Overview of atrial tachycardia with atrioventricular block
Atrial tachycardia with atrioventricular block differs markedly from other paroxysmal supraventricular tachycardias in terms of etiology, basic cardiac status, clinical manifestations, electrocardiographic changes, treatment, and prognosis. The most common etiology is organic heart disease with heart failure in patients who are on digitalis, especially those who have overdosed on digitalis.
Etiology
The most common cause is organic heart disease with heart failure in patients who are using digitalis, especially in those who have overdosed. Those caused by digitalis are most often accompanied by significant hypokalemia, which has a significant effect when treated with potassium supplementation. Another feature is that atrial tachycardia with atrioventricular block can occur in small doses of digitalis preparations. Digitalis toxicity accounts for more than half of atrial tachycardias with AV block.
In patients with atrial tachycardia with AV block not caused by digitalis use, the main causes are hypokalemia and certain organic heart diseases, such as coronary artery disease, myocardial infarction, hypertension, pulmonary heart disease, and rheumatic heart disease. This type of atrial tachycardia has also been reported to occur from quinidine, isoproterenol, etc., and in young people without organic heart disease.
Symptoms
The clinical manifestations of atrial tachycardia with atrioventricular block caused by digitalis are mainly in the following three forms:
1. Heart failure
Heart failure that improves for a time with digitalis treatment and then worsens dramatically again.
2. Arrhythmia
In the process of using digitalis, the heart rate slows down for a while, and then suddenly speeds up and becomes arrhythmic.
3. Other manifestations of digitalis intoxication
Such as nausea, vomiting, yellow vision and so on. Heart failure patients in the use of digitalis in the process of treatment, the heart rate from fast gradually slowed down, often suggesting that the condition improves. If the heart rate suddenly changes from slow and regular to fast and irregular, or the heart failure aggravates significantly again, we should be highly alert to the occurrence of atrial tachycardia with atrioventricular block, and we should measure the blood potassium in time.
Examination
It is mainly based on electrocardiography:
1.P wave is atrial ectopic P wave, in short burst episodes, it can be seen with sinus P wave difference, P wave can also be retrograde P wave, digitalis poisoning caused by atrial tachycardia with atrioventricular conduction block, its ectopic P wave depolarization direction is still normal, but the amplitude is very small, and the sinus tachycardia of the P wave is clear, clear and obviously different.
2. The P wave is located before the QRS wave, and the P-R interval is less than the R-P interval.
3. The atrial rate is 150-250 beats per minute, and the P-P interval in the atrial rhythm can be regular or irregular (even a difference of 0.12 seconds). Half of the patients with overdose caused by digitalis have irregular atrial rate, and the atrial rate gradually increases with the continued use of digitalis.
4. The QRS wave is supraventricular in shape, and the time limit is normal.
5. In atrioventricular block there can be the following forms:
(1) Second-degree type I atrioventricular block.
(2) Second-degree type II atrioventricular block: 2:1 to 4:1 atrioventricular block, with 2:1 atrioventricular block being the most common.
(3) Alternating Vinzel’s phenomenon (double-layer conduction block).
(4) Irregular ventricular rate is caused by the irregularity of the atrium itself, which can be misdiagnosed as atrial fibrillation, and attention should be paid to the P-wave pattern in the V1 lead or esophageal lead.
6. Pressing the carotid sinus is ineffective for digitalis-induced atrial tachycardia with atrioventricular block, but it can cause the aggravation of atrioventricular block, which slows down the ventricular rate, and it is ineffective for non-digitalis-induced atrial tachycardia with atrioventricular block; after pressing the carotid sinus, there is a more obvious slowing of the P-wave frequency, and sometimes it can be terminated. Because digitalis can increase the sensitivity of the carotid sinus, so the carotid sinus pressure with digitalis should be careful, atropine can increase the atrial rate of the non-digitalis-induced people, while the digitalis-induced atrial tachycardia with atrioventricular block has no effect.
7. In the case of digitalis-induced atrial tachycardia with atrioventricular block, ST-T changes due to the effects of digitalis can be seen on the electrocardiogram, and less than half of the cases can be accompanied by ventricular pre-systole.
Diagnosis
The correct diagnosis can be made on the basis of the characteristics of the patient’s history, clinical manifestations and ECG features.
Treatment
Since most of these arrhythmias are due to digitalis overdose, digitalis and diuretics should be discontinued immediately, and potassium chloride should be supplemented (orally or intravenously). In some cases, the addition of magnesium sulfate has obvious therapeutic effects. At this time, the following two aspects should be noted.
1. Whether digitalis has been used
For safety reasons, all should be treated as digitalis overdose. Discontinue digitalis and diuretics, and give potassium chloride treatment.
2. Atrial tachycardia with atrioventricular block should be treated as digitalis overdose.
Since patients are very sensitive to digitalis, atrial tachycardia with atrioventricular block can be induced when using a very small dose. Therefore, in the course of treatment with digitalis, regardless of its dose, if atrial tachycardia with atrioventricular block occurs, it should be treated as an overdose of digitalis.
Atrial tachycardia with atrioventricular block caused by digitalis can be restored to normal sinus rhythm within a few hours after 3-5 grams of potassium chloride is added. If this is not effective, procainamide may be added. The combination of potassium chloride and procainamide has been reported to be often effective, and the respective doses may be reduced when the two are used together. Atrial tachycardia with atrioventricular block in patients who have definitely not used digitalis may be treated with digitalis (Trichoside C) under close electrocardiographic monitoring to slow the ventricular rate, if necessary, but only in the absence of hypokalemia and hypomagnesemia. Potassium chloride and procainamide may be added for poor results.