Cardiac Rhythm Management Implantable Devices

Sinus Node Dysfunction

Sinus node dysfunction, which broadly encompasses sinus bradycardia, sinus pauses, and sinoatrial blocks, is commonly associated with mitral valve diseases. There are several explanations that account for this association.

• 1.

  Atrial remodeling with fibrosis and scar formation is a common endpoint in untreated mitral valve diseases due to chronic exposure to high pressure and volume in the left atrium. Protein fibril deposition replaces normal myocardial architecture and disrupts cell-cell coupling, such that fibrosis around the sinus node can hamper or block the exit of sinus node impulses or directly disrupt intrinsic pacemaker function.

• 2.

  While it is known that atrial arrhythmias, even those manifesting in paroxysms, are associated with sinus node remodeling and dysfunction, it comes without surprise that chronic mitral valve diseases which are often associated with persistent long-standing atrial fibrillation (AF) are closely linked to sinus node disease. Persistent AF can directly influence sinus node function by affecting ion channels (calcium clock) responsible for its function, leading to reduced sinus node reserve and dysfunction, or contribute to further atrial anatomical remodeling.

• 3.

  Additionally, coexisting tachyarrhythmias requiring treatment may indirectly contribute to further disruption in sinus node function when rate or rhythm controlling medications are administered for their management.

Conduction Disease Following Mitral Valve Surgery

Conduction diseases requiring permanent pacemaker implantation (PPI) following cardiac surgery has been reported to occur in 0.8% to 34% of cases and is more frequent after mitral valve surgery than isolated coronary artery bypass graft (CABG). The association of postoperative conduction disorders with mitral valve surgery is well recognized and presents a significant clinical concern as postoperative conduction disorders requiring permanent pacemaker are associated with increased morbidity, in-hospital length of stay, and cost.

Sinus Node Dysfunction

Sinus node dysfunction is a well-recognized complication of the procedure with a wide reported incidence, ranging from 2% to 21%. While most cases are asymptomatic and transient, a small portion persist and lead to more prominent bradycardia, necessitating implantation of a permanent pacemaker. Aside from an acute increase in sinus node recovery time (SNRT), mitral valve surgery with or without maze has also been shown to attenuate chronotropic response, heart rate variability (HRV), and vagal modulation of sinus node function. Documented mechanisms include injury of the nodal tissue by mechanical trauma due to atrial incisions, surgical interruption of nodal arterial supply, and inadequate atrial preservation during cardiopulmonary bypass.

Atrioventricular Block

Conduction disease involving the atrioventricular node can also occur as a complication of surgical ablation of AF, although at a lower incidence compared to sinus node dysfunction. Additionally, atrioventricular block is usually confined to the early postoperative period, while sinus node dysfunction is dominant in the late postoperative period. The risk of atrial and ventricular (AV) block after mitral valve surgery stems from the proximity of the mitral valve apparatus to the atrioventricular node and bundle of His, where trauma or ischemic injury of the conduction system may occur. As compared to aortic valve surgery, mitral surgery has a lower risk of causing complete and permanent AV block. This comes from the fact that the mitral annulus is relatively distant from the His bundle and the predominance of the compact AV node sits closer to the right side of the heart than the left. The most common cause of AV block in mitral surgery is local tissue edema leading to transient AV node dysfunction.