An 82-year-old woman presents with a history of sporadic episodes of light-headedness that began several months earlier and are becoming progressively more frequent. The episodes are unrelated to time of day, degree of activity, or posture. They cause her to feel as if she will lose consciousness, although she has never experienced total syncope.
An 82-year-old woman presents with a history of sporadic episodes of light-headedness that began several months earlier and are becoming progressively more frequent. The episodes are unrelated to time of day, degree of activity, or posture. They cause her to feel as if she will lose consciousness, although she has never experienced total syncope. About half the time, she also experiences palpitations, which resolve in a few minutes. The episodes are not associated with chest pain, dyspnea, nausea, vertigo, or focal neurologic signs.
The patient has mild chronic hypertension that for several years has been well controlled with a low-dose angiotensin-converting enzyme inhibitor. Other long-term medications include a statin for hypercholesterolemia and metformin for mild type 2 diabetes.
This thin woman is in no acute distress. Blood pressure is 115/75 mm Hg; heart rate is 56 beats per minute and regular. No nystagmus or neck bruits are noted. Chest is clear. S1 is soft, but there are no significant murmurs. There are no focal neurologic findings.
LABORATORY AND IMAGING RESULTS
Potassium level is 4.5 mEq/L, and blood glucose level is 129 mg/dL. Hemogram is normal. A routine ECG shows sinus bradycardia of 50 to 56 beats per minute, with no other changes suggestive of acute or remote infarction.
Ambulatory 72-hour Holter monitoring reveals baseline sinus bradycardia with 4 episodes of sinus arrest of more than 3 seconds and several brief episodes of atrial fibrillation with rapid ventricular response. The patient reported symptoms during 2 of these episodes. An echocardiogram shows an ejection fraction of 50%.
Which of the following statements is correct?
The therapy of choice for this patient is placement of an atrial-based pacemaker.
The patient should receive a dual-chamber pacemaker to reduce her 5-year mortality.
Because coronary artery disease is the leading cause of the patient's condition, she should undergo coronary angiography.
Before any pacemaker is placed, a trial of digitalis and a β-blocker should be undertaken.
CORRECT ANSWER: A
This patient has sick sinus syndrome (SSS). SSS encompasses conditions with a variety of causes, all of which result in sinus node dysfunction that renders the atrial rate inappropriate for physiologic need.
Etiology of SSS. Causes are usually categorized as intrinsic (diseases of the sinoatrial [SA] node and conduction system, such as amyloidosis, myo-carditis, sarcoidosis, and hemochromatosis) and extrinsic (conditions that produce adverse effects in an otherwise healthy SA node, such as hyperkalemia or use of digitalis glycosides, β-blockers, most antiarrhythmics, and other pharmacologic agents that suppress the SA node and conduction system). In most patients, including this woman, SSS is idiopathic.
Surprisingly, coronary artery disease that has produced either acute ischemia or chronic ischemia with fibrosis is an uncommon cause of SSS. Thus, choice C is not correct. In any event, there is no evidence on this patient's ECG of recent or remote infarction, and her cardiac history includes neither typical nor atypical angina.
Pathophysiology. Sinus pauses or sinus arrest may result either from failure of impulse formation or from failure of conduction out of the nodal region to the surrounding atrium. Abnormal automaticity and conduction in the atrium can predispose patients to atrial fibrillation and flutter; episodes of atrial fibrillation in combination with episodes of sinus pause or arrest constitute what is known as bradycardia-tachycardia syndrome, a common manifestation of SSS-and the one that is seen in this patient.
Epidemiology and symptoms. SSS occurs most often in older persons (mean age at diagnosis, 68 years).1 Typical symptoms include presyncope or syncope, light-headedness, lethargy, and palpitations. Patients with bradycardia-tachycardia syndrome are at risk for cardiac thromboembolic events, which can be the presenting pathology.1
Diagnosis. There are frequently clues to the diagnosis on an ECG. These include:
However, both definitive diagnosis and selection of appropriate therapy usually require the documentation of sinus node dysfunction and the correlation of dysfunction with symptoms. Typically, Holter monitoring is used to accomplish this.1,2
Treatment. SSS accounts for about 50% of pacemaker placements in the United States.1 This patient fulfills the criteria of the American College of Cardiology/American Heart Association guidelines for pacemaker placement. She has the class I criterion of documented bradycardia, including frequent sinus pauses that result in symptoms.3 Other, less universally accepted critera include:
The key question is which pacemaker to select. Most authorities would agree that atrial-based pacing is preferable to ventricular pacing in patients with SSS.3 Of the 2 types of atrial-based pacemakers-single-chamber atrial and dual-chamber-dual-chamber pacing may have additional benefits in certain subsets of patients. However, these benefits may be more likely to involve quality of life than the hard end point of mortality. Even when compared with ventricular pacing (in a subgroup analysis of one large study of patients with SSS), dual-chamber pacemakers were associated with a slightly lower incidence of atrial fibrillation and somewhat better quality of life-but with no difference in total mortality or stroke.4 In any event, there currently is not a consensus that dual-chamber resynchronization pacing reduces mortality in patients with SSS. Thus, choice B is incorrect and choice A (implantation of either type of atrial-based pacemaker) is correct-at least at this time.
This patient's episodes of light-headedness have been associated with palpitations, and Holter monitoring showed small bursts of atrial fibrillation with rapid ventricular response. However, these episodes of tachyarrhythmia were related to pathologically prolonged sinus arrests and thus were "escape rhythms." An attempt to suppress the atrial tachyarrhythmias with pharmacotherapy alone-especially with SA node-suppressing and atrioventricular conduction-suppressing agents, such as digitalis and b-blockers (choice D)-would introduce a risk of asystole and/or complete heart block. Thus, most authorities would use these agents only in conjunction with a pacemaker.
Outcome of this case. A single-chamber atrial pacemaker was implanted without complication. A low-dose b-blocker was then prescribed. At 3 months, the patient has not had any symptomatic episodes and is tolerating her pacemaker well.
Editor's note: A case of pacemaker malfunction in a woman with sick sinus syndrome is presented in the "ECG Challenge."
Adan V, Crown LA. Diagnosis and treatment of sick sinus syndrome.
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Mangrum JM, DiMarco JP. The evaluation and management of bradycardia.
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Gregoratos G, Abrams J, Epstein AE, et al. ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices. Available at: http://www.acc.org/clinical/guidelines/ pacemaker/index.htm. Accessed February 10, 2006.
Lamas GA, Lee KL, Sweeney MO, et al. Ventricular pacing or dual-chamber pacing for sinus-node dysfunction.
N Engl J Med.