INDICATIONS

Diagnosis of Arrhythmias

Arrhythmias are common during surgery, and their causes are numerous (see Chapter 78 ). They can be classified by heart rate (HR) or by anatomic origin within the heart. Using heart rate criteria, arrhythmias can be broken down into three categories: bradyarrhythmias (HR < 60 beats/min), tachyarrhythmias (HR > 100 beats/min), and conduction blocks (at any heart rate). The anatomic origin of an arrhythmia can be ventricular, supraventricular, junctional, or elsewhere. Using continuous electromagnetic tape recordings, Bertrand and colleagues^[32] reported an 84% incidence of supraventricular and ventricular arrhythmias in 100 patients during surgery. These arrhythmias were most common during endotracheal intubation or extubation and occurred more frequently in patients with pre-existing cardiac disease (60% versus 37%). Angelini and coworkers^[33] reported that significant postoperative arrhythmias developed in 29 (58%) of 50 patients having valve surgery and in 35 (45%) of 78 patients undergoing coronary revascularization. There are several major factors contributing to the development of perioperative arrhythmias:

1. General anesthetics: Volatile anesthetics, such as halothane or enflurane, produce arrhythmias, probably by a reentrant mechanism. ^[34] Halothane also sensitizes the myocardium to endogenous and exogenous catecholamines. Drugs that block the reuptake of norepinephrine, such as cocaine and ketamine, can facilitate the development of epinephrine-induced arrhythmias (see Chapter 7 ).
2. Local anesthetics: Regional anesthesia by central neuraxial blockade, the goal of spinal or epidural anesthesia, may be associated with a profound albeit transient pharmacologic sympathectomy. This phenomenon may cause parasympathetic nervous system dominance leading to bradyarrhythmias from mild to very severe. This is especially true when the blockade extends to very high thoracic levels (see Chapter 43 ).
3. Abnormal arterial blood gases or electrolytes: Edwards and colleagues^[35] showed that hyperventilation to a PaCO₂ of 30 or 20 mm Hg lowered a normal serum potassium to 3.64 or 3.12 mEq/L, respectively. If serum potassium and total-body potassium concentrations start at low levels, it is possible to decrease the serum potassium to the 2-mEq/L range by hyperventilation and precipitate severe cardiac arrhythmias. Alterations of blood gases or electrolytes may lead to arrhythmias by producing reentrant mechanisms or by altering phase 4 depolarization of conduction fibers. Electrolyte disturbances associated with cardiopulmonary bypass can also lead to intraoperative arrhythmias (see Chapter 46 and Chapter 50 ).
4. Endotracheal intubation: This maneuver may be the most common cause of arrhythmias during surgery and is often associated with hemodynamic disturbances (see Chapter 42 ).

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5. Reflexes: Vagal stimulation may produce sinus bradycardia and may allow ventricular escape mechanisms to occur. It may also produce atrioventricular block or even asystole. In vascular surgery, these reflexes may be related to traction on the peritoneum or to direct pressure on the vagus nerve during carotid surgery (see Chapter 52 ). During jugular vein cannulation, stimulation of the carotid sinus may occur because of pressure from fingers and can lead to bradyarrhythmias. Specific reflexes, such as the oculocardiac reflex, can produce severe bradycardia or asystole.
6. Central nervous system stimulation and dysfunction of the autonomic nervous system: Many electrocardiographic abnormalities can occur in patients with intracranial disease, especially subarchnoid hemorrhage. These abnormalities include changes in QT intervals, development of Q waves, ST-segment changes, and the occurrence of U waves^[36] (see Chapter 53 ). The mechanism of these arrhythmias appears to be related to changes in autonomic nervous system tone.
7. Preexisting cardiac disease: Angelini and coworkers^[33] showed that patients with known cardiac disease have a much higher incidence of arrhythmias during anesthesia than patients without known disease.
8. Central venous cannulation: The insertion of catheters or wires into the central circulation often leads to arrhythmias (see Chapter 32 ).
9. Surgical manipulation of the cardiac structures: Arrhythmias are often observed during insertion of atrial sutures or placement of venous bypass cannulas (see Chapter 50 and Chapter 51 ).
10. Location of surgery: Dental surgery is often associated with arrhythmias, because profound stimulation of sympathetic and parasympathetic nervous systems often occurs.^[37] Junctional rhythms are often seen and may be caused by stimulation of the autonomic nervous system by the fifth cranial nerve.

After an arrhythmia is recognized, it is important to determine whether it produces a hemodynamic disturbance, what type of treatment is required, and how urgently therapy should be instituted. Treatment should be initiated promptly if the arrhythmia results in marked hemodynamic impairment. Treatment should be instituted if the arrhythmia is a precursor of a more severe arrhythmia (e.g., frequent multifocal ventricular premature beats [VPBs] with R-on-T phenomenon can lead to ventricular fibrillation) or the arrhythmia may be detrimental to the patient's underlying cardiac disease (e.g., tachycardia in a patient with mitral stenosis). For the detection of rhythm disturbances, the standard limb lead II is preferred because it usually displays large P waves.