Board Review Session IV Friday, August 19, 2011 Questions with Answers and Rationales
48. A 20-year-old, female restrained driver is sideswiped at high speed by another vehicle. The airbag deploys and the patient arrives in the emergency department by air with a short extrication and transit time. She reports left chest pain and has acceptable vital signs, decreased left breath sounds, and crepitation in the left chest. The trachea is midline. Which of the following is the best next step? A. Nasal intubation B. Placement of a large-bore introducer in the subclavian vein C. Needle decompression of the chest D. Left tube thoracostomy E. Left chest thoracotomy
Questions 49 and 50 both use the following information: A 30-year-old, male unrestrained driver is involved in a high-speed motor vehicle collision. He arrives shortly thereafter at the major regional trauma center with acceptable vital signs. Evaluation and workup reveal a sternal fracture, a small subarachnoid hemorrhage and a contained intimal flap in the descending thoracic aorta just distal to the subclavian artery, with evidence of adventitial bleeding.
49. In addition to consultations, which of the following medications should be initiated urgently in the emergency department? A. Systemic heparin B. Norepinephrine C. Epinephrine D. Beta-blocker E. Antibiotics
50. In addition to consultations, which of the following is the best way to address the aortic injury? A. Do nothing for the aorta. B. Perform open repair via thoracotomy. C. Perform repair using an endovascular graft. D. Place an arterial line for monitoring. E. Place a triple-lumen central line for resuscitation.
51. A 63-year-old man is mechanically ventilated in the ICU with multisystem organ failure. After several family meetings, the clinical staff and the patient’s family agree that withdrawal of mechanical ventilation would be consistent both with his previously stated
wishes and his best interests. After removal of his endotracheal tube, the patient shows some signs of respiratory distress. The physician administers IV morphine, 2 mg. Immediately after the dose is administered, the patient has onset of apnea, followed by desaturation and then bradycardia. What should the physician do? A. Nothing; the indications for the morphine and the dose were both appropriate. B. Assist ventilation by hand until the morphine redistributes and the patient resumes breathing. C. Explain to the family that the apnea was most likely unrelated to the morphine and just part of disease progression. D. Administer a small dose of naloxone to reestablish spontaneous respiration. E. Reintubate the patient and wait for the morphine to wear off before attempting to withdraw ventilation again.
52. One of your colleagues is the principal investigator on a research trial comparing 2 approaches to blood transfusion in the ICU, one targeting a hematocrit of 20% and the other targeting a hematocrit of 30%. The study was approved by the institutional review board, which noted the lack of consensus within the medical community on this issue and the importance of determining the best approach for ICU care. One of your patients has just been enrolled in the trial and randomized to the 30% cohort. You have reviewed this
literature carefully, and you are personally convinced that the correct target should be 20%. What should you do? A. Ask to have the patient removed from the study, because it would be unethical for you to treat your patient in a way that you believe to be inferior to available alternatives. B. Ask to have the patient transferred to the care of another physician who is in agreement with the transfusion target of 30%. C. Explain to the family that you have no choice but to administer a treatment that you believe to be inferior. D. Follow the research protocol and use the 30% target, since even though you believe this strategy to be inferior, there is no consensus on this issue in the medical community. E. Encourage the patient’s family to withdraw the patient from the study.
53. A 42-year-old man is admitted to the ICU following a house fire in which he sustained severe smoke inhalation injury and burns to 20% of his total body surface area. His plastic surgeons have asked for supportive care. As part of this regimen, which of the following would you order? a. Enteral nutrition with a high-lipid diet b. Enteral nutrition with a high-carbohydrate diet c. Control of tachycardia with beta-blockers d. Antibiotic prophylaxis using meropenem but no other antimicrobials e. Antimicrobial prophylaxis with meropenem, fluconazole, and acyclovir
54. A 33-year-old man with aplastic anemia received an allogeneic peripheral blood stem cell transplant 20 days ago. Before transplant, both the patient and donor were cytomegalovirus-antibody positive. Since undergoing transplantation, he has received cyclosporine and prednisone as prophylaxis for graft-versus-host disease, dapsone for Pneumocystis carinii pneumonia prophylaxis, and acyclovir for herpes simplex virus prophylaxis. He is receiving vancomycin and imipenem for fever and neutropenia. Two days ago (posttransplant day 18), he developed a pruritic erythematous skin rash involving the chest, back, and extremities including the palms and soles of the feet, which has been associated with voluminous diarrhea and low-grade fevers. Results of several polymerase chain reaction (PCR) assays for Clostridium difficile are negative. Which of the following tests would you recommend as the best option to definitively determine the etiology of the diarrhea? a. Serum PCR testing for cytomegalovirus and adenovirus b. Buffy coat antigen testing for cytomegalovirus c. Culture of stool for cytomegalovirus d. Biopsy of skin e. Flexible sigmoidoscopy or colonoscopy with biopsy
55. A 20-year-old woman with no significant past medical history sustained a traumatic splenic rupture in a car crash 2 days ago. She underwent a successful splenectomy and is recovering well in the surgical ICU. She received a total of 10 units of packed red blood cells in addition to aggressive crystalloid resuscitation. She is extubated, BP is 110/72 mm Hg, and HR is 90/min. She is edematous, but her lungs are clear. Cardiac and neurologic examination findings are normal. Laboratory test results are as follows: hematocrit, 28%; creatinine, 0.8 mg/dL; sodium, 135 mEq/L; potassium, 4.1 mEq/L; chloride, 108 mEq/L; bicarbonate, 18 mEq/L; total calcium, 6.4 mg/dL; ionized calcium, 4.08 mg/dL (1.02 mmol/L); phosphate, 2.8 mg/dL; and magnesium, 1.8 mEq/L. Prothrombin time and partial thromboplastin time are normal. Disseminated intravascular coagulation screen is negative. Her rhythm strip is shown in the Figure. Which of the following is the most appropriate next step in the management of her hypocalcemia?
a. IV calcium gluconate bolus only b. IV calcium gluconate bolus followed by a continuous drip c. Subcutaneous teriparatide (recombinant parathyroid hormone) d. Oral calcium carbonate e. No specific therapy
56. A 32-year-old woman presents with 2 days of swelling of her submandibular area bilaterally with low-grade fever. Her temperature is 38.5°C (101.2°F). The area is brawny and boardlike. Her mouth is open, though she has mild trismus, and her tongue appears to be pushed up so that the rest of her oral cavity is difficult to visualize. She has been unable to drink or eat for a day, and she reports that breathing through her mouth is difficult. She has no masses or nodes that can be palpated. The rest of her examination findings are unremarkable. She is pictured in the Figure below. Her initial WBC count is 22,000/µL (95% neutrophils). CT is pending. The most likely cause of this syndrome is:
a. Facial cellulitis b. Otitis c. Bacterial lymphadenitis d. Dental abscess e. Epstein-Barr virus
57. A 52-year-old man in previous good health, who has not seen a physician for years, presents with progressive headache and fever of 14 days' duration. During the past 24 hours, the patient has also developed photophobia and some double vision. He is oriented to person, place, and time, but drowsy. On examination, the patient has chemosis, mild ptosis and proptosis, and a lateral rectus palsy of the right eye.. WBC count is 18,000/µL (90% neutrophils).. Gram stain of cerebrospinal fluid shows leukocytes but no organisms. MRI of the head reveals a normal orbit but ethmoidal and maxillary sinusitis and a cavernous sinus thrombosis. The most likely microbial cause of this syndrome is:
Deleted: The left eye is normal except for mild ptosis Deleted: Lumbar puncture reveals 25 WBCs per microliter (50% neutrophils, 50% lymphocytes) with protein level of 110 mg/dL and glucose level of 60 mg/dL Deleted: Blood cultures are pending.
a. Herpes simplex b. Mucormycosis c. Pseudomonas aeruginosa d. Mixed flora likely including staphylococci and streptococci e. Neisseria meningitidis
58. A 50-year-old man has a history of diabetes mellitus and chronic obstructive pulmonary disease. He is admitted to the ICU from the emergency department with a pneumonia involving 3 lobes. Sputum shows many polymorphonuclear cells and many gram-positive diplococci. His oxygen saturation is 82% on room air. The last time he received a cephalosporin he developed a diffuse rash with conjunctival suffusion and fever. Which of the following is the best option for initial antibiotic therapy in terms of efficacy and safety? a. Aztreonam b. Ciprofloxacin c. Azithromycin d. Imipenem e. Vancomycin
59. A 37-year-old woman with cancer of her left breast has been receiving chemotherapy at home through a right subclavian Groshong catheter and is now neutropenic. She had been doing well at home, but after 5 days of neutropenia she noted last night that the tunnel site of her Groshong was tender. This morning she had a rigor, fever to 40°C (104°F), and felt faint. She is transferred to the ICU from the emergency department with fever and hypotension. She has been given 2 L of saline plus vancomycin, ceftazidime, and tobramycin.
Deleted: . He had severe myalgias and high fever 7 days ago, and had been improving until 24 hours ago when he developed a fever of 38.7°C (101.7°F), a worsening cough productive of sputum, and shortness of breath. His physical examination reveals a febrile, normotensive man with consolidation at both lung bases Deleted: Laboratory findings include a WBC count of 2,400/µL and s Deleted: with
She looks stable after receiving fluid in the emergency department. Her right arm is not swollen or edematous. Which of the following is the optimal management of this patient's illness? a.Administer vancomycin, alternating infusions between the 2 lumens of the catheter, plus imipenem and gentamicin; leave the catheter in place, and do not perform angiography. b. Administer vancomycin, alternating infusions between the 2 lumens of the catheter, plus imipenem and gentamicin; perform angiography of the catheter to determine if thrombus is present. c. Immediately remove the catheter and infuse vancomycin, imipenem, and gentamicin into the new line. d. Remove the catheter only if the signs of inflammation have not subsided in 72 hours; infuse vancomycin, imipenem, and gentamicin into the new line. e. Immediately remove the catheter and infuse ciprofloxacin and gentamicin into the new line.
60. A 73-year-old man is admitted to the ICU for chest pain and possible myocardial infarction. He has a past history of 2 myocardial infarctions, but he has been pain-free since coronary artery bypass grafting 3 years ago. His left ventricular ejection fraction was 55% by echocardiography 1 month ago. Three sets of ECGs and cardiac enzyme test results are negative for any myocardial necrosis. On the second hospital day, a 3-lead rhythm strip shows a 3-beat run of a wide-complex tachycardia (see Figure below). The patient denies any associated symptoms, and his physical examination findings are normal. What is the best next management step in light of this new finding?
a. Schedule implantation of a cardioverter-defibrillator. b. Administer no further therapy. c. Administer IV lidocaine. d. Begin oral amiodarone.
Deleted: In the ICU, her BP is 155/95 mm Hg, and she is comfortable. Her temperature is 38.2°C (100.8°F). It is decided not to put in a Swan-Ganz catheter. On examination, the only remarkable finding is her catheter: there is no exudate at the exit site, but the tunnel is red and tender from the exit site extending over the palpable length of the catheter.
61. A 74-year-old man with a past medical history of hypertension, asthma, chronic obstructive pulmonary disease, and 2 previous myocardial infarctions enters the ICU with severe dyspnea. Four hours ago, the patient was at home when he noted onset of severe dyspnea without chest pain while walking up a flight of stairs. Although he usually has mild dyspnea with exertion, this dyspnea was severe and persisted. On examination, his pulse rate is 150/min, BP is 100/60 (usually 130/80) mm Hg, respirations are 32/min and labored, and temperature is 38.2°C (100.8°F). He is severely dyspneic, receiving oxygen by face mask. Jugular venous pressure is 8 cm H2O. Chest has crackles bilaterally at the bases with some wheezing. Cardiovascular examination reveals no murmurs, rubs, or gallops. There is 1+ ankle edema bilaterally. Laboratory findings include hemoglobin level of 11.4 g/dL. Arterial blood gases on 40% oxygen by face mask show PaO2 of 85 mm Hg, PaCO2 of 26 mm Hg, pH of 7.30, and oxygen saturation of 97%. Chest radiograph shows lung hyperaeration with some pulmonary vascular redistribution to the upper lobes and moderate cardiomegaly. Previous ECGs have shown sinus rhythm with a complete left bundle-branch block. His present ECG is shown in the Figure below. Carotid sinus massage produces no change in rhythm or rate. A V-lead tracing from an esophageal lead is shown in Figure 63B. The patient receives supplemental oxygen, aerosolized albuterol and ipratropium, and antibiotics (levofloxacin and ceftazidime), but he continues to be severely dyspneic and tachycardic. Which of the following is the most appropriate next step in management of this patient?
a. Diltiazem b. Verapamil c. Lidocaine
d. Metoprolol e. Direct-current cardioversion
62. A 58-year-old man develops cardiac arrest and is resuscitated by a bystander using an automatic external defibrillator (AED) at a shopping center. The AED recorded ventricular fibrillation prior to defibrillation. The patient states that he had a complete workup for dizzy episodes 1 month ago. At another hospital, he was told he had normal results on a stress test, echocardiography, cardiac catheterization, and coronary angiography. Presently, his physical neurologic examination findings are normal. His ECG is shown in the Figure below. Which of the following is the most likely cause of his ventricular fibrillation and cardiac arrest?
a. Occult dilated cardiomyopathy b. Hypertrophic cardiomyopathy c. Myocarditis d. Vasovagal syncope e. Accessory atrioventricular bypass pathway
63. The patient’s preoperative ECG was read as normal and the postoperative ECG shown in the Figure, obtained in a patient after coronary artery bypass grafting, shows:
a. Nonsustained ventricular tachycardia b. Accelerated idioventricular rhythm c. Hyperkalemia d. Left bundle-branch block
Responses and Rationale:
48. Correct Answer: D. Left tube thoracostomy Rationale: This patient has a potential for pneumothorax and has a life-threatening problem. Thus, a tube thoracostomy with large-bore chest tube (size 32 to 40) should be urgently placed and connected to suction through a chest drainage device set at 20 cm H2O. Without mention of shock, although this patient has lost a significant amount of blood, two large-bore IV catheters are adequate at this point. If there were concern of hypotension or decompensation, a large-bore central line introducer should be placed.
49. Correct Answer: D. Beta-blocker
50. Correct Answer: C. Perform repair using an endovascular graft Rationale: This patient has an aortic injury that needs to be addressed because of the adventitial blood. Although an isolated, small intimal flap can be managed with administration of beta-blockers and evaluation of the flap with serial CT scans, this lesion has a potential for rupture. In 2011, for patients with acceptable vital signs and who are controlled with beta-blockers, endovascular repair has a lower morbidity and mortality than an open repair and would be the approach of choice. Increasing dP/dt with pressors
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would only increase the risk of rupture, and heparin in the setting of a fresh intracranial bleed can be catastrophic in leading to further bleeding.
51. Correct Answer: A. Nothing; the indications for the morphine and the dose were both appropriate Rationale: Under the doctrine of double effect, sedatives and analgesics may be administered even if they hasten death, so long as the intention in giving them is to relieve pain and suffering and not to cause death. As former US Supreme Court Chief Justice William Rehnquist wrote in Vacco v. Quill, “It is widely recognized that the provision of pain medication is ethically and professionally acceptable even when the treatment may hasten the patient’s death if the medication is intended to alleviate pain and severe discomfort, not to cause death.” While multiple studies in the literature now show that, on average, titration of sedation and analgesia to patients at the end of life does not hasten their deaths (and may actually prolong their lives), in some cases such as this one, these drugs clearly speed up the dying process. Physicians should know that this does not constitute euthanasia, so long as the doses administered are in a reasonable range for producing comfort, are titrated to behavioral evidence of discomfort and/or suffering, and are administered with the intention of providing comfort, and not to intentionally cause the patient’s death. 52. Correct Answer: D. Follow the research protocol and use the 30% target, since even though you believe this strategy to be inferior, there is no consensus on this issue in the medical community. Rationale: In order for a physician to ethically enroll and treat patients in a clinical trial, a state of clinical equipoise must exist between the various arms of the study. Clinical equipoise is defined as a state of genuine uncertainty within the medical community as a whole, such that if the patient were being treated by different physicians in the community, each of them knowledgeable and competent, they might receive any one of the therapeutic options being studied. Notably, the ethics of clinical research do not require that the clinician be in a state of personal equipoise, such that the clinician is personally undecided about which treatment is best. Indeed, the concept of clinical equipoise encourages a sense of humility among clinicians, such that they recognize that even though they may have strong opinions about which approach is superior, they respect the views of others who disagree and are willing to participate in research that has the potential to answer the question. 53. Correct Answer: C. Control of tachycardia with beta-blockers Rationale: This patient's condition does not warrant antimicrobial prophylaxis. Although gram-negative infections, particularly those caused by Pseudomonas, can be serious problems in burn patients, there is no evidence that prophylactic systemic antibiotics are
helpful, and there is some evidence that they encourage the emergence of resistant organisms and infections from opportunistic organisms such as yeast and mold. Antifungal and antiviral preventive therapy is also not indicated, so options D and E are wrong. Options A and B are wrong: Significant hypermetabolism occurs quickly following major burn injury and persists for weeks. Protein catabolism can lead rapidly to inanition, impaired wound healing, respiratory compromise, and immune dysfunction. High-protein diets (1.5-2 g/kg/day) are recommended for this situation, not high-lipid or highcarbohydrate nutrition. Option C is appropriate: Catecholamine secretion is high following burn injury and is manifested by tachycardia as well as hypermetabolism. Beta blockade can help control heart rate, and may help reduce energy expenditure as well. 54. Correct Answer: E. Flexible sigmoidoscopy or colonoscopy with biopsy Rationale: Diffuse diarrhea in this hospitalized patient could be due to Clostridium difficile, graft-versus-host disease (GVHD), or cytomegalovirus (CMV). Adenovirus has been described to cause enteric disease, but this manifestation is not common. Adenovirus is more likely to cause pneumonitis or hepatic necrosis. A positive result of serum polymerase chain reaction (PCR) testing might well merit treatment with ganciclovir. Since PCR assays are not standardized, there is no absolute level that would demand therapy, but a “high” or “rising” value is ominous for the development of CMV disease and most centers would treat. However, systemic CMV reactivation does not necessarily indicate that the diarrhea is related to CMV disease. Thus, a PCR is not useful for answering the question of etiology of the diarrhea, nor is a buffy coat antigen test for CMV. Thus, options A and B are not the best answers. The buffy coat antigen test is especially problematic when patients have very few neutrophils. Cultures of the stool for CMV are not helpful. Many immunosuppressed patients shed CMV in their oropharyngeal secretions and gastrointestinal tracts without having specific disease that warrants treatment. Such cultures also have little prognostic value. Biopsy of the skin could establish the presence of skin GVHD, but these patients with complications may have more than one problem. Increasing immunosuppression to treat skin GVHD could result in fatal sequelae if the colitis is due to CMV, unless the CMV is adequately diagnosed and treated. The patient does have a low granulocyte count, and endoscopy does therefore carry particular risk for creating bacteremia. However, this patient needs a definitive diagnosis, so colonic inspection via endoscopy is indicated with multiple biopsies looking for evidence of GVHD (eg, characteristic inclusion bodies) or CMV colitis (eg, CMV immunochemistry).
55. Correct Answer: E. No specific therapy Rationale: Hypocalcemia is a common complication of acute illness due to a variety of processes, not of all which are fully understood. In this case, the systemic inflammatory response syndrome and large volume of transfused blood (with citrate) appear to be the most likely cause. The treatment of hypocalcemia aims to limit its toxicity, which is primarily related to hemodynamic instability, cardiac arrhythmias, and seizures. This patient is hemodynamically stable and has a normal cardiac rhythm and QT interval, and unremarkable neurologic examination findings. Because there is no proven value in the treatment of asymptomatic hypocalcemia, she should not be treated, especially as there is experimental evidence that calcium replacement may be detrimental, particularly in the setting of sepsis. Some have argued that patients with severe hypocalcemia (ionized calcium <1 mmol/L or 4 mg/dL) should be treated, even if asymptomatic, though there is no clear agreement about this threshold, and many hospitals use 0.8 mmol/L (3.2 mg/dL) as the “critical value” threshold for reporting. One important side note is that patients with significant hypocalcemia on total calcium levels should have an ionized calcium measurement rather than relying solely on an albumin-adjusted level. 56. Correct Answer: D. Dental abscess Rationale: This is a classic case of Ludwig angina, which is caused most often by an abscess of the second or third mandibular molar. The infection is typically bilateral, involves the submandibular and sublingual areas, spreads quickly without abscess formation or lymphatic involvement, and originates in the floor of the mouth. These patients can have severe toxicity and complications from involvement of adjacent structures, including airway compromise. Surgical drainage of the abscess, broadspectrum antibiotics, and attention to the need for intubation are important for management. The location makes otitis an unlikely cause. Similarly, the location of submandibular involvement with elevation of the tongue and trismus makes facial cellulitis a consideration, but much less likely than Ludwig angina. The term “brawny edema” should suggest Ludwig angina on an examination. No lymph node swelling was noted here, so that lymphadenitis is unlikely, especially with symmetric involvement and the prominent oral manifestations. Epstein-Barr virus, the cause of mononucleosis, can cause severe pharyngitis and remarkable lymphadenitis associated with fever and fatigue. However, Epstein-Barr virus does not cause this acute disease, and does not cause the brawny edema and involvement of the floor of the mouth, as opposed to a pharyngitis. 57. Correct Answer: D. Mixed flora likely including staphylococci and streptococci Rationale: This patient has cavernous sinus thrombophlebitis due to ethmoidal sinusitis. By clinical presentation, this could be orbital cellulitis, but the imaging study rules that out. The microbial etiology is that of acute or chronic sinusitis, ie, mixed flora with
anaerobes, streptococci, and potentially Staphylococcus aureus (including the methicillinresistant type) and gram-negative bacilli. Thus, D is the correct answer. This is treated with an appropriate broad-spectrum regimen pending cultures; anticoagulation is controversial. It is important to recognize suppurative cranial thrombophlebitis. It is defined by the precipitating cause (sinusitis, otitis, facial infection, meningitis, etc) and the venous sinus that is anatomically proximate. Cavernous sinus thrombosis can be caused by facial infections (usually very acute onset) or by sinusitis (subacute) as in this patient. Classic signs of cavernous sinus thrombosis, not all of which are present in every patient, include: 1. Known site of infection 2. Bloodstream invasion 3. Venous obstruction of the retina, conjunctiva, eyelid 4. Paresis of cranial nerves III, IV, and especially VI (these are important clues because of the anatomic association of the cavernous sinus to the cranial nerves that run through them) 5. Meningeal irritation Superior saggital sinus thrombosis presents most often as an extension of meningitis (or occasionally sinusitis) with abnormal mental status, papilledema, and motor defects. Lateral sinus thrombosis is usually an extension of an otic problem and has localizing signs to the ear, including mastoiditis and vertigo. Herpes simplex causes encephalitis with altered mentation, but is not associated with cavernous sinus thrombosis. Mucormycosis could involve the sinuses in patients with some form of immunosuppression or possibly diabetes, but would be very unlikely in this patient with no prior medical history. Bony erosion of the sinus might be a clue in such an immunosuppressed patient. There is no particular reason to suspect Pseudomonas as the sole cause of this syndrome in this patient, and Pseudomonas has no specific association with this cavernous sinus thrombosis, especially in a patient who has not been hospitalized. 58. Correct Answer: E. Vancomycin Rationale: The patient appears to have a severe episode of pneumococcal pneumonia, probably as a complication of influenza. Typically, bacterial pneumonia as a complication of influenza occurs 5-7 days after the influenza onset, when the patient has appeared to be improving. It is usually caused by Streptococcus pneumoniae or Staphylococcus aureus. This patient has multiple risk factors for a poor outcome, including diabetes, chronic obstructive pulmonary disease, severe hypoxemia, and multilobe involvement. Given his severe allergy to cephalosporins (the manifestations are consistent with Stevens-Johnson syndrome), he should not receive a beta-lactam drug, which rules out imipenem. Aztreonam is unique among the beta-lactam drugs for its lack
of cross-reactivity with other beta-lactams; however, it has little activity against pneumococci.
59. Correct Answer: C. Immediately remove the catheter and infuse vancomycin, imipenem, and gentamicin into the new line. Rationale: This patient has a tunnel infection. Such infections are almost never adequately treated by medical therapy alone (ie, antibiotics), and the catheter must be removed. The most likely microbes to cause this infection in a patient who has not been receiving antibiotics would be Staphylococcus epidermidis or S aureus, although many other bacteria or yeasts could be responsible. A broad-spectrum regimen in this neutropenic patient would be appropriate. Ciprofloxacin and gentamicin would not have strong coverage against gram-positive cocci; an initial regimen containing vancomycin would be optimal. Many clinicians elect to infuse antibiotics through each lumen of a catheter that might be infected, as long as the infection is not a tunnel infection and the pathogen is not a fungus or a highly resistant organism. There is no harm in this practice, but there is no evidence that infusing each lumen is helpful. The presence or absence of clot, as defined by angiography, does not contribute to the decision to leave or replace the line in this patient, who has no signs of vascular compromise or septic emboli. 60. Correct Answer: B. Administer no further therapy Rationale: The rhythm strip shows atrial fibrillation at moderate ventricular response (about 120/min) with a long pause after the ninth beat, a short pause following the 10th beat, and then a series of three wide-complexed beats followed by narrow beats similar to the original QRS morphology. The ECG phenomenon shown in this tracing is termed the Ashman phenomenon: the QRS complex timing characterized by a long interval, a short interval, then wide-complexed beats in sequence. This sequence is classical for aberrant conduction of a supraventricular beat. Thus, the three-beat run of a wide-complex tachycardia is actually supraventricular beats being aberrantly conducted (with delayed conduction) down the right bundle because the right bundle has not yet recovered its refractory period from the previous beat. Therefore, these beats are supraventricular in origin, and option B is the correct choice. Identification of Ashman phenomenon is one of the most clinically useful electrocardiographic methods to differentiate supraventricular from ventricular rhythms. The mechanism of this effect is that the duration of the refractory period of one QRS complex is a function of the immediately preceding cycle length: the longer the preceding cycle, the longer the subsequent refractory period. Therefore, the abrupt prolongation (as
in our patient’s tracing) of the immediately preceding cycle can result in aberration (delayed conduction down the right bundle) as part of a long-short cycle sequence. These Ashman beats usually have right bundle morphology, as in our patient (showing an rSR' morphology in lead V1). The Ashman phenomenon is usually seen in atrial fibrillation, where variation in the cycle length is most likely to occur. Since these beats are supraventricular and not ventricular, no antiarrhythmic agents such as lidocaine or amiodarone are indicated. Options C and D are, therefore, incorrect. Also, implanting a cardioverter-defibrillator is not needed, so option A is incorrect. 61. Correct Answer: E. Direct-current cardioversion Rationale: This patient developed atrial flutter with a rapid ventricular response and heart failure. His ECG demonstrates a regular tachycardia at 150/min. The QRS complex is wide because he has a left bundle-branch block, which was previously present. In lead V1, P-wave activity may be seen. However, from the surface ECG, it is not clear whether there is other atrial activity. Carotid sinus massage produces no rhythm change. Adenosine was not used because it may worsen both hypotension and asthma. To diagnose atrial activity, an esophageal V-lead tracing is obtained (see figure). It clearly demonstrates regular atrial activity at a rate of 300/min, making the diagnosis of atrial flutter with 2:1 atrioventricular block.
In this dyspneic, mildly hypotensive patient, electrical cardioversion using 25-50 J with mild sedation is the best choice to convert him back to sinus rhythm. Electrical conversion works in >95% of atrial flutter patients. Alternatives (not listed in this question) to electrical cardioversion include pharmacologic cardioversion with ibutilide (class III antiarrhythmic) or procainamide (class IA). Ibutilide converts about 60-90% of atrial flutter, and procainamide converts about 3050%. Ibutilide produces the side effect of torsade de pointes in about 2% of patients. Another possible therapy in this patient would be insertion of a transvenous pacemaker wire into the right atrium to perform rapid atrial pacing. Rapid atrial pacing converts atrial flutter to sinus rhythm (30%) or atrial fibrillation (70%); the latter rhythm responds better than flutter to atrioventricular nodal blocking agents for rate control. Adenosine, verapamil, and metoprolol block atrioventricular nodal conduction and may slow the ventricular response in atrial flutter, but they will not convert atrial flutter to sinus rhythm. Because of its short half-life, adenosine will only slow the ventricular response for several seconds, which may be useful diagnostically (to reveal flutter waves) but not therapeutically. Verapamil may slow ventricular response but also may produce further hypotension in a borderline hypotensive patient. Metoprolol is contraindicated
because the patient has bronchospasm and chronic obstructive pulmonary disease, which would be worsened by beta-blockade. Lidocaine has no effect on atrial flutter.
62. Correct Answer: E. Accessory atrioventricular bypass pathway Rationale: The patient's ECG demonstrates preexcitation, or the Wolff-Parkinson-White syndrome (WPW), as evidenced by a short PR interval (0.11 s); a delta wave or slurred upstroke particularly prominent in leads V2, V3, I, and II; and ST- and T-wave changes anterolaterally. The so-called inferior “pseudo-infarction” pattern is also seen and is also thought to reflect the preexcitation. Although most patients with WPW are asymptomatic or have conventional supraventricular tachycardias, a small percentage develops atrial fibrillation or atrial flutter with very rapid conduction down the accessory pathway from atrium to ventricle. This may lead to inadequate cardiac output and precipitate ventricular fibrillation. Presumably, a bout of atrial fibrillation preceded the ventricular fibrillation that was seen on the automatic external defibrillator. An electrophysiologic study was performed in this patient, revealing an accessory pathway that was subsequently ablated with radiofrequency energy, thus “curing” him of his life-threatening accessory pathway. Of the other options for this question, dilated or hypertrophic cardiomyopathy should be excluded by a normal echocardiogram and cardiac catheterization. Although myocarditis is a possible cause of sudden death, this patient had a typical pattern of preexcitation and WPW on his ECG. Vasovagal syncope almost never results in cardiac arrest. 63. Correct Answer: A. Nonsustained ventricular tachycardia Rationale: There is a wide-QRS, regular tachycardia, most consistent with ventricular tachycardia. The tachycardia does have a left bundle-branch morphology, and it is possible that the rhythm is sinus with left bundle-branch block; however, this is unlikely since his ECG was read as normal preoperatively. The rate is too fast for an idioventricular rhythm, which is usually less than 110/min.