By Y. Norris. Norfolk State University. 2019.
Occasionally discount 100 mg norpace, following the use of Type I agents or amiodarone cheap norpace 150mg overnight delivery, block in one accessory pathway can lead to manifestation of antegrade conduction over a second 38 accessory pathway cheap 100mg norpace otc. Atrial fibrillation (either spontaneous or induced) may provide the opportunity to see different patterns of preexcitation, thereby allowing one to document the presence of multiple bypass tracts. This has been suggested as an indication for the deliberate induction of atrial fibrillation during an electrophysiologic study. Because multiple bypass tracts are often located in the free walls of the right and left A-V grooves, the use of both right and left atrial pacing occasionally can document the presence of additional bypass tracts that are not manifested if only pacing from the one atrium is performed. This can be seen in Figure 10-95, where right atrial pacing produces ventricular activation over a right-sided bypass tract, and coronary sinus pacing produces ventricular activation over a left-sided bypass tract. In addition, the tachycardias initiated by stimulation at different sites can vary, resulting in two retrograde activation sequences, which document the presence of multiple bypass tracts (see following discussion). If a single bypass tract was present, the V-A interval should be fixed and the retrograde P-wave morphology constant during orthodromic tachycardia. If the V-A interval or P- wave morphology changes during orthodromic tachycardia, the presence of an additional bypass tract should be suspected. During the electrophysiology study, the presence of two distinct retrograde atrial activation patterns documents the presence of multiple bypass tracts and explains changing P-wave morphology and V-A intervals (see Fig. In other cases, during orthodromic tachycardia, a single, fixed retrograde atrial activation pattern is observed in the presence of two or more bypass P. In this instance, additional bypass tracts can be recognized by the appearance of more than one atrial breakthrough site. This is demonstrated in Figure 10-96, where the earliest retrograde atrial activation occurs in the distal coronary sinus, compatible with a left lateral bypass tract. In this instance, atrial activation in the His bundle recording precedes atrial activation of the os by 30 msec, suggesting a second pathway in the anterior septum. With the introduction of a ventricular extrastimulus, retrograde activation may proceed over one bypass tract to initiate orthodromic tachycardia with retrograde conduction over an additional bypass tract (Fig. The site of ventricular pacing is critical because retrograde atrial activation will preferentially proceed over a bypass tract adjacent to the site of stimulation as long as that bypass tract is capable of retrograde conduction. On the other hand, a very early atrial extrastimulus may block in the bypass tract closest to the stimulus site and conduct over a bypass tract at a more distant site (see Fig. In either case, the induction sequence provides another opportunity to compare retrograde atrial activation sequences. Another finding related to retrograde atrial activation that suggests a second bypass tract is the failure to prolong atrial activation at all sites with the development of bundle branch block ipsilateral to the bypass tract. In a similar vein, if one has orthodromic tachycardia and then develops fusion complexes consistent with preexcitation, an additional bypass tract must be operative. Changes in the V-A interval occur with the appearance of antegrade fusion if impairment of A-V nodal or His–Purkinje conduction by drugs, cycle length oscillation, or retrograde concealment was responsible for the sudden appearance of fusion. Analogously, if a preexcited tachycardia demonstrates antegrade fusion, a second bypass tract must be used as the retrograde limb (Fig. In this instance one must document that fusion is not caused by A-V nodal reentry with an innocent bystander accessory pathway (see Fig. As stated earlier in the chapter (see discussion of antidromic tachycardia), the mere presence of a preexcited tachycardia should suggest the likely presence of multiple bypass tracts. Almost 40% of patients with preexcited circus movement tachycardias, incorporating a bypass tract as the antegrade limb, have multiple bypass tracts. Multiple bypass tracts are almost invariably present if the preexcited tachycardia demonstrates antegrade conduction over a posteroseptal bypass tract, because antegrade conduction over such 39 a bypass tract has not been described with “classic antidromic tachycardia. Antidromic tachycardia is only slower than orthodromic tachycardia if retrograde conduction during antidromic tachycardia is slower than antegrade conduction during orthodromic tachycardia. Sometimes there will be no evidence of multiple bypass tracts during spontaneous sinus rhythm, induced atrial fibrillation, right or left atrial pacing, orthodromic tachycardia, or preexcited tachycardias. This most commonly occurs when additional bypass tracts are “concealed” both during sinus rhythm or circus movement tachycardia because of preferential activation over one bypass tract. These bypass tracts can often be recognized by performing atrial or ventricular stimulation during orthodromic tachycardia or, as stated previously, by assessing the effect of bundle branch block on retrograde atrial activation. Thus, it is important to introduce both atrial and ventricular extrastimuli during circus movement tachycardia to see if changing A-V times or retrograde routes of activation allows manifestation of an additional bypass tract. An example of how this stimulation can reveal the presence of additional bypass tracts is shown in Figure 10-100. Circus movement tachycardia using a right anterior bypass tract is present on the left. This results in earlier input to the A-V node, producing a prolongation of A-V nodal conduction. The additional A-V nodal conduction delay allows a previously concealed left lateral bypass tract (owing to antegrade concealment by atrial activation produced by conduction over the right-sided bypass tract) to be manifested. The high incidence of multiple bypass tracts noted in our laboratory (∼25%) probably reflects both the care and detail with which we attempt to document the presence of additional bypass tracts as well as a selected patient population. A: During right atrial pacing, antegrade activation occurs over a right lateral bypass tract. This atrial echo initiates orthodromic tachycardia with simultaneous retrograde atrial activation over both the left- and right-sided bypass tracts. B: Coronary sinus pacing produces antegrade activation over a left lateral bypass tract. A premature stimulus (S2) blocks in the left- sided bypass tract and conducts over a right lateral bypass tract, initiating an atrial echo over the left lateral bypass tract. This echo initiates orthodromic tachycardia with conduction antegradely over the normal conducting system and retrograde conduction over both the left lateral and right-sided bypass tracts. The fact that the right- sided bypass tract is used is suggested by the difference in retrograde atrial activation when conduction proceeds solely over the left-sided bypass tract following antegrade conduction over the right-sided bypass tract (arrow) in the last three complexes. The earlier activation at this site suggests two retrograde atrial breakthrough sites and two bypass tracts. Fusion is seen in the second and seventh complexes, and total preexcitation over the anterior paraseptal bypass tract is seen in the fourth through sixth complexes. Note the difference in V-A intervals associated with different H-V intervals with various degrees of fusion. The change in V- A intervals is due to the relative activation of the ventricles over the bypass tract and the time that the normal conducting system activates the ventricles. Patients with multiple bypass tracts have been associated with a higher incidence of ventricular fibrillation according to some investigators, a higher incidence of preexcited tachycardias, and clearly, more complicated anatomy for catheter-based or surgical ablation. Thus, it is imperative that one make every effort to detect their presence during electrophysiologic studies. In the presence of multiple bypass tracts the complexity and number of the potential tachycardia circuits is large (Fig. If one considers the fact that a given patient may have more than two A-V bypass tracts (20% of our patients with multiple bypass have three or more tracts), enhanced A-V nodal conduction, P.
This idea can be very important in some instances discount norpace 150mg with mastercard, where surviving the early stages of a disease may dramatically decrease the potential of an event occurring in the near future order 150mg norpace. As an example generic 150 mg norpace visa, consider cancer where nonrecurrence, or remission, for a period of 5 years generally increases survivorship. Excellent descriptions of the various models used to represent hazard functions are provided by Allison (4) and Kleinbaum and Klein (1). The method we use was introduced by Kaplan and Meier (5) and for that reason is called the Kaplan–Meier procedure. Since the procedure involves the successive multipli- cation of individual estimated probabilities, it is sometimes referred to as the product-limit method of estimating survival probabilities. As we shall see, the calculations include the computations of proportions of subjects in a samplewho survive for various lengths of time. We use these sample proportions as estimates of the probabilities of survival that we would expect to observe in the population represented by our sample. In mathematical terms we refer to the process as the estimation of a survivorship function. Frequency distributions and probability distributions may be constructed from observed survival times, and these observed distributions may show evidence of following some theoretical distribution of known functional form. When the form of the sampled distribution is unknown, it is recommended that the estimation of a survivorship function be accomplished by means of a nonparametric technique, of which the Kaplan–Meier procedure is one. Calculations for the Kaplan–Meier Procedure We let n ¼ the number of subjects whose survival times are available p1 ¼ the proportion of subjects surviving at least the first time period (day, month, year, etc. For any time period, t, where 1 t k, we estimate the probability of surviving the tth time period, pt, as follows: number of subjects surviving at least t À 1 time periods who also survive the tth period p^t ¼ number of subjects alive at end of time period t À 1 (14. They classified patients as having either low-grade (25 patients) or high-grade (14 patients) tumors. The event (status), time to event (months), and tumor grade for each patient are shown in Table 14. We wish to compare the 5-year survival experience of these two groups by means of the Kaplan–Meier procedure. We begin by listing the observed times in order from smallest to largest in Column 1. Column 2 contains an indicator variable that shows vital status ð 1 ¼ died; 0 ¼ alive or censored. In Column 3 we list the number of patients at risk for each time associated with the death of a patient. We need only be concerned about the times at which deaths occur because the survival rate does not change at censored times. Column 4 contains the number of patients remaining alive just after one or more deaths. Column 5 contains the estimated conditional probability of surviving, which is obtained by dividing Column 4 by Column 3. Note that although therewere two deaths at 15 months in the low-grade group and two deaths at 9 months in the high-gradegroup, we calculate only one survival proportion at these points. Each entry after the first in Column 5 is multiplied by the cumulative product of all previous entries. From the table we note the following facts, which allow us to compare the survival experience of the two groups of subjects: those with low-grade tumors and those with high-grade tumors: 1. We can determine the median survival time by locating the time, in months, at which the cumulative survival proportion is equal to. We can determine the 5-year or 60-month survival rate for each group directly from the cumulative survival proportion at 60 months. Since so many of the times in the low-grade group are censored, the true mean survival time for that group is, in reality, higher (perhaps, considerably so) than 88. The true mean survival time for the high-grade group is also likely higher than the computed 18. Thus, we see that we have still another indication that the survival experience of the low-grade tumor group is more favorable than the survival experience of the high-grade tumor group. From the raw data of each group we may also calculate another descriptive statistic that can be used to compare the two survival experiences. A group with a higher average hazard rate will have a lower probability of surviving than a group with a lower average hazard rate. We compute the average hazard rate, designated h by dividing the number of subjects who do not survive by the sum of the observed survival times. For the high-grade tumor group we compute hH ¼ 13=257 ¼ :05084, We see that the average hazard rate for the high- grade group is higher than for the low-grade group, indicating a smaller chance of surviving for the high-grade group. We note that the graph resembles stairsteps with “steps” occurring at the times when deaths occurred. These observations strongly suggest that the survival experience of patients with low-grade tumors is far more favorable than that of patients with high-grade tumors. The following table shows the status of each patient at various periods of time following surgery. Calculate the survival function using the Kaplan–meier procedure and plot the survival curve. Calculate the survival function using the Kaplan–Meier procedure and plot the survival curve. Total Total Total Duration of Duration of Duration of Remission Remission Remission Remission Remission Remission (Months) Statusa (Months) Statusa (Months) Statusa 3 1 8 2 26 1 3 2 9 2 27 1 3 3 3 4 4 4 5 5 5 5 5 5 (Continued) 14. This includes visualizing the temporal trajectory to find time periods in which there were dramatic changes in survival, finding time periods in which relatively little change occurred, or in finding the approximate median of the data distribution. The construction of survival curves, however, finds its greatest use when comparisons among survival distributions are of interest. For example, one may wish to examine differences in treatment in which subjects were randomly assigned, or may wish to know which medication delays the onset of the event of interest for the longest period of time. The results of comparing the survival experiences of different groups will not always be as dramatic as those of our previous example. For an objective comparison of the survival experiences of different groups, it is desirable that we have an objective technique for determining whether they are statistically significantly different. We know also that the observed results apply strictly to the samples on which the analyses are based. Of much greater interest is a method for determining if we may conclude that there is a difference between survival experiences in the populations from which the samples were drawn. In other words, at this point, we desire a method for testing the null hypothesis that there is no difference in survival experience between populations against the alternative that there is a difference. The log-rank test is an application of the Mantel–Haenszel procedure discussed in Section 12. Though we may wish to compare survival curves of many populations, we will limit our discussion to the comparison of two groups: To accomplish this task, we calculate the log-rank statistic and proceed as follows: 1. Order the survival times until death for both groups combined, omitting censored times.
Sometimes these criteria lead to the use of exces- It is not easy to understand what the patient wants norpace 100 mg discount. Very sively wide implants and pockets that buy norpace 150 mg line, joined with the inad- often she does not have a clear idea of the kind of results she equate coverage by the soft tissues order norpace 150mg free shipping, conditioned unwanted is looking for, while other patients ask for a precise bra size palpability and visibility of the implant edges medially as to be ﬁlled by the new breast, or show a picture of a model or well as laterally. It is the surgeon’s task to mal soft tissues coverage of the implant is extremely explain what can be done and what is actually impossible to important has been well understood and became popular; obtain. It is necessary to use everything that can help in the the adequate coverage must be a priority even in respect to mutual understanding of what the ﬁnal result would be. If the surgical planning does not respect Displace the patient’s tissues – if there are enough tissues this principle, deformities will result, a few of which will to allow this maneuver – medially, laterally and superiorly, in result extremely difﬁcult to correct. The use of very large order to ﬁll the corresponding quadrant and simulate a new implants will enhance the long-term inconveniences proﬁle, while the patient observes the results in a mirror. This related to thinning, stretching and atrophy of overlying helps in obtaining pieces of information particularly about tissues. Ask the patient to bring pictures from magazines showing 8 Implant Positioning (Table 1 ) women with body weight and thoracic conformation similar to theirs, with evidence of breasts of volumes and shapes Dissection of the pocket for the implant can be performed in they like. This condition has to be achieved after ﬁlling it with an implant looks inaccurate and checked with the palpation as well as with the pinch test, the patient deﬁnitely does not understand it. It is considered Augmentation Mastoplasty 133 the more natural position, as the added volume is actually create a ﬂattening effect that will diminish with time in an positioned in the same place where it should be, that is the unpredictable way. By the way, the shape of the breast comes out It is a long time that the complete release of the pectoralis more natural. With respect to the subpectoral positioning, insertions along the inframammary fold together with the postoperative pain is by far inferior and physical restriction partial interruption of the medial ones along the sternum are for the woman is shorter. Furthermore, the retroglandular recommended; in this way the dynamic distortion is reduced position poses no problems in terms of breast distortion dur- and a wider expansion of the inferior pole of the gland is ing the contraction of the pectoralis muscle; this point has to obtained. Actually, the complete release of the inferior inser- be adequately explained to the woman. The optimal expan- ralis fascia is elevated together with the deep layer of the super- sion of the inferior pole of the breast may need additional ﬁcial fascia, including the perimysium, the results are different. According to the classic tech- positive effect on the capsular contracture and a lesser degree nique, the pectoralis muscle insertions to the overlying breast of visibility of the implant edges has been advocated. It must be utilized More recently a technique of selective release of the every time tissue thickness over the implant seems question- pectoralis muscle, tailored to the patient’s anatomy, has able, being aware that aging will worsen the problem of tis- been popularized and is widely used. This decision has to be taken also considering “dual plane” pectoralis detachment minimizes the dynamic two unfavorable aspects of this position, such as the move- forces of the pectoralis contraction, offering at the same ment related distortion of the breast and the more painful and time the best possible tissue coverage for the implants in long postoperative course. The term “dual plane” is of the implant are invaluable, particularly considering related to the fact that dissection is partly performed in the patients in which the device becomes palpable and visible. Distortion of the breast while the pectoralis major contracts Dissection is performed not only behind the pectoralis can be very fastidious for the patient, particularly when no major, but also directly over it, detaching the muscle from manipulation or release of the medial and inferior muscular the gland for a variable distance, according to the required insertions has been done. In this case the muscular contrac- degree of expansion of the inferior pole as well as to the tion pulls the implant superiorly and laterally, leading with level of the ptosis. Included in the technique is also the time to the permanent displacement of the device. The pectoralis muscle retracts upwards the potential expansion of the inferior half of the gland and at different levels, covering only the superior tract of the implant. The dissection over the pectoralis muscle is extended up to Table 1 Implant position the level of the superior border of the areola, in order to cor- rect the ptosis; in this way the implant can ﬁll the lower pole Retroglandular position of the breast and obtain as much as possible of the pseudo-lift Increased incidence of ﬁbrosis effect. Visibility/palpability of the superior border of the implant Rippling The retracted pectoralis ﬂap should be sutured again to the Unﬁt for thin tissues; breast parenchyma; this maneuver has to be performed after Increased evidence of spherical contracture the positioning of the implant with the patient seated, in order Suitable for correction of minimal ptosis to adequately verify the level of replacement. Greater motility A modiﬁed dual plane technique is characterized by a No dynamic distortion during pectoralis muscle contraction horizontal section of the pectoralis muscle 2 cm distally to Subpectoral position the superior limit of the glandular dissection. This will cre- Low degree of pericapsular ﬁbrosis ate a smaller ﬂap, with still a useful weakening of the infer- Reduced evidence of incidental ﬁbrosis olateral border of the muscle, allowing to eventually Less suitable in case of ptosis disguise any glandular defect evidenced by the muscular Dynamic distortion during pectoralis muscle contraction contraction. Exerting a light pressure on the inferior and Implant Selection pole of the gland, the superior limit that has to be ﬁlled up is marked (Fig. This measured These complex formulas have been of great help in the value identiﬁes in most of the patients the width of the implant comprehension of the dimensions concept, caring after to be utilized, as the device deﬁnitely needs to be completely previously omitted details; nevertheless these algorithms can covered by the breast tissues (Fig. The main point is that the edges of the device are not quately select breast implant size are listed here: visible nor palpable either medially or laterally under the thinned tissues. This mea- sure is written down by the manufacturer on the implant Medial and lateral contour. The under tension measure approximately reﬂects medial and lateral parenchymal boundaries are marked, the postoperative condition, when tissues are distended by pushing slightly the gland inwards and outwards, in order to the new volume; its value gives an indication on the degree make the gland boundaries more evident (Fig. The inframammary ridge is marked while tractioning the Nipple-ridge distance with elevated arm. Abducting the arm This line is temporarily considered the potential new mam- of 90°, the nipple will be positioned approximately in the mary ridge. That measure will approximately correspond to the radius of the implant base, whose value has to be compared with the Table 2 Implant selection already measured transverse diameter. Width: breast width minus tissue thickness The position of the new ridge has to be checked. The Height: distance between the expected position of the inframammary nipple-ridge distance on the median line of the body has to ridge and the superior boundary of the area to be ﬁlled up correspond to the sum of the implant radius and the tissue Shape: if the two measures are identical, a round or anatomical thickness of about 1–1. The position of the implant with a round base can be positioned; if the transverse diameter is longer than the vertical one, an anatomical implant with ridge can be pushed down; obviously, it is necessary to be oval base is preferred. Using an anatomical implant with oval base, sure that the ridge is not too tiny and that it can be lowered we can change the shape into an improved aesthetic result without any deformation or double contour. In thin Projection: any base size has 3–4 different projections patients, the lowering of the ridge often involves an inad- a c b d Fig. If under tension the nipple-ridge distance stretches about 1 cm, the compliance is low; if the stretch reaches 3 cm, it is possible – and appropriate – to select a more projecting implant. If under tension the nipple-ridge distance is superior to 8 cm, the patients have a ptosis of the breast that will be corrected with great difﬁ- culty by the implant. Anatomic implants, also called drop devices, have been on the market since many years, with a great variety of shapes and projections; many authors consider them of the greatest importance to obtain in the woman a natural, non-operated look. The main difference between these implants and the round ones resides in the superior pole, which is thinner and can be positioned at different heights with respect to Fig. The implant surface has to capability of receiving the new volume, and thus to their permanently adhere to the patient’s tissues. This patient shows a low superior pole with high oblique view (3/4) postop Augmentation Mastoplasty 137 a b d c Fig. Low texturization items create no • Retroglandular implants are more often palpable, with adherence between the implant and the tissues and do not visible margins. The surgical table in the operating room must have adjustable segments, in order to maintain the patient in the sitting position during the procedure and to evaluate the cor- rect and symmetric positioning of the implants. These reference points are useful while dissecting the implant pocket with the patient lying on Fig.
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