We had introduced sinus rhythm before. Normally, the rhythm of a normal person is controlled by the sinoatrial node, so it is called sinus rhythm, that is, the normal rhythm. The normal sinus heart rate(HR) has been considered tobe between 60 and 100 beats per minute(bpm). Long-lasting sinus tachycardia (HR >100 bpm) or sinus bradycardia (HR < 60 bpm) is of course unhealthy.

Rhythm originated from the outside of sinus rhythm can be considered arrhythmia. Although it may also be caused by ectopic impulses from other parts to lead the HR due to sinus bradycardia (that is escape rhythm), the most commonly seen is rapid arrhythmia, that is, tachycardia. Tachycardia is a complex set of arrhythmias, including various situations. This article will introduce the most common or important tachycardias so that the majority of patients can accurately understand their condition.

Tachycardia can be divided into several categories according to the origins of the lesion:

1, Atrial tachycardia: a tachycardia of over 100 bpm from either the right or left atrium. Tachycardia can be induced by older age, infection, genetic variation, cardiac valvular disease, cardiac surgery, overwork or chronic alcoholism. It mainly includes:

1）Focal atrial tachycardia: often seen in adolescents or the elderly, the lesions are relatively limited. The main manifestation is a short burst of tachycardia, each attack might last only a few seconds. The condition will get worse when patients are tired and nervous. In most cases, this atrial rate is not too harmful, and can be controlled by drugs. If necessary, catheter ablation can also be used to eradicate the lesion.

2）Surgical scar-related atrial tachycardia: It refers to the atrial tachycardia caused by surgical scars after cardiac surgery and usually coexists with atrial flutter. Generally, catheter ablation is required, and also the experienced EP doctors.

3）Atrial flutter: including type I (typical) atrial flutter and type II (atypical) atrial flutter. For type I (or typical) atrial flutter, the ablation success rate of experienced doctors is generally above 90% and may even up to 100%. However, type II atrial flutter is more difficult, and it is often related to the scar tissue, which in often seen in patients who have undergone cardiac surgery or ablation of atrial fibrillation. The ablation procedure might be difficult and the success rate is relatively low, roughly between 50-80%. It depends on patient's condition and the experience of the EP doctors.

2, Supraventricular tachycardia: it mainly includes atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentry tachycardia (AVRT). Then what is the atrioventricular accessory pathway?

Normally, the atrium and ventricle should be completely insulated from each other regarding to current conduction, and there is only one special fiber bundle called the atrioventricular node-His bundle-Purkinje fiber that communicates the atrium and the ventricle. The current conduction allows the atria and ventricles to contract and beat in an order, supplying blood throughout the body. However, an extra pathway (muscle fiber, usually thinner than the hair) might occur during the cardiac development. If this muscle fiber is just between the atrium and the ventricle, it may cause the short circuit trouble of the cardiac electrical conduction. For some patients, this abnormal activation might display on the on the electrocardiogram (ECG), and we call it pre-excitation syndrome. However, most of these patients are usually presented with normal ECG.

Regardless of whether there is AVNRT or AVRT, the ECG of most patients is usually normal, and also the echocardiography, CT, MRI, and laboratory tests. However, some patients might feel palpitation under specific situation (the heart rate can be up to 150 beats / min, or even more than 200 beats / min), and it can be terminated by deep breath, suffocation, cough, throat irritation and eye pressure, and so on. It may also be terminated abruptly on its own. This situation is called supraventricular tachycardia. Supraventricular tachycardia is actually the most common and easiest type of tachycardia. Put it in another way, for EP doctors, supraventricular tachycardia is just like appendicitis in general surgery. For supraventricular tachycardia, the only way is receive catheter ablation as soon as possible. The ablation of supraventricular tachycardia ablation is the basic procedure for EP doctors. The safety and success rate can be well guaranteed, and the success rate is about 92-99% for experienced operators. However, the ablation is not recommend for children only if they get older age. There are also difficult cases in ablation of supraventricular tachycardia, for example, a small number accessory pathway might be too close to the atrioventricular node-His bundle. The ablation should be cautious of the injury of the atrioventricular node-His bundle, which might result in iatrogenic atrioventricular block (in this situation, a pacemaker is needed). In addition, some individual accessory pathways might be difficult to eliminate completely because of their deep location. Of course, these are relatively rare cases.

3, Atrial fibrillation: Atrial fibrillation is the most common arrhythmia. Generally, with the increase of age, every might have the possibility of suffering atrial fibrillation. In addition to genetic, drinking, hyperthyroidism, myocarditis, cardiomyopathy, coronary heart disease, rheumatic heart disease, for most patients, the specific cause of atrial fibrillation is difficult to find under the current medical conditions. For the majority of the elderly people, it is mainly the result of the aging of the myocardium, and it should be frankly faced.

The manifestations of atrial fibrillation varies from person to person. For quite a few male patients, no symptom was presented, and for some patients, symptoms like panic, sweating, fatigue, shortness of breath might gradually appear. For a small part of patients, a large amount of urination may occur in a short period of time and following weakness and uncomfortable feeling might be presented. For some patients, bradycardia will be presented as the aging of atrial muscles and sinus node. These patients can also be presented with atrial fibrillation, as usually called “bradycardia-tachycardia” syndrome. However, in some patients, atrial fibrillation is dominant, and sinus pause might occur at the termination of atrial fibrillation as the aging of atria and sinus node. This sinus pause can be as short as more than 1 second and even as long as 30 seconds and patients may be fainted and left in danger. However, the greatest harm of atrial fibrillation is firstly presented as the impact on quality of life. Stroke is another risk for patients suffering atrial fibrillation. It is reported that 5% of AF patients may suffer thrombotic cerebral infarction or infarction in other parts of the body due to the thrombosis in the atria. This risk increases with age and the patients with AF should to take anticoagulants like warfarin to prevent the thrombotic events. In addition, if the patient was combined with other cardiac disease, for example, heart failure, and AF might deteriorate the cardiac function.

In terms of treatment, anti-arrhythmia drug control is necessary. Especially for patients who are not suitable for surgery due to physical or age conditions should be controlled with anti-arrhythmia drugs. However, for patients who are suitable for AF ablation, catheter ablation or surgical ablation is the only opportunity to cure. Until now, due to the multiple focal of lesions and not that clear pathogenesis leads to the multiple therapeutic ablation approaches. Pulmonary vein isolation, as the most widely used procedure, has been reported that the success rate is about 50% to 60% for a single ablation. Of course, the prognosis is better for patients with proximal atrial fibrillation, especially those with younger age, smaller atria, and normal cardiac function, and the success rate might up to 70%. Otherwise, for those older patients suffered chronic or long-lasting atrial fibrillation presented with enlarge atria, decreased success rate is common. The reason for this situation is not only related to the unclear mechanism, but also related to the limitations of the surgical equipment currently used. Some operators may have some innovations in the operation method, which has increased the success rate to 80%, and of course, it is not yet a widely used and testified approach. This is the current status of ablation of atrial fibrillation. Of course, research in this area is always hot in the field of arrhythmia, and advances for better results might be appeared in the future. Considering the scientific nature of medicine, we have reason to infer that no big breakthrough might occur in the near future.

4, Ventricular tachycardia (VT): That is, tachycardia originating from the ventricle. The ventricle, as the main source of power to transport blood to rest of the body, is the most important part of the heart. Due to the presence of gate-like atrioventricular node-His bundle-Purkinje fiber between the atrium and the ventricle, the atrial arrhythmia has been refined into the atria and usually cannot be transmitted to the ventricle. Thus most cases, there is no danger to life.

However, VT occurs directly in the ventricle, and there is no gate like atrioventricular node anymore. Moreover, the occurrence of VT generally means that there are lesions in the ventricles. In this case, the risk of VT is undoubtedly increased. In fact, cardiac arrhythmia is the main cause of the feeling of helpless when facing heart disease for most doctors, and VT is definitely the most dangerous condition in cardiac arrhythmia, or even worse-ventricular fibrillation, which is one of the main causes of sudden cardiac death.

However, there is also a type of idiopathic ventricular tachycardia that occurs in patients with normal cardiac function. The relative risk of this type of ventricular tachycardia is relatively much lower, with the most presented pattern of outflow tract VT and fascicular VT. However, some VTs, for example, arrhythmogenic right ventricular cardiomyopathy, VT related to coronary artery disease, VT in hypertrophic or dilated cardiomyopathy, and other structural heart diseases related VT, have been along with both highest risk and most difficult therapeutic regimens.

For patients who have had had blacked out or syncope, they should be referred to the arrhythmia specialist for further examination as soon as possible. If necessary, an implantable cardioverter defibrillator, also called ICD, should be considered. However, it must be pointed out that some idiopathic VT might also be presented with syncope or blackout, an ICD should be cautious recommend since VT can be cured by catheter ablation with low cost.

In addition to an ICD, catheter ablation can also be considered for VT related to structural heart disease. What should be emphasized is that, this kind of VT ablation is the most difficult operation among all ablation procedures. Not only should patients be chosen carefully, but doctors should also be strictly follow the rules of the procedures. Moreover, because ablation is performed in the ventricle, patients and doctors must be aware of the importance of protecting the ventricular muscles as much as possible, and so-called "perfect" effectiveness should not be pursued the to avoid the over-treatment related potential harm.