Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content +++ KEY FEATURES +++ ESSENTIALS OF DIAGNOSIS ++ Sinus bradycardia with rate < 50 bpm Sinoatrial exit block second-degree type I: progressively shorter P-P intervals followed by failure of occurrence of a P wave Sinoatrial exit block second-degree type II: pauses in sinus rhythm that are multiples of basic sinus rate First-degree and third-degree sinoatrial exit blocks are difficult to diagnose Sinus arrest or pause: failure of occurrence of P waves at expected times +++ GENERAL CONSIDERATIONS ++ Also referred to as sick sinus syndrome Usually caused by a degenerative process associated with aging Negative chronotropic drugs may cause a similar problem Tachycardia–bradycardia syndrome (bradycardia secondary to sinus node dysfunction coupled with supraventricular arrhythmia such as atrial fibrillation) Differentiation between sinus arrest and high-grade exit block is not possible without direct recordings of sinus node discharge Myocardial infarction (MI), digitalis toxicity, stroke, and excessive vagal tone all may cause this problem +++ CLINICAL PRESENTATION +++ SYMPTOMS AND SIGNS ++ Syncope Lightheadedness Dizziness Symptoms of concomitant illness such as MI +++ PHYSICAL EXAM FINDINGS ++ Bradycardia Irregular heart sounds Other findings depend on precipitating cause +++ DIFFERENTIAL DIAGNOSIS ++ Blocked premature atrial contraction may resemble sinoatrial exit block Marked sinus arrhythmia Conditions with high vagal tone (eg, young athletic individual, cough, micturition) +++ DIAGNOSTIC EVALUATION +++ LABORATORY TESTS ++ Depends on suspected concomitant illness or precipitating causes CBC, basic metabolic panel, thyroid-stimulating hormone +++ ELECTROCARDIOGRAPHY ++ ECG to document rhythm disturbance +++ IMAGING STUDIES ++ None required for the rhythm alone Echocardiogram may be done if the precipitating cause is MI or myocarditis +++ DIAGNOSTIC PROCEDURES ++ Electrophysiologic study rarely indicated +++ TREATMENT +++ CARDIOLOGY REFERRAL ++ If associated with syncope or symptoms of cerebral hypoperfusion, then referral to an electrophysiologist is required +++ HOSPITALIZATION CRITERIA ++ Syncope Usually hospitalized for precipitating cause +++ MEDICATIONS ++ Avoid or eliminate negative chronotropic drugs +++ THERAPEUTIC PROCEDURES ++ Symptomatic patients without reversible cause need a pacemaker Although atrial pacing may be sufficient because most patients subsequently develop atrioventricular nodal disease, dual-chamber pacemakers are recommended +++ SURGERY ++ None required +++ MONITORING ++ ECG monitoring for hospitalized patients +++ DIET AND ACTIVITY ++ General healthy lifestyle Depends on underlying medical illness +++ ONGOING MANAGEMENT +++ HOSPITAL DISCHARGE CRITERIA ++ After pacemaker implantation... GET ACCESS TO THIS RESOURCE Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth Get Free Access Through Your Institution Contact your institution's library to ask if they subscribe to McGraw-Hill Medical Products. Access My Subscription GET ACCESS TO THIS RESOURCE Subscription Options Pay Per View Timed Access to all of AccessCardiology 24 Hour $34.95 (USD) Buy Now 48 Hour $54.95 (USD) Buy Now Best Value AccessCardiology Full Site: One-Year Individual Subscription $595 USD Buy Now View All Subscription Options