If present and not incised buy 10mg benicar blood pressure and heart rate, this structure can contrib- When an anterior approach is associated with a lateral ute to the recurrence of bands with the appearance of a approach the former is carried out ﬁrst through the submen- “cord-like” deformity in the long run buy discount benicar 10mg arteria lingual. It is particularly tal approach and then the section is completed via the lateral important in thin necks that the proximal and caudal borders approach benicar 10 mg visa heart attack telugu movie review. We prefer to use scissors for the muscular incision of the muscular ﬂaps are chamfered (tapered down to a duck- as diathermy can damage the surrounding tissues. This will minimise the risk of scar tissue forma- Once the anterior section has been completed, we proceed tion along the incision lines which may be visible or felt, to the lateral section. The submuscu- undermined from the underlying structures, we insert the lower blade of lar tunnel has been created. There is an easy cleavage plane underneath the scissors into the tunnel and section the muscle to its full thickness to the muscle and bleeding is usually absent when this manoeuvre is per- reach the anterior incision. Once we are certain that the platysma has been fully pletely separate Mandibular border Fig. The forceps pull the muscle upwards and the scissors create an approximately 4–5 cm caudal to the mandibular border, 1–1. The scissors are inserted have to ensure that the whole muscle has been included in the ﬂap, i. To antero-medial direction following a trajectory parallel to the mandibu- the right we can see the tunnel created by the scissors underneath the lar border. In some albeit rare cases, when we wish to limit skin under- into the tunnel and the entire lateral portion of the platysma is incised to mining, we can perform the entire section from the lateral approach. The forceps continue to incise the muscle in a latero- This manoeuvre is not easy as the medial border of the muscle is not medial direction to reach the incision made through the anterior readily identiﬁed through the lateral approach 4. The ﬁrst is performed as previously angle in order to avoid creating new inaesthetisms. This is described, starting from a point 4–5 cm caudal to the man- therefore the preferred option in cases of chin ptosis, pro- dibular border and continues to reach the midline at the level truding chin or prominence of the superior border of the of the upper border of the thyroid cartilage. The high section facilitates the creation of an acute cervico- One of the positive effects of sectioning the platysma mandibular angle due to its positioning at a point where (either at a high or low level) is the increased mobility of the the internal structures are deeper (subhyoid fossette). We must avoid carrying tion associated to the cranial suspension of the posterior ﬂap creates a out this technique in patients with very thin skin as this may create a gap of approximately 3 cm between the upper and lower ﬂaps. In these situations a tun- improves the deﬁnition of the transition between the two neck segments nelled section is preferred (as explained later in this same chapter) or imbrication. Following this reasoning, act the loss of volume caused by ageing in the mandibular reconstructing the anterior continuity of the muscle by area and consequently, will improve the contour of the man- medial traction through an anterior plication represents a dible (Fig. Others believe that the platysma tends to In certain cases such as patients (thin cutis, sufﬁcient sub- migrate towards the midline over time; consequently, the cutaneous fat and visible platysmal bands), we can opt to per- optimal treatment would be to place the muscle under lateral form a “tunnel section” of the platysma to avoid creating a traction and suspension to recreate its tone. After mented with both theories and our experience has brought us undermining the skin ﬂap, we create a tunnel approx. We believe This manoeuvre permits us to section the bands while that the platysma as a continuous muscular sheath can help leaving intact the overlying adipose apron. The muscular gap form a supporting “harness” which helps create a tonic cervical is less evident as it is covered by a continuous fat layer and contour across the entire neck. Therefore, we do not base our also due to the fact that the borders of the two muscular ﬂaps treatment on the application of either a medial or lateral trac- tend to separate less due to the effect of the overlying adher- tion vector but depending on the objective, we take into consid- ent adipose mantle. If the platysma is solid in its medial portion and does not present any bands then we prefer to adopt lateral traction to 4. Furthermore, considering that facial tissues tend to ment of the neck attribute particular valence to traction of the slacken in a vertical direction, we should also reposition crani- platysma. So much so that the opposite sides of this sion vector to the two that we have mentioned previously. However, a frequent conse- mal results in improving the mandibular contour, correcting hypertonic quence of this manoeuvre is that the thyroid cartilage may be empha- platysmal bands, deepening the cervico-mandibular and deﬁning the sised in some patients 4. Some months after surgery, however, relapse together at the midline by the application of various manoeu- of ﬂaccidity is a frequent occurrence. Applying lateral traction to a reinforced anterior muscular The preoperative plan is very important when carrying layer gives additional support to the entire area and helps out a medial plication. Observing the volun- of anterior ﬂaccidity of the platysma and evident high sepa- tary contraction of the platysma facilitates the identiﬁcation ration of the muscle. Sometimes we may opt for a low section to ditioning factors in opting for a low section is the presence of a create a less sharp cervico-mandibular angle and a less-deﬁned transi- prominent thyroid cartilage (such as this case) in which a high section tion between the horizontal and vertical neck segments. In order to achieve this, we prefer to leave intraop- In the presence of a high decussation and a ﬂaccid pla- eratively a slight convexity in the horizontal segment which tysma, we remove some excess muscular tissue from the will tend to disappear over a couple of months with the reab- medial borders of the platysma in a cranio-caudal direction. A horizontal segment which is During this manoeuvre, we have to remember that in most already ﬂat in the intraoperative phase risks becoming con- cases the muscle will also be tractioned laterally and there- cave when the postsurgical swelling abates. The ideal treatment option was plication at the muscular excess, hypotonic platysma bands and obtuse cervico- midline associated with anterior muscular section mandibular angle. This patient required a deeper angle and a longer In the case of high separation of the platysma with a procedure is as follows: we perform a complete undermining depression between the medial borders, we prefer overlap of the cutaneous ﬂaps placing the two hemifaces in communi- the muscular margins to alleviate this inaesthetism. At this point, we locate the medial borders of the pla- we prefer to remove a more signiﬁcant quantity of muscle at tysma and join them with a running suture to approximate the the midline followed by approximation of the borders. This shortens When the muscle separates at a low level then, we can also the muscle transversally and progressively remodels the opt for an invaginating plication over the midline without neck contour. This entails not only bringing invaginated at the level of the hyoid bone where the apex of the muscular borders together by approximation but also sutur- the cervico-mandibular angle is. The midline suture of the platysma normally starts at the The two main advantages of this technique are the submental sulcus and reaches the superior border of the following: hyoid bone or in some cases, may continue to reach the infe- rior border hyoid bone or even the thyroid cartilage. Another interesting treatment option for the anterior pla- (b) The tension created by this manoeuvre deepens the angle tysma is a corset platysmaplasty or corsetplasty (Feldman). This is a very useful technique which produces good results and relatively minor risk of dys- (a) A long plication entails undermining a wide area of the ante- function to the perioral mimic. The technique is based on the rior and lower neck with the risk that this manoeuvre incurs. The invaginating manoeuvre performed at the midline cle, latero-medial traction does not improve the contour creates a greater level of tone in the anterior muscle and results of the region of the mandibular angle as it happens when in a deﬁnite concavity of the cervical contour. The latter manoeuvre is carried out in the female neck to the lower limit of a high plication (photograph to the left ) whereas in the render a prominent cartilage (Adam’s Apple) less visible low plication (photograph to the right ), suturing continues to the thy- Fig. If performed correctly, a suprahyoid segments and a straight chin hyoid bone line. Both these factors contrib- plication can improve the rapport between the horizontal and vertical ute to improving the general aesthetic(s) of the entire cervical region neck segments. This also creates a distinct transition between the two Therefore, this technique is performed only when there spite of the traction created by the invaginating suture which are no contraindications to extensive undermining (well- works in the opposite direction. The quality of the results are similar those obtainable with If the mandibular angle is ill-deﬁned and we need to treat a full platysma section. Due to the lower risk of dysfunction the lateral platysma then a corsetplasty can be performed on of the perioral mimic, we tend to prefer corsetplasty over the condition that we limit the amount of invagination. This total muscular section for patients in which the platysma has will allow us to associate a lateral pull on the platysma in a signiﬁcant role in the smile mimic. In this patient we have chosen to per- mandible, creating an “artiﬁcial” rather than the “natural” look which is form a plication extended to the level of the cranial border of the thyroid routinely requested by the patient.
In response to a sudden increase in bladder pressure discount benicar 20 mg blood pressure chart for age 50+, such as during a cough order benicar without prescription heart attack mortality rate, laugh buy benicar 40mg low cost hypertension 4th report, or sneeze, a more rapid somatic storage reflex (pelvic-to-pudendal reflex), also called the guarding or continence reflex, is initiated. The evoked afferent activity travels along myelinated Aδ afferent nerve fibers in the pelvic nerve to the sacral spinal cord, where efferent somatic urethral motor neurons, located in the nucleus of Onuf, are activated. Axons from these motor neurons of the nucleus of Onuf travel in the pudendal nerve and release acetylcholine, which activates nicotinic cholinergic receptors on the rhabdosphincter, which contracts. During sudden abdominal pressure increases, however, it becomes dynamically active to contract the rhabdosphincter. During micturition, this reflex is strongly inhibited via spinal and supraspinal mechanisms to allow the rhabdosphincter to relax and permit urine passage through the urethra. In addition to this spinal somatic storage reflex, there is also supraspinal input from the pons, which projects directly to the nucleus of Onuf and is of importance for volitional control of the rhabdosphincter . Other regions in the brain, important for micturition, include the hypothalamus and cerebral cortex [10,34,35]. Bladder filling leads to increased activation of tension receptors within the bladder wall and thus to increased afferent activity in Aδ-fibers. These fibers project on spinal tract neurons mediating increased sympathetic firing to maintain continence as discussed earlier (storage reflex). In addition, the spinal tract neurons convey the afferent activity to more rostral areas of the spinal cord and the brain. The threshold is believed to be set by the inputs from more rostral regions in the brain. In cats, lesioning of regions above the inferior colliculus usually facilitates micturition by elimination of inhibitory inputs from more rostral areas of the brain. Vesico-Spinal-Vesical Micturition Reflex Spinal lesion rostral to the lumbosacral level interrupts the vesico-bulbo-vesical pathway and abolishes the supraspinal and voluntary control of micturition. This results initially in an areflexic bladder accompanied by urinary retention . An automatic vesico-spinal-vesical micturition reflex develops slowly, although voiding is generally insufficient due to bladder sphincter dyssynergia, i. It has been demonstrated in chronic spinal cats that the afferent limb of this reflex is conveyed through unmyelinated C-fibers, which usually do not respond to bladder distension , suggesting changed properties of the afferent receptors in the bladder. Accordingly, the micturition reflex in chronic spinal cats is blocked by capsaicin, a neurotoxin that is believed to block C-fiber-mediated neurotransmission [37,38]. Several transmitters and their receptors are involved in the reflexes and sites described earlier and may be targets for drugs aimed for control of micturition. It has been well established that morphine, given by various routes of administration to animals and humans, can increase bladder capacity and eventually cause urinary retention. Further side effects of opioid receptor agonists comprise respiratory depression, constipation, and abuse. Attempts have been made to reduce these side effects by increasing selectivity toward one of the different opioid receptor types . At least three different opioid receptors—µ, δ, and κ—bind stereospecifically with morphine and have been shown to interfere with voiding mechanisms. Theoretically, selective receptor actions, or modifications of effects mediated by specific opioid receptors, may have useful therapeutic effects for micturition control. By itself, it is a weak µ-receptor agonist, but it is metabolized to several different compounds, some of them almost as effective as morphine at the µ- receptor. A total of 76 patients 18 years or older were given 100 mg tramadol sustained release every 12 hours for 12 weeks. Tramadol significantly reduced the number of incontinence periods and induced significant improvements in urodynamic parameters. Central stimulation of δ-opioid receptors in anesthetized cats and rats inhibited micturition [56,57] and parasympathetic neurotransmission in cat bladder ganglia . In humans, nalbuphine, a µ-receptor antagonist, and κ-receptor agonist, increased bladder capacity . Buprenorphine (a partial µ-receptor agonist and κ-receptor antagonist) decreased micturition pressure and increased bladder capacity more than morphine . In addition, further exploration of these non-µ-opioid receptor mediated actions on micturition seems motivated. The regulation of the frequency of bladder reflexes is presumably mediated by a suppression of afferent input to the micturition-switching circuitry in the pons, whereas the regulation of bladder contraction amplitude may be related to an inhibition of the output from the pons to the parasympathetic nuclei in the spinal cord. Gabapentin is also widely used not only for seizures and neuropathic pain, but for many other indications such as anxiety and sleep disorders due to its apparent lack of toxicity. The drug was generally well tolerated and was considered to be an option in selective patients when conventional treatment modalities have failed. It was suggested that doxazosin has a site of action at the level of the spinal cord and ganglia. The primary end point was percent change from baseline in average daily micturitions assessed by a voiding diary. Aprepitant significantly decreased the average daily number of micturitions compared with placebo at 8 weeks. Aprepitant was generally well tolerated and the incidence of side effects, including dry mouth, was low. The effects were abolished by infracollicular transection of the brain and by prior intraperitoneal administration of the centrally acting dopamine receptor blocker, spiroperidol. The effect of dopaminergic drugs on micturition has produced conflicting results , and Winge et al. In contrast, in advanced stages of the disease, the drug improved bladder storage function . Peripheral Targets Possible peripheral targets for pharmacological intervention may be (1) the efferent neurotransmission, (2) the smooth muscle itself, including ion channels and intracellular second messenger systems, and (3) the afferent neurotransmission. The five gene products correspond to pharmacologically defined receptors, and M –M is used to describe both the1 5 molecular and pharmacological subtypes. These receptors are also functionally coupled to G-proteins, but the signal transduction systems vary [114–119]. Detrusor smooth muscle contains muscarinic receptors of mainly the M and M subtypes [2 3 114–119]. The M receptors in the human bladder are believed to be the most important for detrusor contraction. Supporting a role of Rho-kinase in the regulation of rat detrusor contraction and tone, Wibberley et al. Thus, the main pathway for muscarinic receptor activation of the detrusor via M receptors may be calcium influx via L-type calcium channels and increased sensitivity3 to calcium of the contractile machinery produced via inhibition of myosin light chain phosphatase through activation of Rho-kinase . In certain disease states, M2 receptors may contribute to contraction of the bladder. Thus, in the denervated rat bladder, M receptors2 or a combination of M - and M -mediated contractile responses and the two types of receptor seemed to2 3 act in a facilitatory manner to mediate contraction [127–129].
Such a depic- tion might lead one to conclude that overzealous paramedics had worked on a decedent who was decomposing best order for benicar arrhythmia quotes. What this case really illustrates is the rapidity with which bacteria buy discount benicar 10mg arteria zygomaticoorbitalis, already present within the bloodstream at the time of death generic benicar 40 mg without a prescription heart attack pathophysiology, can disseminate and propagate throughout the blood system, leading to accelerated postmortem putrefactive change. Note the top image shows multiple nitroglycerin patches in an individual with known signifcant heart disease. Cleaning of this surface area with removal of the superfcial layers of skin made visualization easier. Note the small circular perforations caused by maggots tunneling through skin and soft tissue. Comparison to an old photograph of the decedent showed the same gap between the upper central incisors. This was the historical remains of an Egyptian mummy skull that was most likely used in religious ceremonies. His body was in a slight state of putrefaction due to the preservation by the freezing cold winter temperature. Once the body thawed out for autopsy, putrefaction advanced at a markedly accelerated rate. The womb is normally a sterile environment and there should not be putrefaction unless there is an infection such as chorioamnionitis. Note the skull fracture with hemorrhage and dark discoloration due to putrefaction. Also, animals and insects will often more readily feed from injured areas with exposed soft tissue and blood, further obscuring these fndings. Note the feathery appearance of the soft tissue on the x-ray due to gas accumulation. As central nervous system putrefaction advances, the brain will develop into a liquid, oatmeal-like consis- tency with few or more recognizable structures. Large amounts of blood had drained from the body to the bedding that was further spread about by the dog. This region of the body was noted to be scraping against a rocky surface just prior to retrieval from the water. In many cases, there may be activity from several different animals in the same environment. In this case, the damage appears to mostly be from the canine family (likely wild) with evidence of tearing of the skin and ribs. In these cases one must consider whether the postmortem activity has obscured injuries sustained during life. One arm, a larger portion of the chest, and most of the internal organs were absent. When the eggs hatch, maggots develop and are shown in this picture in varying sizes as small, white, and wormlike. In order to properly evaluate perinatal deaths Evaluating potential forensic issues across such a spec- such as these, postmortem artifacts must be correctly trum of age requires a commanding knowledge of recognized and interpreted, organ maturation must be normal growth and maturation, as well as a thought- assessed as reliably as possible, and natural pathology ful consideration of the unique anatomy and physi- must be considered. Another challenging task confronting forensic Unfortunately, very few forensic pathologists are spe- pathologists involves determining the cause and man- cifcally trained in pediatric pathology, and the number ner of death when an infant, who was previously in of hospital-based pediatric pathologists who engage in good health, is found dead by a caretaker minutes or medicolegal death investigation is equally small, espe- hours afer being put to sleep. Te consequences of incom- anomalies and complications of low birth weight rep- petent pediatric medicolegal death investigation can be resent the most common causes of death in the frst devastating for multiple members of a community. Te neonatal period, defned served two important functions: it helped remove stig- as the frst 28 days of extrauterine life, marks the begin- matism from caretakers who lost an infant to unknown ning of terrestrial life with dependence on lungs for causes, and it identifed a vexing problem for epidemi- respiration. Even though the etiology of and neonate is the perinatal period, which includes some infant deaths remains a mystery today, the term the time immediately before and afer birth. Death is always due and neonatal deaths are related to natural patholo- to at least one anatomic and/or physiologic derange- gies afecting mother, placenta, and/or baby, and are ment (whether presently identifable or not), and, as therefore commonly—and appropriately—investigated any pathologist involved with investigating infant by hospital-based perinatal pathologists. Or, considering infants can die in their sleep occurred in the 1980s, that a person’s risk of being murdered is greatest on the when the Back to Sleep Campaign (now the Safe to frst day of life, the rare but tragic discovery of a baby Sleep campaign) raised awareness about infant sleeping 193 194 Color Atlas of Forensic Medicine and Pathology position. A child with severe enactments to illustrate the position in which an infant vitamin D defciency, as another example, may sustain was put to sleep and subsequently found unresponsive, one or more fractures that appear inconsistent with the frequently reveal potentially dangerous infant sleep amount of applied force or which simply would not arise environments. In such cases, failure to Exciting research over the past few decades and con- recognize the presence or contribution of underlying tinuing today complements the emphasis appropriately disease can lead to misinterpretation of pathologic fnd- placed on safe infant sleep environments. Unraveling ings, and such mistakes may have disastrous medicole- developmental pathways and biochemistry in the infant gal implications. Furthermore, the discovery of and because of impressive surgical and medical advance- evolving capability to detect cardiac channelopathies in ments. When some children unfortunately succumb recent years exemplify the progress being made in eluci- to these diseases in spite of appropriate intervention, it dating molecular causes of sudden death in infants and is ofen the responsibility of the forensic pathologist to older individuals as well. Tese and related advances in determine whether the intervention may have caused medical research highlight the important roles foren- or altered the manner of death. As an example, a young sic pathologists play in accurately determining cause adult may succumb to complications of hepatic cirrho- and manner of death and in collecting and preserving sis years afer successfully undergoing a Fontan pro- appropriate specimens so that such progress continues. Although heart disease is the underlying cause of diligent scene investigation, competent autopsy per- of death, recognizing that liver cirrhosis potentially formance including traditional and emerging ancillary represents a complication of the Fontan procedure tests, and thoughtful review of a medical history is what may allow the death to be more appropriately classi- allows a substantial number of sudden infant deaths to fed as a therapeutic complication. Interpreting injuries is another area that can be Beyond infancy, throughout adolescence, and extremely challenging. Perhaps one of the most illus- into adulthood, most deaths are caused by accidental trative examples of this concept that children are not trauma, with suicidal and homicidal injuries emerging just small adults is the assessment of nonaccidental or as important causes of death in older pediatric popu- inficted head trauma in infants and very young chil- lations. An understanding of this type of injury would must always remain vigilant for the possibility of child not be possible without being thoroughly acquainted abuse, perpetrated by either intention or negligence. Although uncommon, lethal short falls and matter water content substantially higher than that of delayed clinical deterioration are well-documented phe- an adult, imparting a consistency of unset gelatin and nomena in forensic pathology and neuropathology. Te making the brain more vulnerable to shearing forces; assessment of the timing (the aging) of the head trauma and (5) the top-heavy calvaria and the weak, underde- should be made with extreme caution, and a layer-wise veloped neck muscles that fail to efectively dampen the examination (of the scalp, skull, dura leptomeninges, oscillations that are initiated when rotational move- and brain) is critical for a complete study. It is the interface of pediatric a posterior neck dissection for potential sof tissue, bony and forensic pathology that allows the most complete (vertebral), ligamentous, spinal cord, and spinal nerve and comprehensive understanding of these concepts trauma should always be performed. As a result, foren- pediatric age group, specifcally in infants and young sic pathologists may beneft signifcantly by relying on children, is one that continues to generate a consider- pediatric pathologists, neuropathologists, and neuro able amount of controversy. While such controversy is or pediatric radiologists when they are evaluating dif- desirable in the sense that it stimulates ongoing research fcult, complex, or problematic deaths in the pediatric and data-gathering, thus advancing the overall body of population. It is estimated that 2000 being profered by experts in forensic pathology and children die in the United States annually from abuse pediatric neurotrauma. However, when the triad is must be acknowledged that the clinical information is separated into isolated components, each component potentially impeachable, and that the injuries may be could result from abusive (inficted) trauma, accidental discordant with the event as it is presented. Typically, onto a padded or carpeted foor, or from a chang- they require approximately 18–24 hours following the ing table or car seat onto some similar surface; (2) the time of the primary brain injury to manifest themselves. Te forensic pathologist activity—all signs of profound brainstem derangement; almost never observes punctate hemorrhages within the or (3) the infant or child is found dead. It is precisely vulnerable neuroanatomical regions on gross examina- because these infants present as moribund (“gravely ill”) tion.
The next two complexes have left anterior hemiblock generic benicar 40 mg arrhythmia nutrition, and the V-A interval returns to 150 msec buy 10mg benicar with amex blood pressure chart when to go to the hospital. Note the sharp spike of the bypass tract potential is observed on the unipolar and bipolar signals and precedes the local ventricular electrogram and the delta wave generic 20 mg benicar visa blood pressure regulation. This was recorded with a standard quadripolar catheter with electrodes spaced at 5 mm. This is consistent with that signal being a recording of a left posterior bypass tract which was located in a coronary sinus diverticulum. Schema of pacing maneuvers to prove a signal is a bypass tract potential using the second component of a split atrial electrogram to mimic a bypass tract potential. Assessment of pacing maneuvers used to validate anterograde accessory pathway potentials. Therefore, demonstration that the bypass tract plays a critical role in the genesis of the arrhythmia is imperative and is essential for appropriate therapy, especially catheter ablation or surgery. If the propensity to develop atrial fibrillation was based solely on primary intra-atrial pathophysiology, ablation of the bypass tract could cure circus movement tachycardia but would fail to prevent recurrences of atrial fibrillation later in life. Atrial tachycardia must be distinguished from antidromic tachycardia, or more accurately, “preexcited circus movement tachycardia. During atrial pacing the atrial electrogram is (A and A′) with an isoelectric interval of 35 msec. The shortest coupled atrial extrastimulus that captured produced an increase in A-A′ to 80 msec. Assessment of pacing maneuvers used to validate anterograde accessory pathway potentials. Assessment of pacing maneuvers used to validate anterograde accessory pathway potentials. During atrial pacing (S1-S1) at a cycle length of 500 msec an atrial extrastimulus (S2) was delivered, which depolarizes both components of the split electrogram mimicking block between the accessory pathway and the ventricle. Assessment of pacing maneuvers used to validate anterograde accessory pathway potentials. Assessment of pacing maneuvers used to validate anterograde accessory pathway potentials. The observations 32 38 102 103 104 111 indicating the presence of a bypass tract are well-described , , , , , and include: 1. The amount of A-V delay allows the bypass tract to recover and an atrial echo (Ae) results from retrograde conduction over the bypass tract. That impulse conducts slowly through the A-V node (A-H 300 msec) but blocks below the recorded His bundle deflection. Thus, during rapid tachycardias, a single right ventricular stimulus might not reach a left lateral bypass tract in time to preexcite the atrium. This is shown in Figure 10-84, in which the first of two ventricular extrastimuli fails to affect retrograde atrial activation while the second can terminate the tachycardia. This early activation of the atrium then resets the tachycardia with a longer A-H and a delay in the return cycle. The ability to preexcite the atria when the His bundle is refractory with the same atrial activation sequence as seen during the orthodromic tachycardia confirms the presence of functioning posteroseptal bypass tract. The tachycardia terminates by retrograde block in the bypass tract when the His is refractory. This confirms the necessary participation of the bypass tract in the tachycardia circuit. Only conditions 2, 3, 5, 6, and 7 absolutely demonstrate participation of the bypass tract in the reentrant circuit, because they demonstrate requirement of the ventricle in the tachycardia circuit. Atrial preexcitation alone is compatible with the presence of a bypass tract if the atrial activation sequence of the preexcited atrial activation is identical to that of the atrial activation sequence seen during tachycardia. Although this supports the involvement of a bypass tract in the reentrant circuit, atrial tachycardia or intra-atrial reentry conceivably could occur at the site of the atrial insertion of the bypass tract. Then, retrograde atrial activation during ventricular preexcitation would look identical to that of the atrial tachycardia. However, if atrial tachycardia were present, there would be a V-A-A-V return cycle. The V-A-V return cycle with a constant V-A excludes atrial tachycardia and makes the diagnosis of orthodromic tachycardia. Condition 1 is compatible with the presence of a bypass tract but does not demonstrate its requirement to maintain the tachycardia, because it is theoretically possible, although highly unlikely, that retrograde atrial activation over a bypass tract may be an unrelated epiphenomenon to another tachycardia mechanism. For example, we have seen ventricular tachycardia with retrograde atrial activation over a bypass tract. In this instance, ventricular tachycardia certainly does not require the bypass tract for its persistence. These are theoretical possibilities; however, in the vast majority of cases, all the conditions mentioned are useful in diagnosing the presence of a bypass tract. The first ventricular extrastimulus fails to affect the tachycardia with the antegrade His and retrograde atrial activation over the bypass tract being unaltered. The second extrastimulus, which is introduced earlier in the cardiac cycle, conducts over the bypass tract retrogradely. The inability of a right ventricular extrastimulus to affect circus movement tachycardia demonstrates the lack of requirement of the right ventricle in tachycardias using a left-sided bypass tract. As noted earlier, the most common rhythm associated with a regular preexcited tachycardia is atrial flutter or atrial 40 tachycardia. Whether or not conduction proceeds over the bypass tract is obvious by the appearance of a typical preexcited complex. Usually, there are runs of total preexcitation and/or runs of normal ventricular activation (Fig. Obviously, in these instances, the bypass tract is used only passively during anterograde conduction during fibrillation or flutter. Retrograde activation of the atrium over the bypass tract during normal anterograde conduction has been observed and may contribute to perpetuation of atrial fibrillation as well as anterograde 113 conduction over the normal conduction system. Atrial tachycardia is more difficult to distinguish from preexcited circus movement tachycardias. Resetting the tachycardia by an atrial extrastimulus with an A-V-A with an identical V-A interval or termination of the tachycardia by ventricular stimulation in the absence of an A excludes an atrial tachycardia. Demonstration of resetting a preexcited tachycardia with atrial fusion by atrial stimulation, excludes a focal tachycardia. The latter phenomenon, particularly when stimulation is performed from the atrium opposite that demonstrating earliest atrial activation, suggests the presence of a macro-reentrant circuit associated with antegrade conduction over one bypass tract and retrograde conduction over another bypass tract, one of the more common mechanisms of preexcited circus movement tachycardias (Fig. A ventricular extrastimulus delivered from the right ventricle after the His bundle has been depolarized antegradely can preexcite the atrium using the right anterior paraseptal bypass tract. During atrial flutter, antegrade conduction usually occurs over the bypass tract, resulting in marked preexcitation (first six complexes).
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