Tachycardia: Difference between revisions

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>

*** <b>Surgical treatment:</b> Surgery is a more invasive, but effective modality to treat AF. The classical cut and sew Maze procedure is an open chest procedure that requires extra-corporeal circulation. In this procedure the atrium is cut and sewn again to compartmentalize the atrium en therefore prevent the atrium maintaining AF.<cite>cox1,cox2</cite> In recent years a less invasive procedure has developed to treat AF. This minimal invasive surgery is performed through thoracotomy or thoracoscopy and is performed on a beating heart.<cite>wolf</cite> A pulmonary vein isolation is performed with a clamp and if patients have persistent AF additional left atrial lesions are made on the atrium to compartmentalize the atrium. Finally the left atrial appendage is removed to reduce the occurrence of stroke. This procedure has a success rate of 68% after one year.<cite>boersma,krul1,lameir</cite> Recently hybrid surgical procedures have been described that combine the minimal invasive thoracoscopic surgery with (epicardial or endocardial) elektrophysiological measurement. Patients with a large left atrium (diameter>45mm) or a failed catheter ablation are eligible for AF surgery.<cite>Krul1, Pison</cite>

Studies have shown no benefit of rhythm control over rate control, thus the selection of strategy is mainly dependent of patient and AF characteristics.<cite>Carlsson, Hohnloser, Opolski, VanGelder1, Wyse, Ogawa, IonescuIttu</Cite> Patients with AF and heart failure have limited medical options of rate control, as most anti-arrhythmic drugs are contra-indicated, and no benefit of rate vs. rhythm control was detected in studies.<cite>roy2,shelton</cite> This means that, since rate control is easier to achieve, rate control should be the initial strategy in all patients, especially in old patients and patients with no or few symptoms of AF. The target heart rate to achieve in rest is <110 beats per minute.<cite>VanGelder2</Cite> In patients with persistent complaints of AF rhythm control can be initiated on top of rate control. Young patients with paroxysmal AF and no underlying heart disease might benefit from early (invasive) rhythm control to halt progression of the disease.<cite>Camm3</cite> However, independent of the treatment strategy, proper anti-coagulation is important and necessary in patients with risk factors.<Cite>Camm2012,Camm2010</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.

==AV-nodal arrhythmias==

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>

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>

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.

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:

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>