Upon recognition of the PR interval prolongation, a thorough history should be obtained, with a specific focus on any history of congenital or acquired heart disease, risk factors for heart disease, family history of cardiac disease, the presence of neuromuscular disease, or family history of neuromuscular disease. Patients will frequently be unaware of the condition until it appears on routine electrocardiography. Poor ventricular filling due to prolonged PR intervals may also result in mitral regurgitation, which exacerbates conditions such as heart failure.įirst-degree AV block is almost universally without associated symptoms. As the PR interval extends beyond 0.30 seconds, synchrony of atrial and ventricular systole worsens, potentially resulting in poor ventricular preload and symptoms of the “pacemaker syndrome,” further characterized below. Prolonged conduction is well-tolerated, especially when the PR interval remains shorter than 0.30 seconds. Patients with conduction abnormalities originating in the His or Purkinje systems are more likely to have prolonged QRS intervals as well as the prolonged PR interval of first-degree AV block. Delayed conduction in these areas is more often due to underlying heart disease and more frequently progresses to higher degree AV blockade. The conduction delay may also be due to dysfunction in the atria, at the bundle of His, or in the Purkinje system. Įven though conduction slows, every impulse originated from the atrium is passed to the ventricles. The presence of first-degree AV block on ECG represents prolonged conduction in the AV node, commonly due to increased vagal tone in younger patients and fibrosis of the conduction system in older patients. Morphology and size of the QRS complex reflect that the His Purkinje system is the site of conduction delay. However, the most commonly affected place is the AV node. The abnormality "blocks" the electrical impulse from continuing through the normal pathways and usually results in a slower heart rate.Electrophysiological studies have shown that PR interval prolongation could be due to conduction delay located at the atrioventricular node, right atrium, or the His Purkinje system. Heart block refers to an abnormality in the way electricity passes through the normal electrical pathways of the heart. Blood-thinning medicines might be used to help prevent a stroke. Medicines might be used to prevent the heart from beating too fast. Treatment may include a pacemaker to prevent the heart from beating too slowly. You may have symptoms such as palpitations and lightheadedness. There is a risk of complications with this syndrome. It can occur when the heart's natural pacemaker is damaged. This abnormal heart rhythm problem is often seen in people who have been diagnosed with atrial fibrillation. In tachy-brady syndrome, also called tachycardia-bradycardia syndrome, the heart sometimes beats too quickly (tachy) and sometimes beats too slowly (brady). People with this syndrome can have slow arrhythmias or a combination of fast and slow arrhythmias. Various irregular heart rates (arrhythmias) or combinations of arrhythmias can happen. Sick sinus syndrome happens when the normal pacemaker of the heart (the sinus node) does not work properly. If there is a cause that is identified, that condition may be treated first. If sinus pause occurs often or over an extended period of time, a person may have symptoms now and then and need a pacemaker. Sinus pause (also called sinus arrest)ĭuring a sinus pause, the heart may miss one or more beats because its natural pacemaker fails to activate the electrical system throughout the rest of the heart.ĭepending on the cause, there is a risk of complications with this type of bradycardia. Then a pacemaker may be implanted if there is no cause that can be easily treated. It rarely requires treatment unless it causes symptoms. This type is not likely to cause complications, unless the heart rate is very slow (less than 40 beats per minute). This type of slow heart rate is often seen in healthy, athletic people. When a person has sinus bradycardia, the heart rate is less than 60 beats per minute. Each type carries a specific risk of complications and treatment options. There are several types of slow heart rates (bradycardias or bradyarrhythmias).
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