PQ interval extension

The prolongation of the PQ interval, according to the decoding of the cardiogram, means a delay in the conduct of the pulse, or a partial or complete intrapartum (atrioventricular) blockade.

To keep the blood constantly circulating throughout the body, the heart continuously pumps it, contracting during the day approximately 100,000 times. The contractions and relaxation of the myocardium are regulated by electrical impulses. Special diagnosis by recording the electrical activity of the heart - electrocardiography (ECG) - registers these impulses and enables physicians to see all the nuances of the heart.

For the diagnosis of cardiac diseases, an ECG indicator such as the time of passage of excitation on the right and left atriums to the myocardium of the ventricles of the heart is of paramount importance. This is the so-called PQ interval. 

[1], [2], [3], [4], [5], [6], [7], [8]

The reasons for extending the interval PQ

Beginning at the beginning of atrial contraction, the PQ interval ends at the onset of ventricular contraction. Its duration (which normally is 0.12-0.2 seconds) is an indicator of how quickly rhythmic excitation pulses from the synotrial node in the upper right atrium are transmitted to the ventricles via the atrioventricular node (AV node). The reasons for the prolongation of the PQ interval are most often covered in the AV node, more precisely, in the problems of its conductivity.

The role of the AV node, which lies in the posterior wall of the right atrium, is that in it the impulse should be delayed by 0.09 seconds, so that the atria have enough time to contract and throw out another portion of blood further - into the ventricles of the heart. From the point of view of the bioelectric system of the heart, this process looks like the need for "recharging" (repolarization) after each heartbeat. And lengthening the interval PQ means that this process takes longer than usual.

The difficulty of atrioventricular conduction, which cardiologists call the AV blockade (I, II and III degrees), is functional, congenital or acquired (including pharmacologically induced). For example, the functional lengthening of the PQ interval, which indicates the slowing of the signal through the atrioventricular node for more than 0.2 seconds (AV blockade of the 1st degree), may be in athletes - with increased vagal tone, as well as in adolescents and young people who do not have problems with the heart. It should be borne in mind that complaints about the heartbeat of every third child and adolescent have a so-called phantom character. They are associated with age-related vegetative-vascular features, and there are no violations of the heart rhythm, and there is only respiratory arrhythmia. Respiratory arrhythmia is caused by a change in the tone of the vagus nerve and manifests itself in the form of an increase in the frequency of cardiac contractions during inspiration and a decrease in exhalation.

Elongation of the PQ interval in children may be congenital - with a congenital defect of the interatrial septum, an open arterial duct and such anomalies of the conduction system of the heart as Wolf-Parkinson-White syndrome and Laun-Genong-Levine syndrome. In the course of the research it was found that the congenital syndrome of PQ interval prolongation in children can be caused by genetic mutations. Several genes play an important role in the formation of ion channels in the cell membrane, and thus mutations in these genes disrupt the normal conduction of cardiac pulses. In addition, this syndrome manifests itself in newborns who have suffered intrauterine hypoxia or significant asphyxia during labor.

Acquired prolongation of the PQ interval on the ECG is observed with posterior diaphragmatic myocardial infarction and myocardial ischemia; diseases of the conduction system of the heart (Lenegr's disease and Lev's disease); with cardiomyopathy, amyloidosis or sarcoidosis. Among the causes of this pathology may be diseases such as myocarditis and infective endocarditis, systemic scleroderma, rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis.

In addition, the prolongation of the PQ interval in adults involved metabolic electrolyte disorders in the body (hyperkalemia or hypomagnesemia); tumors (lymphogranulomatosis, melanoma, etc.); significant weight loss associated with psychogenic anorexia; damage to the atrioventricular node during surgical interventions on the heart.

The syndrome of PQ interval elongation and heart rhythm disorder in healthy people can cause some antibiotics, antidepressants, antihistamines, diuretics, cardiac glycosides, beta-blockers, cholesterol lowering drugs, antidiabetic medications, and some antifungal and antipsychotic drugs.

Symptoms of lengthening the PQ interval

In clinical cardiology, prolongation of the PQ interval on the ECG is considered a pathology of the electrical activity of the heart, which leads to violations of the contraction of the heart muscle.

The difficulty of atrioventricular conduction is usually divided into incomplete AV blockade (I and II degrees) and complete (grade III). AV blockade I has no clinical manifestations, and cardiac rhythm disturbances can be recorded only with ECG. For example, in newborns, the prolongation of the PQ interval on the ECG is on average more than 0.13-0.16 seconds.

In adults, with a physiological prolongation of the PQ interval, spontaneously occurring and exactly the same stopping "tingling" in the region of the heart is most often noted.

The acquired prolongation of the PQ interval (AV blockade II and III degree) has specific symptoms:

• bradycardia or bradyarrhythmia (lowering the heart rate to 60 beats per minute and below);
• tachycardia of the lower chambers of the heart (increased frequency of contractions - over 90 beats per minute);
• flutter-atrial fibrillation (paroxysmal atrial fibrillation, atrial fibrillation);
• short-term syncope (syncope) with cyanosis and convulsions;
• asystole (cardiac arrest).

Diagnostics of lengthening the interval PQ

The main method for diagnosis of PQ interval elongation and cardiac arrhythmias is a comprehensive clinical examination that includes:

• collection of complaints and anamnesis (with mandatory clarification of the circumstances of the onset of symptoms, the presence of all diseases, as well as clarifying the family history of heart rhythm disturbances);
• determination of heart rate and auscultation of the heart (in lying and standing, and also after physical exertion);
• determination of frequency, regularity and duration of cardiac contractions with the help of ECG.

[9], [10], [11], [12], [13]

Treatment of lengthening of the PQ interval

Therapy of this pathology depends on the cause of its occurrence. Thus, the physiological prolongation of the PQ interval does not require treatment, since it arises without obvious organic prerequisites and is associated with autonomic dysfunction or emotional stress.

The syndrome of lengthening the PQ interval suggests a certain restriction of physical activity and a refusal to use drugs that can provoke it.

Traditional treatment of PQ interval elongation, which is a consequence of the above diseases, includes - in addition to their therapy - oral administration of beta-blockers. The mechanism of action of the drugs of this pharmacological group is directed to the temporary blocking of β-adrenoreceptors, which reduces the influence of the sympathetic nervous system on the heart. Although beta-blockers are not able to correct violations in the ion channels of the heart cells, they can reduce the incidence of cardiac arrhythmias. However, these drugs are not effective in all cases, and in the presence of certain diseases are simply contraindicated.

With progressive atrioventricular blockade, which is associated with myocardial infarction, ischemic heart disease, myocarditis, or Lenegra's disease, cardiologists recommend the installation of a pacemaker with parallel administration of antiarrhythmic drugs.

Prevention of lengthening the PQ interval

Arrhythmias associated with prolongation of the PQ interval, in almost two thirds of cases, show no symptoms: they are detected accidentally during ECG.

The risk of cardiac arrhythmias due to acquired forms of AB blockade can be reduced, avoiding medications and situations that cause abrupt changes in the rhythm of heart contractions.

And people who inherited or acquired the PQ interval prolongation syndrome, must necessarily have a cardiologist in the list of their attending physicians and consult him about their condition and taking appropriate medications.

Forecast of lengthening the interval PQ

Persons who have PQ lengthening syndrome in a timely manner are not identified, are at increased risk of fainting and sudden death. The complexity of this cardiological pathology is its transient nature: an ECG in the interictal period may not reveal violations of the rhythm of the heart. After prolonged asystole, ventricular tachycardia or ventricular fibrillation sometimes occurs, which can lead to prolonged coma or sudden death.

The prognosis for life after community-acquired cardiac arrest is as follows. According to some reports, 21% of patients die in the first year after a sudden cardiac arrest, 82% die within the next 10 years of life. And in 80% of them the cause of death is fibrillation of the ventricles of the heart.

As you can see, the prolongation of the PQ interval indicates serious problems with the heart. Even if this syndrome does not have a negative impact on the state of health and the general state of a person for a long time, it can appear unexpectedly - as a life-threatening symptom of the underlying disease or as a side effect of the constantly taken medications.

[14], [15], [16], [17]