Anatomy and Pathology of the Cardiac Conduction System

The cardiac conduction system is formed of histologically and electrophysiologically distinct specialized tissues uniquely located in the human heart. Understanding the anatomy and pathology of the cardiac conduction system is imperative to an interventional electrophysiologist to perform safe ablation and device therapy for the management of cardiac arrhythmias and heart failure. The current review summarizes the normal and developmental anatomy of the cardiac conduction system, its variation in the normal heart and congenital anomalies, and its pathology and discusses important clinical pearls for the proceduralist.

Anatomy and Pathology of the Cardiac Conduction System

The cardiac conduction system is formed of histologically and electrophysiologically distinct specialized tissues uniquely located in the human heart. Understanding the anatomy and pathology of the cardiac conduction system is imperative to an interventional electrophysiologist to perform safe ablation and device therapy for the management of cardiac arrhythmias and heart failure. The current review summarizes the normal and developmental anatomy of the cardiac conduction system, its variation in the normal heart and congenital anomalies, and its pathology and discusses important clinical pearls for the proceduralist.

Atrioventricular Septal Defects: Pathology, Imaging, and Treatment Options

PURPOSE OF REVIEW

Atrioventricular septal defects (AVSD) represent a broad spectrum of congenital anomalies from simple to the most complex heart defects including some distinct types. Clinical presentation and timing of intervention differ by morphological subset and functional anatomy. Herein, we review morphological variations and characteristics that determine appropriate intervention and provide insights into functional anatomy based on detailed three-dimensional (3D) assessment of AVSDs.

RECENT FINDINGS

The understanding of functional morphology of AVSDs has improved significantly with detailed 3D echocardiographic evaluation of the atrioventricular junction and valve morphology. As prenatal detection of AVSDs has increased significantly, it has become the most common fetal cardiac diagnosis enabling antenatal counseling and delivery planning. Advances in diagnosis and perioperative care have resulted in optimal outcomes. The diagnosis and management of AVSDs have improved over the years with enhanced understanding of anatomy and perioperative care resulting in optimal short and long-term outcomes.

Can Fetal Echocardiographic Measurements of the Left Ventricular Outflow Tract Angle Detect Fetuses with Conotruncal Cardiac Anomalies?

OBJECTIVES

The angle between the inter-ventricular septum and the ascending aorta can be measured during a sonographic fetal survey while viewing the left ventricular outflow tract (LVOT angle). Our aim was to compare the LVOT angle between fetuses with and without conotruncal cardiac anomaliesrmations.

METHODS

In this prospective observational study, we compared the LVOT angle between normal fetuses, at different gestational age, and fetuses with cardiac malformations.

RESULTS

The study included 302 fetuses screened at gestational age of 12-39 weeks. The LVOT angle ranged from 127 to 163 degrees (mean 148.2), in 293 fetuses with normal hearts, and was not correlated with gestational age. The LVOT angle was significantly wider in fetuses with D-transposition of the great arteries (D-TGA, eight fetuses) and valvar aortic stenosis (AS, three fetuses), than in fetuses with normal hearts (164.8 ± 5.0 vs. 148.2 ± 5.4, respectively, p < 0.001). Conversely, the LVOT angle was significantly narrower in fetuses with complete atrioventricular canal defect (AVC, eight fetuses), than in fetuses with normal hearts (124.8 ± 2.4 vs. 148.2 ± 5.4, respectively, p < 0.001). On ROC analysis, an angle of 159.6 degrees or higher had a sensitivity of 100% and a specificity of 97.3% for the detection of TGA or AS, whereas an angle of 128.8 degrees or lower had a sensitivity of 100% and a specificity of 99.7% for the detection of AVC defect.

CONCLUSIONS

The LVOT angle is constant during pregnancy, and differs significantly in fetuses with TGA/AS, and AVC, compared to fetuses with normal hearts (wider and narrower, respectively).

"Repair of common atrioventricular junction in isolation and when associated with other congenital heart defects"

Management of atrioventricular septal defects has grown leaps and bounds since the first correction of this malformation. Main reasons considered for the improvement are good understanding of lesion anatomy, precise preoperative diagnosis including imaging, progress in surgical technique, myocardial protection, and post-operative care. In this article we review the anatomy, pathophysiology, clinical features, associations, diagnosis, surgical therapy, complications, and results of atrioventricular septal defects.

Percutaneous edge-to-edge repair for common atrioventricular valve regurgitation in a patient with heterotaxy syndrome, single ventricle physiology, and unbalanced atrioventricular septal defect

Congenital heart disease patients, specifically with unbalanced atrioventricular septal defects and common atrioventricular valves requiring single ventricle palliation, have substantial morbidity and mortality. Atrioventricular valve regurgitation (AVVR) is associated with poor outcomes in single ventricle patients, and many of them require surgical treatment of AVVR in their lifetimes. We describe a unique case of transcatheter edge-to-edge valve repair using the MitraClip system (Abbott, Chicago, IL) in a single ventricle patient with severe common AVVR.

Left Valvar Morphology Is Associated With Late Regurgitation in Atrioventricular Canal Defect

BACKGROUND

Left atrioventricular valve regurgitation (LAVVR) after atrioventricular canal (AVC) repair remains a significant cause of morbidity. Papillary muscle arrangement may be important. To investigate the implications of left mural leaflet morphology, we examined anatomic characteristics of the LAVV to determine possible associations with postoperative LAVVR.

METHODS

All patients with biventricular AVC repair at our institution between January 1, 2011, and December 31, 2016, with necessary imaging were retrospectively reviewed. We assessed papillary muscle structure and novel measures of the left mural leaflet from preoperative echocardiograms and the degree of LAVVR from the first and last available follow-up echocardiograms. Associations with degree of early and late postoperative LAVVR were assessed with t tests, analysis of variance, or χ² or Fisher exact tests, and multivariable logistic regression.

RESULTS

There were 58 of 156 patients (37%) with significant (moderate or severe) early postoperative LAVVR, and 30 of 93 (32%) had significant LAVVR after 6 or more months. Fewer patients with closely spaced or asymmetric papillary muscles had moderate or severe late LAVVR vs those with widely spaced papillary muscles (17% vs 40%, P = .019). Controlling for weight at operation, genetic syndromes, and bypass time, widely spaced papillary muscles increased the odds ratio for late LAVVR to 3.6 (P = .026). Larger mural leaflet area was also associated with late LAVVR on univariable (P = .019) and multivariable (P = .023) analyses. One-third of patients with significant late LAVVR had no significant early postoperative regurgitation.

CONCLUSIONS

Mural leaflet and papillary muscle anatomy are associated with late LAVVR after AVC repair. Late regurgitation can develop in the absence of early LAVVR, suggesting different mechanisms.

Comprehensive echocardiographic imaging of atrioventricular valves in children with atrioventricular septal defect: Accuracy of 2D and 3D imaging and reasons for disagreement

OBJECTIVE

To compare the accuracy and reasons for disagreement of two-dimensional (2D) and three-dimensional (3D) echocardiography findings in the assessment of the atrioventricular valve complex in patients with atrioventricular septal defect.

METHODS

A total of 20 children (mean age 8 months) with atrioventricular septal defect were enrolled prospectively into this study. The accuracy of and the reasons for disagreement in the assessment of the atrioventricular valve features were analyzed between 2D and 3D echocardiography and surgical findings.

RESULTS

We found that in assessing the Rastelli type and the extension of the inferior leaflet into the right ventricle, 3D echocardiography was more accurate compared to 2D echocardiography. In all other features, 2D and 3D echocardiography showed similar accuracy. A significant reason for inaccuracy by both echo modalities was that the technique itself could not visualize the feature, although the image quality was considered to be adequate. In most cases, where it was not possible to visualize the atrioventricular feature by 2D, it was possible by 3D, and vice versa.

CONCLUSION

The accuracy of 2D and 3D echocardiography and understanding the potential reasons for disagreements in assessing the atrioventricular valve complex with 2D and 3D can guide the use of those two techniques when combining them in the clinical practice.

Annuloplasty band implantation in adults with partial atrioventricular septal defect: a propensity-matched study

OBJECTIVES

The incidence of recurrent left atrioventricular valve (LAVV) regurgitation is generally high after repair of partial atrioventricular septal defect (AVSD). This study aimed to evaluate the effect of implanting an additional annuloplasty band into the LAVV during partial AVSD repair and to assess the late outcomes of recurrent LAVV regurgitation.

METHODS

This study enrolled 133 patients who underwent repair of partial AVSD at our institution from January 2005 to December 2015. All patients underwent repair of the ostium primum atrial septal defect and closure of the LAVV cleft; 37 patients underwent additional annuloplasty band implantation. To minimize differences in preoperative data, propensity score matching was used to identify 33 well-matched patient pairs.

RESULTS

Cardiopulmonary bypass time and aorta cross-clamp time were significantly longer in the band implantation group (P < 0.05). The 2 groups had similar durations of intensive care and hospital stay (P > 0.05). There was 1 in-hospital death in the band implantation group. During follow-up, conduction block occurred in 6 patients in each group. After follow-up of more than 10 years, freedom from late recurrent LAVV regurgitation was 91% in the band implantation group and 57% in the isolated cleft closure group (P < 0.05). In patients with preoperative severe regurgitation and moderate/mild regurgitation, the rates of freedom from recurrent LAVV regurgitation were 85% and 37%, respectively (P < 0.05).

CONCLUSIONS

In patients with moderate/severe LAVV regurgitation or severe annular dilation, additional band implantation significantly reduces the incidence of recurrent regurgitation and improves long-term outcomes.

Long-Term Outcome After Pulmonary Artery Banding in Children With Atrioventricular Septal Defects

BACKGROUND

Patients with atrioventricular septal defect (AVSD) may require pulmonary artery banding (PAB), either as a part of a staged univentricular palliation or to allow delayed biventricular repair in patients presenting with early heart failure. The long-term outcomes of PAB in children with AVSD have not been previously reported.

METHODS

All children with AVSD who underwent PAB at a single institution were included in the study. Data were obtained from medical records and correspondence with general practitioners and cardiologists.

RESULTS

A total of 68 patients with complete AVSD underwent PAB, of whom 58.8% of patients (40 of 68) had balanced AVSD (bAVSD) and underwent PAB with intent to subsequently perform biventricular repair. The remaining 41.2% of patients (28 of 68) had unbalanced AVSD (uAVSD) and underwent PAB as part of staged univentricular repair. PAB was not associated with a short-term increase in atrioventricular valve (AVV) regurgitation (p = 0.24). In patients with bAVSD, 83.8% (95% confidence interval [CI]: 67.4% to 92.4%) achieved biventricular repair. Survival was 73.4% (95% CI: 54.3% to 85.5%) and freedom from left AVV operation was 60.0% (95% CI: 36.1% to 77.4%) at 20 years of follow-up. In patients with uAVSD, 61.9% (95% CI: 40.5% to 77.5%) had achieved Fontan completion at 10 years of follow-up. Survival was 60.9% (95% CI: 36.2% to 78.5%) and freedom from AVV operation was 78.6% (95% CI: 55.5% to 90.6%) at 20 years.

CONCLUSIONS

PAB can be used in patients with AVSD without compromising AVV function. Most patients with bAVSD progress to biventricular repair, albeit with a high rate of AVV reoperation. Patients with uAVSD who undergo PAB have similar outcomes to the overall uAVSD population.

[Atrioventricular septal defect in an adult patient: There are 'clefts' and clefts]

In this report, we present the case of an adult male with severe mitral regurgitation due to an atrioventricular septal defect. Anatomical assessment by two- and three-dimensional transesophageal echocardiography was essential for detailed morphological characterization and surgical planning. The different features of a 'cleft' in an atrioventricular septal defect compared to an anterior leaflet cleft in an otherwise normal mitral valve are here discussed.

Assessment of viscous energy loss and the association with three-dimensional vortex ring formation in left ventricular inflow: In vivo evaluation using four-dimensional flow MRI

PURPOSE

To evaluate viscous energy loss and the association with three-dimensional (3D) vortex ring formation in left ventricular (LV) blood flow during diastolic filling.

THEORY AND METHODS

Thirty healthy volunteers were compared with 32 patients with corrected atrioventricular septal defect as unnatural mitral valve morphology and inflow are common in these patients. 4DFlow MRI was acquired from which 3D vortex ring formation was identified in LV blood flow at peak early (E)-filling and late (A)-filling and characterized by its presence/absence, orientation, and position from the lateral wall. Viscous energy loss was computed over E-filling, A-filling, and complete diastole using the Navier-Stokes energy equations.

RESULTS

Compared with healthy volunteers, viscous energy loss was significantly elevated in patients with disturbed vortex ring formation as characterized by a significantly inclined orientation and/or position closer to the lateral wall. Highest viscous energy loss was found in patients without a ring-shaped vortex during E-filling (on average more than double compared with patients with ring-shape vortex, P < 0.003). Altered A-filling vortex ring formation was associated with significant increase in total viscous energy loss over diastole even in the presence of normal E-filling vortex ring.

CONCLUSION

Altered vortex ring formation during LV filling is associated with increased viscous energy loss. Magn Reson Med 77:794-805, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Partial and intermediate atrioventricular septal defects without major associated cardiac anomalies

Partial and intermediate atrioventricular septal defects (p-i AVSDs) constitute approximately 20-40% of all AVSDs. Children with p-i AVSDs are usually asymptomatic and typically undergo surgery at the preschool age or earlier if the signs of heart failure have developed. Surgical treatment for repair of p-i AVSDs has been successful for more than 60 years and is mainly directed towards closing septal defects, and maintaining or creating competent, non-stenotic left and/or right atrioventricular valves. By most measures, the outcomes of surgical management of p-i AVSDs have improved over the last 5 decades. In spite of significantly reduced mortality, the need for reoperation and long-term morbidity remains an issue in some patients from this population. The purpose of this article is to review current options and outcomes concerning the surgical management of the p-AVSD and i-AVSD variants without major associated cardiac malformations.

How Normal is a 'Normal' Heart in Fetuses and Infants with Down Syndrome?

BACKGROUND

Congenital heart disease is present in 44-56% of fetuses with Down syndrome (DS). There are, however, signs that hearts in DS without apparent structural heart defects also differ from those in the normal population. We aimed to compare the atrioventricular (AV) septum and valves in 3 groups: DS without AV septal defect (DS no-AVSD), DS with AVSD (DS AVSD) and control hearts.

METHODS

The ventricular septum, membranous septum and AV valves were examined and measured in histological sections of 15 DS no-AVSD, 8 DS AVSD and 34 control hearts. In addition, the ventricular septum length was measured on ultrasound images of fetal (6 DS AVSD, 9 controls) and infant (10 DS no-AVSD, 10 DS AVSD, 10 controls) hearts.

RESULTS

The membranous septum was 3 times larger in DS no-AVSD fetuses compared to control fetuses, and valve dysplasia was frequently (64%) observed. The ventricular septum was shorter in patients with DS both with and without AVSD, as compared to the control group.

CONCLUSION

DS no-AVSD hearts are not normal as they have a larger membranous septum, shorter ventricular septum and dysplasia of the AV valves as compared to control hearts.

Three-dimensional echocardiography of congenital abnormalities of the left atrioventricular valve

Congenital abnormalities of the left atrioventricular (AV) valve are a significant diagnostic challenge. Traditionally, reliance has been placed on two-dimensional echocardiographic (2DE) imaging to guide recognition of the specific morphological features. Real-time 3DE can provide unique views of the left AV valve with the potential to improve understanding of valve morphology and function to facilitate surgical planning. This review illustrates the features of congenital abnormalities of the left AV valve assessed by 3DE. The similarities and differences in morphology between different lesions are described, both with respect to the valve itself and supporting chordal apparatus. The potential advantages as well as limitations of this technique in clinical practice are outlined.

Electrophysiologic and anatomical relationships studied in primum atrioventricular septal defect

Anatomy and pattern of electrical activation predict the function and contraction pattern of the heart. Patients with primum atrioventricular septal defect (primum AVSD) present with abnormality of both anatomical arrangements and electric activation and serve therefore as an interesting population for studying electro-anatomic relationships in the heart. Understanding the relationships between anatomic and electrophysiologic abnormality is appropriate not only for diagnosis, therapy, and prognosis in patients with primum AVSD but also for understanding the developmental relationship between the conduction system and heart structures, in general. This article presents a review of the anatomical and electrophysiologic characteristics of patients with primum AVSD and provides recent knowledge of electroanatomical relationships of the heart.