Bradyarrhythmias are cardiac rhythm disorders characterized by a slower-than-normal heart rate, typically defined as fewer than 60 beats per minute. Some of which are discussed here:
Sinus Bradycardia
Sinus bradycardia presents a heart rate lower than 60 beats per minute, with a regular rhythm originating from the SA node. The ECG typically shows normal P waves preceding each QRS complex, a normal PR interval (0.12 to 0.20 seconds), and a normal QRS duration (0.06 to 0.10 seconds).
First-Degree AV Block
First-degree AV block is identified by a prolonged PR interval greater than 0.20 seconds on the ECG, with each P wave followed by a QRS complex. The heart rate is usually normal, and the rhythm is regular.
Second-Degree AV Block: Type I (Mobitz I, Wenckebach)
Type I second-degree AV block presents with progressive prolongation of the PR interval until a P wave is not succeeded by a QRS complex, causing a "dropped beat." The ECG pattern shows grouped beating, with one less QRS complex than P waves. The atrial rate remains regular, but the ventricular rate is slower and irregular due to the dropped beats. Heart rates can vary depending on the number of conducted beats.
Second-Degree AV Block: Type II (Mobitz II)
In Mobitz II, the ECG reveals a consistent PR interval for conducted beats, but not all P waves are followed by QRS complexes. This block type occurs below the AV node, often in the His-Purkinje system, leading to the sudden non-conduction of atrial impulses to the ventricles without prior PR interval lengthening. The ventricular rate is often slow and irregular, while the atrial rate remains regular.
Third-degree AV Block (Complete Heart Block)
Third-degree AV block or heart block, involves complete dissociation between atrial and ventricular activity. The atrial rate is usually within the normal sinus range of 60 to 100 beats per minute, while the ventricular rate varies depending on the block's location. If the block happens in the AV node, the ventricular rate typically ranges from 40 to 60 beats per minute; within the His-Purkinje system, it may drop from 20 to 40 beats per minute.
The ECG shows normal P waves with no consistent relationship to the QRS complexes. The PR interval is variable. The QRS complex is normal if the escape rhythm originates at or above the bundle of His and widened if it originates below, indicating a ventricular escape rhythm. This severe condition often requires urgent intervention with a pacemaker due to symptoms like fatigue, dizziness, and syncope.
Bradyarrhythmias are dysrhythmias with heart rates under 60 beats per minute. These conditions often involve issues with the heart's electrical conduction system.
Here are some common types:
Firstly, sinus bradycardia is characterized by heart rates below 60 beats per minute with normal P waves on the ECG.
Next, first-degree atrioventricular block features a prolonged PR interval with a normal heart rate, indicating delayed conduction from the atria to the ventricles.
The second-degree atrioventricular block is divided into two types.
Type I, or Mobitz I, is characterized by a lengthening PR interval until a beat is dropped, potentially resulting in a slower ventricular rate.
Conversely, type II, or Mobitz II, is characterized by constant PR intervals with some P waves not followed by QRS complexes.
Lastly, third-degree or complete atrioventricular block shows no conduction between the atria and ventricles, causing a slow ventricular rate that depends on the site of the block, with a variable PR interval.
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