Tachycardia Diagnosis

• Establish that the signs of cardiovascular compromise are rate-related
• Provide immediate synchronized cardioversion for unstable and deteriorating patients
• If the patient is stable, evaluate cardiac rhythm and its possible etiology to determine treatment options
  • Patient history and physical examination should focus on the presence of underlying cardiac diseases, duration of symptoms, past and current medications, and use of implants (cardioverter defibrillator, pacemaker)
  • Identify triggers, alleviating or predisposing factors, onset, nature and frequency of symptoms, and family history of arrhythmias
• Consider referral to a specialist

• Divided into supraventricular and ventricular tachycardia
  • Supraventricular tachycardias (SVTs) include tachycardias with triggering circuits originating from tissues above the level of the ventricles (sinus node, atria, atrioventricular node, His bundle)
    • Paroxysmal SVTs are SVTs with regular rhythm and abrupt onset and termination, and include atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), sinoatrial nodal reentrant tachycardia (SANRT), intraatrial reentrant tachycardia (IART), junctional ectopic tachycardia, and focal atrial tachycardia
    • SVTs with irregular rhythm include atrial fibrillation, atrial flutter, and multifocal atrial tachycardia (MAT)
  • Ventricular tachycardias (VTs) are tachycardias with driving circuits originating from the ventricles or Purkinje fibers

Interpretation of ECG

• Determine if narrow-complex or wide-complex tachycardia
• Determine regularity 
• Identify sinus from non-sinus tachycardia

Narrow-Complex Tachycardia

• HR of >100 beats per minute (bpm) with QRS complex of <0.12 seconds duration
• Ventricles are being activated in a rapid manner suggesting that the driving circuit is that of sinus or supraventricular origin

Wide-Complex Tachycardia

• HR of >100 bpm with QRS complex of ≥0.12 seconds duration
• Aberrant driving circuit originating from ventricular tissues or any site outside the normal conduction system
• Other SVTs can also produce wide-complex tachycardias

Regular Narrow-Complex Tachycardias

Sinus Tachycardia

• Occurs when the sinus node discharge rate is >100 per minute as a physiological response to a variety of stimulus
• A normal physiologic response to increased adrenergic stimulation or decrease in parasympathetic tone producing accelerated sinus node depolarization
  • May result from physiological causes (eg emotion, pain, physical exercise, pregnancy, sexual intercourse), pathological causes (eg anemia, anxiety, dehydration, fever, infection, malignancies, panic attack, pheochromocytoma, etc), caffeine or alcohol intake, drugs (Atropine, beta agonists, Daunorubicin, Dobutamine, Dopamine, Doxorubicin, Epinephrine, methylxanthines, Norepinephrine, amphetamines, cocaine, beta-blocker withdrawal)

• Upper limit of sinus tachycardia is age-related
• Uniform and upright P waves on leads I, II, III and aVL, negative in aVR
• P wave appears before every QRS complex with normal PR intervals

Inappropriate Sinus Tachycardia (IST) (Chronic Nonparoxysmal Sinus Tachycardia)

• Characterized by sinus heart rate of >100 bpm at rest and mean 24-hour heart rate of >90 bpm not caused by underlying diseases such as anemia, fever or hyperthyroidism; it is caused by increased automaticity of the sinus node or an automatic atrial focus near the sinus node resulting from a defect in the sympathetic nerve control of the SA automaticity
• Occurs in persons without apparent heart disease and they may present asymptomatically or with accompanying symptoms such as palpitations, lightheadedness, and fatigue
• P wave axis and morphology similar to sinus rhythm

Postural Orthostatic Tachycardia Syndrome (POTS)

• Characterized by an increase in heart rate of ≥30 bpm when standing for >30 seconds or ≥40 bpm in individuals aged 12-19 years, without orthostatic hypotension defined as >20 mmHg drop in systolic blood pressure
• Predominantly seen in young women without structural heart disease and symptoms such as exercise intolerance, fatigue, lightheadedness and palpitations manifest upon assuming a standing position

Supraventricular Tachycardia (SVT)

• Surpasses the upper limits of sinus tachycardia at rest (>150 bpm) with or without discernible P waves
• Regarded as ventricular in origin if the QRS complex is narrow or if the QRS complex is wide and bundle branch aberrancy is present
• QRS complex identical to sinus rhythm

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

• The most common SVT originating from the AV node with a QRS complex of supraventricular origin
• Characterized by rate of 150-250 bpm and regular rhythm, with the P wave hidden within the QRS complex
• The presence of an atrial premature beat or a premature ventricular stimulation, which causes prolongation of AV nodal conduction time, precipitates AV nodal reentry
  • In typical AVNRT (also known as slow-fast AVNRT), anterograde conduction passes through the slow AV nodal pathway with retrograde conduction occurring in the fast pathway when an atrial complex blocks anterograde conduction in the fast pathway
  • Atypical AVNRT utilizes anterograde conduction through the fast AV nodal pathway with retrograde conduction in the slow pathway, or anterograde conduction via the slow pathway and another slow pathway for retrograde conduction

12-Lead Electrocardiogram (ECG)

• Main test used to detect and diagnose cardiac arrhythmias
• Initial assessment of ECG findings should include rate, rhythm, morphology, axis, and QRS complex duration
  • Normal sinus rhythm is defined as a heart rate of 60-100 bpm, an upright P wave in leads I, II and aVF, and a negative P wave in lead aVR; PR interval of 0.12-0.20 seconds, QRS complex duration of <0.11-0.12 seconds and corrected QT interval (QTc) of ≤0.44-0.45 seconds
  • Normal values may vary between individuals reflecting the differences in age, body habitus, race, sex, heart orientation and physiology
• Differences between tachyarrhythmias usually depend on the presence of P waves and QRS complexes
• A 24-hour ambulatory ECG monitor may be considered when signs and symptoms of arrhythmia occur at least once a day and the abnormal rhythm has not been captured on a resting 12-lead ECG

Other Tests

• The following blood work may be performed to identify other underlying causes of tachycardia
  • Complete blood count (CBC): To check for anemia or infection
  • Basic metabolic panel: To check for electrolyte imbalance
  • B-type natriuretic peptide (BNP): Present in congestive heart failure (CHF)
  • Cardiac enzymes: To determine the presence of myocardial infarction or ischemia
  • Thyroid-stimulating hormone (TSH): Decreased in hyperthyroidism

Echocardiography

• Used to assess ventricular function and detect structural abnormalities
• Indicated in patients highly suspected of having structural cardiac disease and are at increased risk for ventricular arrhythmia (eg history of acute myocardial infarction, dilated right ventricular cardiomyopathies) especially if with positive family history of sudden cardiac death
• Stress echocardiography is recommended for patients at risk of ventricular arrhythmias triggered by ischemia and unable to tolerate exercise, or those with resting ECG abnormalities

Cardiac Magnetic Resonance Imaging (CMR)

• Used to evaluate cardiac structure (chamber volume, left ventricular mass) and ventricular function
• Also used as a guide prior to catheter ablation

Cardiac Computed Tomography (Cardiac CT)

• Alternative imaging test used to evaluate cardiac structures when echocardiography and CMR are not available
• Used to quantify chamber volumes, ejection fraction and mass, and coronary artery calcification
• Myocardial perfusion single-photon emission CT (SPECT) may be considered in patients suspected of having ventricular arrhythmias triggered by ischemia who are unable to tolerate exercise, or if with resting ECG abnormalities