The following cases and commentary, which focus on atrial fibrillation, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 16).
Case 1: Episodes of atrial fibrillation after MI
A 56-year-old man is evaluated in the hospital for paroxysmal episodes of atrial fibrillation. The patient develops increasing shortness of breath during these episodes. Five days ago, he was admitted for an acute myocardial infarction and cardiogenic shock and received a drug-eluting stent in the left anterior descending coronary artery. Medications are lisinopril, digoxin, furosemide, aspirin, clopidogrel, eplerenone, simvastatin, and unfractionated heparin.
On physical examination, the patient is afebrile, blood pressure is 92/65 mm Hg, and pulse rate is 75/min. Oxygen saturation is 95% with 3 L oxygen by nasal cannula. Cardiac examination reveals estimated central venous pressure of 12 cm H2O. Heart sounds are distant and regular. There is a grade 2/6 holosystolic murmur at the cardiac apex. A summation gallop is present. Crackles are auscultated bilaterally in the lower lung fields.
Transthoracic echocardiogram shows left ventricular ejection fraction of 32%.
Which of the following is the most appropriate treatment for this patient's atrial fibrillation?
Case 2: Dizziness, shortness of breath, and afib
A 76-year-old woman is evaluated in the emergency department for dizziness, shortness of breath, and palpitations that began acutely 1 hour ago. She has a history of hypertension and heart failure with preserved ejection fraction. Medications are hydrochlorothiazide, lisinopril, and aspirin.
On physical examination, she is afebrile, blood pressure is 80/60 mm Hg, pulse rate is 155/min, and respiration rate is 30/min. Oxygen saturation is 80% with 40% oxygen by face mask. Cardiac auscultation reveals an irregularly irregular rhythm, tachycardia, and some variability in S1 intensity. Crackles are heard bilaterally one-third up in the lower lung fields.
Electrocardiogram demonstrates atrial fibrillation with a rapid ventricular rate.
Which of the following is the most appropriate acute treatment?
Case 3: Tachycardia and afib in pneumonia patient
An 82-year-old man is intubated and admitted to the intensive care unit (ICU) for sepsis and hypotension from community-acquired pneumonia. According to his wife, the patient had coronary artery bypass graft surgery 2 years ago and has had intermittent atrial fibrillation since that time that is treated with amiodarone, 200 mg/d. He has no history of thyroid abnormalities. Other medications administered in the ICU are vasopressors, ceftriaxone, and azithromycin.
Physical examination shows a sedated, ill-appearing older man who is intubated and cannot respond to questions. Temperature is 37.8 °C (100.0 °F), blood pressure is 90/50 mm Hg (with vasopressors), pulse rate is 110/min and irregular, and respiration rate is 18/min while intubated; BMI is 30. Cardiac examination reveals an irregular rate without murmurs, rubs, or gallops. Examination of the lungs reveals bibasilar crackles and rhonchi. The thyroid gland is not palpable. No cervical lymphadenopathy is noted. No bowel sounds are heard on abdominal examination. The extremities show 2+ peripheral edema. A few scattered ecchymoses are present on the skin.
Laboratory studies show random cortisol 28 µg/dL (773 nmol/L), thyroid-stimulating hormone (TSH) 16 µU/mL (16 mU/L), free thyroxine (T4) 0.6 ng/dL (8 pmol/L), and triiodothyronine (T3) 45 ng/dL (0.7 nmol/L). Thyroid antibodies are pending.
An electrocardiogram shows tachycardia and atrial fibrillation, and a chest radiograph shows bibasilar infiltrates.
Which of the following is the most likely underlying endocrine disorder in this patient?
A. Adrenal insufficiency
B. Euthyroid sick syndrome
D. TSH-secreting pituitary tumor
Case 4: Nausea and confusion in afib patient
A 75-year-old woman is evaluated in the emergency department for a 7-day history of nausea, poor oral intake, and confusion. Medical history is significant for persistent atrial fibrillation and hypertension. Medications are metoprolol, digoxin, and warfarin.
On physical examination, temperature is normal, blood pressure is 105/74 mm Hg, and pulse rate is 49/min. She is oriented to name, but does not know the date or that she is in the emergency department. The remainder of the examination is normal.
Laboratory studies reveal a serum creatinine level of 3.2 mg/dL (283 µmol/L), potassium level of 4.8 meq/L (4.8 mmol/L), and INR of 2.3.
The electrocardiogram is shown.
Which of the following is the most appropriate management?
A. Direct-current cardioversion
B. Insert a temporary pacemaker
C. Measure the digoxin level
D. Start dobutamine
Case 5: Palpitations and tetralogy of Fallot
A 32-year-old man is evaluated in the emergency department for palpitations and dyspnea of 1 week's duration. His medical history is remarkable for tetralogy of Fallot that was repaired in childhood. He has not had recent cardiovascular follow-up.
Blood pressure is 110/70 mm Hg bilaterally, and pulse rate is 100/min. Estimated central venous pressure is 10 cm H2O; jugular pulsations include a large v wave. The apical impulse is displaced. A parasternal impulse is present and there is a single S2. A grade 2/6 holosystolic murmur and a grade 2/6 diastolic murmur are noted at the left sternal border that increase with inspiration. Pulsatile hepatomegaly and lower extremity edema are present.
The electrocardiogram demonstrates atrial fibrillation and right bundle branch block. The chest radiograph demonstrates cardiomegaly and a right aortic arch. Transthoracic echocardiography demonstrates marked right-sided cardiac chamber enlargement and severe pulmonary and tricuspid valve regurgitation. There is no evidence of pulmonary hypertension. The ventricular septum is intact.
The patient is started on intravenous unfractionated heparin therapy and is treated with intravenous diltiazem that controls the heart rate response. Atrial fibrillation persists.
Which of the following is the most appropriate management?
A. Cardioversion, warfarin, and amiodarone
B. Pulmonary valve replacement, tricuspid valve repair, and maze procedure
C. Radiofrequency atrial fibrillation ablation
D. Referral for heart transplantation
Case 6: Periop care with implantable ICD
A 62-year-old woman is awaiting a procedure in the presurgical area. She has a single-chamber implantable cardioverter-defibrillator (ICD) and is about to undergo a hemicolectomy for colon cancer. Medical history is pertinent for ischemic cardiomyopathy, chronic atrial fibrillation, complete heart block, and pacemaker dependence. Medications are aspirin, carvedilol, lisinopril, digoxin, warfarin (withheld), and rosuvastatin. Perioperative anticoagulation is provided with unfractionated heparin.
Which of the following is the most appropriate perioperative management of the patient's ICD?
A. Insert a temporary pacemaker
B. Place a magnet over the ICD
C. Turn shock therapy off and change to asynchronous mode
D. No programming changes needed to ICD
Answers and commentary
Correct answer: A. Amiodarone.
Amiodarone is the best option for managing symptomatic atrial fibrillation in the setting of heart failure. Patients with heart failure and myocardial infarction are at an increased risk of developing atrial fibrillation. Although amiodarone has many extracardiac side effects, it is the most effective agent for preventing atrial fibrillation recurrences, and it is one of the few agents proved safe in patients with heart failure, left ventricular hypertrophy, coronary artery disease, or previous myocardial infarction. In addition, amiodarone has β-blocking properties that can help with rate control. This patient is not currently taking a β-blocker because of the cardiogenic shock, but one should be started as soon as the patient's heart failure is stabilized.
Disopyramide has negative inotropic effects, which can be detrimental to someone with reduced left ventricular function and heart failure, and is contraindicated in this setting.
Dronedarone increases mortality in patients with New York Heart Association class IV heart failure or class II or III heart failure with recent decompensation, such as this patient, and thus should not be used.
Flecainide is contraindicated after a myocardial infarction because it increases the risk of polymorphic ventricular tachycardia.
Like amiodarone, sotalol is a class III antiarrhythmic agent, but because of its more potent β-blocking effects, it should not be used in the setting of acute heart failure.
While not one of the options listed, dofetilide is another medication for prevention of atrial fibrillation in the setting of heart failure, but this agent requires careful monitoring of the QT interval.
- Amiodarone is the best option for managing symptomatic atrial fibrillation in the setting of structural heart disease or heart failure.
Correct answer: C. Cardioversion.
This patient with atrial fibrillation is hemodynamically unstable and should undergo immediate cardioversion. She has hypotension and pulmonary edema in the setting of rapid atrial fibrillation. In patients with heart failure with preserved systolic function, usually due to hypertension, the loss of the atrial “kick” with atrial fibrillation can sometimes lead to severe symptoms. The best treatment in this situation is immediate cardioversion to convert the patient to normal sinus rhythm. Although there is a risk of a thromboembolic event since she is not anticoagulated, she is currently in extremis and is at risk of imminent demise if not aggressively treated. In addition, she acutely became symptomatic 1 hour ago, and while this is not proof that she developed atrial fibrillation very recently, her risk of thromboembolism is low if the atrial fibrillation developed within the previous 48 hours.
Adenosine can be useful for diagnosing a supraventricular tachycardia and can treat atrioventricular node-dependent tachycardias such as atrioventricular nodal reentrant tachycardia, but it is not useful in the treatment of atrial fibrillation.
Amiodarone can convert atrial fibrillation to normal sinus rhythm as well as provide rate control, but immediate treatment is needed and amiodarone may take several hours to work. Oral amiodarone may be a reasonable option for long-term atrial fibrillation prevention in this patient given the severity of her symptoms, especially if she has significant left ventricular hypertrophy.
Metoprolol or diltiazem would slow her heart rate; however, she is hypotensive and these medications could make her blood pressure lower. In addition, she is in active heart failure, and metoprolol or diltiazem could worsen the pulmonary edema.
- Patients with atrial fibrillation who are hemodynamically unstable should undergo immediate cardioversion.
Correct answer: C. Hypothyroidism.
This patient most likely has hypothyroidism, which is strongly suggested by his exceedingly high serum thyroid-stimulating hormone (TSH) level and his low free thyroxine (T4) and total triiodothyronine (T3) levels. Additionally, he has been taking amiodarone, which causes hypothyroidism in approximately 10% of North Americans who take it chronically and hyperthyroidism in approximately 1%. Although the role that this patient's hypothyroidism is playing in his medical condition cannot be determined with certainty, judicious administration of exogenous levothyroxine may help his general metabolism, his ability to respond beneficially to corticosteroids, and his hypotension.
Adrenal insufficiency alone is an unlikely explanation for this patient's laboratory test results and clinical presentation. The patient's random serum cortisol level is not consistent with frank adrenal insufficiency, and his TSH level is elevated. Adrenal insufficiency is rare in critically ill patients but must be considered in those with septic shock, who may develop severe, protracted hypotension that is not responsive to standard therapy. Most of these patients have elevated serum total and free cortisol levels. A recent study showed that hydrocortisone therapy (300 mg/d) given to patients with septic shock did not influence mortality but resulted in a faster reversal of shock. Such therapy is not directed at treating an adrenal dysfunction, but rather at controlling the associated overwhelming inflammatory response.
Nonthyroidal illness can alter the results of thyroid function tests, an effect referred to as euthyroid sick syndrome, which is more common in critically ill patients. The mechanisms by which nonthyroidal illness cause thyroid function test abnormalities are unknown but could relate to the systemic release of multiple cytokines. However, the serum TSH level is not expected to increase to greater than 10 microunits/mL (10 milliunits/L) in a patient with nonthyroidal illness, except perhaps in the recovery phase of a serious illness. This patient is acutely and seriously ill, is not in the recovery phase of a serious illness, and has a TSH level of 16 microunits/mL (16 milliunits/L).
A TSH-secreting pituitary tumor is typically associated with inappropriately elevated serum free T4 and total T3 levels; this patient's levels are low.
- Hypothyroidism is characterized by an elevated thyroid-stimulating hormone level in the setting of low triiodothyronine (T3) and thyroxine (T4) levels and is a common side effect of amiodarone therapy.
Correct answer: C. Measure the digoxin level.
The patient's serum digoxin level should be evaluated. Manifestations of digoxin toxicity are nonspecific, and a high index of suspicion is necessary in patients taking digoxin who present with arrhythmias or constitutional symptoms. The electrocardiogram in this patient demonstrates coarse atrial fibrillation with a regularized ventricular response (in addition to a premature ventricular contraction). These findings indicate complete heart block with a junctional or ventricular escape rhythm, one of the rhythms that can be seen with digoxin toxicity. Nearly every rhythm abnormality can be seen with digoxin toxicity, although the most frequent are sinus arrest, atrial tachycardia, junctional tachycardia, atrioventricular block, premature ventricular contractions, and ventricular tachycardia. Noncardiac signs and symptoms of digoxin toxicity include nausea, anorexia, fatigue, vision abnormalities, and mental status changes. Digoxin is primarily cleared by the kidneys, and, in the setting of acute kidney injury or chronic kidney disease, the risk of toxicity is increased. Taken together, the complete heart block seen on this patient's electrocardiogram, her presenting signs and symptoms, and her increased creatinine level raise the strong possibility of digoxin toxicity.
Cardioversion would be appropriate if the patient had significant symptoms from atrial fibrillation, but that is not true in this case. In addition, cardioversion can increase intracellular calcium and possibly increase ventricular arrhythmias in the setting of digoxin toxicity. If present, some degree of hypocalcemia should be tolerated in these patients, as calcium replacement can also increase intracellular calcium.
In this patient, it is unlikely that the bradycardia is symptomatic given that the heart rate is 49/min with an acceptable blood pressure, and neither a temporary pacemaker nor dobutamine is indicated.
Treatment depends on the severity of symptoms. Digoxin cannot be removed by hemodialysis. If rapid treatment is needed, digoxin-specific Fab antibody fragments can reverse toxicity within 4 hours. Digoxin toxicity is associated with hyperkalemia because the drug interferes with Na+,K+-TPase pumping of potassium into cells. Once the patient is treated with Fab fragments, the sodium-potassium pump is restored and a rapid drop in potassium may occur.
- A regularized ventricular rate in the setting of atrial fibrillation is concerning for complete atrioventricular block with a junctional or ventricular escape and the possibility of digoxin toxicity.
Correct answer: B. Pulmonary valve replacement, tricuspid valve repair, and maze procedure.
This patient should undergo pulmonary valve replacement, tricuspid valve repair, and a maze procedure. The patient presents with symptomatic atrial fibrillation. This is related to long-standing severe pulmonary valve regurgitation and is the most common postoperative problem after tetralogy of Fallot repair due to placement of a patch across the right ventricular outflow tract. Pulmonary valve regurgitation is well tolerated for many years, but it eventually results in right-sided cardiac chamber enlargement, right ventricular dysfunction, tricuspid valve annulus dilatation, and tricuspid regurgitation. Atrial fibrillation is a common initial presenting symptom due to progressive dilatation of the right atrium. Surgical maze procedures to cure atrial fibrillation have been quite successful but require cardiopulmonary bypass and are usually performed in concert with other cardiac surgical procedures.
Cardioversion with anticoagulation and amiodarone is not sufficient therapy for a tetralogy of Fallot patient with severe pulmonary and tricuspid valve regurgitation, severe right-sided cardiac chamber enlargement, and atrial fibrillation. Recurrent atrial fibrillation and progressive right-sided heart failure will occur if the patient does not have the pulmonary and tricuspid valve regurgitation addressed.
Radiofrequency ablation is an effective method of treatment for atrial fibrillation; however, this patient has underlying structural heart disease that has precipitated atrial fibrillation, which must be treated before considering radiofrequency ablation.
Cardiac transplantation is rarely required in a patient with repaired tetralogy of Fallot. Transplantation should be considered only if the patient has progressive severe symptoms of biventricular dysfunction that cannot be appropriately treated with other modalities.
- Patients with repaired tetralogy of Fallot frequently develop pulmonary valve regurgitation, which leads to right-sided heart enlargement, tricuspid valve regurgitation, and atrial fibrillation.
Correct answer: C. Turn shock therapy off and change to asynchronous mode.
In this pacemaker-dependent patient about to undergo surgery, the shock therapy function of the implantable cardioverter-defibrillator (ICD) should be turned off and the pacing function changed to an asynchronous mode. All ICDs have pacemaker capabilities. When a patient with an ICD undergoes surgery, the use of electrocautery affects what the device “thinks” is happening with cardiac activity. When electrocautery is used, the ICD recognizes the rapid electrical signal and will treat the patient as if ventricular fibrillation is occurring, by inhibiting pacing and delivering a high-energy shock. Therefore, for a patient with an ICD who is pacemaker dependent, the best management is to reprogram the device to turn off shock therapy and change to an asynchronous mode such as VOO, which means that ventricular pacing will continue regardless of any native electrical activity or electrocautery.
A temporary pacemaker is not needed because the pacemaker function of the ICD can still be used during the surgery.
In general, placing a magnet over an ICD disables the shock function but does not affect the pacemaker settings. In a patient with a pacemaker (rather than an ICD) and complete heart block, placing a magnet over the device would be an acceptable option because it changes the pacemaker to an asynchronous pacing mode. If a patient with an ICD is not pacemaker dependent, it would be reasonable to place a magnet over the ICD to disable the shock function. In a pacemaker-dependent patient, however, if shock therapy is turned off but no changes are made to the pacemaker, the patient will not receive an ICD shock, but pacing could be inhibited during electrocautery.
After a procedure, it is imperative that the device be reprogrammed to its original settings by a knowledgeable person.
- For a patient with an implantable cardioverter-defibrillator about to undergo surgery, the device should be reprogrammed to turn off shock therapy.