Tachycardia: Difference between revisions

[[File:overview.png|thumb|300px|'''Figure 1.''' Classification of tachyarrhythmias.<cite>ECGPedia</Cite>]]

Differentiation between supraventricular tachycardias (SVT) and ventricular tachycardias (VT) can be challenging, especially in acute emergency settings. SVT's are arrhythmias in the atria or AV-node arrhythmias in which these structures are involved. Supraventricular arrhythmias are relatively common and rarely life-threatening. VT's are rhythm disorders that originate from the ventricles. VTs can both take place in the myocardial tissue and the conduction system tissue (Figure 1).

=Supra-ventricular tachycardia=

==Atrial arrhythmias==

The following arrhythmia arise in the atrium. Dependent on the refractory period of the AV-node the ventricles follow the atrial activation at the same rate. At higher atrial rates the AV-node starts to block conduction from atrium to ventricle.<cite>Blomstrom-Lundqvist, ESC</cite>

===Sinus Tachycardia===

====Pathophysiology:====

When the sinus node fires with a rate between 100-180bpm, the term sinustachycardia is used. The maximum heart rate a person can achieve during exercise can be estimated by subtracting the age in years from 210, although it is not uncommon for sinus rates to peak above 200 bpm during vigorous exercise. Usually it is a physiological reaction to stress (exercise, inflammation, stress). External factors can increase the heart rate like coffee and alcohol or drugs.<cite>Ghuran</cite> The term inappropriate sinus tachycardia is a persistent increase in resting heart rate or sinus rate unrelated to or an exaggerated response to stress in a person without structural heart disease.<cite>Cossu</cite>

====Clinical diagnosis:====

A sinus tachycardia usually has a gradual start and ending. Diagnosis on the ECG can be made by the morphology of the P-wave. The P-wave has the same morphology during sinus tachycardia as during normal sinus rhythm (Figure 2).<cite>Robles, ECGpedia</cite> An inappropriate sinus tachycardia is diagnosed by when the sinus tachycardia is persistent (therefore non-paroxysmal) and no trigger can be identified.

====Management:====

No treatment is indicated; usually the sinustachycardia will pass when the external trigger is removed. If patients have persistent complaints, the trigger cannot be removed or in case of an inappropriate sinus tachycardia a beta-blocker can be administered. Patients with a contra-indication for beta-blockers can use nondihydropyridine calcium-channel blockers.

===Atrial Tachycardia (AT)===

====Pathophysiology:====

Atrial tachycardia (AT) is a tachycardia resulting from fast firing in an ectopic focus or micro re-entry circuit in the atria.<cite>Saoudi</cite> It has a rate of >100bpm. In some patients the tachycardia has multiple foci (multifocal atrial tachycardia). This results in different P-wave morphologies on the ECG during the arrhythmia. Atrial tachycardia can be caused by all the mechanisms of arrhythmia formation. Patients after earlier surgery or catheter ablation usually present with macro re-entry AT located around functional or anatomical sides of block. Atrial flutter is a distinct type of AT, but due to its unique mechanism it is discussed separately.

ATs have a wide range clinical presentation. They can occur in paroxysms or can be the permanent underlying rhythm. Complaints of palpitation and a fast regular heart rate are common and as a result of the tachycardia complaints of dizziness, dyspnoea and syncope can be experienced. Focal AT that with a progressive increase at onset and decrease before termination are likely based on abnormal automaticity. Digoxine intoxication is a common cause for ATs. On the ECG an atrial tachycardia can be detected through the P-wave morphology. The P-wave has a different morphology depending on the foci of the atrial tachycardia (Figure 2). An ECG in resting condition of sinus rhythm can help distinguish different morphologies and help in localization of the source of the atrial tachycardia. Vagal manoeuvres or administration of adenosine can block the AV-conduction and reveal firing from the atrium, thereby clearly identifying the atrial source of the tachycardia. Some ATs are sensitive to adenosine and will terminate after administration of adenosine. However sometimes only an electrophysiological study can differentiate between the different SVT and localize the precise location or circuit of the AT.<cite>Robles,Wellens,ECGpedia</cite>

====Management:====

[[File:atrial arrhythmias.svg|thumb|500px|'''Figure 2.''' The different atrial arrhythmias. Note the differences in P wave morphology or absence of P-waves in case of atrial fibrillation.<cite>ECGPedia</Cite>]]

===Atrial Flutter (AFL)===

====Pathophysiology:====

Atrial flutter (AFL) is the most common type of atrial tachycardia. Typical AFL is dependent of the cavotricuspid isthmus.<cite>Saoudi</cite> The isthmus between the caval vein and tricuspid is an area of slow conduction. Due to this slow conduction counter clockwise re-entry around the tricuspid annulus can exist. This re-entry produces a typical arrhythmia with activates the atria at a rate between 250-350 beats per minute. If the re-entry circuit moves counter clockwise a typical AFL is produced. If the re-entry circuit moves clockwise, a atypical AFL is seen.<cite>Yang</cite> The causes and risk are comparable with atrial fibrillation.

====Clinical diagnosis:====

An AFL is usually paroxysmal, with a sudden onset, and is diagnosed on the ECG by it typical saw tooth pattern. Patients experience complaints of palpitations, dyspnoea, fatigue or chest pain. An AFL typically has an atrial rate of 280-320 bpm, which conducts to the ventricles in 2:1, 3:1 or 4:1 manner. The P-wave morphology has a saw tooth like appearance and in a typical AFL has a negative vector in the inferior leads. The upstroke or down stroke of the first part of the P-wave is fast, the second part slow (Figure 2). In an atypical AFL the inferior leads have a positive vector. Atrial fibrillation is a common finding in patients with an AFL (up to 35%).<cite>Robles,Wellens,Bochoeyer,ECGpedia</cite>

====Management:====

A patient with an acute episode of AFL requires cardioversion. This can be achieved with anti-arrhythmic drugs or electrical cardioversion. Vagal manoeuvres increase the AV-block on the ECG and demonstrate the AFL more clearly. Anti-arrhythmic drugs are modestly effective in the acute setting (ibutilide or dofetilide) and have the risk of pro-arrhythmic effects.<cite>Volgmann, Singh, Stambler</cite> DC cardioversion is an effective methods to cardiovert AFL, especially in patients with heart failure or hemodynamic instability. AFL is amendable to catheter ablation and this is the treatment of choice in AFL. Targeted ablation of the area between the inferior vena cava and the tricuspid annulus can block the re-entry circuit. This is a very successful procedure, with few complications in the hands of an experienced electrophysiologist.<cite>Kottkamp, Natale, Chen3</cite> If patients are not eligible for ablation, anti-arrhythmic drugs class IC or III can be started. However they are of limited efficacy and class IC drugs not be administered without AV-nodal slowing agent because of atrial slowing can result in 1:1 AV conduction. Patients with AFL require anti-coagulation as in atrial fibrillation according to the CHADSVASc score.<cite>Dunn, Lip5</cite>

===Atrial Fibrillation (AF)===

====Pathophysiology:====

The pathophysiology of AF is complex and incompletely understood.<cite>Schotten</cite> In most patients the trigger of AF results from extra beats in from the pulmonary veins.<cite>hais</cite> This is due to myocardial sleeves growing into the pulmonary veins, which are triggered to fire extra beats due a variety of modulators (i.e. the autonomic nerve system).<cite>Patterson</cite> These triggers can trigger the atria into forming multiple self-perpetuating re-entry circuits. These multiple wavelets, are self-perpetuating circuits than constantly change and move through the atria. The ability of the atria to sustain AF is dependable on atrial structural changes (fibrosis/inflammation). AF induces electromechanical changes in the atrium. These changes make it easier for AF to perpetuate: AF begets AF.<cite>Wijfels</cite> Due to the fast and rapid activation of the atria, there is no functional mechanical activity left. This results in the most feared complication of AF, namely forming of blood clots (with for instance stroke as a result). During atrial standstill the atria  do not effectively pump blood to the ventricle, and blood can coagulate the left atrium or left atrial appendage.<cite>Watson</cite> The strokes resulting from AF are often more severe than other causes of stroke. Another complication of AF is a tachycardiomyopathy. Due to the constant chaotic activity in the atria, the AV-node can conduct these signals at high rate. The result is an irregular fast ventricular activation. These fast activation of the ventricle can lead to a (reversible) dilated cardiomyopathy.<cite>Packer</cite>

====Clinical diagnosis:====

AF is the most common supraventricular arrhythmia in Western society. Patients can experience complaints from palpitations, dyspnoea and dizziness. Prevalence increases with age and reaches 7-10% in octogenarians <cite>Heemstra</cite>. It is characterized by the absence of clear P-waves on the surface ECG and an irregular ventricular rate (Figure 2). On physical examination an irregular pulse can be felt, however this is not diagnostic of AF as other causes can cause an irregular pulse (mainly atrial or ventricular extra systoles). The cardiac output is reduced by 10% due to lack of atrial kick. Furthermore due to the higher ventricular rate the heart has not enough time to completely fill with blood thereby reducing stroke volume. The development of AF is associated with different diseases e.g. hypertension, mitral valve disease, thyroid disease and diabetes.<cite>Nieuwlaat</cite> AF usually starts with short single isolated episodes of AF which are self terminating. Progressively over time these episodes are of longer duration and occur more frequently. These episodes progress to persistent AF, which is defined as AF lasting longer than 7 days or which can only be terminated by cardioversion. In the end AF is permanent and cardioversion is not possible or duration of sinus rhythm is short.<cite>Jahangir</cite> Episodes of AF can be symptomatic, but patients can experience no symptoms during AF. However it is important to note that the risks of complications of AF are unrelated to the duration of the episodes. <cite>Friberg</cite> AF is classified according to the clinical presentation of AF:<cite>Camm2010</cite>

* Paroxysmal atrial fibrillation: Episodes AF lasting shorter than 7 days and terminating spontaneously usually within 48 hours.

* Persistent atrial fibrillation: Episodes of AF not terminating spontaneously or lasting longer than 7 days or requires cardioversion

* Long standing persistent atrial fibrillation: Persistent AF for more than one year.

* Permanent atrial fibrillation: Accepted AF, no strategies of rhythm control are pursued.

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====Management:====

=====Acute Management:=====

The acute management of AF depends on the presentation of the patient. In stable patients with little complaints, rate control can be initiated with beta-blockers, non-dihydropyridine Ca-antagonists and digoxine. If the patient has recent onset of AF, is highly symptomatic or hemodynamicly compromised, cardioversion is indicated. Cardioversion can be performed medically or with electricity. The most effective drug for chemical cardioversion is flecainide, although this drug is contra-indicated in patients with structural heart disease or ischemia.<cite>Martinez</cite> Another option is ibutilide, but this is mostly used and more effective to terminate AFL, and has a small risk of ventricular arrhythmias.<cite>Stambler</cite> In patients with severe structural heart disease amiodarone can be given.<cite>Chevalier</cite> Electrical cardioversion can achieved by a DC shock after sedation of the patient. If the AF persist for longer than >48 hours or the start of the episode is not clear, anti-coagulation should be initiated before (medical or electrical) cardioversion. Three weeks of adequate anti-coagulation (INR 2-3)is advised before cardioversion and it should be continued after cardioversion for 4 weeks to minimize thromboembolic risk.

* '''Anticoagluation treatment:''' Proper anti-coagulation is important in patients with AF to reduce the occurrence of stroke.<cite>Watson</cite> In patients with AF the indication of anti-coagulation is based on certain patient-related risk-factors. A score is created to facilitate this the clinical decision making. The CHADS₂VASc2 score incorporates these risk factors. A patient has no indication for anti-coagulation if there is a low-risk of thromboembolic complications.<cite>lip1,lip2</cite> These patients are defined as males or females <65 years old with no other risk factors. This translates in a CHADSVASc score of 0, or a CHADSVASc score of 1, where 1 point is based on the female sex. In all other cases anti-coagulation with coumarins or other new anticoagulation drugs (dabigatran, rivaroxiban, apixaban)<cite>Connolly, Patel, Granger </cite> is indicated if no strong bleeding-risk exist. It is important to note that anti-coagulation is independent of the underlying rhythm.

This section covers the arrhythmias in which the AV-node is critical in maintaining the arrhythmia. Most of these arrhythmias share the common characteristic that AV-node blocking or delaying manoeuvres or medication (adenosine) can terminate the arrhythmia.<cite>Blomstrom-Lundqvist, ESC</cite>

[[file:AVNRT.png|thumb|400px|'''Figure 3.''' The mechanism of AV-nodal re-entry.<cite>ECGPedia</Cite>]]

====Pathophysiology:====  

AVNRT is a regular arrhythmia relying on the dual AV-physiology for its maintenance. The AV-node usually has two pathways in these patients; a fast pathway with fast conduction times and a slow pathway, which conducts slowly. The fast pathway has a longer refractory period than the slow pathway. Due to these characteristics re-entry formation is possible. Normally the impulse from the atria is conducted through the fast pathway to the ventricle. The impulse also travels through the slow pathway, but reaches tissue still in the refractory period at the end of the AV-node (as the fast pathway has already conducted the impulse and activated this part of the AV-node). When an extra premature atrial contraction occurs it encounters a refractory fast-pathway (which has a longer refractory period). It enters the slow pathway and when it reaches the end of this pathway it can conduct to the (now restored) end of the AV-node to the ventricles and back up into the fast pathway. The result is a ventricular activation with a retrograde P-wave. If the slow pathway is restored when the impulse reaches the beginning (atrial side) of the fast pathway, the impulse can re-enter the slow-pathway and a re-entry mechanism is established. This is the mechanism of a typical AVNRT, which is found in 90% of the patient with an AVNRT (Figure 3). Two other forms of AVNRT exist that take a different route through the AV-node. Firstly there is an atypical AVNRT in which the impulse travels through the fast pathway and returns through the slow pathway. The result of this AVNRT is a retrograde P-wave which appears far from the QRS complex. Finally there is a rare AVNRT which in patients with two slow pathways. The impulse enters en re-enters through a slow pathway.<cite>Mazgalev, Wu, Robles</cite>

It is a fast regular small complex tachycardia with a rate of 180-250 bpm. It is more common in women than in men (3:1) and has a sudden onset. Palpitations are experienced due to the fast regular heartbeat. The Frog sign can be observed; neck vein pulsations which occur due to simultaneous contraction of the atria and ventricles. The atria cannot empty into the ventricles and therefore expulse their contents into the venous circulation. A typical AVNRT can be diagnosed on the ECG by a RP distance of < 100ms, resulting in a P wave hidden in the QRS complex or appearing directly after the QRS complex. An atypical AVNRT has a retrograde P appearing far away from the QRS, as it has to travel through the slow pathway. A registration of the onset can often be quite helpful in establishing the diagnosis AVNRT.<cite>Robles, Wellens</cite>

Termination of acute episodes is possible by vagal manoeuvres (blowing on the wrist, carotid sinus massage) or medication (adenosine, verapamil, diltiazem).<cite>Akhtar</cite> If vagal manoeuvres or medication fail ECV can be performed. Catheter ablation can be the treatment of first choice in AVNRT. Electrophysiological studies can demonstrate dual AV-node physiology and evoke the arrhythmia in these patients. Selective ablation of the slow pathway has a high success rate (up to 98%) and the risk of inducing AV-block is low (<0,5%).<cite>Clague</cite> Long term medical therapy can be initiated in patients not suitable for catheter ablation, or who do not desire a catheter ablation. Calcium channel blocker, beta-blockers and digoxin are used as first option or in a pill in the pocket approach.<cite>Alboni</cite> Other options are class IC or class III anti-arrhythmic drugs.

[[file:OCT_ACT.svg|thumb|400px|'''Figure 4.''' An example of orthodrome AVRT and antidrome AVRT. Note the differences in the direction of the arrhythmia.<cite>ECGPedia</Cite>]]

====Pathophysiology:====  

AVRT are tachycardias with a re-entry circuit comprising the entire heart. The atria, AV-node, ventricles and an extra bundle are essential parts of this circuit. The pre-requisite for an AVRT is the existence of an accessory pathway (AP) between the atrium and the ventricle. This bundle can bypass the AV-node and connect directly to the His bundle, ventricular myocardium or one of the fascicles. Bundles have variety of anatomical locations and can run epicardially.<cite>Becker,Cosio</cite> The conduction direction of these bundles can be anterograde (atrium-ventricle), retrograde (ventricle-atrium) or bidirectional. Some of the bundles exhibit AV-nodal conduction properties, these are also known as Mahaim fibres. If a bundle can conduct anterograde at a high rate (a refractory period of <260ms), then a risk of VF exists if the patients develops AF due to fast conduction of fibrillatory activity. Depending on the conduction characteristics of the bundle and the direction of conduction two different AVRT circuits can manifest (Figure 4):

* Orthodrome AV re-entry tachycardia: The impulse travels through the normal conduction system in the standard direction and returns to the atria via the accessory bundle.

* Antidrome AV re-entry tachycardia: The impulse travels antrograde through the accessory bundle and activates the ventricles. The impulse returns through the normal conduction system to the atria.

If an accessory bundle excites the ventricle earlier than normal AV-conduction, thus has antegrade conduction properties, and can activate the ventricles, pre-excitation is visible on the ECG. Pre-excitation can be visible on the ECG by a shortened PQ interval and a widened QRS complex due to slurring of the initial part of the QRS complex (delta wave). This is also called the Wolf-Parkison-White symptom and can occur intermittently. If a patient has pre-excitation and complaints of arrhythmia caused by an AVRT the combination of these two is called the Wolf-Parkinson-White syndrome.<cite>WPW</cite> Some patient have an AVRT, but no traces of pre-excitation. The bundle is then called a concealed bundle, which only conducts in one direction: from ventricles to atria. Patients can be asymptomatic if they only have pre-excitation and this ECG pattern is commonly an incidental finding.<cite>Wellens, Robles</cite> When an arrhythmia develops using the AP, both types of AVRT can develop depending on the conduction characteristics of the bundle:

* Orthodrome AV re-entry tachycardia: There is a P-wave (other morphology than sinus rhythm) followed by a narrow QRS-complex

* Antidrome AV re-entry tachycardia: This is a wide-complex tachycardia, where the wide QRS complex is followed by a retrograde P-wave originating from the AV-node.

The circuit of the arrhythmia uses the AV-node; therefore vagal maneuvers are able to terminate the AVRT. However adenosine should be used with care, as it may induce AF and cause 1:1 conduction.<cite>Tebbenjohanns</cite> Anti-arrhythmic drugs (Class IC, II, III, IV) can be useful to prevent paroxysms of arrhythmia, and a pill-in-the-pocket approach can be used for patients with infrequent episodes.<cite>Alboni</cite> Catheter ablation can target the accessory pathway and destroy the bundle. The success of the procedure is dependent on the location of the bundle as not all anatomical positions can be easily targeted with ablation.<cite>jackman, calkins5</cite> It is controversial if patients with an asymptomatic WPW ECG pattern and no co-morbidities should have an ablation. To determine the risk of 1:1 conduction, an exercise test can be performed to determine the response of the accessory bundle to an increased atria rate. If the pre-excitations persists an electrophysiological procedure can be performed to assess the conduction properties of the accessory bundle. While the characteristics of the bundle predict the risk for an event, the life-style and\or profession of the patient can influence the decision for ablation.<cite>cohen, pappone, priori</cite>