Over the especially in patients with pre-existing ﬁrst 24 hours cheap fluticasone 100 mcg overnight delivery asthmatic bronchitis with exacerbation, 39±16% of the administered renal impairment order 100mcg fluticasone amex asthma treatment walmart. Other risk factors dose is recovered in the urine fluticasone 250 mcg for sale asthmatic bronchitis antibiotics, while the are: increasing age, repeated cycles remainder is principally bound to bone of bisphosphonates, concomitant tissue. Molecular weight 401 (443 as ● Antibacterials: increased risk of (daltons) acetate), (473. Te sulphoxide metabolites are mainly ● Beta-blockers: increased risk of ventricular excreted in the urine while unchanged drug arrhythmias with sotalol – avoid. Because the 10–19 100% dose drug sensitivities of malaria parasites change <10 50% dose with time and place, the most up-to-date information on prophylaxis should always be Proguanil: ● Transplant patients dose according to the obtained from an appropriate travel clinic. Chloroquine: ● Malaria prophylaxis: no dose adjustment necessary for renal impairment. The ﬁrst or into anatomical systems, such as vascular, gastrointestinal, report of harmful physical effects was made in the British and urological. Public concern after the death of one of the ﬁrst radi- Interventional procedures for pain management have been ologists (William Ironside Bruce) from radiation-induced developing new techniques and precision techniques since injuries in 1921 led to the establishment of the British 1960. What was previously the role of anesthesiologists to do X-Ray and Radium Protection Committee. Imaging techniques have become a national (X-ray and Radium) Protection Committee began. In patients with pain symptoms, the goal is to of angiography in the late 1920s by a Portuguese group. Consideration should be given to cost, availabil- ing the artery by transluminal angioplasty in 1964. A Coronary angioplasty began in humans with the ﬁrst radiographic test should be obtained only when the results case in 1977 by Andreas Gruentzig and has since developed may alter the patient’s subsequent management. It is now the most More than ever, it is important to consult with a radi- common interventional procedure in the world. The electrons are often compared to “planets” directly results in a more accurate diagnosis and ultimately that orbit the nucleus or “sun” of the atom (Figure 1-1). The negative charge from the electrons keeps them orbit- ing the nucleus in ﬁve electron shells labeled K, L, M, N, and O (Figure 1-2). If an electron is moved from a higher energy shell to Before the mid-1970s, plain ﬁlm radiography, conven- a lower one, energy is released. A displaced orbital electron and the available for imaging abnormalities involving the vertebrae, atom from which it originated is called an ion pair. By 1975, ation can occur with electron bombardment of matter, x-ray a nonionic intrathecal contrast agent, metrizamide, was bombardment of matter, thermionic emission with electron approved for clinical use. If the ionized contrast carried negligible risk for arachnoiditis and was electron is moved to a higher orbit, this is called excitation. In absorbable, and thus eliminated the need for its removal an excited state, the displaced electron will return to its from the thecal sac. Second, its neurotoxicity was minimal, original orbit or be replaced by another electron. Often the compared with ionic water-soluble media, which never additional energy to ionize the atom is released as photons of achieved widespread acceptance in the United States. Nevertheless, this procedure still requires a lumbar puncture, with its attendant hazards to the patient. Most signiﬁcantly, the parenchyma of the spinal cord could now be imaged and assessed for intrinsic pa- thology, such as multiple sclerosis plaques. A typical atom consists of a nucleus (N), which contains be further broken down into electrons, protons, and neutrons. This rep- All known substances, living and nonliving, are comprised of resentation of the carbon atom is not in scale. Combinations of these ele- protons each constitute 1838 times more mass than electrons. The binding force on C the electron shells holding the electrons in orbit around the nucleus weakens as the number of shells increase. The electrons in the K shell require the most energy to dis- lodge from orbit, whereas the electrons in the peripheral shells are easier to displace. This energy travels in the A form of sine wave–like oscillations at the speed of light. Electromagnetic energy is transported through space in the form of sine wave-like oscillations. This energy travels at the speed of (angstrom) is the distance from one wave to the next. Components of the sine wave include amplitude, wavelength and of waves passing by a speciﬁc point in a given unit of frequency. X-ray photons are commonly between 18 21 to another and represents the distance between two corresponding points 0. Frequency is determined by the number of crests or valleys passing through a speciﬁc point in a given time. The relation of voltage and amperage The relationship of medical x-ray to the electromagnetic spectrum. In to resistance can be expressed by Ohm’s law, which states this abbreviated illustration the electromagnetic spectrum runs from that gamma radiation (short wavelength) to electrical waves (long wave- length). In the medical x-ray range, a short I V/R wavelength will be produced with high kilovoltage values, whereas a long wavelength will be generated by low kilovoltage values. The remaining energy is divided among bremsstrah- the application of an alternating voltage with its polarity and lung and characteristic radiation. Heat is produced by the values reversing direction at regularly occurring intervals, energy derived from the movement of the atoms and their typically 60 times per second (60 Hz) in the United States. The greater the kinetic en- Electrical energy in the form of voltage and amperage is ergy (energy of motion or vibration) produced, the greater usually supplied by commercial power companies and deliv- the temperature. Production of greatly increased or decreased by employing a simple device bremsstrahlung radiation is from the “braking” action that called a transformer (see “Transformers” section). This negatively charged electrons and the positively charged nu- current is easier to put to use but difﬁcult to transmit over clei causes the electrons to be deﬂected and decelerated great distances. Since energy cannot be destroyed, the energy lost by the electrons is transformed and emitted as x-ray photons. In the 80- to 100-kVp range, the branches of the circuit and is expressed as I i1 i2 i3. For An electrical circuit is used to gather, carry, or direct example, to produce characteristic radiation with a tung- ﬂowing electron energy. Electrical energy is carried sten target, at least 70 kVp are required for K-shell inter- through the circuit by electrical current (electrons in mo- action because the K-shell electron of tungsten is held tion). Current (I) or electron ﬂow is istic radiation produced in the interaction of x-rays with measured in amperes (A). There is resistance (opposition) matter is usually referred to as secondary radiation and is a to the electron ﬂow in all circuits, with some absorption form of scatter. The resistance of a conduc- In diagnostic radiology, there are three types of x-ray ener- tor is directly proportional to the resistivity of the material gies of importance: primary x-rays or photons emitted by of which the conductor is formed.
The increased output improves coronary perfusion pressure and coronary blood flow cheap fluticasone 500mcg with mastercard asthma krysten ritter. It has therefore been argued that greater levels of support may be required in patients in cardiogenic shock buy fluticasone 500mcg without a prescription asthma like symptoms but not asthma. Even so order cheap fluticasone on-line asthma 6 step plan, as outlined next, even with greater levels of hemodynamic support, survival may not be improved. While the Impella device is safe, hemolysis caused by the high rotational speed of the axial flow pump, access bleeding, and limb ischemia are known complications. The TandemHeart involves the continuous centrifugal pump circulation of oxygenated blood from the left atrium (via transseptal cannula placement) into the lower abdominal aorta or iliac arteries (via cannula 56 placement through common femoral artery). Indeed, performing a fluoroscopy-guided transseptal puncture and to advance a 21F inflow cannula into the left atrium in a patient in cardiogenic shock requires courage and skill. Taken together, while conceptually intriguing, the challenges of the insertion of the TandemHeart may limit its use. Deoxygenated blood is aspirated from the right atrium into the centrifugal pump by a cannula placed through a common femoral venous approach. The oxygenated blood is then returned into the descending aorta by an outflow cannula placed through a common femoral artery. It has also been used in the cardiac catheterization laboratory for patients who developed cardiorespiratory arrest during interventional procedures. Disadvantages are potential bleeding complications, limb ischemia, and the need for specialized care, including the availability of perfusionists. Transseptal left heart catheterization: a review of 450 studies and description of an improved technic. Hydraulic formula for calculation of the area of the stenotic mitral valve, other cardiac valves, and central circulatory shunts. The history of interventional cardiology: cardiac catheterization, angioplasty, and related interventions. American College of Cardiology/American Heart Association Ad Hoc Task Force on Cardiac Catheterization. History of right heart catheterization: 100 years of experimentation and methodology development. Appropriate use criteria to reduce underuse and overuse: striking the right balance. Radiation dose reduction in the invasive cardiovascular laboratory: implementing a culture and philosophy of radiation safety. The effect of information presentation on beliefs about the benefits of elective percutaneous coronary intervention. Access and non-access site bleeding after percutaneous coronary intervention and risk of subsequent mortality and major adverse cardiovascular events: systematic review and meta-analysis. Comparison of femoral bleeding complications after coronary angiography versus percutaneous coronary intervention. Haematoma after coronary angiography and percutaneous coronary intervention via the femoral artery frequency and risk factors. Complications of cardiac catheterization in the current era: a single-center experience. Silent cerebral infarcts after cardiac catheterization: a randomized comparison of radial and femoral approaches. Ultrasound-guided catheterization of the femoral artery: a systematic review and meta-analysis of randomized controlled trials. Impact of length and hydrophilic coating of the introducer sheath on radial artery spasm during transradial coronary intervention: a randomized study. Radial artery anomaly and its influence on transradial coronary procedural outcome. Radial versus femoral access in patients with acute coronary syndromes undergoing invasive management: a randomised multicentre trial. Ultrasound guidance versus anatomical landmarks for internal jugular vein catheterization. Percutaneous transthoracic ventricular puncture for diagnostic and interventional catheterization. Transthoracic left ventricular puncture for the assessment of patients with aortic and mitral valve prostheses: the Massachusetts General Hospital experience, 1989–2000. Exercise hemodynamics enhance diagnosis of early heart failure with preserved ejection fraction. Constrictive pericarditis in the modern era: novel criteria for diagnosis in the cardiac catheterization laboratory. Effects of vasodilation in heart failure with preserved or reduced ejection fraction implications of distinct pathophysiologies on response to therapy. Sodium nitroprusside in patients with mixed pulmonary hypertension and left heart disease: hemodynamic predictors of response and prognostic implications. Systemic hypertension in low-gradient severe aortic stenosis with preserved ejection fraction. The role of endomyocardial biopsy in the management of cardiovascular disease: a scientific statement from the American Heart Association, the American College of Cardiology, and the European Society of Cardiology. Endorsed by the Heart Failure Society of America and the Heart Failure Association of the European Society of Cardiology. Contribution and risks of left ventricular endomyocardial biopsy in patients with cardiomyopathies: a retrospective study over a 28-year period. Comparative evaluation of left and right ventricular endomyocardial biopsy: differences in complication rate and diagnostic performance. Coronary artery fistula in the heart transplant patient: a potential complication of endomyocardial biopsy. Comparison of fluoroscopic versus real-time three- dimensional transthoracic echocardiographic guidance of endomyocardial biopsies. The carina as a useful radiographic landmark for positioning the intraaortic balloon pump. A randomized clinical trial to evaluate the safety and efficacy of a percutaneous left ventricular assist device versus intra-aortic balloon pumping for treatment of cardiogenic shock caused by myocardial infarction. The history of coronary angiography starts in the 19th century with the discovery of x-rays by Roentgen in 1895. One month later, Haschek and Lindenthal injected a mixture of calcium carbonate in the blood vessels of an amputated hand and were able to visualize the vascular bed using a roentgenogram. Meanwhile, Frédérick Cournand and Dickinson Richards at Columbia University performed the first experiments on cardiac catheterization in animals, which led to the description of heart hemodynamics and the development of crucial techniques and principles, such as the Fick method to measure cardiac output and pressure manometry (see Chapter 19). Forssmann performed the first human cardiac catheterization on himself in 1928, advancing a catheter through an antecubital vein into his right atrium, and acquired roentgenograms to document it.
Huang  suggested placing the needle below in needle in order to introduce a 22-gauge spinal needle the coccyx transverse process discount 100mcg fluticasone with visa asthma definition in hindi. Studies utilizing numerous needle sizes for possible to complete needle introduction in a position just this intervention have been published safe fluticasone 100mcg asthma treatment before inhalers, with the small- anterior to the sacrococcygeal joint generic fluticasone 500mcg visa asthma treatment that is not a steroid. An angled needle allows for Thermocoagulation easier maneuvering and is a modifed version of the corkscrew maneuver initially prepared by McAllister • Thermocoagulation (radiofrequency ablation) of the gan- . There is no need to identify the coccygeal trans- glion impar is performed with identifcation of patients verse process and use a shorter needle for reducing tis- with positive diagnostic injections. The physi- cian then begins radiofrequency ablation at 80 °C • Direct approach through the intercoccygeal joint space is for 80 s through each needle (Table 37. This performed under lateral fuoroscopic view which may procedure may result in the reduction of reported, often be compromised by the bilateral cornua from the chronic nonmalignant pain in all subjects by an frst coccygeal bone. Additionally, it has been noted that injectate typi- cally fows in a cephalad direction, so needle insertion 1. Place patient in prone position and sterile drape the area inferior to the ganglion impar may yield improved results 2. Prepare cross-table lateral view of the pelvis including the sacrum and coccyx to fnd and note on the skin both the [38, 42, 43]. Gently advance Needle 1 toward and into the sacrococcygeal joint with constant, fuoroscopic guidance. Once Needle 1 and 2 are in place, sensory and motor testing must about one third the length of the coccyx. Use 50 Hz for sensory testing and 2 Hz for motor point toward the lateral coccyx testing prior to radioablation. Three: Rotate the needle back to a one quarter turn by twisting it 90 degrees counterclockwise. Move the needle 7 After sensory and motor testing, inject 1 cc of 2% lidocaine anteromedially until the tip is just anterior to the coccyx on through Needle 1 and 1 cc of 2% lidocaine through Needle 2. Inject local anesthetic or steroids ablation at 80 degree Celsius 37 Ganglion Impar Blockade 593 Table 37. Pelvic pain is often ill-defned and diffcult to diagnose, Radiofrequency Ablation: Needle-in-Needle and patients may present with signifcant undiagnosed Technique physical and psychological pathology. Blocking of the ganglion impar may relieve pain from • The needle-in-needle technique for radiofrequency malignant and nonmalignant sources of pain in the pel- ablation of the ganglion impar is similar to the trans- vis and perineum. This includes the distal rectum and sacrococcygeal approach; however, Tefon coating of a most urogenital structures. For this reason, it is recommended that a sacrococcygeal junction and relays pain information for 22-gauge needle is entered frst for protection. Injectates typically include steroids, local anesthetics, medical history and lab results in order to avoid potential and clonidine. Chemical neurolysis may be accom- complications in patients with contraindications. For example, patients with a approach is a promising technique for the ganglion history of coccygectomy, arthritis, and radiation to the lower impar block and utilizes loss of resistance as indication pelvis are at increased risk for calcifcation of the sacrococ- for appropriate needle placement cygeal ligament. Patients should be followed up the next day to assess for Randomized, double-blind, placebo-controlled trials are complications and the necessity of pain relief due to local necessary in order to evaluate its effcacy in managing anesthetic. Ganglion impar block with botu- linum toxin type a for chronic perineal pain -a case report. Clinical implications of topographic anatomy on blocks and neuroablation of the ganglion impar (Walther) in peri- ganglion impar. Paracoccygeal corkscrew approach to ganglion of ganglion of Walther for the management of chronic pelvic pain. Celiac Plexus Blocks and Splanchnic 38 Nerve Blocks Vijay Babu, Karthik Kura, and Karina Gritsenko uses. It is most frequently used for pain secondary to Introduction abdominal malignancies (commonly those of gastric or pancreatic origin) but can be used to provide visceral analge- Chronic abdominal pain is commonly seen in medical sia for multiple sources of intra-abdominal syndromes and practices and is a major health-related issue. Although celiac plexus and to be present in 75% of adolescents and 50% of adults, leading splanchnic nerves are often used interchangeably secondary to frequent visits to healthcare professionals . Chronic to their anatomic proximity, they are in fact distinct struc- abdominal pain may be secondary to both malignant and tures. Medical management and surgery occasionally These blocks are effective and superior for pain relief over may not be adequate to treat chronic abdominal pain. A Cochrane review  also concluded that fculty in managing chronic abdominal pain with interven- a celiac plexus block causes fewer adverse effects than tional techniques relates to the abdominal viscera’s rich neural opioids; thus, it is important for patients. Celiac plexus blocks and splanchnic nerve blocks have successfully been used to treat a variety of painful conditions of the abdominal viscera with availability of the History most signifcant literature on nonspinal blocks related to celiac plexus block. A Cochrane review described pancreatic cancer The percutaneous approach to blocking the splanchnic nerves as the ffth leading cause of cancer-related mortality in the and the celiac plexus was initially devised for surgical anes- United States, with an estimated 33,370 deaths attributable to thesia by Kappis in 1914 . Thus, management of abdomi- technique and eventually published a case series in 1918 . Celiac plexus block (also known as solar plexus block, Subsequently, Popper, in a 1948 publication , intro- celiac ganglion block, or splanchnic plexus block) is the duced the use of splanchnic nerve block as a diagnostic tool largest of the three great plexuses in the chest and abdomen, to differentiate between somatic and visceral components of with the other two being the cardiac and hypogastric plex- abdominal pain. Ethanol-induced neurolysis of the celiac plexus and splanchnic nerves for long-term pain relief was described by Jones in a 1957 publication . Recently, An  described an trials of celiac plexus blocks for pain associated with pan- alternate method for retrocrural approach during celiac creatic cancer. This meta- Pathophysiology analysis included trials not included in the Cochrane review [33, 34]. The pain that originates from the upper abdominal viscera is – The results showed that the combined celiac plexus carried by special visceral afferent fbers that relay through groups had signifcantly lower pain scores at 4 weeks, splanchnic nerves and the celiac plexus [22, 23]. Such visceral pain may be seen with control groups treated with pharmaceutical chronic benign disorders, however, more commonly with analgesics. Of all the vis- ceral pain conditions seen by interventional pain physicians, Indications pancreatic cancer is the most common which is the ffth lead- ing cause of cancer-related mortality in the United States . This has been stud- • Celiac plexus blockade has been reported to be benefcial ied only for pancreatic cancer pain in adults. A Cochrane in managing severe nausea and vomiting in patients with review  published its results in 2011. Anatomy • The Cochrane review included six studies [26–31] pub- lished from 1993 to 2008. Sympathetic trunk Spinal Dorsal (posterior) root Thoracic part sensory of spinal cord (dorsal Intermediolateral root) cell column ganglion Ganglion of sympathetic trunk Spinal nerve to vessels and glands of skin Ventral (anterior) root Meningeal branch to spinal meninges and spinal perivascular Stretch plexuses (usually arises from (distention) White ramus communicans spinal nerve) Gray ramus communicans Abdominopelvic (greater, lesser, Ganglion of and least) thoracic sympathetic trunk splanchnic nerves Vagus Pain nerve (X) Celiac ganglion Enteric Ganglion of plexuses sympathetic trunk of gut Superior mesenteric ganglion Sympathetic Preganglionic Parasympathetic Preganglionic Afferent fibers fibers fibers Postganglionic Postganglionic Fig. By the same level of the L1 vertebral body and anterior to the crura of token, the medial pathway is impeded by the kidney on the diaphragm (Fig. The left celiac ganglion is saline may be utilized to penetrate the crura of the slightly lower than the right ganglion. Once • It is extremely important to correctly identify the bony contact is made, the depth of the needle is T12 spinous process by following the twelfth rib noted. The needle is then withdrawn and redirected medially and also by counting cephalad from the L5 at a steeper angle (60 degrees from midline) so the spinous process.
Patients with impaired diastolic function or impaired systolic function are most dependent on atrial transport order 250mcg fluticasone visa asthmatic bronchitis 101. Effect of Ventricular Pacing on Synchrony of Ventricular Contraction Adverse Consequences of Right Ventricular Pacing purchase fluticasone canada asthma definition eloquent. Pacemaker Mode and Timing Cycles Definitions Pacing modes describe which chambers are sensed and paced and are characterized by a four-letter code (Table 41 purchase 100mcg fluticasone overnight delivery asthma definition 3pl. The first letter indicates the chamber paced: A for atrium, V for ventricle, and D for dual— both atrium and ventricle. The third letter describes pacemaker function: I for inhibition, T for triggered, and D for dual—tracking of atrial activity but inhibited by ventricular activity. Often it is easier to analyze timing cycles in terms of their associated time intervals measured in milliseconds (msec) rather than in rate measured in beats per minute (bpm). Since 1 minute is equivalent to 60,000 milliseconds, the interval in milliseconds corresponding to a rate in beats per minute can be determined by dividing the 60,000 by the rate (eTable 41. Pacing occurs when the ventricular rate slows below the programmed lower rate limit (Fig. The interval corresponding to the lower rate limit is the ventricular pacing interval. Usually, this is equal to the interval between a sensed ventricular event and the next paced ventricular event, referred to as the “ventricular escape interval. Because no ventricular sensed event occurs within 1000 milliseconds after the paced event, a second ventricular paced event occurs. Because a ventricular sensed event occurs 800 milliseconds later, a ventricular paced event does not occur. Because no atrial sensed event occurs within 1000 milliseconds after the paced event, a second atrial paced event occurs. Because an atrial sensed event occurs 800 milliseconds later, an atrial paced event does not occur. Hence the intrinsic atrial event is “tracked” and followed by a paced ventricular event. When the atrial rhythm slows sufficiently, the mode switches back to an atrial tracking mode (Fig. The third channel displays atrial intervals above the line and ventricular intervals below the line. However, it may mimic intermittent failure of ventricular pacing for a single beat (Fig. Single- versus Dual-Chamber Pacing Mode and Pacemaker Selection An expert consensus document provides recommendations for selection of single- versus dual-chamber 7 pacemakers. Rate-adaptive pacing is recommended for patients with significant, symptomatic chronotropic incompetence, the inability to increase heart rate for metabolic needs of exertion. Expert consensus recommends dual-chamber pacing over single-chamber ventricular pacing provided sinus rhythm is present. After each paced or sensed event, the sense amplifier is turned off for a short hardware blanking period (20 to 250 msec) to prevent multiple sensed events during a single cardiac depolarization. Following each blanking period, there is usually a software refractory period during which sensed events are not used to reset the timing cycle but may be used to calculate rate for features such as mode switching (Fig. Events “sensed” during software blanking periods are not used to control timing cycles, but may be used for specialized functions, such as detecting oversensing or atrial arrhythmias. There are two ventricular blanking periods, one after the atrial paced event, which prevents atrial paced events from being sensed on the ventricular channel, and one after the ventricular event. A ventricular sensed event in the crosstalk sensing window will result in safety pacing. The most common pacing problems can be classified as failure to capture, failure to pace, pacing at a rate inconsistent with the programmed rate, and unanticipated rapid pacing (Table 41. It can be related to the pacing system, the patient, or patient-system interactions. The most common cause is an elevated pacing threshold caused by changes at the electrode-myocardial interface. System-related causes are common in the perioperative period, especially lead dislodgment. An otherwise sufficient stimulus will fail to capture if it occurs in the physiologic refractory period of a spontaneous depolarization. Failure to Pace Failure to output an indicated pacing stimulus is most frequently caused by oversensing of physiologic or nonphysiologic signals, resulting in inhibition of the pacing output (Fig. Rarely, failure to pace can be caused by failure of the output circuit in the pulse generator or an open circuit (e. The combination of failure to capture and failure to pace usually indicates a pacing-system problem rather than a physiologic problem. Myopotentials are relatively uniform, low-amplitude signals with a dominant frequency in the range 80 to 200 Hz. Oversensing inhibits pacing, resulting in ventricular asystole best identified on the shock channel. Crosstalk is a specific form of oversensing in which the pacing stimulus is sensed in the opposite chamber. Settings that promote crosstalk include high atrial output, ventricular sensing parameter programmed to a very sensitive value, and short duration of ventricular blanking after atrial pacing. The fourth is not sensed and is followed approximately 360 milliseconds later by a paced event (V) that corresponds to an escape interval timed from the event marked “R. Pacing at a Rate Inconsistent With Programming Pacing with a shorter-than-expected escape interval usually indicates undersensing (eFig. Pacing with a longer-than-expected escape interval usually indicates oversensing (Fig. As with oversensing, undersensing can be related to the pacing system, the patient, or patient-system interactions. Consistent pacing at a rate slower than the programmed lower rate limit usually indicates oversensing of a constant signal during each cardiac cycle (usually T wave oversensing). In contrast, ventricular tracking of rapid, sensed atrial signals can be caused by failure to mode switch during atrial tachyarrhythmias or sensing of extracardiac signals (e. Less frequently, rapid sensor-driven rates may occur if the sensor responds to signals that are unrelated to patient activity, such as an accelerometer responding to vibrations in a helicopter or a minute ventilation sensor responding to respiratory rate in an asthma attack. The final atrial sensed event following the last ventricular paced beat is not tracked and is followed by an atrial paced beat that is conducted to the ventricle. Fusion indicates that depolarization occurs in part because of intrinsic activation and in part because of capture from the pacemaker stimulus. This occurs when the stimulus is delivered after intrinsic activation depolarizes the ventricles. These include high-risk patients with less common diseases, including specific cardiomyopathies (e. Usually, the generator is implanted pectorally, and a single, transvenous defibrillation lead is implanted in the right ventricle (analogous to a ventricular pacemaker lead) (Fig. The amplitude of the alternate vector is smallest (as in this tracing) because it often overlies atrial tissue and the sternum.