Tachycardia: Difference between revisions

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

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

When the sinus node fires with a frequency between 100-180bpm, the term sinustachycardia is used. The maximum heart rate a person can achieve during exercise can be calculated by subtracting the age in years from 210. 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.<cite>Cossu</cite>

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 frequency of above the 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. The atrial flutter is a type of AT, but due to its unique mechanism it is discussed separately.

Vagal manoeuvres or adenosine can be effective in terminating focal AT.<cite>Markowitz</cite> If AT persist and is drug-resistant DC cardioversion can be indicated. Recurrent episodes of AT can be prevented with anti-arrhythmic medication, for instance with beta-blockers or calcium antagonists. However not all AT are sensitive to medication and success rate of medication is usually low. If these drugs are unsuccessful Class IC in combination with AV-nodal-blocking agents or Class III drugs can be tried.<cite>Chen1</cite> The treatment of choice for symptomatic AT is catheter ablation. In an experienced centre up to 90% of the ATs can be ablated. Multifocal atrial tachyardia is difficult therapy is usually directed at the management of underlying disease.<cite>Chen2, Anguere</cite>

===Atrial Flutter (AFT)===

Atrial flutter (AFT) is the most common type of atrial tachycardia. The typical AFT 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 frequency between 250-350 beats per minute. If the re-entry circuit moves counter clockwise a typical AFT is produced. If the re-entry circuit moves clockwise, a atypical AFT is seen.<cite>Yang</cite> The causes and risk are comparable with atrial fibrillation.

An AFT 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 AFT has a frequency of 300 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 AFT 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 AFT the inferior leads have a positive vector. Atrial fibrillation is a common finding in patients with an AFT (up to 35%).<cite>Robles,Wellens,Bochoeyer,ECGpedia</cite>

A patient with an acute episode of AFT 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 AFT more clearly. Anti-arrhythmic drugs are modestly effective in the acute setting (ibutilide or dofetilide), but have the risk of pro-arrhythmic effects.<cite>Volgmann, Singh, Stambler</cite> DC cardioversion is an effective methods to cardiovert AFT, especially in patients with heart failure or hemodynamic instability. AFT is amendable to catheter ablation and this is the treatment of choice in AFT. 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 AFT require anti-coagulation as in atrial fibrillation according to the CHADSVASc score.<cite>Dunn, Lip5</cite>

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). The atrial standstill does 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>

AF is the most common supraventricular arrhythmia in Western society. Patients can experience complaints from palpitations, dyspnoea and dizziness. 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 (atrial or ventricular extra systoles). The cardiac output is reduced due to lack of atrial kick. Furthermore due to the higher ventricular rate the heart has not enough time to completely fill with blood. The development of AF is associated with different diseases for instance 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 last longer than 7 days or 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>

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. Most effective drug is flecainide, although this drug is contra-indicated in patients with structural heart disease.<cite>Martinez</cite> Another option is ibutilide, but this is mostly used and more effective to terminate AFT, 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 anti-coagulation is advised before cardioversion and it should be continued after cardioversion for 4 weeks to minimize thromboembolic risk.

The management of AF consists of several key targets. Firstly, any underlying potential reversible cause of AF should be treated. Secondly, care should be taken to prevent the complications of AF. This means that adequate oral-anticoagulation should be initiated and rate control should be started to reduce heart rate. Thirdly, symptoms should be treated with medical or invasive therapy. There are two strategies to reduce symptoms of AF. Rate control is a strategy where a reduction of ventricular heart rate is the main goal. In rhythm control the aim is to maintain sinus rhythm and prevent recurrences of AF.<Cite>Camm2012,Camm2010</Cite>

* <B>Rate control:</b> In AF the ventricle can have a fast irregular rate that can lead to complaints of palpitations and a tachycardiomyopathy. One of the strategies in managing AF is to control ventricular rate <110bpm.<cite>VanGelder1, Groenveld</cite> In patients with persistent complaints or with heart failure a resting heart rate of <80 is advised. In this strategy no attempt is made to achieve sinus rhythm. This is the only treatment option in patients with permanent AF.  Due to the fast irregular ventricular rate a dilated tachycardiomyopathy can develop and proper rate control can revert these ventricular changes. Rate control can be achieved with beta-blockers, non-dihydropyridine Ca-antagonists. Digoxine can be added to rate control, however a recent study showed an increase in mortality in patients using digoxine.<cite>Whitbeck</cite>

*** <b>His-Ablation with pacemaker implantation: </b>Patients with accepted AF and complaints of a fast irregular ventricular frequency who do not tolerate medication can be helped with a targeted His bundle ablation with catheter ablation to induce complete AV-block. An implanted pacemaker can take over the ventricular firing frequency independent of the atrium. A pacemaker might be indicated if rate control leads to an iatrogenic bradycardia.

* <b>Rhythm control:</b> In rhythm control all efforts are made to achieve and maintain sinus rhythm. This can be done with anti-arrhythmic drugs. Most effective are the Class IC and III anti-arrhythmic drugs.<cite>Lafuente</cite> Overall rhythm control is difficult and anti-arrhythmic drugs might have (pro-arrhythmic) side effects, if patients have contra-indications.<cite>Echt, Roy1</cite> Therefore prescription of these drugs should occur with caution. If patients experience serious side effects of anti-arrhythmic drugs or have a low frequency of AF episodes an one month treatment with anti-arrhythmic drugs after cardioversion can prevent the majority of recurrences.<cite>Kirchhof</cite> Amiodarone is unsuitable for short-term treatment due to its pharmacological properties.<cite>Ahmed</cite>

*** <b>Catheter ablation:</b> Medical therapy is not always sufficient to maintain sinus rhythm. In the last decade of 20th century it was discovered that AF is triggered from the pulmonary veins and that selective ablation of these trigger sites can reduce AF recurrence.<cite>Hais</cite> As this technique evolved it is now common to ablate an area around the pulmonary veins to isolate them from the atrial tissue. The left atrium is approached through the inter-atrial septum and with the use of imaging and electrocardiographic signals a 3D map is made to navigate the atria. The pulmonary vein isolation can be performed with multiple energy sources (cryo-cooling, radiofrequent energy). This is a complex procedure that depending on the technique used has a minor chance of (severe) complications, primarily caused by damage of the surrounding structures. The one year success rate of the procedure varies on the experience of the operator and is a freedom of AF in 57-71% of the patients after one or more procedures.<cite>Calkins2,Cappato</cite> Catheter ablation is suitable for patients with a with drug-refratory rhythm control strategy.<cite>Nielsen</cite> Certain selected patients with heart failure might benefit from catheter ablation, although success are lower.<Cite>Khan,Hsu</Cite>

* '''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 is 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.

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 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 frequency 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. The P wave is sometimes hidden in the QRS complex or appears 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>

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 extra bundle 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 even 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 Maheim bundles. 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):

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 of >120ms due to slurring 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. 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 accessory bundle, 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 small QRS-complex

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