Atrial tachycardia with variable block (AT/VB) is a heart rhythm disorder where the heart’s upper chambers beat unusually fast. It involves a rapid atrial rate and irregular conduction to the lower chambers. This article explains its mechanisms, signs, causes, diagnosis, and management.
Understanding Atrial Tachycardia with Variable Block
Atrial tachycardia (AT) describes a rapid heart rhythm that begins in the heart’s upper chambers, called the atria, but outside of the heart’s natural pacemaker, the sinoatrial node. In AT, an abnormal electrical impulse repeatedly fires, causing the atria to contract quickly, often at rates between 150 and 250 beats per minute. This rapid firing can stem from a single, abnormally active spot in the atria or from a circular electrical pathway within the atrial tissue.
The “variable block” component of AT/VB refers to the behavior of the atrioventricular (AV) node, a specialized cluster of cells located between the atria and the ventricles. The AV node acts as a gatekeeper, slowing down electrical signals before they reach the ventricles, allowing the lower chambers to fill with blood. In AT/VB, the AV node receives many rapid impulses from the atria but cannot conduct every single one to the ventricles. This results in an irregular and often fast ventricular rhythm because the AV node blocks a varying number of these rapid atrial impulses. For instance, it might allow every second or third atrial beat to pass, or the blocking pattern can be more unpredictable.
Recognizing the Signs
Individuals with AT/VB may experience symptoms like palpitations, a feeling of the heart racing, fluttering, or pounding. They might also feel lightheaded or dizzy if the rapid heart rate reduces blood flow to the brain. Shortness of breath, chest discomfort, or fatigue can also occur. Medical attention is important if these symptoms arise.
Causes and Risk Factors
Atrial tachycardia with variable block can arise from various underlying conditions or factors that influence the heart’s electrical activity. Lung diseases, such as chronic obstructive pulmonary disease (COPD), are frequently associated with this condition. Certain heart conditions also increase the risk, including heart failure and coronary artery disease, which can alter atrial tissue.
Electrolyte imbalances within the body, particularly those involving potassium, sodium, or calcium, can disrupt the heart’s normal electrical signaling and contribute to AT/VB. Some medications can also lead to or worsen this arrhythmia. Digoxin toxicity, for example, is a known cause. In some instances, AT/VB may occur without any clear underlying cause.
Diagnosis and Treatment Approaches
Diagnosing atrial tachycardia with variable block typically begins with a thorough medical history and a physical examination by a healthcare professional. During the physical exam, a rapid and potentially irregular pulse might be detected. The primary diagnostic tool is an Electrocardiogram (ECG or EKG), which records the heart’s electrical activity and can identify the specific patterns characteristic of AT/VB. For symptoms that occur intermittently, a Holter monitor or event recorder may be used to capture the heart’s rhythm over an extended period, such as days or weeks. These portable devices allow for continuous monitoring, increasing the chance of recording the irregular rhythm when symptoms arise.
Once diagnosed, managing AT/VB focuses on controlling the heart rate, restoring a normal rhythm, and alleviating symptoms. Treatment approaches often involve addressing any underlying medical conditions contributing to the arrhythmia.
Medications are often used to regulate heart rate or rhythm. These may include beta-blockers or calcium channel blockers, which slow the heart’s response to rapid atrial signals. Antiarrhythmic drugs might also be prescribed to help maintain a normal heart rhythm.
If medications are ineffective, procedures like catheter ablation may be considered. During ablation, thin tubes are guided to the heart, and energy is used to create small scars that block faulty electrical pathways. This corrects the arrhythmia by targeting its origin.