tachy brady syndrome vs sick sinus syndrome

Angina: often caused by rate-related myocardial ischaemia.Pre-syncope or syncope due to cerebral hypoperfusion.Palpitations during periods of arrhythmia.Typical symptoms of sick sinus syndrome may include: Therefore, the clinical presentation is not specific to sinus node dysfunction. Symptoms and signs arise due to arrhythmias which reduce cardiac output and lead to end-organ hypoperfusion. Sick sinus syndrome often develops over a long time course and many patients are asymptomatic. Medication: particularly negative chronotropes/antiarrhythmics which may unmask subclinical sinus node dysfunction in those with additional risk factors.in patients with renal impairment or in those on medications which cause hyperkalaemia) Electrolyte derangement: especially hyperkalaemia (e.g.Cardiac disease: ischaemic, inflammatory, structural or congenital.Advancing age: the most important risk factor.Risk factors for the development of sick sinus syndrome include: 1,3 The ECG will show a chaotic but bradycardic ventricular rhythm (irregularly irregular) with no evidence of any organised atrial activity in the form of p waves. Atrial fibrillation with a slow ventricular responseĪtrial fibrillation with a slow ventricular response may be seen in the absence of beta-blocker therapy. There are multiple different grades of sinoatrial exit block according to severity. Sinoatrial exit block is similar to atrioventricular heart blocks but instead of affecting the atrioventricular node, here the cause is a failure of the sinoatrial node transitional cells to propagate the impulse across the atria. This is called an escape rhythm and it acts to preserve cardiac output.Įscape rhythms may arise from atrial tissue (atrial escape rhythm) the AVN (junctional escape rhythm) or the ventricular myocytes (ventricular escape rhythm) and give characteristic appearances on the ECG. To prevent asystole and syncopal episodes, the heart may ‘rescue’ a severe sinus bradycardia or sinus arrest by utilising pacemaker tissue that is outside of the SAN to generate a new action potential and allow systole to occur. A period of sinus arrest (no p-waves seen for >3 seconds This is caused by abnormal conduction within the atrial tissue and is the most common manifestation of sick sinus syndrome, affecting at least 50% of patients.įigure 2a and 2b are two ECGs taken from a patient with tachy-brady syndrome.įigure 4. Tachy-brady syndrome is identified by periods of bradycardia or sinus arrest interspersed with periods of tachycardia, most commonly atrial fibrillation. 3 Tachycardia-bradycardia (“tachy-brady”) syndrome Some important examples of arrhythmias include tachycardia-bradycardia syndrome, sinus bradycardia and sinus arrest, sinoatrial exit block and slow atrial fibrillation. transitional cells).Īrrhythmias seen may change over time and are often intermittent. Several different arrhythmias may arise according to the specific dysfunction of the SAN (e.g. For example, there may be a degree of age-related fibrosis of the SA node which is exacerbated by infarction of the SA node after an inferior myocardial infarct, or by the addition of medications such as beta-blockers. The exact cause is often difficult to identify and there may be multifactorial precipitants.

‘Hypers’: hyperkalaemia, hyperthyroidism.

‘Hypos’: hypothermia, hypothyroidism, hypoxia.

Drugs: digoxin, beta-blockers, calcium channel blockers, anti-arrhythmics.

Iatrogenic: for example, damage to the SA node during open-heart surgery.

sarcoidosis, amyloidosis, haemochromatosis)

Idiopathic fibrosis: age-related degeneration of the SAN is the most common cause of sinus node dysfunction.

The causes of sick sinus syndrome can be divided into intrinsic and extrinsic causes. The electrical conduction system of the heart. In sick sinus syndrome, dysfunction of the SAN leads to an atrial rate that is inappropriate for normal requirements. 3įor more information on the cardiac conduction system, see the Geeky Medics article here.

Transitional cells facilitate the propagation of the impulse across the atria (Figure 1). Pacemaker cells have intrinsic pacemaker activity and initiate action potentials at regular intervals. The SAN contains two types of specialised cells. You might also be interested in our medical flashcard collection which contains over 2000 flashcards that cover key medical topics.

Tachy brady syndrome vs sick sinus syndrome