4.
5.
6.
7.
J. V., Harper, A. M., and Farrar, K.: Effects of acutely induced hypertension in cats on pial arteriolar caliber, local cerebral blood flow, and the blood brain barrier, Circ. Res. 39:33, 1976. Kety, S. S., Hafkenschiel, J. H., Jeffers, W. A., Leopold, I. H., and Shentum, H. A.: The blood flow, vascular resistance and oxygen consumption of the brain in essential hypertension, J. Clin. Invest. 57:511, 1948. Strandgaard, S., Mackenzie, E. T., Sengupta, D., Rowan, J. O., Lassen, N. A., and Harper, A. M.: Upper limit of autoregulation of cerebral blood flow in the baboon, Circ. Res. 34:435, 1974. Strandgaard, S., Jones, J. V., Mackenzie, E. T., and Harper, A. M.: Upper limit of cerebral blood flow autoregulation in experimental renovascular hypertension in the baboon, Circ. Res. 37:164, 1975. Standgaard, S., Olesen, J.. SkinhGj, E., and Lassen, N. A.: Autoregulation of brain circulation in severe arterial hypertension, Br. Med. J. 1:507, 1973.
Intramural branch
ramification
9.
10.
11. 12.
Jones, J. V., Fitch, W., Mackenzie, E. T.. Standgaard, S., and Harper, A. M.: Lower limit of cerebral blood flow autoregulation in experimental renovascular hypertension in the baboon, Circ. Res. 39:555, 1976. Folkow, B., Hallbiick, M., Lundgren, Y., Sivertsson, R.. and Weiss, L.: Importance of adaptive changes in vascular design for establishment of primary, hypert,ension, studied in man and in spontaneously hypertensive rats, Circ. Res. 32 and 33: (Suppl. 1):2. 1973. Graham, D. I.: Ischaemic brain damage of cerebral perfusion failure type after treatment of severe hypertension. Br. Med. J. iv:739, 1975. Editorial: Hypertension in the elderly. Lancet. 1:684. 1977. Strandgaard, S.: Autoregulation of cerebral blood flow in hypertensive patients. The modifying influence of prolonged antihypertensive treatment on the tolerance to acute, drug-induced hypotension. Circulation 53:720. 1976.
of the left bundle
Attention has been focused, recently, upon location and distribution of the fascicles of the left bundle branch (LBB) in the human heart, since these anatomical details may have an important bearing on pathophysiology of intraventricular conduction.‘. ? It can be useful, therefore, to briefly illustrate an unusual variety in morphology of the LBB. The different, and largely unpredictable,* patterns of
Fig. 1. Left, myocardium.
8.
the root of the LBB (black Right, further intramural
arrow) course
subdivision of the LBB, hitherto described, only refer to the sagittal plane; indeed, the ramifications of the branch are well known to fan and flatten out in thin bands, over the left subendocardial surface of the ventricular septum? Occasional anastomoses of individual LBB fibers with the underlying myocardium are too short to be considered as true extensions of the branch on the frontal plane.
gives off a medial fascicle of the LBB ramification
(open (Azan
arrow) stain;
penetrating the septal original magnification
x 12).
0002-8703/78/#296-0271$00.20/O
0 1978 The
C. V. Mosby
Co.
American
Henrt Journal
271
Annotations
In turn, the right bundle branch (RBB), which is a compact fascicle, in its middle course normally exhibits a medial bent on the frontal plane, entering the myocardial context of the septum (intramural or “mimetic” tract). Sometimes, the entire RBB has been seen to travel inside the septal myocardium.’ In a 51-year-old man, who died from heart failure without conduction blocks, the conducting system was examined histologically with the technique of longitudinal serial sections’, 5 and an intramural ramification of the LBB was observed. The atrioventricular (AV) node and His bundle were normal; at the Hisian bifurcation the root of the LBB was subdivided, on the frontal plane, into two thin fascicles, one lying in the ipsolateral subendocardium while the other penetrated medially the muscle of the upper ventricular septum (Fig. 1). This intramural ramification belonged to the posterior part of the LBB, and took a straight intraseptal course among thick bundles of working myocardium, surrounded by a sheath of loose interstitial tissue (Fig. 1). The specific fascicle could be followed, downwards and anteriorly, over a length of about 1.2 cm. along the series of sections, and eventually melted with the septal muscle. The present evidence of a distinct, proximal intramural division of the LBB, in an otherwise normal AV system, can be regarded as an apparently unique anatomical variety. In a previously described case,’ the intramural root of the LBB belonged to an aberrant Hisian bifurcation, completely embedded within the septal myocardium. Besides the morphological interest, the intramural location of tracts of the LBB is worthwhile our attention in discussing pathophysiology of LBB conduction disturbances,6 from acute septal infarction particularly.5 It has been pointed out that a lower oxygen uptake makes the conducting myocells more resistant than the working
Of the myocardium
and myotonia
myocardium to ischemic damage.’ Moreover, the LBB, owing to ita widespread subendocardial layout and closeness to the left ventricle’s cavity, can be protected from anoxia by transendocardial oxygen diffusi0n.j. ’ Intramural tracts of the LBB are not likely to share this latter oxygen source with the rest of the branch, and thus are comparatively more vulnerable by impaired blood supply through the nutrient arteries.
L. Rossi, L.D.Path.Univ. Via Annunciata 23/4 20121 Milan, Italy REFERENCES
1. Lev, M., Unger,
2.
3.
P. N., Rosen, K. M., and Bharati, S.: The anatomic base of electrocardiographic abnormality. Left bundle branch block: Recent advances in ventricular conduction, in Advances in Cardiology, vol. 14, Basel, 1975, S. Karger, p. 16. Massing, G. K., and James, T. N.: Anatomical configuration of the His bundle and bundle branches in the human heart, Circulation 53609, 1976. Truex, R. C., and Smythe, M. Q.: Recent observations on the human cardiac conduction system, with special consideration of the atrioventricular node and bundle, in Electrophysiology of the heart, Taccardi, B., and Marchetti, G., eds., Oxford, 1965, Pergamon Press, p. 177. Rossi, L.: Histopathologic features of cardiac arrhythmias, Milan, 1969, Casa Editrice Ambrosiana. Rossi, L.: Histopathology of conducting system in left anterior hemiblock, Br. Heart J. 38:1304 1976. Burch, G. E.: Of the conduction system and myocardial function, AM. HEART J. 92809, 1976. Hackel, D. B., Wagner, G., Ratliff, N. B., Cies, A., and Estes, E. H.: Anatomic studies of the cardiac conducting system in acute myocardial infarction, AM. HEART J. 83~77, 1972.
atrophica
The striated cardiac muscle and the striated skeletal muscle are known to be different physiologically. Although both muscles are striated, their differences are further reflected by the differences in their behavior in myotonia congenita and myotonia atrophica. For example, it is obvious what would happen if the myocardium were to manifest myotonia, as skeletal muscle does, and the heart were to go into systole and remain contracted for a fairly long period of time, as skeletal muscle does. Fortunately, this state does not develop in heart muscle to any clinically measureable degree. If it did, the patients would die of systolic arrest. It is also interesting that cardiomyopathy and related cardiac disturbances are reported’, 2 not to exist in association with myotonia congenita, but skeletal muscle does develop myotonia. It is of further interest that patients with myotonia atrophica have a high incidence of conduction tissue dysfunction,3.’ with impairment of conduction manifested by various degrees of heart block to complete A-V block and complete SA node block. Because of
this high incidence of pathophysiology of the conduction tissue, one wonders if this is not additional evidence that, although the disease tends to “skip” the myocardium itself, it strikes the conduction tissue just as it strikes skeletal muscle and, therefore, cardiac muscle and conduction tissue in the heart are different. The mechanism for the block of the excitation wave front in conduction tissues and within the SA node itself stimulates interesting speculative physiologic considerations. For example, it is interesting to speculate that the excitation impulse attempts to flow through conduction tissue but a “myotonic phenomenon” occurs within the cells so that the wave front cannot progress and an additional one cannot even get started. This would be “myotonia electrica.” In the case of the SA node, the impulse might even be considered to be generated, but it is unable to spread through the SA node and escape the node (SA node exit block) to stimulate the atria. Pathologic studies of the myocardium, both by light and
272
0002~8703/78/0296-0272$00.20/O
August,
1978, Vol. 96, No. 2
0 1978 The
C. V. Mosby
Co.
5.
6.
7.
J. V., Harper, A. M., and Farrar, K.: Effects of acutely induced hypertension in cats on pial arteriolar caliber, local cerebral blood flow, and the blood brain barrier, Circ. Res. 39:33, 1976. Kety, S. S., Hafkenschiel, J. H., Jeffers, W. A., Leopold, I. H., and Shentum, H. A.: The blood flow, vascular resistance and oxygen consumption of the brain in essential hypertension, J. Clin. Invest. 57:511, 1948. Strandgaard, S., Mackenzie, E. T., Sengupta, D., Rowan, J. O., Lassen, N. A., and Harper, A. M.: Upper limit of autoregulation of cerebral blood flow in the baboon, Circ. Res. 34:435, 1974. Strandgaard, S., Jones, J. V., Mackenzie, E. T., and Harper, A. M.: Upper limit of cerebral blood flow autoregulation in experimental renovascular hypertension in the baboon, Circ. Res. 37:164, 1975. Standgaard, S., Olesen, J.. SkinhGj, E., and Lassen, N. A.: Autoregulation of brain circulation in severe arterial hypertension, Br. Med. J. 1:507, 1973.
Intramural branch
ramification
9.
10.
11. 12.
Jones, J. V., Fitch, W., Mackenzie, E. T.. Standgaard, S., and Harper, A. M.: Lower limit of cerebral blood flow autoregulation in experimental renovascular hypertension in the baboon, Circ. Res. 39:555, 1976. Folkow, B., Hallbiick, M., Lundgren, Y., Sivertsson, R.. and Weiss, L.: Importance of adaptive changes in vascular design for establishment of primary, hypert,ension, studied in man and in spontaneously hypertensive rats, Circ. Res. 32 and 33: (Suppl. 1):2. 1973. Graham, D. I.: Ischaemic brain damage of cerebral perfusion failure type after treatment of severe hypertension. Br. Med. J. iv:739, 1975. Editorial: Hypertension in the elderly. Lancet. 1:684. 1977. Strandgaard, S.: Autoregulation of cerebral blood flow in hypertensive patients. The modifying influence of prolonged antihypertensive treatment on the tolerance to acute, drug-induced hypotension. Circulation 53:720. 1976.
of the left bundle
Attention has been focused, recently, upon location and distribution of the fascicles of the left bundle branch (LBB) in the human heart, since these anatomical details may have an important bearing on pathophysiology of intraventricular conduction.‘. ? It can be useful, therefore, to briefly illustrate an unusual variety in morphology of the LBB. The different, and largely unpredictable,* patterns of
Fig. 1. Left, myocardium.
8.
the root of the LBB (black Right, further intramural
arrow) course
subdivision of the LBB, hitherto described, only refer to the sagittal plane; indeed, the ramifications of the branch are well known to fan and flatten out in thin bands, over the left subendocardial surface of the ventricular septum? Occasional anastomoses of individual LBB fibers with the underlying myocardium are too short to be considered as true extensions of the branch on the frontal plane.
gives off a medial fascicle of the LBB ramification
(open (Azan
arrow) stain;
penetrating the septal original magnification
x 12).
0002-8703/78/#296-0271$00.20/O
0 1978 The
C. V. Mosby
Co.
American
Henrt Journal
271
Annotations
In turn, the right bundle branch (RBB), which is a compact fascicle, in its middle course normally exhibits a medial bent on the frontal plane, entering the myocardial context of the septum (intramural or “mimetic” tract). Sometimes, the entire RBB has been seen to travel inside the septal myocardium.’ In a 51-year-old man, who died from heart failure without conduction blocks, the conducting system was examined histologically with the technique of longitudinal serial sections’, 5 and an intramural ramification of the LBB was observed. The atrioventricular (AV) node and His bundle were normal; at the Hisian bifurcation the root of the LBB was subdivided, on the frontal plane, into two thin fascicles, one lying in the ipsolateral subendocardium while the other penetrated medially the muscle of the upper ventricular septum (Fig. 1). This intramural ramification belonged to the posterior part of the LBB, and took a straight intraseptal course among thick bundles of working myocardium, surrounded by a sheath of loose interstitial tissue (Fig. 1). The specific fascicle could be followed, downwards and anteriorly, over a length of about 1.2 cm. along the series of sections, and eventually melted with the septal muscle. The present evidence of a distinct, proximal intramural division of the LBB, in an otherwise normal AV system, can be regarded as an apparently unique anatomical variety. In a previously described case,’ the intramural root of the LBB belonged to an aberrant Hisian bifurcation, completely embedded within the septal myocardium. Besides the morphological interest, the intramural location of tracts of the LBB is worthwhile our attention in discussing pathophysiology of LBB conduction disturbances,6 from acute septal infarction particularly.5 It has been pointed out that a lower oxygen uptake makes the conducting myocells more resistant than the working
Of the myocardium
and myotonia
myocardium to ischemic damage.’ Moreover, the LBB, owing to ita widespread subendocardial layout and closeness to the left ventricle’s cavity, can be protected from anoxia by transendocardial oxygen diffusi0n.j. ’ Intramural tracts of the LBB are not likely to share this latter oxygen source with the rest of the branch, and thus are comparatively more vulnerable by impaired blood supply through the nutrient arteries.
L. Rossi, L.D.Path.Univ. Via Annunciata 23/4 20121 Milan, Italy REFERENCES
1. Lev, M., Unger,
2.
3.
P. N., Rosen, K. M., and Bharati, S.: The anatomic base of electrocardiographic abnormality. Left bundle branch block: Recent advances in ventricular conduction, in Advances in Cardiology, vol. 14, Basel, 1975, S. Karger, p. 16. Massing, G. K., and James, T. N.: Anatomical configuration of the His bundle and bundle branches in the human heart, Circulation 53609, 1976. Truex, R. C., and Smythe, M. Q.: Recent observations on the human cardiac conduction system, with special consideration of the atrioventricular node and bundle, in Electrophysiology of the heart, Taccardi, B., and Marchetti, G., eds., Oxford, 1965, Pergamon Press, p. 177. Rossi, L.: Histopathologic features of cardiac arrhythmias, Milan, 1969, Casa Editrice Ambrosiana. Rossi, L.: Histopathology of conducting system in left anterior hemiblock, Br. Heart J. 38:1304 1976. Burch, G. E.: Of the conduction system and myocardial function, AM. HEART J. 92809, 1976. Hackel, D. B., Wagner, G., Ratliff, N. B., Cies, A., and Estes, E. H.: Anatomic studies of the cardiac conducting system in acute myocardial infarction, AM. HEART J. 83~77, 1972.
atrophica
The striated cardiac muscle and the striated skeletal muscle are known to be different physiologically. Although both muscles are striated, their differences are further reflected by the differences in their behavior in myotonia congenita and myotonia atrophica. For example, it is obvious what would happen if the myocardium were to manifest myotonia, as skeletal muscle does, and the heart were to go into systole and remain contracted for a fairly long period of time, as skeletal muscle does. Fortunately, this state does not develop in heart muscle to any clinically measureable degree. If it did, the patients would die of systolic arrest. It is also interesting that cardiomyopathy and related cardiac disturbances are reported’, 2 not to exist in association with myotonia congenita, but skeletal muscle does develop myotonia. It is of further interest that patients with myotonia atrophica have a high incidence of conduction tissue dysfunction,3.’ with impairment of conduction manifested by various degrees of heart block to complete A-V block and complete SA node block. Because of
this high incidence of pathophysiology of the conduction tissue, one wonders if this is not additional evidence that, although the disease tends to “skip” the myocardium itself, it strikes the conduction tissue just as it strikes skeletal muscle and, therefore, cardiac muscle and conduction tissue in the heart are different. The mechanism for the block of the excitation wave front in conduction tissues and within the SA node itself stimulates interesting speculative physiologic considerations. For example, it is interesting to speculate that the excitation impulse attempts to flow through conduction tissue but a “myotonic phenomenon” occurs within the cells so that the wave front cannot progress and an additional one cannot even get started. This would be “myotonia electrica.” In the case of the SA node, the impulse might even be considered to be generated, but it is unable to spread through the SA node and escape the node (SA node exit block) to stimulate the atria. Pathologic studies of the myocardium, both by light and
272
0002~8703/78/0296-0272$00.20/O
August,
1978, Vol. 96, No. 2
0 1978 The
C. V. Mosby
Co.
