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A variety of different rhythm disturbances may be seen in critically ill patients in an intensive care unit (ICU). These arrhythmias include supraventricular and ventricular tachyarrhythmias, which result from acute illness, electrolyte abnormalities, or drug use. Arrhythmias may also be preexisting and can be worsened by extrinsic factors or metabolic abnormalities in the acute setting. In addition, bradyarrhythmias may occur and may potentially be worsened by drugs or metabolic abnormalities. This chapter will review common types of bradyarrhythmias and tachyarrhythmias seen in the intensive care setting and offer diagnostic approaches and options for acute treatment.
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Bradyarrhythmias. A 78-year-old woman presents to the emergency room and is admitted to the ICU with complaints of dizziness and chest pain over the past week with mild right-side weakness noted on the morning of admission, which resolved prior to arrival at the hospital. Past medical history is remarkable for hypertension, hypothyroidism, paroxysmal atrial fibrillation, peptic ulcer disease, and coronary artery disease. Admission medications include Synthroid 25 μg daily, amiodarone 200 mg daily, metoprolol 50 mg twice daily, aspirin 81 mg daily, warfarin 5 mg daily, and isosorbide 60 mg daily. Vital signs on arrival include a heart rate of 40 bpm, blood pressure of 70/30 mm Hg, oral temperature of 37.1°C (98.7°F), pulse oximetry of 99% on room air, and respiratory rate of 16 breaths/min. The presenting rhythm is shown in Figure 32-1. Physical examination revealed an elderly diaphoretic woman in mild distress. Cardiac examination was remarkable for a nondisplaced point of maximal impulse (PMI) with a bradycardic S1 and S2, which was physiologically split, with a II/VI systolic ejection murmur at the left upper sternal border. Lungs were clear to auscultation and percussion (A&P). Extremities were cool and clammy. Neurologic examination was remarkable for the absence of any weakness or other neurologic deficits.
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What is the presenting rhythm?
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The presenting rhythm is marked sinus bradycardia (Figure 32-1). Sinus bradycardia is defined as a heart rate less than 60 bpm. There is a P wave before every QRS complex with a constant PR interval. In this case, bradycardia may be related to medications, although underlying sinus node dysfunction cannot be excluded.
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How are bradyarrhythmias classified?
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Electrical activation of the heart originates in the sinoatrial (SA) node at a rate of 60 to 100 bpm. If the SA node fails to generate an impulse, a subsidiary pacemaker (the atrioventricular [AV] node) takes over but at a slower rate (typically < 60 bpm). Bradyarrhythmias are due to either failure of impulse formation in the SA node (sinus node dysfunction) or failure of impulse conduction out of the SA node through the AV node and His-Purkinje system. In the intensive care setting, the most common manifestation of sinus node dysfunction is sinus bradycardia, which may be associated with “brady-tachy syndrome.” AV conduction abnormalities include first-degree AV block or delay, which represents slowing of conduction through the AV node and His-Purkinje system, as well as second- and third-degree AV block. The latter includes “dropped beats,” described in more detail later.
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What are potential causes of sinus bradycardia?
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Sinus bradycardia can be a sign that the sinus node itself is dysfunctional. Sinus bradycardia can also be due to increased vagal tone, myocardial ischemia, ...