Cardiac dysrhythmias are a common occurrence in the perioperative period. The Multicenter Study of General Anesthesia reported a 70.2% incidence of tachycardia, bradycardia, and dysrhythmias in patients undergoing general anesthesia. Due to the high incidence and potential deleterious effects of dysrhythmias, prompt recognition and management is of utmost importance.
The sinoatrial node is the physiologic pacemaker located in the right atrium. The signals that arise in the SA node stimulate the atria to contract and travel to the atrioventricular node, which is an area of specialized tissue between the atria and ventricles which conducts the signal to the ventricles. The AV node is a critical delay in the conduction system and forms much of the PR segment of the ECG. The impulse travels from the AV node to the Bundle of His, which splits into the left and right bundle branches in the inter ventricular septum. Each bundle branch produces numerous Purkinje fibers, which stimulate the myocardium to contract. Arrhythmias can arise at any point along the conduction cycle. They can be divided into supraventricular arrhythmias, or those that originate at or above the AV node, and ventricular arrhythmias, or those at originate in the ventricles.
Supraventricular dysrhythmias are dysrhythmias that arise from above the Bundle of His. They can be further divided based on the foci of origin, including the sinoatrial node, atria, and AV node. Since conduction through the ventricles is normal in these patients, supraventricular arrhythmias have narrow QRS complexes on ECG.
Sinoatrial and Atrial Foci
Sinus arrhythmia—Sinus arrhythmia is defined as a rhythm that arises from the sinoatrial node with a normal heart rate (60–100 beats per minute [bpm]) but irregularly spaced R–R intervals (Figure 68-1). These intervals alter with respiration due to the Bainbridge reflex. Also referred to as the atrial reflex, the Bainbridge reflex is an increase in heart rate due to an increase in central venous pressure as a result of the increased blood volume detected by baroreceptors in the atria. Sinus arrhythmia is typically a normal finding and no treatment is necessary.
Sinus bradycardia—Sinus bradycardia is defined as rhythm that arises from the senatorial node with a heart rate of less than 60 bpm or 50 bpm in patients on chronic beta blocker therapy (Figure 68-2). The pacemaker site is in the sinus node but the pacing rate is slower than normal. It accounts for 11% of intraoperative arrhythmias and is generally asymptomatic. However, patients with a heart of rate less than 40 bpm can be symptomatic. Bradycardia can be a normal finding in young athletes. However, it can also be due to spinal anesthesia (T1–T4 sympathectomy), vagal stimulation, hypothermia, hypothyroidism, hypoxia, myocardial infarction, increased intracranial pressure, or medications. Usually, no treatment is necessary. However, if hemodynamic instability occurs or the patient is symptomatic, treatment is ...