Sinus node dysfunction primarily affects older patients, especially those with another heart disorder or diabetes. Sinus pause is the temporary cessation of sinus node activity, seen on electrocardiography (ECG) as the disappearance of P waves for seconds to minutes.
The pause often triggers the escape recreation in lower pacemakers, preserving heart rate and function, but long pauses cause dizziness and syncope. In the SA output block, the SA node is depolarized, but the conduction of the impulses to the atrial tissue is affected.
In the first degree SA block, the impulse of the SA node simply slows down and the ECG is normal.
The second degree SA block type I (SA Wenckebach), the impulse conduction slows down before the block, seen in the ECG as a PP interval that decreases progressively until the P wave falls completely, creating a pause and the appearance of pooled beats; The duration of the pause is less than 2 P-P cycles.
In the second grade SA type II block, the impulse conduction is blocked without slowing down beforehand, producing a pause that is a multiple (usually twice) of the P-P interval and the occurrence of pooled beats.
The third degree SA block, the conduction is blocked; P waves are absent, giving the appearance of sinus arrest.
Symptoms and signs
Many patients with sinus node dysfunction are asymptomatic, but depending on the heart rate, all symptoms of bradycardia and tachycardia may occur.
Alterations of the arrhythmia and conduction can be causes of palpitations (feeling of skipped beats or fast or strong beats). The symptoms of hemodynamic compromise (e.g., dyspnea, chest discomfort, presyncope, syncope) or cardiac arrest.
Occasionally, polyuria is the result of the release of the atrial natriuretic peptide during prolonged supraventricular tachycardia (SVT).
Pulse palpation and cardiac auscultation can determine the ventricular frequency and its regularity or irregularity. The jugular venous pulse wave test can help in the diagnosis of AV blockages and tachyarrhythmias.
For example, incomplete AV block, the atria contract intermittently when the AV valves are closed, producing large waves to (cannon) in the jugular venous pulse. Other physical findings of arrhythmias are few.
A slow and irregular pulse suggests the diagnosis of sinus node dysfunction, which is confirmed by ECG, rhythm band or 24-hour continuous ECG recording. Some patients have atrial fibrillation (AF) and underlying sinus node dysfunction manifests only after conversion to sinus rhythm.
The prognosis of sinus node dysfunction is mixed; Without treatment, mortality is approximately 2% / year, mainly as a result of an underlying structural heart disorder. Each year, approximately 5% of patients develop AF with their risks of heart failure and stroke.
The treatment of sinus node dysfunction is pacemaker implantation. The risk of atrial fibrillation is greatly reduced when a physiological pacemaker (atrial or atrial and ventricular) is used instead of a ventricular pacemaker.
Newer dual-chamber pacemakers that minimize ventricular pacing can further reduce the risk of AF. Antiarrhythmic medications can prevent paroxysmal tachyarrhythmias after pacemaker insertion.
Theophylline and hydralazine are options for increasing heart rate in healthy and younger patients who have bradycardia without syncope.