Interventricular septum

An internodal conduction pathway also extends from the SA node and transmits the impulse directly to the atrioventricular (AV) node. This node is located at the base of the right atrium near the interventricular septum, which is the wall of myocardium separating the two ventricles. Because the atria and ventricles are separated from each other by fibrous connective tissue, the electrical impulse cannot spread directly to the ventricles. Instead, the AV node serves as the only pathway through which the impulse can be transmitted to the ventricles. The speed of conduction through the AV node is slowed, resulting in a slight delay (0.1 sec). The cause of this AV nodal delay is partly due to the smaller fibers of the AV node. More importantly, however, fewer gap junctions exist between the cells of the node, which... 

From the AV node, the electrical impulse spreads through the AV bundle or the bundle of His. This portion of the conduction system penetrates the fibrous tissue separating the atria from the ventricles and enters the interventricular septum where it divides into the left and right bundle branches. The bundle branches travel down the septum toward the apex of the heart and then reverse direction, traveling back toward the atria along the outer ventricle walls. This route of conduction of the impulse facilitates ejection of blood from the ventricles. If the impulse were to be conducted directly from the atria to the ventricles, the ventricular contraction would begin at the top of the chambers and proceed downward toward the apex. This would trap the blood at the bottom of the chambers. Instead, the wave of ventricular electrical stimulation and, therefore, contraction moves from the apex of the heart toward the top of the chambers where the semilunar valves are located and ejection takes place. 

Myocardial hypertrophy Myocardial hypertrophy has been reported in association with the administration of tacrolimus and generally is manifested by echocardiographically demonstrated concentric increases in left ventricular posterior wall and interventricular septum thickness. Hypertrophy has been observed in infants, children, and adults. This condition appears reversible in most cases following dose reduction or discontinuance of therapy. 

Shamim W, Yousufuddin M, Wang D, et al, Nonsurgical reduction of the interventricular septum in patients with hypertrophic cardiomyopathy. N Engl J Med 2002 347 1326-1333. 

Long-term chloroquine can cause cardiac comphca-tions, such as conduction disorders and cardiomyopathy (restrictive or hypertrophic), by structural alteration of the interventricular septum (4). Thirteen cases of cardiac toxicity associated with long-term chloroquine and hydroxychloroquine have been reported in patients with systemic autoimmune diseases. The cumulative doses were 600-2281 g for chloroquine and 292-4380 g for hydroxychloroquine. 

AO Aorta MPA Main pulmonary artery RSCV Right superior vena cava TV Tricuspid valve MV Mitral valve PV Pulmonary valve AV Aortic valve RA Right atrium LAA Left atrial appendage RV Right ventricle LV Left ventricle LV-PM Left ventricle, muscle IVS Interventricular septum CR Crista supraventricularis SN sinus node AVN + B Atrioventricular node LBB Left bundle branch. 

The most important mechanical complications of ACS evolving to MI occur in transmural infarctions, usually Q-wave infarction. They consist in cardiac rupture, which may occur in the free wall, the interventricular septum or the papillary muscles and the ventricular aneurisms. 

Atrioventricular (AV) node A highly specialized cluster of neuromuscular cells at the lower portion of the right atrium leading to the interventricular septum the AV node delays sinoatrial, (SA) node-generated electrical impulses momentarily (allowing the atria to contract first) and then conducts the depolarization wave to the bundle of His and its bimdle branches. 

A detailed description of the morphogenesis of the muscle fiber system in the developing heart is not available but there is evidence of an organized myofiber pattern by day 12 in the fetal mouse heart that is similar to that seen at birth (day 20) [25], Abnormalities of cardiac muscle fiber patterns have been described in some disease conditions. In hypertrophic cardiomyopathy, which is often familial, there is substantial myofiber disarray, typically in the interventricular septum [10,26]. 

Fig 1 41 Section of interventricular septum from a patient who underwent cardiac transplantation 676 days after implantable cardioverter-defibrillator lead implantation and 7 days after last defibrillator shock (a). Right ventricular surface of interventricular septum (R) is at the top and left ventricular surface (L) at bottom. Characteristic fibroelastic tissue encircles the lead curved arrow). Trichrome-stained section of tissue (b) band of fibroelastic tissue curved arrow) encircles lead (L), and beneath, in myocardium, lies fibrous connective tissue F). Area of confluent fibrous connective tissue immediately adjacent to lead also extends into surrounding myocardium, forming radial pattern of interstitial fibrosis arrows), suggesting that shocks have caused lines of electrical injury (courtesy [51])... 

Fig. 304. Attachment of a leucocyte to an interendothelial junction from the interventricular septum (block 1461) of a rat (No. 15) treated for 8 consecutive days with intraperito-neal injection of 15 mg carbocromene per kg body weightx-day. On the last 5 days of experimentation the animal was exposed to an atmosphere containing only 5% oxygen for 30 min. On August 6, 1976 under pentobarbital anaesthesia, the animal was perfused from the abdominal aorta with 2.5 % glutarddehyde in 0.1 M sodium cacodylate buffer. Postfixa-tion with 1 % osmium tetroxide in sodium cacodylate buffer. Embedded in Epon 812 and sectioned at 50 nm. Lead citrate and uranyl acetate. Film 623-01...

It has been this author s practice to reserve the positive screw-in fixation lead in the ventricle for unique circumstances. Such circumstances include a dilated cardiomyopathy where the right ventricle is extranely thin with little or no trabeculations for fined fixation. The positive fixation screw-in lead is also ideal if atypical electrode position is desired. Such a circumstance includes electrode placement high on the interventricular septum. 

In RBBB, the initial impulse activates the interventricular septum from left to right, just as in normal activation (arrow 1). Next, the left bundle branch activates the left ventricle (arrow 2). The impulse then crosses the interventricular septum to activate the right ventricle (arrow 3). 

Umazume T, Funabashi N, Inoue T, Nishi T, Shimizu T, Jo K, et al. Adverse effects of cilostazol on left ventricular function in a patient with a sigmoid shaped interventricular septum. Int J Cardiol May 25,2013 165(3) 551-5. 

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