Sick Sinus Syndrome (SSS)

Confirm the diagnosis and the device - SSS requires symptoms and ECG findings together, so review the 12-lead ECG plus the Holter or event-monitor tracing that correlated them. Most symptomatic patients end up paced: interrogate the pacemaker for mode, underlying rhythm, and pacing dependence before induction.

Chronotropic incompetence - Defined on treadmill testing as failing to reach 80% of maximal predicted heart rate. These patients cannot raise cardiac output in response to surgical stress or vasodilation, so plan a chronotropic backup rather than waiting for a reflex that will not come.

Hunt the reversible causes - Before blaming the node, look at the medication list (beta-blockers, non-dihydropyridine calcium channel blockers, digoxin, antiarrhythmics, acetylcholinesterase inhibitors), TSH, potassium and calcium, and the patient's oxygenation and temperature. Each depresses SA node function and each is fixable.

Reversal agents depress the node - Acetylcholinesterase inhibitors are a documented cause of sinus node depression. Pair neostigmine with its antimuscarinic, watch the rate closely, and have a plan ready if the bradycardia does not respond.

Vagal load is the intraoperative trigger - Laryngoscopy, peritoneal traction, and carotid manipulation raise vagal tone, which alone can produce sinus arrest in this node. A sinus pause over 3 seconds after carotid sinus massage is itself suggestive of sinus node dysfunction.

Unstable bradycardia - Follow the ACLS bradycardia algorithm: atropine 0.5 mg IV, repeated every 3 to 5 minutes to a total of 3 mg. Atropine must not delay transcutaneous pacing or a chronotropic infusion (epinephrine, dopamine, or isoproterenol). Transcutaneous pacing is a bridge to transvenous pacing, not a destination.

Tachy-brady is the trap - The syncope comes from the prolonged pause when the atrial tachyarrhythmia terminates, not from the tachycardia itself. Rate-controlling an intraoperative AF episode can unmask exactly that pause.

Stroke risk and anticoagulation - Paroxysmal AF or flutter in SSS carries a real thromboembolic burden and these patients are frequently anticoagulated. Confirm the agent and last dose, and take neuraxial timing from the current ASRA guidance rather than a remembered interval.

Rate is fixed, so preload carries the output - When the node cannot speed up, cardiac output rides on stroke volume. Treat hypotension with volume and a vasopressor rather than waiting for a compensatory tachycardia.

Sympatholytics and antiarrhythmics - Class I through IV antiarrhythmics, digoxin, lithium, and sympatholytic drugs all depress SA node pacing; anticipate an exaggerated bradycardic response.

The risk is hypoperfusion, not sudden death - Sudden cardiac death risk in SSS is low whether or not a pacemaker is placed. The perioperative problem is CNS, renal, and coronary hypoperfusion during pauses.

Sick sinus syndrome (SSS), also called sinus node dysfunction, is the failure of the sinoatrial node to generate or transmit an impulse fast enough to meet demand. The usual cause is age-related fibrous replacement of nodal tissue, which frequently extends into the AV node. Infiltrative disease (amyloidosis, sarcoidosis, hemochromatosis, scleroderma), cardiothoracic surgery, and narrowing of the sinoatrial nodal artery - off the right coronary about 60% of the time and the circumflex 40% - do the same.

External depressors matter just as much in the OR: high vagal tone, hypothyroidism, hypoxia, hypothermia, hyperkalemia or hypokalemia, raised intracranial pressure, and beta-blockers, non-dihydropyridine calcium channel blockers, digoxin, antiarrhythmics, and acetylcholinesterase inhibitors. The result is sinus bradycardia, pauses or arrest, exit block, or chronotropic incompetence - and when atrial tachyarrhythmia alternates with bradycardia, tachy-brady syndrome.