PQ interval prolongation

Prolongation of the PQ interval, according to the decoding of the cardiogram, means a delay in impulse conduction or partial or complete intra-atrial (atrioventricular) block.

To keep the blood circulating throughout the body, the heart pumps it continuously, contracting about 100,000 times a day. The contractions and relaxations of the myocardium are regulated by electrical impulses. Special diagnostics using recordings of the heart's electrical activity - electrocardiography (ECG) - registers these impulses and allows doctors to see all the nuances of the heart's work.

For the diagnosis of cardiac diseases, the ECG indicator of primary importance is the time it takes for excitation to pass through the right and left atria to the myocardium of the ventricles of the heart. This is the so-called PQ interval.

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Causes of prolongation of PQ interval

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

The role of the AV node, which is located in the back wall of the right atrium, is that the impulse must be delayed there for 0.09 seconds so that the atria have enough time to contract and throw the next portion of blood further - into the ventricles of the heart. From the point of view of the bioelectrical system of the heart, this process looks like the need for "recharging" (repolarization) after each heartbeat. And the prolongation of the PQ interval means that this process takes longer than usual.

Difficulty in atrioventricular conduction, which cardiologists call AV block (I, II and III degrees), can be functional, congenital or acquired (including pharmacologically induced). For example, functional prolongation of the PQ interval, which indicates a slowdown in signal conduction through the atrioventricular node over 0.2 seconds (AV block I degree), can occur in athletes - with increased vagus nerve tone, as well as in adolescents and young people who do not have heart problems. It should be borne in mind that complaints of palpitations in every third child and adolescent have a so-called phantom nature. They are associated with age-related vegetative-vascular features, and there are no heart rhythm disturbances, but only respiratory arrhythmia. Respiratory arrhythmia is caused by a change in the tone of the vagus nerve and manifests itself as an increase in heart rate on inhalation and a decrease on exhalation.

Prolongation of the PQ interval in children can be congenital - with congenital atrial septal defect, patent ductus arteriosus, and such anomalies of the cardiac conduction system as Wolff-Parkinson-White syndrome and Lown-Genong-Levine syndrome. In the course of studies, it was found that congenital syndrome of long PQ interval 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 impulses. In addition, this syndrome manifests itself in newborns who have suffered intrauterine hypoxia or significant asphyxia during birth.

Acquired prolongation of the PQ interval on the ECG is observed in posterior diaphragmatic myocardial infarction and myocardial ischemia; diseases of the cardiac conduction system (Lenegre disease and Lev disease); cardiomyopathy, amyloidosis or sarcoidosis. The causes of this pathology may include such diseases as myocarditis and infective endocarditis, systemic scleroderma, rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis.

In addition, prolongation of the PQ interval in adults is associated with metabolic electrolyte disturbances in the body (hyperkalemia or hypomagnesemia); tumors (lymphogranulomatosis, melanoma, etc.); significant weight loss associated with psychogenic anorexia; damage to the atrioventricular node during cardiac surgery.

Long Q syndrome and heart rhythm disorder in healthy people can be caused by certain antibiotics, antidepressants, antihistamines, diuretics, cardiac glycosides, beta blockers, cholesterol-lowering drugs, antidiabetic drugs, and some antifungal and antipsychotic drugs.

Symptoms of Prolonged 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 disturbances in the contraction of the heart muscle.

Atrioventricular conduction obstruction is usually divided into incomplete AV block (I and II degrees) and complete (III degree). AV block I has no clinical manifestations, and cardiac arrhythmia can only be recorded by ECG. For example, in newborns, the prolongation of the PQ interval on ECG is on average more than 0.13-0.16 seconds.

In adults, with a physiological prolongation of the PQ interval, a spontaneously occurring and similarly stopping “tingling” in the region of the heart is most often observed.

Acquired prolongation of the PQ interval (AV block II and III degrees) has specific symptoms:

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

Diagnosis of prolongation of the PQ interval

The main method for diagnosing prolongation of the PQ interval and cardiac arrhythmias is a comprehensive clinical examination, which 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 clarification of the family history regarding heart rhythm disturbances);
• determination of pulse rate and auscultation of the heart (in lying and standing positions, as well as after physical exertion);
• determination of the frequency, regularity and duration of heart contractions using ECG.

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Treatment of PQ prolongation

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

Long Q syndrome requires a certain limitation of physical activity and avoidance of medications that may trigger it.

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

In case of progressive atrioventricular block, which is associated with myocardial infarction, coronary heart disease, myocarditis or Lenegre's disease, cardiologists recommend the installation of a pacemaker with the parallel use of antiarrhythmic drugs.

Prevention of PQ interval prolongation

Arrhythmias associated with prolongation of the PQ interval are asymptomatic in almost two-thirds of cases: they are discovered by chance during an ECG.

The risk of cardiac arrhythmias due to acquired forms of AV block can be reduced by avoiding medications and situations that cause sudden changes in the heart's rhythm.

And people who have inherited or acquired long Q syndrome should definitely have a cardiologist on their list of treating doctors and consult with him about their condition and taking the appropriate medications.

Prognosis of PQ interval prolongation

Individuals whose PQ prolongation syndrome is not promptly identified are at increased risk of syncope and sudden death. The complexity of this cardiac pathology lies in its transient nature: an ECG between attacks may not reveal any cardiac arrhythmia. Prolonged asystole is sometimes followed by ventricular tachycardia or ventricular fibrillation, which can lead to prolonged coma or sudden death.

The prognosis for life after out-of-hospital cardiac arrest is as follows. According to some data, 21% of patients die during the first year after sudden cardiac arrest, 82% die during the next 10 years of life. Moreover, in 80% of them, the cause of death is ventricular fibrillation.

As you can see, an extended PQ interval indicates serious heart problems. Even if this syndrome does not have a negative impact on a person’s well-being and general condition for a long time, it can manifest itself unexpectedly – as a life-threatening symptom of an underlying disease or a side effect of regularly taken medications.

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