Dysrhythmias

Although atrial fibrillation (AF), the most frequently occurring postoperative dysrhythmia after cardiac surgery, usually develops 2 to 4 days postoperatively, both supraventricular and ventricular dysrhythmias can develop intraoperatively after CPB. Irrespective of the time of onset of dysrhythmias, they may develop for the first time after surgery (the most frequent circumstance) or may represent an exacerbation of ongoing preoperative dysrhythmias. Although no specific intraoperative intervention can definitively attenuate the incidence of postoperative dysrhythmias, certain intraoperative interventions may exert salutary effects. One example is optimizing electrolyte balance, including magnesium homeostasis.

Supraventricular tachycardia, primarily AF, develops in 15% to 40% of cardiac surgery patients.^{[314] [315] [316]} Nonsurgical risk factors include preexisting AF and age. Surgical risk factors include combined valve/coronary surgery, duration of aortic cross-clamping, bicaval cannulation, and pulmonary vein venting.^[317] Although AF is associated with a prolonged hospital stay, an increased incidence of cerebral vascular accidents, and ventricular fibrillation/tachycardia, it is not independently associated with an increase in mortality.^{[314] [315]} These findings are in contrast to postoperative AF in noncardiac surgery patients.^{[318] [319]} The goals of treatment of supraventricular tachycardia are to control the ventricular response rate and convert to sinus rhythm. Any drug that slows atrioventricular conduction helps the former. However, in the immediate post-cross-clamp period, one hesitates to use agents that have negative inotropic effects to that end. Moreover, the onset of action of digoxin is too slow to render it effective monotherapy. Like β-blockers, magnesium probably modifies the ventricular response rate and promotes conversion to sinus rhythm.^[320] Pharmacologic conversion to sinus rhythm is also problematic, either because the agents are relatively ineffective (amiodarone)^[321] or because the treatment may have unacceptable proarrhythmic risks (e.g., increased QT interval). In practice, management of intraoperative AF is influenced by (1) whether it is associated with hemodynamic compromise, (2) the efficacy of electrical cardioversion, (3) the role of pacing, and (4) the recognition that agents with negative inotropy may be better avoided in this specific setting.

The Cox-maze procedure involves multiple surgical incisions in the atria placed such that chaotic atrial conduction is interrupted. It is an effective surgical approach for AF, but it is associated with morbidity. The concept underlying the Cox-maze procedure has been simplified: conduction pathways in the left atrium/pulmonary veins only that are involved in the genesis and maintenance of AF are interrupted. Moreover, the mechanism of tissue injury has been modified and uses epicardial radio-frequency ablation and perhaps other types of energy in the future, for example, microwave irradiation. This approach has the added advantage, when compared with performing the Cox procedure, of decreasing aortic cross-clamp time. In patients with chronic AF and associated mitral valve disease, this technique has been demonstrated to render 78% of patients free of AF at 3 years.^[322] The role of radiofrequency ablation in the treatment of isolated AF (i.e., in the absence of cardiopathy) is less clear. In light of the risks (e.g., pulmonary vein stenosis) of even the seemingly more benign radiofrequency ablation procedure and the relatively benign course of isolated AF, some authors do not recommend its use in these circumstances. ^[323]

Nonsustained ventricular tachycardia is common after cardiac surgery and occurs in 50% of patients, but it does not adversely influence long-term outcome. ^[324] The significance of sustained ventricular fibrillation/tachycardia (VF/VT) after cardiac surgery and its influence on long-term outcome is modified by the presence of other indices of myocardial well-being. Sustained VF/VT is most likely to occur if left ventricular function is depressed,^[317] in association with ischemia, even if it is latent and not clinically apparent, and perhaps also after aortic valve replacement. VF/VT may be especially likely to occur in the latter situation if the aortic valve replacement is performed in the setting of left ventricular dilatation. Long-term management is contingent on appropriate electrophysiologic studies. Intraoperatively, the underlying cause (ischemia) should be treated when possible, electrolyte balance optimized, and pharmacologic therapy initiated when appropriate after cardioversion. Though often used, lidocaine may not be as effective as either bretylium or amiodarone if one extrapolates from the general medical literature.^[325] In out-of-hospital shock-resistant ventricular fibrillation, amiodarone has been demonstrated to be superior to lidocaine (as indicated by higher survival and increased hospital admission rates).^[326] The risk and benefits of any therapy, including amiodarone, should be evaluated before initiating therapy.