ZenToks Publication

Chapter 24

Modern Diagnostic Modalities in Sinus Node Dysfunction

Abstract/Preface

Sinus node dysfunction (SND) is a group of rhythm abnormalities caused by impaired function of the heart’s intrinsic pacemaker, the sinoatrial node. There are following types of sinus node dysfunction: “persistent” sinus bradycardia, chronotropic incompetence, sinoatrial blocks, conversion pauses, tachy-brady syndrome. Chronotropic incompetence is defined as failure to achieve 85% of the age-predicted maximum heart rate. Sinoatrial block is classified as first-degree SA block (undetectable on the surface ECG), type I second-degree SA block (progressive shortening of PP interval prior to the dropped P wave), type II second-degree SA block (intermittent dropped out P waves and QRS complexes, while subsequent P waves and QRS complexes arrive “on time”), third-degree SA-block (pauses lasting more than twice of the subsequent P-P interval). Conversion pauses referred to pauses just after termination of atrial fibrillation/flutter or supraventricular tachycardia. Tachy-brady syndrome is alternating between sinus bradycardia and paroxysmal atrial fibrillation/flutter or supraventricular tachycardia. Diagnostic methods include conventional (surface) ECG, ambulatory ECG monitoring, implantable loop recorder, exercise testing, tilt table test, carotid sinus massage, electrophysiological study. Only symptomatic individuals without any transient cause of SND require permanent pacing. DDD pacemaker is generally preferred over AAI pacemaker, except for young age and limited venous access. In the case of chronotropic incompetence, pacemaker with rate responsive pacing is preferred. In the case of conversion pauses, pacemaker is often implanted, although ablation of atrial fibrillation/flutter or supraventricular tachycardia may be an option.