Syncope and Heart Block Case File

Syncope and Heart Block Case File

Eugene C. Toy, MD, Gabriel M. Aisenberg, MD

Case 9

A 72-year-old man is brought to the emergency department after fainting while in church. He stood up to sing a hymn and then fell to the floor. His wife, who witnessed the episode, reports that he was unconscious for approximately 2 or 3 minutes. When he woke up, he was groggy for another minute or two and then seemed himself. No abnormal movements were noted. This had never happened to him before, but his wife does report that for the last several months he has had to curtail activities, such as mowing the lawn, because he becomes weak and feels light-headed. His only medical history is osteoarthritis of the knees, for which he takes acetaminophen. 

On examination, he is alert, talkative, and smiling. He is afebrile, his heart rate is 35 beats per minute (bpm), and his blood pressure is 118/72 mm Hg, which remains unchanged on standing. He has contusions on his face, left arm, and chest wall, but no lacerations. His chest is clear to auscultation, and his heart rhythm is regular but bradycardic with a nondisplaced apical impulse. He has no focal deficits. Laboratory examination shows negative cardiac enzymes and normal blood counts, renal function, and serum electrolyte levels. His rhythm strip is shown in Figure 9–1. 

Figure 9–1. Electrocardiogram. (Reproduced with permission, from Stead LG, Stead SM, Kaufman MS. First Aid for the Medicine Clerkship, 2nd ed. 2006. Copyright © McGraw Hill LLC. All rights reserved.)

▶ What is the most likely diagnosis? 

▶ What is your next step?

ANSWERS TO CASE 9:

Syncope and Heart Block

Summary: A 72-year-old man presents with

• A witnessed syncopal episode, brief and without seizure activity
• Decreased exercise tolerance recently because of weakness and presyncopal symptoms
• Bradycardia, with third-degree atrioventricular (AV) block on electrocardiogram (ECG)

Most likely diagnosis: Syncope as a consequence of third-degree AV block. The arrows in Figure 9–1 point to P waves.

Next step: Placement of a temporary transcutaneous or transvenous pacemaker and evaluation for placement of a permanent pacemaker.

ANALYSIS

Objectives

1. Identify the major causes of syncope and important historical clues to the diagnosis. (EPA 1, 2)
2. Understand the basic evaluation of syncope based on the history. (EPA 1, 3, 10)
3. Recognize vasovagal syncope and carotid sinus hypersensitivity. (EPA 1, 3)
4. Describe diagnosis and management of first-, second-, and third-degree AV block. (EPA 4, 10)

Considerations

There are two major considerations to the management of this patient: recognizing the cause and managing his AV block. He should be evaluated for myocardial infarction and structural cardiac abnormalities. If this evaluation is negative, he may simply have conduction system disease because of aging. Atropine or isoproterenol can be used as a temporary measure when the conduction block is at the level of the AV node. However, in this case the heart rate is less than 40 bpm and the QRS is widened, suggesting that the defect is below the AV node, in the bundles of His. A permanent pacemaker will likely be required.

APPROACH TO:

Syncope

DEFINITIONS

CARDIOGENIC SYNCOPE: Syncope due to the heart’s intrinsic failure to generate sufficient cardiac output.

ORTHOSTATIC SYNCOPE: Syncope due to failure of appropriate systemic vasoconstriction, measured by a 20 mm Hg decrease in systolic pressure and a 10 mm Hg decrease in diastolic pressure.

SYNCOPE: A transient loss of consciousness and postural tone with subsequent spontaneous recovery.

VASOVAGAL SYNCOPE: Fainting due to excessive vagal tone causing impaired autonomic responses such as hypotension without appropriate rise in heart rate or vasomotor tone.

CLINICAL APPROACH

Epidemiology

Syncope is a very common phenomenon, resulting in 3% of emergency center visits and 1% of subsequent hospitalizations. The causes are varied, but they all result in transiently diminished cerebral perfusion, leading to loss of consciousness. The prognosis is quite varied, ranging from a benign episode in an otherwise young, healthy person with a clear precipitating event, such as emotional stress, to a more serious occurrence in an older patient with cardiac disease. In the latter situation, syncope has been referred to as “sudden cardiac death, averted.” For that reason, higher-risk patients routinely undergo hospitalization and sometimes extensive evaluation to determine the cause.

Pathophysiology

Traditionally, the etiologies of syncope have been divided into neurogenic, vasovagal, orthostatic, and cardiogenic—either arrhythmias or outflow obstruction. Table 9–1 lists the most common causes of syncope. By far, the most useful evaluation for diagnosing the cause of syncope is the patient’s history. Because, by definition, the patient was unconscious, the patient may only be able to report preceding and subsequent symptoms, so finding a witness to describe the episode is extremely helpful.

Neurogenic Syncope

Neurogenic syncope results from dysfunction of the autonomic function, which leads to orthostatic hypotension as described in diabetes mellitus, multisystem atrophy, and idiopathic dysautonomia. Other neurologic diseases in the differential diagnosis for syncope include vertebrobasilar insufficiency, seizures, and transient ischemic attacks (TIAs). Vertebrobasilar insufficiency with resultant loss of

consciousness is often discussed yet rarely seen in clinical practice. Seizure episodes are a common cause of transient loss of consciousness, and distinguishing seizure episodes from syncopal episodes based on history often is quite difficult. Loss of consciousness associated with seizure typically lasts longer than 5 minutes, with a prolonged postictal period, whereas patients with syncope usually become reoriented quickly. To further complicate matters, the same lack of cerebral blood flow that produced the loss of consciousness can lead to postsyncopal seizure activity. Seizures are best discussed elsewhere, so our discussion here is confined to syncope. Syncope is essentially never a result of TIAs because syncope reflects global cerebral hypoperfusion, and TIAs are a result of regional ischemia.

Vasovagal Syncope

Vasovagal syncope refers to excessive vagal tone causing impaired autonomic responses, that is, a fall in blood pressure without appropriate rise in heart rate or vasomotor tone. This is, by far, the most common cause of syncope and is the usual cause of a “fainting spell” in an otherwise healthy young person. Episodes often are precipitated by physical or emotional stress or by a painful experience. There is usually a clear precipitating event by history and, often, prodromal symptoms such as nausea, yawning, or diaphoresis. The episodes are brief, lasting seconds to minutes, with a rapid recovery. Syncopal episodes also can be triggered by physiologic activities that increase vagal tone, such as micturition, defecation, or coughing in otherwise healthy people. Vasovagal syncope needs to be differentiated from orthostatic hypotension.

Carotid sinus hypersensitivity is also vagally mediated. This usually occurs in older men, and episodes can be triggered by turning the head to the side, wearing a tight collar, or even shaving the neck over the area. Pressure over one or both carotid sinuses causes excess vagal activity with resultant cardiac slowing and can produce sinus bradycardia, sinus arrest, or even AV block. Less commonly, carotid sinus pressure can induce a fall in arterial pressure without cardiac slowing. When recurrent syncope as a result of bradyarrhythmia occurs, a demand pacemaker is often required.

Orthostatic Hypotension

Patients with orthostatic hypotension typically report symptoms related to positional changes, such as rising from a seated or recumbent position. In orthostatic hypotension, the postural drop in systolic blood pressure by more than 20 mm Hg, or 10 mm Hg diastolic, within 3 minutes of standing, can be demonstrated on examination. This can occur because of hypovolemia (hemorrhage, anemia, diarrhea, or vomiting) or with impaired autonomic response despite adequate circulating blood volume. The most common reason for this autonomic impairment probably is iatrogenic as a result of antihypertensive or other medications, especially in elderly persons. It also can be caused by autonomic insufficiency seen in diabetic neuropathy, in a syndrome of chronic idiopathic orthostatic hypotension in older men, or in other primary neurologic conditions (Parkinsonism or idiopathic dysautonomia). Multiple unwitnessed events (not corroborated) or those that occur only in periods of emotional upset suggest factitious symptoms.

Cardiogenic Syncope

Etiologies of cardiogenic syncope include rhythm disturbances and structural heart abnormalities. Certain structural heart abnormalities will cause obstruction of blood flow to the brain, resulting in syncope. These include aortic stenosis and hypertrophic obstructive cardiomyopathy (HOCM). Syncope due to cardiac outflow obstruction can also occur with cardiac tamponade, massive pulmonary embolism, and severe pulmonary hypertension. Syncope caused by cardiac outflow obstruction typically presents during or immediately after exertion. An echocardiogram often is obtained to elucidate such abnormalities.

Arrhythmias. Arrhythmias, usually bradyarrhythmias, are the most common cardiac cause of syncope. Sinus bradycardia, most often due to degenerative sinoatrial (SA) node dysfunction, and AV node block are bradyarrhythmic causes of syncope. Sick sinus syndrome (SSS) in elderly patients is one of the most common causes for pacemaker placement. Patients with SSS may experience sinus bradycardia or arrest, alternating with a supraventricular tachycardia (SVT), most often atrial fibrillation (tachycardia-bradycardia syndrome). Additionally, prolonged QT interval may induce syncope. This can be acquired due to hypokalemia, hypomagnesemia, or medication use (eg, ondansetron). Also, some patients have congenital prolonged QT syndromes. Tachyarrhythmias such as atrial fibrillation or flutter, SVT, ventricular tachycardia, or ventricular fibrillation are more likely to produce palpitations than syncope. Often, the rhythm abnormality is apparent by routine ECG, or if it occurs paroxysmally, it can be recorded using a 24-hour Holter monitor or an event monitor. Sometimes evaluation requires invasive electrophysiologic studies to assess sinus node or AV node function or to induce supraventricular or ventricular arrhythmias.

Heart Block. There are three types of AV node block, all based on ECG findings.

First-degree AV block is a prolonged PR interval longer than 200 ms (more than one large box in ECG). This is a conduction delay in the AV node. Prognosis is good, and there is usually no need for pacing.

Second-degree AV block comes in two types. Mobitz type I (Wenckebach) is a progressive lengthening of the PR interval, until a dropped beat is produced. The resulting P wave of the dropped beat is not followed by a QRS complex. This phenomenon is caused by abnormal conduction in the AV node and may be the result of an inferior myocardial infarction. Prognosis is good, and there is generally no need for pacing unless the patient is symptomatic (ie, bradycardia, syncope, heart failure, asystole > 3 seconds). On the other hand, Mobitz type II produces dropped beats without lengthening of the PR interval. This is usually caused by a block within the bundle of His. Permanent pacing is often indicated in these patients because the Mobitz type II AV block may later progress to complete heart block.

Third-degree AV block is a complete heart block, where the SA node and AV node fire at independent rates. The atrial rhythm is faster than the ventricular escape rhythm. Permanent pacing is indicated in these patients, especially when associated with symptoms such as exercise intolerance or syncope.

CASE CORRELATION

• See also Case 8 (Atrial Fibrillation/Mitral Stenosis) and Case 36 (Transient Ischemic Attack).

COMPREHENSION QUESTIONS

9.1 An 18-year-old woman is brought to the emergency center because she fainted at a rock concert. She apparently recovered spontaneously, did not exhibit any seizure activity, and has no medical history. Her heart rate is 90 bpm, and blood pressure is 110/70 mm Hg. The neurologic examination is normal. A pregnancy test is negative, and an ECG shows normal sinus rhythm. Which of the following is the most appropriate management?

A. Admit to hospital for cardiac evaluation.

B. Obtain an outpatient echocardiogram.

C. Use 24-hour Holter monitor.

D. Reassure the patient and discharge home.

9.2 A 67-year-old woman has diabetes and mild hypertension. She is noted to have diabetic retinopathy, and she states that she cannot feel her legs. She has recurrent episodes of light-headedness when she gets up in the morning. She comes in now because she fainted this morning. Which of the following is the most likely cause of her syncope?

A. Carotid sinus hypersensitivity

B. Pulmonary embolism

C. Autonomic neuropathy

D. Critical aortic stenosis

9.3 A 74-year-old man with no prior medical problems faints while shaving. He has a quick recovery and has no neurologic deficits. His blood sugar level is normal, and an ECG shows a normal sinus rhythm. Which of the following is the most useful diagnostic test of his probable condition?

A. Carotid massage

B. Echocardiogram

C. Computed tomographic scan of the head

D. Serial cardiac enzymes

9.4 A 49-year-old man is admitted to the intensive care unit with a diagnosis of an inferior myocardial infarction. His heart rate is 35 bpm, and blood pressure is 90/50 mm Hg. His ECG shows a Mobitz type I heart block. Which of the following is the best next step?

A. Atropine

B. Transvenous pacer

C. Lidocaine

D. Observation

ANSWERS

9.1 D. A young patient without a medical history, without seizure activity, and with a history suggestive of emotionally mediated vasovagal syncope has an excellent prognosis. The other answer choices for further evaluation or hospitalization are not needed in this patient.

9.2 C. This diabetic patient has evidence of microvascular disease, including peripheral neuropathy, and likely has autonomic dysfunction. Although this is the most likely etiology, one must be concerned about a possible cardiac issue since the patient has numerous cardiovascular risk factors; an evaluation should include an ECG. Answer A (carotid sinus hypersensitivity) is associated with fainting when wearing a tight collar or turning one’s head. Answer B (pulmonary embolism) is associated with shortness of breath and chest pain. Answer D (critical aortic stenosis) is associated with angina and a harsh systolic ejection murmur.

9.3 A. This patient likely has carotid hypersensitivity; thus, careful carotid massage (after auscultation to ensure no bruits are present) may be performed in an attempt to reproduce the symptoms. Carotid massage in an older patient should be used with caution because it may lead to cerebral ischemia, plaque embolization, or atrial fibrillation. Computed tomography of the head (answer C) would be appropriate if a stroke were suspected, and serial cardiac enzymes (answer D) would be indicated if angina were present or to rule out a myocardial infarction.

9.4 A. This patient’s bradycardia is severe, probably a result of the inferior myocardial infarction. Atropine is the agent of choice in this situation. Mobitz type I block has a good prognosis (vs complete heart block), so transvenous pacing (answer B) is not usually required. Pacing would be required for a Mobitz type II block or complete heart block. Answer C (lidocaine) is usually used for ventricular ectopy such as frequent premature ventricular contractions. Answer D (observation) may be considered in a patient with mild bradycardia (such as a heart rate of 50-60 bpm) and normal BP.

    CLINICAL PEARLS    

▶ Vasovagal syncope is the most common cause of syncope in healthy young people. It often has a precipitating event, prodromal symptoms, and an excellent prognosis.

▶ Carotid sinus hypersensitivity causes bradyarrhythmias in older patients with pressure over the carotid bulb and sometimes requires a pacemaker.

▶ Syncope caused by cardiac outflow obstruction, such as aortic stenosis, occurs during or after exertion.

▶ Syncope is a very common problem, affecting nearly one-third of the adult population at some point, but a specific cause is identified in less than half of cases.

▶ Permanent pacing usually is indicated for symptomatic bradyarrhythmias (eg, sick sinus syndrome), Mobitz II AV block, or third-degree heart block.

REFERENCES

Spragg DD, Tomaselli GF. The bradyarrhythmias: disorders of the atrioventricular node. In: Jameson J, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J, eds. Harrison’s Principles of Internal Medicine. 20th ed. New York, NY: McGraw Hill; 2018.

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