TSRA Content:
Author: Rebekah Boyd, MD
Arrhythmia recognition and management are key skills for the cardiothoracic trainee. Arrhythmias in the post-operative setting are quite common. The most common causes for arrhythmia include hypoxia, electrolyte derangement, and intra-operative injury to the conduction system. When called to assess a post-operative patient with new-onset arrhythmia, it is important to have a systematic way in which to approach the patient. Ensuring adequate oxygenation (both in terms of supplemental oxygen and blood volume) and checking electrolytes (particularly potassium and magnesium) should be the first step. A 12-lead EKG should also always be obtained. Arrhythmias should then be broadly grouped into two categories: stable or unstable, as unstable arrhythmias will require emergent intervention. An arrhythmia should be considered unstable if the patient is hemodynamically compromised, regardless of the type or etiology of the arrhythmia. Hemodynamic instability can manifest as hypotension, altered mental status, chest pain, dyspnea, cool/clammy skin, acute drop in urine output, and other evidence of inadequate perfusion at the tissue level. In the case of an unstable tachyarrhythmia with a pulse, the patient should be immediately cardioverted with synchronized cardioversion starting at a rate of 120 - 200J. If the patient has an unstable bradyarrhythmia with a pulse, administration of atropine followed by transcutaneous or transvenous pacing if no response to atropine is required to restore a heart rate adequate to maintain cardiac output (CO = HR x SV). Once hemodynamic stability is restored, attention can be turned to assessing underlying etiologies (eg electrolyte derangement, pneumothorax, hypoxemia, etc.) and developing an ongoing management plan.
In this section we will go over some of the most common arrhythmias you will encounter as a cardiothoracic trainee with the caveat that this is not an exhaustive list. These can largely be grouped into supraventricular tachyarrhythmias, bradyarrhythmias, and ventricular arrhythmias.
Supraventricular tachyarrhythmias
Atrial fibrillation:
This is one of the most commonly encountered post-operative arrhythmias and is characterized by an “irregularly irregular” heart rate with no discernible P waves on EKG and an erratic ventricular response. If the ventricular rate is > 150, it is deemed atrial fibrillation with rapid ventricular response (RVR). If a patient with new-onset atrial fibrillation is hemodynamically unstable, synchronized cardioversion is required. In patients with stable new-onset atrial fibrillation, chemical cardioversion with medications can be attempted. Amiodarone is typically used for this purpose with a loading bolus of 150 mg over 10 minutes followed by an amiodarone infusion at 1 mg/min infusion for 6 hours followed by a 0.5 mg/min infusion for 18 hours after which the patient can be transitioned to oral amiodarone. In addition to the potential for conversion to sinus rhythm, amiodarone will also provide rate control – it should be noted that bradycardia can result, and the infusion should be paused if the ventricular HR drops below 50-55. Conversion should not be attempted in patients who present with atrial fibrillation with unknown onset who have not been anticoagulated as there may be thrombus within the left atrial appendage or left ventricle that can be embolized with restoration of sinus rhythm. In these patients, rate control can be achieved with use of IV metoprolol or diltiazem. It is important to note that patients with uncontrolled atrial fibrillation with RVR may have hypotension due to loss of filling time and that, counterintuitively, giving beta- or calcium-channel blockade will lead to improvement in blood pressure as rate slows. Once rate control is obtained, patients may be transitioned to oral metoprolol or diltiazem for maintenance. It is also important to note that atrial fibrillation is common following intraoperative ablation and is most common in the first six months following the procedure.
Atrial flutter:
This arrhythmia occurs secondary to a reentrant circuit around the tricuspid annulus; it is characterized by saw-tooth flutter P waves on the EKG. Unlike atrial fibrillation, atrial flutter can be a regular rhythm with a ratio of flutter P waves to QRS complexes. In instances of a 2:1 flutter ratio, the ventricular rate will be ~150 and very regular. It is not possible to visualize flutter waves at that rate, so suspicion should be high for a 2:1 flutter if faced with a patient with a regular tachyarrhythmia at 150. Adenosine 6 mg IV rapid push can be given to generate a pause after which flutter waves can be visualized – please note, the patient should have cardioversion pads placed and be attached to a 12-lead EKG machine prior to pushing adenosine. Atrial flutter is notoriously difficult to convert with adenosine and may require cardioversion if hemodynamically unstable and ultimately ablation of the reentrant circuit. Rate control with beta- or non-dihydropyridine calcium-channel blockade can be achieved if needed.
Multifocal atrial tachycardia:
Characterized by at least 3 P waves with differing morphologies on EKG, this arrhythmia represents multiple different foci of atrial activation. It is often secondary to an underlying pulmonary etiology such as chronic obstructive pulmonary disease and is exacerbated by hypoxia. Treatment is supplemental oxygen and rate control with beta- or non-dihydropyridine calcium-channel blockade.
Atrioventricular Nodal Reentrant Tachycardia (AVNRT):
The most common cause of supraventricular tachycardia, this arrhythmia is caused by re-entry at or near the AV node. Patients present with HR typically between 140-280. If the patient is unstable, synchronized cardioversion should be attempted. If the patient is hemodynamically stable, vagal maneuvers (blowing into a syringe, cold water/ice to the face) can be attempted. If unsuccessful, adenosine 6 mg IV push can be attempted - please note, the patient should have cardioversion pads placed and be attached to a 12-lead EKG machine prior to pushing adenosine. This can be repeated up to three times or a maximum dose of 18 mg. If adenosine fails to terminate the AVNRT, beta-blockade or non-dihydropyridine calcium channel blockers can be attempted. Patients with refractory or paroxysmal AVNRT may ultimately require ablation of the accessory pathway.
Atrioventricular Reentrant Tachycardia (AVRT) – Wolff-Parkinson-White:
Typically associated with a diagnosis of Wolff-Parkinson-White (WPW) syndrome, this arrhythmia is caused by an atrioventricular accessory pathway and can be classified as orthodromic (narrow QRS complex, antegrade conduction through AV node, ~95% of cases) or antidromic (wide QRS complex, antegrade conduction over accessory pathway). A classic EKG will show extremely high ventricular rates approaching 250 or greater with inverted P waves. Orthodromic AVRT can be treated similarly to AVNRT with adenosine and verapamil as first-line agents and beta-blockade as second-line agents. Antidromic AVRT, however, adenosine, verapamil, and beta-blockers should be avoided, and procainamide is the drug of choice. In some cases, patients with WPW may develop atrial fibrillation with preexcitation – similarly to antidromic AVRT, it is important to know that giving beta-blockade or non-dihydropyridine calcium channel blockers is CONTRAINDICATED in these patients as this will lead to blockade of the antegrade normal conduction system and preferentially cause impulses to travel through the accessory pathway, leading to hemodynamic instability. Procainamide and ibutilide are acceptable options for treatment of atrial fibrillation with preexcitation.
Bradyarrhythmias
Atrioventricular Blocks:
AV blocks are the most common arrhythmias generated at the AV node. A first-degree AV block refers to a prolonged PR interval > 0.2 seconds. This is typically a benign arrhythmia identified incidentally on EKG and does not require treatment. Second degree AV blocks can be divided into type 1 and type 2. A type 1 second-degree AV block is also known as a Mobitz Type 1 or a Wenckebach AV block. In this block, the PR interval gets progressively longer with consecutive beats until a QRS complex is dropped. This block is also typically benign and does not usually require treatment, although it will likely respond to atropine if needed. A type 2 second-degree AV block is also known as a Mobitz Type 2 and is characterized by random dropping of QRS complexes after p-waves with no discernible pattern. This block should be considered more serious than a type 1 second-degree block as it is more likely to progress to complete heart block or cardiac arrest and consideration should be given to starting transvenous pacing when the block is identified until a permanent pacemaker can be placed. A third degree, or complete, heart block is characterized by total disassociation between the atria and ventricles and will present with p waves marching out at regular intervals and QRS complexes at regular intervals in no relation with each other (ventricular response rate usually low ~30-50). Patients in complete heart block are considered unstable and require immediate intervention to include transcutaneous or transvenous pacing in preparation for permanent pacemaker. Atropine may be given but may not work as its mechanism of action is primarily at the AV node.
Sinus Node Dysfunction:
Commonly seen in elderly patients and attributed to senescence of the SA node. This can be characterized by sinus pause or arrest with p waves not originating at regular intervals. This will require pacemaker implantation and can be bridged with transvenous or transcutaneous pacing if the patient is unstable.
Ventricular arrhythmias:
Ventricular arrhythmias include ventricular tachycardia (with a pulse or pulseless) and ventricular fibrillation. Management of pulseless ventricular tachycardia and ventricular fibrillation is covered in the TSRA primer section on cardiac arrest. Ventricular tachycardia with a pulse should be treated with synchronized cardioversion if hemodynamically unstable. If the ventricular tachycardia is refractory to shock, amiodarone, procainamide, and sotalol can be used.