Miniseries 2-septal and paraseptal accessory pathways-Part I: The anatomic basis for the understanding of para-Hisian accessory atrioventricular pathways

AIMS

Although the anatomy of the atrioventricular conduction axis was well described over a century ago, the precise arrangement in the regions surrounding its transition from the atrioventricular node to the so-called bundle of His remain uncertain. We aimed to clarify these relationships.

METHODS AND RESULTS

We have used our various datasets to examine the development and anatomical arrangement of the atrioventricular conduction axis, paying particular attention to the regions surrounding the point of penetration of the bundle of His. It is the areas directly adjacent to the transition of the atrioventricular conduction axis from the atrioventricular node to the non-branching atrioventricular bundle that constitute the para-Hisian areas. The atrioventricular conduction axis itself traverses the membranous part of the ventricular septum as it extends from the node to become the bundle, but the para-Hisian areas themselves are paraseptal. This is because they incorporate the fibrofatty tissues of the inferior pyramidal space and the superior atrioventricular groove. In this initial overarching review, we summarize the developmental and anatomical features of these areas along with the location and landmarks of the atrioventricular conduction axis. We emphasize the relationships between the inferior pyramidal space and the infero-septal recess of the subaortic outflow tract. The details are then explored in greater detail in the additional reviews provided within our miniseries.

CONCLUSION

Our anatomical findings, described here, provide the basis for our concomitant clinical review of the so-called para-Hisian arrhythmias. The findings also provide the basis for understanding the other variants of ventricular pre-excitation.

Miniseries 1-Part III: 'Behind the scenes' in the triangle of Koch

AIMS

To take full advantage of the knowledge of cardiac anatomy, structures should be considered in their correct attitudinal orientation. Our aim was to discuss the triangle of Koch in an attitudinally appropriate fashion.

METHODS AND RESULTS

We reviewed our material prepared by histological sectioning, along with computed tomographic datasets of human hearts. The triangle of Koch is the right atrial surface of the inferior pyramidal space, being bordered by the tendon of Todaro and the hinge of the septal leaflet of the tricuspid valve, with its base at the inferior cavotricuspid isthmus. The fibro-adipose tissues of the inferior pyramidal space separate the atrial wall from the crest of the muscular interventricular septum, thus producing an atrioventricular muscular sandwich. The overall area is better approached as a pyramid rather than a triangle. The apex of the inferior pyramidal space overlaps the infero-septal recess of the subaortic outflow tract, permitting the atrioventricular conduction axis to transition directly to the crest of the muscular ventricular septum. The compact atrioventricular node is formed at the apex of the pyramid by union of its inferior extensions, which represent the slow pathway, with the septal components formed in the buttress of the atrial septum, thus providing the fast pathway.

CONCLUSIONS

To understand its various implications in current cardiological catheter interventions, the triangle of Koch must be considered in conjunction with the inferior pyramidal space and the infero-septal recess. It is better to consider the overall region in terms of a pyramidal area of interest.

The normal variants in the left bundle branch system

This article reviewed the main anatomic and physiopathological aspects of the left bundle branch from its origin in the His bundle and its intraventricular distribution on the left endocardial surface. The results are based on the relevant literature and on personal observations executed on 206 hearts distributed as follows: 67 dogs, 60 humans, 45 sheep, 22 pigs, 10 cows, 2 monkeys, 1 guanaco, and 1 sea lion. The main anatomical features of the His-Purkinje conducting system may be summarized as follows: The bundle of His is composed by two segments: the penetrating and branching portions. LBB originates in the branching portion located underneath the membranous septum. There is no true bifurcation of the bundle of His in a human heart. Short after its origin the LBB gives rise to its two main fascicles, anterior and posterior, both heading the anterior and posterior papillary muscles, respectively. The anterior division is thinner and longer than the posterior one. The RBB and the most anterior fibers of the LBB arise at the end of the branching portion. In some cases a well-defined left septal fascicle can be identified, usually arising from the posterior division. Each division gives off small fibers and false tendons crossing the left ventricular cavity connecting the papillary between them or the papillary muscles with the septal surface. From each division of the LBB, their corresponding Purkinje networks emerge covering the subendocardium of the septum and the free wall of the left ventricles. There are critical relationships of the proximal segments of the His-Purkinje system with the surrounding cardiac structures whose pathologic processes may damage the conducting tissue.

Electrophysiocardiogram: For the first time EPCG has been recorded on human body surface

Since ECG was invented in 1903, this is the first time in history that a full information multi-band and multi-linear electrophysiological cardiogram has been used to successfully scan and record on the human body surface. Since it is able to record various multi-band, multi-track linear electric signals of cardiac electrophysiological activities that correspond to different regions of the entire heart, it has thus been denominated as "electrophysiocardiogram" (EPCG). A traditional ECG is always represented by a characteristic wave form, which resembles a string. For a long period of time, ECG has had a lot of mysteries surrounding it, it maybe because ECG has a lot of mixed signals buried in such convolutionary forms, which limits the amount of the signals that are discernable and determinable. For the first time, the EPCG technology has allowed cardiac signals to be convoluted into the linear wave form, which is then processed through various new approaches featuring multiple frequency bands, multiple dimensions and multiple patterns, and consequentially recorded as the following types of signals within the ranges of P wave and T wave: multiple frequency band signals, signals of different regions and different locations, forward waves and negative waves. Therefore, EPCG may help to solve many puzzling scientific questions regarding heart, such as exactly how many electric signals are involved in heart excitation, pacing, conduction and action, as well as many other intriguing questions about heart, and thus would become a very helpful tool in clinical practice.

Intra-His bundle block in 2:1 atrioventricular block

Intra-hisian atrioventricular (AV) block is not a common phenomenon, but it is important for the development of advanced or complete AV block. We observed a 77-year-old female patient with the 2:1 AV block due to an intra-hisian block. In this case we tried to detect the block site, but an alternating pattern of the AH conduction was noted on the His-electrogram in the electrophysiological study (EPS). The cause of the confusing finding might have been the instability of the catheter to record a His potential. We could detect a splitting of the His-electrogram with an intra-hisian block after minimal manipulation of the catheter. The authors’ observations suggest that catheter stability is important for a precise recording in the EPS and radiofrequency catheter ablation procedure.

Joseph Erlanger (1874-1965): the cardiovascular investigator who won a Nobel Prize in neurophysiology

Born in San Francisco in 1874 into the family of German immigrants in which he was the only one to proceed beyond elementary education, Joseph Erlanger graduated from the University of California (Berkeley) in 1894. He was about to enter the local Cooper Medical School when he was told that the new medical school in Johns Hopkins University (Baltimore) aimed to surpass all others, and there he graduated and was later coached for a career in academic life by William H Howell (1860-1945). In due course he held the Chairs of Physiology in the University of Wisconsin (Madison) and Washington University at St Louis, Missouri. He showed that the Bundle of His is indeed the functional link between the atria and the ventricles in the mammalian heart and that the Korotkoff sounds are produced by a 'breaker' phenomenon resulting from instability of the pulse wave in a partially occluded artery. With Herbert S Gasser (1888-1963) he was awarded the Nobel Prize in 1944 for their work on action currents in peripheral nerve fibres. The history of science occupied him during his retirement. He died at St Louis in 1965.

Supraventricular tachycardia and sinus rhythm with contralateral bundle branch block patterns

A contralateral bundle branch block (BBB) aberration during tachycardia with a preexisting BBB strongly suggests the presence of ventricular tachycardia. We report on a middle-aged, female patient presented with wide QRS tachycardia. The patient had orthodromic atrioventricular tachycardia with a left BBB aberration in the presence of a preexisting right BBB due to an abnormal His-Purkinje system. We learned that the contralateral BBB aberration with supraventricular tachycardia could be seen when the His-Purkinje system was abnormal.

Catheter ablation of parahisian premature ventricular complex

Catheter ablation is performed in selected patients with a symptomatic premature ventricular complex (PVC) or PVC-induced cardiomyopathy. Ablation of PVC from the His region has a high risk of inducing a complete atrioventricular block. Here we report successful catheter ablation of a parahisian PVC in a 63-year-old man.