The electrocardiogram (Electrocardiogram, ECG or EKG) is a non-invasive diagnostic technique that detects the electrical activity of the heart through electrodes placed on the skin surface, converting it into visual waveform graphs. This test is primarily used to assess cardiac rhythm, myocardial electrical conduction, and to determine the presence of cardiac abnormalities. The ECG can capture real-time electrophysiological changes in the heart and is crucial for diagnosing acute cardiac events.
ECGs are widely used in routine health screenings, differential diagnosis of chest pain or palpitations, and monitoring responses to cardiac treatments. Its core value lies in providing rapid, objective evidence of cardiac electrical activity, assisting physicians in formulating further diagnostic or therapeutic strategies.
The ECG mainly divides into static ECG and dynamic monitoring. Static ECG is performed with the patient at rest, using a 12-lead system to comprehensively capture electrical signals from different angles of the heart. Dynamic ECG includes 24-hour Holter monitoring and event recorders, used to track long-term or intermittent arrhythmias.
The physiological mechanism involves the depolarization process of myocardial cells before contraction, which generates weak electrical currents. These signals are transmitted through body fluids to the skin surface. The electrodes receive and amplify these signals through signal processing systems, ultimately forming waveform graphs with P waves, QRS complexes, and T waves for physicians to analyze cardiac rhythm and structural abnormalities.
This test is especially suitable for evaluating myocardial ischemia, atrial fibrillation, ventricular hypertrophy, and other structural abnormalities. For patients taking anti-arrhythmic drugs, ECG can monitor drug efficacy and potential side effects.
The procedure requires the patient to lie flat, with healthcare personnel placing 10-12 electrodes on the limbs and chest. The test duration is approximately 5-10 minutes; static ECG requires the patient to remain still, while dynamic monitoring involves continuous wearing of a recorder for 24-48 hours. No special dosage or preparation is needed, but movement or poor electrode contact should be avoided during the test.
In special cases, exercise stress testing involves the patient gradually increasing exercise intensity on a treadmill to induce potential ischemic phenomena. This type of test must strictly follow the physician’s instructions regarding exercise intensity and duration.
The real-time diagnostic capability is vital in acute myocardial infarction with ST-segment elevation (STEMI), enabling rapid differentiation between angina and heart attack. For chronic arrhythmia patients, regular ECGs can detect disease progression early.
The ECG itself carries extremely low risk; most patients do not experience direct physiological harm. Possible discomfort includes skin irritation or allergic reactions at electrode contact sites, which usually resolve after electrode removal.
Important Notice: Patients with open wounds or severe skin conditions at electrode contact sites should avoid direct contact with electrodes. In terms of interpretation errors, a single static ECG may not capture intermittent arrhythmias; dynamic monitoring can improve diagnostic accuracy.
Contraindications include open wounds or severe skin infections at electrode sites, and significant body movements during the test. Patients with pacemakers should inform healthcare staff to adjust electrode placement accordingly.
In special cases, pregnant women should notify staff to avoid abdominal electrode contact that might cause skin irritation. Before the test, caffeine or vigorous exercise should be avoided to prevent transient arrhythmias.
ECG itself does not have direct drug interactions, but attention should be paid to:
Doctors should consider the patient’s medication history and ECG results to avoid misdiagnosis due to drug interference. During exercise stress testing, medications affecting cardiac load (such as nitrates) should be temporarily discontinued.
According to the American Heart Association guidelines, static ECG has over 90% accuracy in diagnosing ST-segment elevation myocardial infarction. Dynamic ECG has an 85% sensitivity for intermittent angina and is a standard tool for assessing unstable angina.
Multiple clinical studies have confirmed that combining ECG with myocardial enzyme tests can shorten the diagnosis time of acute cardiac events to within 30 minutes. Long-term follow-up studies show that regular ECG examinations can detect potential ventricular hypertrophy or myocardial damage 6-12 months in advance.
Other diagnostic methods include:
ECG is usually the first-line screening tool. When abnormal results of unknown cause are found, physicians may add stress testing or imaging examinations. Cases suspected of structural heart abnormalities should be evaluated with echocardiography as part of a comprehensive assessment.
Do I need to fast or avoid exercise before the test?
Generally, fasting is not required before an ECG, but it is recommended to avoid vigorous exercise, coffee, or tea before the test, as these can cause transient arrhythmias that affect interpretation. On the day of the test, wear clothes that allow easy exposure of the chest for electrode placement.
Will the test cause discomfort?
ECG is non-invasive and involves attaching electrodes to specific locations on the limbs and chest, with no pain involved. Some patients may experience slight discomfort due to skin sensitivity at electrode sites, but this is usually tolerable. The test lasts about 5 to 10 minutes, requiring the patient to remain still for accurate data collection.
How long does it take to get the results?
Initial results of a standard ECG can be interpreted immediately by healthcare staff, but detailed reports typically take 1 to 3 working days for specialist physicians to analyze. If abnormal waveforms are detected during the test, additional 24-hour dynamic ECG or stress tests may be required for further assessment.
In what situations is an urgent ECG necessary?
If symptoms such as chest pain, syncope, palpitations, or difficulty breathing occur, especially if myocardial infarction is suspected, immediate medical attention and urgent ECG should be arranged. Patients with acute cardiac events should have the ECG completed within 10 minutes of hospital arrival for timely diagnosis and treatment.
Can patients with pacemakers undergo ECG?
Patients with pacemakers can still have ECGs, but should inform healthcare staff in advance to adjust electrode placement and exclude interference signals. The report should be evaluated by a cardiologist to interpret both artificial pacing signals and natural cardiac activity to avoid misdiagnosis.
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