Sinus Arrhythmia, Bradycardia, & Tachycardia

Essentials of Diagnosis

• Wide variation in sinus rate is common in young, healthy individuals and generally not pathologic

• Symptomatic bradycardia especially in the elderly or patients with underlying heart disease may require permanent pacemaker implantation

• Sinus tachycardia usually secondary to another underlying process (ie, fever, pain, anemia, alcohol withdrawal)

• Sick sinus syndrome manifests as sinus bradycardia, pauses, or inadequate heart rate response to physiologic demands (chronotropic incompetence)

General Considerations

• Sinus arrhythmia

  • Defined as an irregularity of the normal heart rate defined as variation in the PP interval of more than 120 milliseconds (ms)

  • Occurs commonly in young, healthy people due to changes in vagal influence on the sinus node during respiration (phasic) or independent of respiration (nonphasic)

• Sinus bradycardia

  • Defined as a heart rate slower than 60 beats/min and may be due to increased vagal influence on the normal sinoatrial pacemaker or organic disease of the sinus node

  • Rates of 50 beats/min or lower (especially during sleep) is a normal finding in healthy individuals, particularly well-trained athletes

  • However, may be an indication of true sinus node pathology in elderly patients and individuals with heart disease

  • When the sinus rate slows severely, the atrial-nodal junction or the nodal-His bundle junction may assume pacemaker activity for the heart, usually at a rate of 35–60 beats/min

• Sinus tachycardia

  • Defined as a heart rate faster than 100 beats/min that is caused by rapid impulse formation from the sinoatrial node

  • It is a normal physiologic response to exercise or other conditions in which catecholamine release is increased

  • The rate infrequently exceeds 160 beats/min but may reach 180 beats/min in young persons

  • The onset and termination are usually gradual, in contrast to paroxysmal supraventricular tachycardia due to reentry

  • In rare instances, otherwise healthy individuals may present with "inappropriate" sinus tachycardia where persistently elevated basal heart rates are not in-line with physiologic demands

• Sick sinus syndrome

  • Defined as a broad diagnosis applied to patients with

    • Sinus arrest

    • Sinoatrial exit block (recognized by a pause equal to a multiple of the underlying PP interval or progressive shortening of the PP interval prior to a pause)

    • Persistent sinus bradycardia

  • May also manifest as chronotropic incompetence

    • Defined as an inappropriate heart rate response to the physiologic demands of exercise or stress

    • An underrecognized cause of poor exercise tolerance

• Sinus arrhythmia (bradycardia or tachycardia): does not cause symptoms in the absence of underlying cardiac disease or other comorbidities

• When severe sinus bradycardia results in low cardiac output, however, patients may present with

  • Weakness

  • Confusion

  • Syncope, if cerebral perfusion is impaired

• Atrial, junctional and ventricular ectopic rhythms are more apt to occur with slow sinus rates

• Sinus tachycardia

  • Most often a normal physiologic response to conditions that require an increase in cardiac output including

    • Fever

    • Pain

    • Anxiety

    • Anemia

    • Heart failure

    • Hypovolemia

    • Thyrotoxicosis

    • Response to many medications

  • Alcohol and alcohol withdrawal are common causes of sinus tachycardia and other supraventricular arrhythmias

  • May cause dyspnea or chest pain due to increased myocardial oxygen demand or reduced coronary artery blood flow in patients with underlying cardiac disease

• Sick sinus syndrome

  • A common presentation in elderly patients is of recurrent supraventricular tachycardias (often atrial fibrillation) accompanied by bradyarrhythmias ("tachy-brady syndrome")

  • The long pauses that often follow the termination of tachycardia cause the associated symptoms

• Symptoms from sinus node dysfunction are nonspecific and may be due to other causes

• Sinus arrhythmia

  • Generally not a pathologic arrhythmia

  • Requires no specific cardiac evaluation

• Sinus bradycardia

  • Often an incidental finding on ECG monitoring, but it can be suspected if the jugular venous pulse shows cannon a waves

  • Often exacerbated by medications (digitalis, calcium channel blockers, beta-blockers, sympatholytic agents, antiarrhythmics)

  • Agents that may be responsible should be withdrawn prior to making the diagnosis

• Prolonged ambulatory monitoring or use of an event recorder may be required to demonstrate symptoms of sinus node dysfunction coincide temporally with arrhythmias

• Asymptomatic patients generally do not require treatment

• Implantation of a permanent pacemaker is usually indicated for symptomatic patients with bradycardia or sick sinus syndrome

• In patients without evidence of AV nodal or bundle branch conduction abnormality, a single chamber atrial pacemaker is reasonable

• Based on the results of several randomized controlled trials, atrial-based pacing (single or dual chamber) is superior to ventricular-only pacing for patients with sinus node dysfunction

• For patients with "tachy-brady syndrome," treatment of the associated tachyarrhythmia is often difficult without first instituting pacing, since beta-blockers, calcium channel blockers, digoxin, and other antiarrhythmic agents may exacerbate the bradycardia

• Sinus tachycardia: Improves or resolves in most cases when underlying cause is treated

• Inappropriate sinus tachycardia

  • Can be treated with a trial of beta-blockers or calcium channel blockers although treatment is often challenging

  • Ivabradine

    • A selective inhibitor of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel responsible for the cardiac pacemaker I(f) 'funny' current, which regulates heart rate in the sinus node

    • Dosage: 5–7.5 mg twice daily

    • Appears to be an effective treatment option

Prognosis

• Sinus tachycardia: Long-term consequences are few

When to Refer

• Patients with symptoms related to bradycardia or tachycardia when reversible etiologies have been excluded