Many people experience heartburn, and this is when clinical examination often reveals a diagnosis of sinus arrhythmia. There are three types of arrhythmias: sinus arrhythmias, premature contractions, and paroxysmal tachycardia, each with different ECG implications.
What are the causes of sinus arrhythmias?
Sinus arrhythmias are caused by irregularities in the frequency of excitation released from the sinus node, which can lead to significant irregularities in the heart rate, and are called sinus arrhythmias.
Depending on the cause, sinus arrhythmias are clinically classified as respiratory sinus arrhythmias, non-respiratory sinus arrhythmias, wandering rhythms in the sinus node, sinus arrhythmias related to ventricular systolic blood displacement, and ectopic rhythm-induced sinus arrhythmias.
Respiratory-induced sinus arrhythmias are the most common type of sinus arrhythmia, occurring mostly in children, young adults, and the elderly. The mechanism is due to changes in the tension of the vagus and sympathetic nerves in the body during respiration, which changes the frequency of sinus node autoregulation in a periodic and regular manner. The heart rate speeds up during inspiration, slows down during expiration, and is regular when the heart stops breathing.
Non-respiratory sinus arrhythmias are less common and the etiology is unknown. They may be related to mood swings or the application of drugs such as digitalis or morphine. The point of excitation of the wandering rhythm is not fixed, but moves within the sinus node. Abnormal ventricular systolic blood drainage can lead to impaired blood supply to the sinus node, which can cause altered autoregulation of the sinus node and trigger arrhythmias.
Sinus arrhythmias induced by ectopic rhythms may be caused by points of excitation in the myocardium other than the sinoatrial node, mostly ectopic excitations originating from the atria. These ectopic excitations can affect the rhythm of the sinoatrial node, causing early onset of sinus node excitation and sinus arrhythmia.
What does the ECG of arrhythmia look like?
1.Sinus arrhythmia
Sinus rhythm: The heart rhythm in which the excitation originates from the sinus node is a normal heart rhythm. The characteristics of ECG are as follows: heart rate 60-100 beats/min. avR lead P-wave inversion, LnLm and avF lead P-wave upright, also called sinus P-wave. PR interval is greater than 0.12 s. R-wave interval difference is less than 0.12 s.
Sinus tachycardia: The same characteristics as sinus rhythm, only the heart rate is greater than 100 beats/min. Usually less than 160 beats/min.
Sinus bradycardia: the same as sinus rhythm, only the heart rate is less than 60 beats/min. Usually not less than 40 beats/min. Sinus arrhythmia: the same as sinus rhythm, only the difference between R-wave intervals is greater than 0.12 seconds.
2. Pre-phase contraction
A part of the heart other than the sinus node sends out electrical excitation in advance to temporarily control the heartbeat, called pre-term contraction, which can be divided into three categories.
Atrial pre-term contraction: the shape and width of the QRS wave appearing in advance is the same as the sinus QRS waveform, which is preceded by a P wave but has a slightly different shape from the sinus P wave, followed by an incomplete compensatory interval.
Atrioventricular node precontraction: the shape and width of the QRS waveform appear in advance is the same as the sinus QRS waveform, and there is no P wave in front of it or there is a retrograde P wave in the opposite direction of the sinus P wave (P wave in R lead is upright, LnLm and avFP wave are inverted), followed by a complete compensatory interval.
Ventricular precontraction: early appearance of QRS waves, width greater than 0.12 seconds, wide morphological deformity, no P waves in front of them, T waves in the opposite direction of the main QRS waves, followed by a complete compensatory interval.
3.Paroxysmal tachycardia
Paroxysmal tachycardia is called paroxysmal tachycardia when there are three or more consecutive precontractions. It can be divided into two types: supraventricular and ventricular.
Supraventricular tachycardia: three or more consecutive atrial or atrioventricular node precontractions.
The rhythm is absolutely uniform, the heart rate is 160-220 beats/min, the QRS wave width is less than 0.12 seconds, the morphology is normal, and there may be ST-segment descent and T-wave inversion. It is called supraventricular tachycardia because there is often an overlap of P and T waves, and it is impossible to distinguish atrial from AV nodal regionality.
Ventricular tachycardia: three or more consecutive ventricular precontractions with basic or mildly arrhythmic rhythm, heart rate of 160-200 beats/min, QRS wave width greater than 0.12 seconds, wide morphologic deformity, and T-wave inversion in the opposite direction of the main QRS wave. Sinus P waves are sometimes seen, but they are not causally related to QRS waves.