Sinoatrial block, also known as sinoatrial exit block, is a cardiac abnormality in which inability of the heart to conduct impulses from the sinoatrial node leads to a range of arrhythmias and associated symptoms. The diagnosis rests on clinical findings and electrocardiography.
Sinoatrial (SA) block is one of the forms of sinus node dysfunction (SND), and its main pathological entities, bradycardia (and less commonly tachycardia) cause low cardiac output and the appearance of various symptoms   . Patients can be asymptomatic for a prolonged period of time, but the unpredictable and often sudden appearance of dizziness, palpitations, vertigo and syncope without an identifiable cause are main clinical manifestations of SA block  . Angina, dyspnea, fatigue, lethargy and premature mental incapacity may point to initial stages of congestive heart failure, which may occur in the setting of profound arrhythmias . In addition to bradycardia, numerous forms of tachyarrhythmia appear in diseases of the SA node, including SA block, most common entities being supraventricular tachycardias - atrial flutter and atrial fibrillation . In fact, tachycardia seems to be responsible for the onset of palpitations and heart failure, whereas hypotension, syncope, and weakness arise due to bradycardia . Paradoxically, atrial fibrillation can reduce the burden of symptoms in patients with persistent bradycardia, as it directly increases heart rate . In rare cases, cardiac arrest and death have been noted, while other generalised symptoms include slurred speech, irritability, and poor infant feeding.
A thorough patient history and a detailed physical examination are essential steps in making an initial diagnosis of an SA block. Severe bradycardia or other rhythm abnormalities, weak arterial pulses and hypotension can be observed during cardiac auscultation. When such findings are documented, electrocardiography (ECG) studies should be done. On the basis of ECG findings, SA block is classified into four subtypes    :
Because SA blocks present with various ECG manifestations, use of devices that ensure long-term monitoring of cardiac impulse conduction, as well as exercise testing and intracardiac electrophysiologic tests, are recommended when valid clinical criteria exist .