By M. Kerth. Abraham Baldwin Agricultural College.

The mean vector originates at the center of disorders) in part by its bowl-shaped configura- Einthoven’s triangle purchase vytorin 30mg line. Each lead is represented by a line whose moves away from zero in an upward cheap vytorin 20mg without prescription, counterclockwise continuous portion constitutes the projection on the direction marks a decrease up to –180 determine the orientation of the cardiac vectors 1. The standard and augmented trode produce positive deflections; those limb leads are mapped onto a diagram so that moving away from the exploring electrode they intersect at a common point at the center of produce negative deflections. Identifying the direction of the To calculate the electrical axis, one identifies mean electrical axis provides insight into the the lead in which the vector is most positive, the morphology of the tracings obtained with each one in which it is most negative, and the one in limb lead and makes it possible to identify cer- which it produces a isobiphasic complex. What kind of correlation is there between the erly connected; in an unconscious patient, it atrial and ventricular activity? These conditions are that is, rhythms differing from the normal sinus characterized by increases in the slope of phase rhythm, which is characterized by heart rates rang- 4 of the action potential and in the firing rate of ing from 60 to 100 beats per minute (bpm). First, the trocardiographic analysis of an arrhythmia is not electrical stimulus reaches a closed circuit, limited, however, to heart rate (increased versus anatomical or functional, which consists of two decreased): it also includes the rhythm (which can pathways with different conduction velocities be regular or irregular), the origin (supraventricu- and refractory periods. One offers slow conduction but a rela- absent formation and/or conduction of the tively short refractory period, which means it can impulse at any level of the conduction system be reexcited fairly early; the other pathway offers. Both of these bundle-branch block or ventricular origin) conditions are related to anatomical reentry circuits (i. The third mechanism of tachyarrhythmia involves afterdepolarizations, oscillating currents present during the repolarization phase that are sometimes large enough in amplitude to generate repetitive firing. Under normal conditions, car- diac muscle fibers generate rhythmical electrical impulses as a manifestation of their spontaneous automaticity. In “triggered" activity, the action potential may be generated before phase 4 of the previous potential reaches the threshold level: afterdepolarizations therefore appear in relation to one or more of the previous electrical stimuli (which explains the term “triggered. In (b), the increased slope of phase 4 of the potential facilitates the onset of an arrhythmia The mechanism of reentry Extrasystole A B A B A B Bidirectional Unidirectional block Reentry conduction. Anterograde transmission Left: Under normal conditions, the impulse is simulta- along the fast pathway (B), which is still refractory, is neously transmitted along the two conduction pathways. Right: When the fast pathway becomes excitable Center: In the presence of extrasystole and two pathways again, the wavefront travels along it in a retrograde direc- that differ in conduction velocity and refractoriness, the tion, perpetuating the reentry circuit ectopic impulse moves ahead along the slow pathway (A), a b Prolonged plateau Early afterdepolarizations Late Ca++ overload afterdepolarizations. The third complex represents a ven- ventricular extrasystole that triggers the torsades de tricular extrasystole followed by a long pause. They can be onset of the A deflection to the onset of the H broadly classified as tachyarrhythmias, char- deflection. It divides to form the right located in at the junction between the right atrium and the and left bundle branches, which supply the right and left superior vena cava. Here, we will use the system proposed some years ago by the Italian Association of Sinus Bradycardia Hospital Cardiologists (Table 5. It can be further classified as mild (rates between 50 and 59 bpm), Arrhythmias Caused by Abnormal moderate (40–49 bpm), or severe (<39 bpm) Impulse Formation (s. It is important to recall that in young, healthy subjects, nocturnal sinus Healthy individuals at rest exhibit a sinus rhythm rhythms at rates of 35–40 bpm are considered with rates ranging from 60 to 100 bpm. Junctional or ventricular escape mon type of sinoatrial block is a second-degree beats may appear after sinus pauses of variable 2:1 block. The P-P cycle preceding the block (which occurs after the second complex from the left) has a duration of 1080 ms, half as long as the 2220-sec P-P cycle that includes the pause. Less com- normal activation of the ventricles) or wide monly the delay occurs within the bundle of His (indicating a concomitant delay in ventricular (H deflection lasting >25 ms or split His bundle activation). In some forms, however, no fixed pattern in these cases is almost always wide because the 36 5 The Bradyarrhythmias. The impulses are generated by a complex will be wide, and the escape rhythm will subsidiary pacemaker (junctional or ventricular have a rate of 25–40 bpm. It causes recurrent episodes of syn- sinus syndrome, this disorder stems from cellular cope or presyncope. Depending on the actual node while the latter is still refractory, and in this location, they are described as supraventricular case it will not be conducted to the ventricles or ventricular. The last followed by a premature P wave that is not conducted complex is an atrial extrasystole that has been aberrantly (nonconducted premature atrial complex or blocked atrial conducted (right bundle-branch-block pattern). This arrhythmia is This type of tachycardia is characterized by generally the result of increased automaticity, morphologically identical P waves, heart rates which is manifested by the so-called warm-up ranging from 150 to 250 bpm, and clearly dis- phenomenon consisting of progressive rate cernible isoelectric lines between the atrial increases soon after the onset of tachycardia deflections. The arrhythmia is therefore ectopic atrial tachycar- and an atrioventricular conduction ratio of 1:1 (tachycar- dia. For details, see no means simple: is this a paroxysmal supraventricular text on diagnosis of the supraventricular tachycardias tachycardia or atrial tachycardia? In (b) the response to Multifocal Atrial Tachycardia with at least three different configurations. The electrical basis is probably This supraventricular arrhythmia is characterized increased automaticity. It is commonly seen in by an atrial frequency of >100 bpm and P waves patients with chronic respiratory disease. The stimulus) generally decreases and increases pro- ventricular response to the high-rate atrial activ- portionally with the length of the cardiac cycle. The long cycle before replaced by rapid, irregular oscillations of the an Ashman complex prolongs the refractory isoelectric line known as f waves, and the rhyth- period of the bundle-branch cells, and the next micity of the ventricular complexes is lost complex is widened.

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Given the side‐effect profile of misoprostol and limited evidence of risk reduction purchase vytorin 30mg with visa, many providers base its use on risk factors for cervical or uterine injury best 30mg vytorin. Common indications are age 17 years or less, prior cervical sur- gery, and gestational age over 12 weeks. Pain management options for vacuum aspiration include local cervical anaesthesia with oral analgesia, conscious sedation, and general anaesthesia. Reproduced with permission of remains a lack of consensus on the ideal cervical anaes- Womancare Global. At this stage, the woman may feel a strong Advantages of local anaesthesia include faster recov- cramp. Calm and comforting conversation to distract the ery, a greater sense of control for the woman, and a woman and explaining the meaning of unpleasant sensa- reduction in procedural risks such as haemorrhage and tions will help her tolerate the procedure. The vulsellum or tenaculum is not eliminate discomfort and some women may find removed and the cervix inspected for bleeding. For women who want greater of low rates of haemorrhage, oxytocics are not routinely pain and anxiety management than local anaesthesia administered. The operator should ascertain that the provides but do not want to be asleep, low‐dose intrave- gestational sac and any fetal parts, consistent with the nous fentanyl and midazolam can be provided to achieve gestational age, have been removed. Women’s preference, risk sound guidance is increasingly used but is not required if factors for anaesthetic complications, setting and the aspirate will be inspected. Once the operator is cer- resources should be considered when choosing a method tain of completion, the woman should be reassured. Vacuum aspiration is a straightforward procedure but careful practice is important so that pregnancies are Surgical abortion in the second trimester evacuated completely and safely. Asepsis cannot be maintained during an abortion because contamination Electric vacuum aspiration can be performed up to 16 of gloved hands occurs once the woman is touched. Careful and preparation and removal of the fetus and placenta with gentle instrumentation avoids injury to the cervix or specialized forceps, D&E is associated with a low risk of uterus and good communication is needed between the complications and is highly acceptable to women. When operator, the woman and other members of the surgical second‐trimester surgical abortion was compared in a team. Precise techniques vary among providers and with randomized trial with medical abortion, significantly anaesthetic regimens. This section describes electric fewer women found the surgical option worse than vacuum aspiration with local anaesthesia. After confirming the position, size and extraction (D&X), is performed after very wide (median shape of the uterus by bimanual examination, a bivalve 5cm) cervical dilation is achieved using osmotic dilators speculum is placed in the vagina. This is followed by an assisted are cleansed with an antiseptic solution such as chlo- partial breech delivery, decompression of the calvarium, rhexidine. Local anaesthetic is administered by first and delivery of the fetus otherwise intact. Hysterotomy injecting 1–2mL 1% buffered lidocaine at the 12 o’clock and hysterectomy are outdated methods and only used position on the cervical face. Obstruction is applied and, with gentle outward traction, an addi- by a large, distorting cervical or uterine tumour is an tional 18 mL of buffered lidocaine is injected in equal ali- example of when these methods might be employed. Adequate cervical preparation is essential for safe Cervical dilation to the diameter of the suction cannula D&E provision. The amount of cervical expansion is performed with tapered metal or plastic dilators (e. As a general rule, dilation inserted into the mid to upper fundus, taking care not to should be sufficient to insert and open the extraction touch the fundus which causes pain. After this point, longer forceps with wider 604 Early Pregnancy Problems (a) facilitates an easier, faster and safer evacuation. It is also used in response to patient preference or to avoid the risk of transient signs of life should extramural delivery occur. The most frequently used methods are intra-amniotic or intra-fetal injection of digoxin, and fetal intra-cardiac potassium chloride injection. Research is limited, but the few existing comparative studies suggest that feticide before D&E does not confer a clinical benefit and may increase risks. The only randomized controlled trial avail- able found that intra‐amniotic digoxin administered 24 hours before D&E did not reduce the duration of the pro- cedure, blood loss or subjective difficulty of the procedure compared with placebo [38]. In addition, a before and after study found low but increased risks of extramural delivery and infection with the digoxin compared to non- (b) use [39]. Cohort studies of fetal intracardiac potassium chloride injection before D&E differ as to whether it decreases operative times but found increased risks of cervical laceration and uterine atony compared with non- use or D&E in the setting of spontaneous demise [40,41]. D&E can be performed with local anaesthesia, conscious sedation or general anaesthesia.

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When evidence of ischemia persists after catheter removal discount 30mg vytorin otc, anticoagulation cheap vytorin 20mg fast delivery, thrombolytic therapy, embolectomy, surgical bypass, or cervical sympathetic blockade are treatment options and should be pursued aggressively [23,44]. Cerebral Embolization Continuous flush devices used with arterial catheters are designed to deliver 3 mL per hour of fluid from an infusion bag pressurized to 300 mm Hg. It was demonstrated that with rapid flushing of radial artery lines with relatively small volumes of radiolabeled solution, traces of the solution could be detected in the central arterial circulation in a time frame representative of retrograde flow [48]. Moreover, injection of greater than 2 mL of air into the radial artery of small primates results in retrograde passage of air into the vertebral circulation [35]. Factors that increase the risk of retrograde passage of air are patient size and position (air travels up in a sitting patient), injection site, and flush rate. Air embolism has been cited as a risk mainly for radial arterial catheters but logically could occur with all arterial catheters, especially axillary and brachial artery catheters. The risk is minimized by clearing all air from the tubing before flushing, opening the flush valve for no more than 2 to 3 seconds at a time, and avoiding overaggressive manual flushing of the line. It is a particular problem for patients with standard arterial catheter setups that are used as the site for sampling, because 3 to 5 mL of blood are typically wasted (to avoid heparin/saline contamination) every time a sample is obtained. Protocols that are designed to optimize laboratory utilization have resulted in significant cost savings and reduced transfusion requirements in our, as well as in other, institutions [50]. Other Mechanical and Technical Complications Other noninfectious complications reported with arterial catheters are pseudoaneurysm formation, hematoma, local tenderness, hemorrhage, neuropathies, and catheter embolization [20]. The data supporting the use of heparin to maintain patency of arterial catheters is poor and does not provide sufficient proof for continuation of this practice [52]. Infections Infectious sequelae are the most important clinical complications caused by arterial cannulation. Catheter-associated infection is usually initiated when skin flora invades the intracutaneous tract, causing colonization of the catheter, and when not locally contained, bacteremia. An additional source of infection is contaminated infusate from the pressure monitoring system, which is at greater risk of infection than central venous catheters because (a) the transducer can become colonized as a consequence of stagnant flow, (b) the flush solution is infused at a slow rate (3 mL per hour) and may hang for several days, and (c) the stopcocks in the system can serve as entry sites for bacteria when they are accessed by several different personnel to obtain blood samples. It should be noted that only one study evaluated the impact of maximum barrier precautions for the placement of radial and dorsalis pedis catheters [53] and that no studies have addressed this matter for larger arteries. With those considerations in mind, it is our practice to use full barrier precautions for all large artery insertions. Chlorhexidine should be used for skin preparation [54] and use of a chlorhexidine soaked dressing at the insertion site is an excellent practice. Breaks of sterile technique during insertion mandate termination of the procedure and replacement of compromised equipment. Nursing personnel should follow strict guidelines when drawing blood samples or manipulating connections. Blood withdrawn to clear the tubing prior to drawing samples should not be reinjected unless a specially designed system is in use [55]. Inspection of the site at the start of every nursing shift is mandatory, and the catheter should be evaluated and removed promptly when indicated. Routine change of the pressure monitoring system does not reduce infectious complications and may represent another opportunity to introduce colonization. Historically, it was thought that arterial catheters had a lower risk for infection than central venous catheters, but research has proven this to be no longer true. Using modern techniques, arterial catheter-related colonization may occur in up to 5% to 10% of catheters, but the incidence of catheter-related bacteremia is in the range of 0. The site of insertion as an important factor impacting the incidence of infection has been a controversial issue. Previous research studies had conflicting reports about the risk of infection of femoral catheterizations, and the consensus among physicians was that they were generally safe [18–21,30]. Based on these findings, placement of a catheter in the femoral artery should be avoided, when feasible, by cannulating another arterial site. In this regard, we have had a change of practice in our institution, where more brachial and axillary cannulations are done now. We believe 5 to 7 days is an appropriate time to reassess the need for and the location of arterial catheterization [21,57], but each institution should determine its own catheter-associated infection rate so that rational policies can be formulated based on existing local infection rates. Gram-negative organisms are less frequent; they are predominantly contaminated infusate or equipment-related infections. Infection with Candida species is a greater risk for prolonged catheterization of the glucose-intolerant or immunocompromised patient but has been reported for all types of patients. Catheter-associated bacteremia should be treated with a 7- to 14-day course of appropriate antibiotics. The optimal evaluation of febrile catheterized patients can be a challenging problem (see Chapter 79). If the site appears abnormal or the patient has sepsis of no other identified etiology, the catheter should be removed.

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