The Bainbridge reflex causes the heart rate to rise with inhalation and drop with expiration. The ECG criterion for diagnosing sinus arrhythmia is a fluctuation of the P-P interval of at least 0.12 seconds, or 120 milliseconds, from one pulse to the next. The presence of this reflex along with other factors such as age, gender, and physical activity may help diagnose sinus arrhythmia.
Sinus arrhythmia is a common finding in an electrocardiogram (ECG) and does not necessarily mean that someone has heart disease. Sinus arrhythmia occurs when there is a lack of control of the sinoatrial node--the body's natural pacemaker. This can happen due to aging or disease. Although sinus arrhythmia is usually not cause for concern, it may be a sign of another problem if it is persistent or if the patient experiences symptoms such as fatigue, dizziness, or fainting.
Sinus arrhythmia can also be caused by drug use. Certain medications may cause sinus bradyphrenia (slow heart rate) or sinus arrest (complete stop of all heartbeats). These patients should not take drugs that affect the heart rhythm. Other medications can cause sinus arrhythmia because they act on the cardiovascular system or interfere with certain electrical impulses between cells.
Respiratory sinus arrhythmia is defined as a cyclical change in heart rate characterized by a quicker heart rate during inspiration and a slower heart rate during expiration but otherwise typical ECG features of normal sinus rhythm (RSA; see Figure 3.1). The term RSA is also applied to describe an increase in heart rate that occurs primarily during sleep when there is no significant change in tidal volume or respiration rate. This increase in heart rate is called parasympathetic activation because it occurs when the body needs more energy (sympathetic activation causes a reaction similar to that which follows breathing into a balloon: your heart rate increases to deliver more blood to your muscles). Respiratory sinus arrhythmia is most commonly seen in healthy subjects at rest. It has been reported in patients with obstructive sleep apnea syndrome (OSAS) and seems to be particularly common in those who have recently been diagnosed with this condition.
The presence of RSA on an ECG indicates that the autonomic nervous system is playing a role in controlling the heart rate, although the exact mechanism responsible for this effect is not known. Some have suggested that it is part of a homeostatic response designed to maintain stable blood pressure through alterations in cardiac output. Others have proposed that it serves to minimize oxygen consumption by the heart during periods of decreased ventilation (when the heart is slowed by the autonomic nervous system, less energy is used up per minute).
The form of the P wave in each of the 12 conventional ECG leads should be consistent with a "typical P vector" of +50deg to +80deg for an ECG to be classified as indicating sinus rhythm. This means that in leads I, II, and aVF, the P wave should always be positive, whereas in lead aVR, it should always be negative. A PVC or premature ventricular contraction (PVC) may appear on the ECG record as a small square box with a number inside it to indicate how many beats out of normal rhythm there are. The closer together in time two such boxes are, the more likely they are related to one another and not just random noise.
An ECG showing a regular rhythm with no apparent abnormalities is called a normal ECG. It does not necessarily mean that there are no problems with the heart's electrical system. Many other factors can affect the appearance of the ECG recording, including the patient's level of activity, the placement of the electrodes, electrolyte levels, muscle tone, size of the chest cavity, cardiac structure, and disease severity. Therefore, a normal ECG does not rule out certain conditions, such as myocardial infarction, hypertrophy, or blockage due to coronary artery disease, which can all cause abnormal rhythms.
A physician can interpret an ECG report by carefully reviewing it for evidence of any potential problem areas. The doctor may ask questions about your history and perform a physical examination before reaching any conclusions about your condition.
Sinus rhythm (also known as normal sinus rhythm) is the normal heartbeat that originates from the sinoatrial node. This is reflected in the ECG as an upright P wave in lead II. The heart beats regularly and continuously without any interruptions or irregularities.
A sinus arrhythmia is a variation in the rate or regularity of the sinus beat. Such variations may be due to changes in posture or activity, but they can also be a sign of some other problem with the heart's electrical system. These variations are classified according to their cause: sinus arrest, sinus bradycardia, and sinus tachycardia. A sinus arrhythmia is called "paroxysmal" if it occurs at random times or "permanent" if it persists for more than 24 hours.
Permanent sinus arrhythmia does not require treatment; it is usually only checked against progression to more serious conditions. However, sinus arrhythmia that occurs at random times may be a sign of underlying heart disease which needs to be diagnosed by a physician.
Sinus arrest is when the heart stops beating altogether for several minutes or longer. This can happen when too much blood gets into the heart causing it to fill up fast.