Assessment of the Patient With a Cardiac Arrhythmia

Introduction

Evaluation of the patient suspected to have a cardiac arrhythmia is a frequent reason for referral to a cardiologist. In patients presenting with an acute, ongoing arrhythmia, the role of the cardiologist is to quickly gather and synthesize the necessary data to arrive at a diagnosis and form both a short-term and long-term treatment plan. More commonly, in the otherwise stable patient, sinus rhythm is present. Assessment of the risk for potentially serious or even fatal arrhythmia that warrants prompt evaluation or treatment as opposed to a more benign condition guides initial evaluation and management. Serious arrhythmias are usually associated with underlying heart disease. Hence the initial evaluation also focuses on identification of other cardiac abnormalities. Potentially fatal arrhythmias do occur in patients with structurally normal hearts who have genetic ion channel diseases. In other diseases, minimal structural abnormalities may be present. Often, the sinus rhythm electrocardiogram (ECG) provides critical clues. Symptoms and signs of cardiac arrhythmia can be vague or even absent. On the contrary, even when patients describe symptoms compatible with arrhythmia, the cause may be unrelated to an arrhythmia. Palpitations are associated with sinus rhythm in up to one-third of cases. As such, the role of the health care provider is likened to that of a detective; history, clues, and objective evidence must be gathered and carefully correlated to arrive at the correct diagnosis. This chapter presents a general approach to these situations.

Acute Tachycardia

Assessment of Hemodynamic Stability

For a patient presenting with an acute arrhythmia, initial assessment of hemodynamic stability is critical. In addition to blood pressure, evaluation of the patient’s overall appearance, with pallor, labored breathing, diaphoresis, anxiety or fear, as well as decreased level of consciousness, chest pain, and hypoxia, are all signs of potential hemodynamic compromise that trigger urgent management.

Diagnostic Evaluation

In the hemodynamically unstable patient, initial assessment seeks to determine whether the rhythm is sinus tachycardia or chronic atrial fibrillation (AF) with a fast ventricular rate in response to an underlying acute illness versus a pathologic tachycardia that requires directed intervention. Treatment of the acute arrhythmia takes precedent over all diagnostic maneuvers that are not necessary to make a treatment decision. In this setting, telemetry data, physical examination, and vital signs are often the extent of the diagnostic information available. Advanced cardiac life support algorithms should be followed. ^,

In the hemodynamically stable patient, it is important to obtain a 12-lead ECG because arrhythmias can be transient and making an accurate diagnosis is the first step to effective long-term care. If a diagnostic maneuver is to be performed, such as carotid sinus massage or adenosine administration, continuous ECG recordings (preferably a 12-lead ECG when available) should be captured if possible.

Physical Examination

In addition to assessing the hemodynamic impact of the arrhythmia, examination during an arrhythmia can also be useful for assessing the atrioventricular (AV) relationship. In the jugular venous pulse, regular, rapid cannon A waves (Frog sign) are associated with typical AV nodal reentrant tachycardia (AVNRT), which produces near simultaneous ventricular and atrial contraction, resulting in atrial systole against a closed tricuspid valve. Patients may report that they feel this sensation as well. On the contrary, irregular cannon A waves can be a physical sign of AV dissociation, raising the likelihood of ventricular tachycardia (VT) in the setting of tachyarrhythmia and complete AV block for bradyarrhythmia.

Vagal Maneuvers

Maneuvers that increase vagal tone and potentiate AV nodal slowing or AV block have both diagnostic and therapeutic value. Classically, tachycardia mechanisms involving the AV node, such as AVNRT or AV reentry using an accessory pathway (AVRT), will terminate with AV block, whereas non-AV node–dependent tachycardias, such as focal atrial tachycardia and atrial flutter, transiently slow with greater exposure to nonconducted p waves. In some instances, however, the non-AV node–dependent tachycardias (ectopic atrial tachycardia and, rarely, idiopathic VT) will terminate. The observation of AV block with continuation of the arrhythmia has the most diagnostic reliability, effectively ruling out AVRT and AVNRT.

Vagotonic maneuvers include carotid sinus massage (the clinician should carefully auscultate for carotid bruits before performing this maneuver and consider alternatives in an elderly patient to avoid rupturing or dislodging an atherosclerotic plaque), the Valsalva maneuver, or placement of ice packs over the face/eyes (dive reflex). The Valsalva maneuver is performed with the patient in the supine position and instructed to exhale vigorously against a closed glottis for 10 to 15 seconds, followed by abrupt release and resumption of normal breathing. The initial high intrathoracic pressure generated is transmitted to the great vessels, increasing BP and decreasing venous return. As this phase is maintained, stroke volume falls, eliciting peripheral vasoconstriction. With release, venous return increases and stroke volume increases, briskly ejecting into a vasoconstricted periphery, producing an increase in BP that elicits a reflex increase in vagal tone. This response can be augmented by passively elevating the legs to about 45 degrees after release, further increasing venous return (the modified Valsalva maneuver).

Adenosine

The administration of adenosine leads to rapid and transient AV nodal block when given at sufficient doses. Adenosine may be administered as a diagnostic and therapeutic maneuver during regular narrow complex tachycardias. It should absolutely not be administered to a patient with an irregular wide complex tachycardia (specifically preexcited AF) because it may lead to a more rapid ventricular rhythm and can potentially precipitate cardiac arrest. Resuscitation equipment should be available when giving adenosine because it can precipitate AF, which could have a dangerously rapid response if an accessory pathway capable of anterograde conduction is present. Adenosine should be avoided in patients with a history of heart transplantation because they have adenosine hypersensitivity; profound bradycardia and hypotension may occur. Similar to the response to vagal maneuvers, AV nodal–dependent tachycardias would be expected to terminate with adenosine administration, although some non-AV nodal–dependent rhythms, such as focal atrial tachycardia, and even some forms of VT also terminate with adenosine. AV block with continuation of arrhythmia establishes a non-AV nodal–dependent arrhythmia. Adenosine has a half-life of less than 10 seconds. If arrhythmia termination is followed by immediate reinitiation, a longer acting AV nodal blocking agent can be useful, such as IV administration of verapamil, diltiazem, or a β-adrenergic blocker.

Assessment of the Patient with Suspected Arrhythmia

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