myocardium is consistent with direct atrial-ventricular myocardial connections at the left lateral atrioventricular junction; however, functional evidence for a preferential conduction pathway within the ventricles was present before septation.

Echocardiography of the coronary sinus in adults.

The coronary sinus (CS) is a small tubular structure just above the posterior left atrioventricular junction. The CS can be imaged in several different echocardiographic views. Using zoom M-mode recordings of the CS in apical two-chamber view, CS caliber can be sharply imaged and easily measured during different phases of the cardiac cycle. We have recently shown that the CS narrows during atrial contraction in persons with sinus rhythm, but does not narrow at all if atrial fibrillation is present. Attenuation of CS narrowing occurs in patients with congestive heart failure and inferior vena cava plethora. Maximal CS caliber occurs during ventricular systole. Patients with poor left ventricular systolic function show mild CS dilatation. Greater CS dilatation is present in patients with persistent left superior vena cava, and huge dilatation when this anomaly is accompanied by absence of a right superior vena cava. Injection of sonicated saline into a left and then a right arm vein is diagnostically useful in confirming these two venous anomalies. Pulsed-wave Doppler of the CS can be recorded in the parasternal right heart inflow view. From this and from the CS cross-section area it may be possible to estimate coronary blood flow.

Anatomy of the atrioventricular junctions with regard to ventricular preexcitation.

In the normal heart, the atrioventricular junctions surround the orifices of the mitral and tricuspid valves. The septal area of the junctions is much smaller than generally thought, being made up of the fibrous membranous septum and the muscular atrioventricular septum. The left atrioventricular junction gives the potential for muscular atrioventricular contiguities only in relation to the mural leaflet of the mitral valve. The right junction extends from the area posterior to the muscular atrioventricular septum to the supraventricular crest of the right ventricle. Anomalous pathways for conduction, which produce pre-excitation, can be found anywhere within these atrioventricular junctions. The pathways usually are the muscular accessory connections responsible for the Wolff-Parkinson-White syndrome, which can exist in the left, septal, or right junctions. Specific muscular connections are found in the presence of Purkinje cell tumors, diverticulums of the coronary sinus, or when taking origin from nodes of Kent at the acute margin of the ventricular mass. The latter connections are responsible for most examples of so-called Mahaim conduction, and are also described as atriofascicular tracts. The true Mahaim fibers are best described as nodoventricular or fasciculo-ventricular connections, while the pathway previously labelled as atriofascicular by the European Study Group is now best distinguished as an atrio-Hisian tract. The slow and fast pathways into the atrioventricular node are composed or ordinary atrial myocardium, the orientation of the fibers probably producing preferential conduction.

Is a cleft in the anterior leaflet of an otherwise normal mitral valve an atrioventricular canal malformation?

Objectives. This study sought to ascertain the surgical anatomy of a cleft in the left atrioventricular (AV) valve.Background. Important morphologic differences exist between hearts with a cleft in the anterior leaflet of an otherwise normal mitral valve and those with a so-called cleft in the left AV valve when there is an AV septal defect, but it has been customary to link the lesions together on developmental grounds.Methods. Eight autopsied specimens with a cleft in the aortic (or anterior) leaflet of the mitral valve were studied in detail, and echocardiograms from 21 patients with such a cleft were compared with the specimens and with findings typical of the so-called partial AV canal and other forms of AV septal defect.Results. The structure and direction of the cleft, location of the papillary muscles within the left ventricle and AV junctional morphology of hearts with an otherwise normally structured mitral valve were significantly different from typical findings in hearts with AV septal defects.Conclusions. It is necessary to distinguish morphologically a cleft in an otherwise normally structured mitral valve in hearts with separate right and left AV junctions from the trifoliate left component of a common AV valve in hearts with an AV septal defect and a common AV junction because the disposition of the AV conduction tissues varies markedly between the lesions.