What is inappropriate sinus tachycardia?
Sinus tachycardia is a form of supraventricular tachycardia originating from the sinus node. It can be secondary to various physiological or pathophysiological stressors. Inappropriate sinus tachycardia (IAST) is a disease characterized by a persistent increase in resting heart rate or sinus rate in otherwise healthy individuals, which is unrelated to, or out of proportion with, the level of physical, emotional, physiological, or pharmacological stress. It has a considerable overlap in clinical presentation and pathogenic mechanisms with postural orthostatic tachycardia syndrome (POTS), in which symptoms and tachycardia predominantly develop in the upright position.
This is a normal sinus rhythm, typically occurring at a rate above 100 beats per minute, when the individual is at rest. This accompanies exercise and anxiety but is a feature of some disorders, e.g., fever, hyperthyroidism, and some cardiac conditions.
Mechanisms of inappropriate sinus tachycardia
The pathological basis of inappropriate sinus tachycardia is not well defined. It is generally believed that the underlying mechanisms are likely to be multifactorial, and significant heterogeneity exists among individuals with this condition. The proposed pathogenic mechanisms can be broadly divided into cardiac and extracardiac. It was recently suggested that the predominant primary pathogenesis is autonomic, and IAST is merely a secondary manifestation.
EPIDEMIOLOGY
The epidemiology of this patient population has not been extensively studied. Once considered a relatively uncommon condition, it has been diagnosed with increasing frequency. The prevalence has been estimated to be 1.16 percent in the general population. The majority of IAST patients are young women. IAST was also recognized as being associated with health professional workers and hypertension.
Clinical approach “Coronary circulation”: What are the characteristics and 9 factors?
Inappropriate sinus tachycardia is an exclusion diagnosis. Examinations and investigations should aim to establish the diagnosis, exclude other supraventricular tachyarrhythmias and secondary causes of sinus tachycardia, and assess the patient’s autonomic function.
The major diagnostic criteria recommended by the ACC/AHA/ESC guidelines include-
- The presence of persistent sinus tachycardia (heart rate >100 bpm) during the day with an excessive rate increase in response to activity and nocturnal normalization of rate, as confirmed by a 24-hour Holter recording.
- Tachycardia and symptoms are non-paroxysmal.
- P-wave morphology and endocardial activation are identical to sinus rhythm.
- Exclusion of secondary causes (hyperthyroidism, pheochromocytoma, physical deconditioning)
History: Key point
- Symptoms – Patients may present with varying degrees of disability. The most common symptom is palpitation; others include lightheadedness, presyncope/syncope, orthostatic intolerance, chest pain, headache, myalgia, dyspnoea, fatigue, abdominal discomfort, anxiety, and depression.
2. Characteristics of palpitation– Gradual onset and termination, non-paroxysmal, triggered by minimal exertion.
3. Concomitant medical history– Absence of pathologies that can give rise to secondary sinus tachycardia, ex-anemia, hyperthyroidism, etc
4. Drug history– Use of drugs that can produce sinus tachycardia (atropine, catecholamines, thyroid medications)
5. Social history– Alcohol consumption, cigarette smoking, caffeine.
Examination
- Regular and increased heart rate
- There is no evidence of structural heart disease.
Investigations of sinus tachycardia
BLOOD TESTS
- ROUTINE AND SCREENING
- Complete blood count
- Fasting blood glucose
- Thyroid function screening
2. ELECTIVE
- Orthostatic plasma noradrenaline
- Urine metanephrines
- 24-hour urinary sodium excretion
ELECTROCARDIOGRAPHY
- Tachycardia may not always be detected
- P wave: The axis and morphology during tachycardia are similar to sinus rhythm.
ECHOCARDIOGRAPHY
- To rule out structural heart diseases and heart failure
- Left ventricular function: mostly normal
24-HOUR HOLTER MONITORING
- Persistent elevated heart rate (>100) during the day
- Excessive increase in response to activity
- Normal or near-normal heart rate during sleep
- Mean heart rate >90
- Symptoms correlate with episodes of tachycardia
Exaggerated heart rate response to minimal exercise: increased to >130 during the first 90 seconds on a standard Bruce protocol.
Diagnostic electrophysiological study
- Indicated when the etiology of tachycardia is uncertain or other supraventricular tachycardias are suspected
- Gradual increase and decrease of heart rate spontaneously or during initiation and termination of isoproterenol infusion
- Not influenced by atrial pacing ( in contrast to re-entry or triggered atrial arrhythmias )
- Surface P wave morphology is similar to that observed during sinus rhythm
- During mapping, the earliest endocardial activation is near the area of the sinus node, with a craniocaudal direction along the crista terminalis. The site of earliest activation shifts superiorly at a higher heart rate and inferiorly at a lower rate.
TILT TABLE TEST
AUTONOMIC FUNCTION ASSESSMENT
Complications
Inappropriate sinus tachycardia is a chronic condition. During a follow-up period of 6 years, there were only minor changes in the heart rate of patients. The prognosis of IAST is benign. Tachycardia-induced cardiomyopathy was reported as a possible but uncommon complication. The majority of patients develop no clinical or echocardiographic evidence of structural heart disease.
MANAGEMENT OR TREATMENT OF – IAST
Management of inappropriate sinus tachycardia is predominantly symptom-driven. Pharmacological treatments are indicated when symptoms are not well controlled by non-pharmacological means. Interventional therapies should be restricted to refractory cases. A heart rate of 80-90 bpm should be aimed for as the target endpoint.
- NON-PHARMACOLOGICAL APPROACHES
- Sleeping with the head of the bed elevated
- Plasma volume expansion
- Compenssive stockings
- Physical counter-manoeuvres
- Resistance training
2. PHARMACOLOGICAL TREATMENTS
Beta-blockers
- As the first-line medical therapy
- A non-selective beta-blocker, such as propranolol (30-160 mg/day) or nadolol (40-160 mg/day), can be started at the lowest dose and titrated upward gradually to the maximum tolerable dose.
- Response can be heterogeneous. Some patients may not respond even at high doses.
Non-dihydropyridine calcium channel blockers
- Verapamil (120-480 mg/day) and diltiazem (180-360 mg/day) may be effective.
- Ivabradine (2.5-7.5 mg bd) may be used to specifically inhibit the pacemaker if current.
- Some individual reports suggest side effects are few but include visual disturbances (phosphenes, blurring), bradyarrythmias, and headache.
INTERVENTIONAL TREATMENTS
- Total ablation of the sinus node was reported to have a high short-term success rate.
- The high risk of the need for a permanent pacemaker makes it less favourable.
- INDICATION- IAST refractory to medical treatment.
- CONTRINDICATION- POTS must be excluded because ablative procedures are shown to worsen symptoms.
- PROGNOSIS- short-term success rate reaches 76-100%. However, the long-term outcome is often incomplete or suboptimal. Most cardiac and extra-cardiac symptoms persist despite a slower heart rate.
- POTENTIAL ADVERSE EFFECTS- pericarditis, phrenic nerve injury, superior vena cava syndrome, need for permanent pacing.
REFERENCES
OXFORD DESK REFERENCE CARDIOLOGY (SOUTH ASIA EDITION)
Hung-Fat Tse | Gregory Y. H. Lip
Andrew J. Stewart Coats