tachycardia
TACHYCARDIA

Tachycardia or tachyarrhythmia is used to describe the presence of cardiac rhythm abnormality in states when cardiac rate is increased to >100 bpm.

Divided into supraventricular and ventricular tachycardia.

Signs and symptoms related to rapid heart rate are altered sensorium, angina, shortness of breath, myocardial infarction, hypotension and other signs of shock (eg cold clammy skin, low urine output), heart failure or pulmonary congestion.

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)
  • Consider referral to a specialist

Classification

  • 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 are tachycardias with driving circuits originating from the ventricles or Purkinje fibers

Evaluation of Cardiac Rhythm

Interpretation of ECG

  • Identify sinus from non-sinus tachycardia
  • Determine regularity 
  • Determine if narrow-complex or wide-complex 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 infection, anemia, dehydration, pheochromocytoma, caffeine intake, drugs (beta agonists, amphetamines, cocaine, beta-blocker withdrawal)
  • Upper limit of sinus tachycardia is age-related
  • Uniform and upright P waves on leads I, II and aVF
  • P wave appears before every QRS complex with constant 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 similar to sinus rhythm

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 atrioventricular (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, 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

Atrioventricular Reentrant (or Reciprocating) Tachycardia (AVRT) Associated with an Accessory Pathway

  • A reentrant tachycardia utilizing the atrioventricular accessory pathway for conduction of impulses
  • Reentry of impulses may be concealed during retrograde excitation, producing an AV reciprocating tachycardia
  • Types of atrioventricular reentrant tachycardia (AVRT) include orthodromic and antidromic atrioventricular reentrant tachycardia (AVRT)
    • Orthodromic AVRT, the more common type of AVRT (90-95%) especially in patients with Wolff-Parkinson-White (WPW) syndrome, is characterized by anterograde conduction of atrial premature beats via the atrioventricular nodal pathway and retrograde conduction using the accessory pathway, and vice versa for ventricular premature beats
    • Antidromic AVRT uses the accessory pathway to direct reentrant impulse anterogradely from the atrium to the ventricles, and vice versa via the atrioventricular node to direct impulse in the retrograde direction
  • Depression in the ST segment signifies reentry involving the accessory pathway
  • Permanent form of junctional reciprocating tachycardia (PJRT), an uncommon form of AVRT, features a long RP interval
    • Due to the delayed atrial activation coming from an accessory pathway with slow retrograde conduction

Focal Atrial Tachycardia

  • Characterized by rate of 100-250 bpm and regular atrial rhythm with activity originating from one localized site in the atrium
  • P wave may appear similar to sinus tachycardia when foci is near the sinus node
    • Left atrium foci: Positive P wave in lead V1, negative P waves in leads I and aVL
    • Cranial portion of the left or right atrium: Positive P waves in leads II, III and aVF
    • Paraseptal tissue or left or right atrial free wall: Shorter P-wave duration
    • An isoelectric interval may be seen between P waves
  • Commonly seen in patients with significant structural heart disease (coronary heart disease, MI, heart failure, cor pulmonale), and Digitalis intoxication

Intraatrial Reentrant Tachycardia (IART)

  • A type of paroxysmal reentrant SVT, is a macroreentrant atrial tachycardia that does not use the cavotricuspid pathway for reentry
  • Initiated by atrial premature beats and atrial pacing; ventricular premature beat triggers are rare
  • Incisional IART is a subtype of IART used to diagnose patients with a history of surgical procedure (congenital cardiac disease repair, incisional tachycardia, surgical or catheter-based management of atrial fibrillation) usually present in patients with IART
    • Occurrence depends on the patient’s underlying cardiac condition and type of surgery

Junctional Ectopic Tachycardia

  • Also called focal junctional tachycardia 
  • Pathologic impulse arises from the atrioventricular junction which may feature irregular rhythm and atrioventricular dissociation
  • Rate of 120-220 bpm
  • An ectopic focus in the AV junction producing erroneous automaticity may be the cause
  • Most often seen in post-op infants for management of a congenital heart disease

Nonparoxysmal Atrioventricular (AV) Junctional Tachycardia (Accelerated AV Junctional Rhythm)

  • Rate of 70-150 bpm
  • Often associated with automaticity, Digoxin toxicity, or myocardial infarction
  • Features retrograde atrial capture, AV dissociation with sinus node atrial control, and AV dissociation with atrial fibrillation

Sinoatrial Nodal Reentrant Tachycardia (SANRT)

  • Also called sinus node reentry or sinus node reentrant tachycardia
  • A microreentrant tachycardia that does not use the atrioventricular node or accessory pathways for reentry, with an activation sequence similar to normal sinus rhythm
  • Rate 100-150 bpm with P waves identical to sinus rhythm but with abrupt onset and termination of arrhythmias

Irregular Narrow-Complex Tachycardias

Atrial Fibrillation

  • Most common
  • SVT with low amplitude baseline oscillations, ventricular response is irregularly irregular with rate ranging from 100-200 bpm, narrow QRS complex, and without aberrant conduction or preexisting bundle branch block
  • No clear atrial activity, absent P waves and irregular R-R intervals

Atrial Flutter

  • A type of IART, characterized by the re-entrant loop just above the atrioventricular node in the right atrium
    • Cardiac rate tends to be faster that intraatrial reentrant tachycardia (IART)
  • Less common; may also have regular rhythm
  • Classified into cavotricuspid isthmus (CTI)-dependent atrial flutter or non-isthmus-dependent atrial flutter
    • CTI-dependent atrial flutter
      • Characterized by regular “sawtooth” P-waves on inferior ECG leads and a positive P wave in lead V1
      • Conducts signals around the tricuspid valve in a counterclockwise direction (typical CTI-dependent atrial flutter)
      • When impulse travels in a clockwise direction, this is referred to as reverse typical CTI-dependent atrial flutter
    • Non-isthmus-dependent atrial flutter (atypical flutter) uses other pathways other than the CTI (eg perimitral flutter, left atrial roof reentry, left or right atrial scar region reentry)
      • Biphasic V1 deflection with clockwise rotation around the tricuspid valve; positive P waves in leads II, III, and aVF
      • May co-exist with CTI-dependent atrial flutter
  • Rate usually >250-350 bpm

Multifocal Atrial Tachycardia (MAT)

  • Also called chaotic atrial tachycardia
  • Often associated with an underlying disease in older patients such as chronic obstructive pulmonary disease (COPD), pulmonary hypertension, coronary heart disease, congestive heart disease, or Theophylline therapy
  • Characterized by atrial rates of 100-130 bpm, irregular rhythm, with atrial activation originating from numerous sites, and ≥3 P wave morphologies
  • A 12-lead ECG is needed to distinguish MAT from atrial fibrillation; distinct isoelectric period between P waves differentiate MAT from atrial fibrillation

Regular Wide-Complex Tachycardia

Urgent care should be given to unstable patients with ventricular tachycardia

Ventricular Tachycardia (VT)

  • Includes outflow tract ventricular tachycardias, ventricular tachycardias of miscellaneous origin, and idiopathic ventricular fibrillation
  • Series of >3 consecutive, abnormally-shaped, wide-complex beats
  • Rate 70-250 bpm, which may last for <30 minutes and stop spontaneously, or for >30 seconds and patients experience hemodynamic collapse
  • Likely ventricular tachycardia (VT) when initial R wave is present with peak time of ≥50 milliseconds, initial R or Q wave >40 milliseconds, QRS complex is not observed on all precordial leads
  • There is AV dissociation with increased ventricular rate more than atrial rate
  • Fatal VTs include ventricular flutter and ventricular fibrillation
  • Presence of these severe tachyarrhythmias is a diagnostic sign that death may occur within minutes if not resolved
  • Heart rate of 150-300 bpm; ventricular fibrillation can go as high as 400-600 bpm
  • QRS complexes, ST segments, and T waves are absent; irregular contour and amplitude can be seen

Irregular Wide-Complex Tachycardias

  • Most commonly SVT (atrial fibrillation) with bundle branch block
  • Other possible causes: Atrial fibrillation with ventricular pre-excitation in Wolff-Parkinson White (WPW) syndrome, polymorphic ventricular tachycardia (VT), SVT with intraventricular conduction defect, electrolyte or metabolic disorder, use of accessory pathway
    • The long QT syndrome (LQTS) is associated with increased risk of life-threatening cardiac arrhythmia which is polymorphic VT, also known as torsades de pointes
  • Pre-excitation syndrome: Visible delta wave characteristic of WPW syndrome during normal sinus rhythm prior to the onset of atrial fibrillation

Laboratory Tests

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

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: Present in congestive heart failure
    • Cardiac enzymes: To determine the presence of myocardial infarction or ischemia
    • Thyroid stimulating hormone (TSH): Decreased in hyperthyroidism

Imaging

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 unable to tolerate exercise, and 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

Electrophysiological Study (EPS) and Cardiac Mapping

  • Electrophysiological Study (EPS) is used to identify the presence of ventricular tachycardia, as a guide prior to catheter ablation or implantable cardioverter defibrillator (ICD) placement, and to evaluate the cause of syncope
  • Cardiac mapping is performed during EPS to pinpoint specific site/s of origin of an aberrant signal in the myocardium for possible ablation
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