From the Guidelines
The electrocardiogram (ECG) is a crucial diagnostic tool that records the heart's electrical activity, allowing clinicians to identify specific heart conditions non-invasively, and its mechanism involves detecting small electrical changes on the skin through electrodes placed on the chest, arms, and legs, which sense the electrical impulses that originate in the sinoatrial node and travel through the heart's conduction system. The ECG machine amplifies these signals and produces a tracing on paper or a digital display, showing different waves (P wave, QRS complex, and T wave) that represent atrial depolarization, ventricular depolarization, and ventricular repolarization, respectively. In cardiac pathologies, characteristic changes appear in the ECG pattern, such as:
- Myocardial infarction (heart attack) showing ST-segment elevation or depression and Q waves in leads corresponding to the damaged area 1
- Atrial fibrillation presenting with irregular rhythm and absence of P waves, replaced by fibrillatory waves
- Left ventricular hypertrophy demonstrating increased QRS voltage and secondary ST-T changes
- Bundle branch blocks showing widened QRS complexes with specific morphology patterns
- Electrolyte disturbances like hyperkalemia causing tall, peaked T waves, while hypokalemia leads to flattened T waves and prominent U waves These ECG changes are valuable diagnostic tools because they directly reflect the altered electrical activity resulting from structural, functional, or metabolic cardiac abnormalities. The ECG is an integral part of the diagnostic work-up of patients with suspected myocardial infarction, and should be acquired and interpreted promptly, with dynamic changes in the ECG waveforms during acute myocardial ischemic episodes often requiring acquisition of multiple ECGs 1. The ECG by itself is often insufficient to diagnose acute myocardial ischemia or infarction, since ST deviation may be observed in other conditions, such as acute pericarditis, left ventricular hypertrophy, left bundle branch block, Brugada syndrome, stress cardiomyopathy, and early repolarization patterns 1. However, the presence of ST-segment elevation is the most sensitive and specific ECG marker for acute myocardial infarction, and usually appears within minutes after the onset of symptoms 1. The ECG is also critical in providing prognostic information based on the pattern and magnitude of the abnormalities, and a recording made during an episode of the presenting symptoms is particularly valuable 1. Overall, the ECG is a fundamental tool in clinical practice, and its interpretation is essential for the diagnosis and management of patients with cardiac pathologies.
From the Research
ECG Mechanism
The electrocardiogram (ECG) is a noninvasive diagnostic tool that detects and records cardiac electrical activity, and can identify cardiac pathology 2. The electrical conduction system of the heart is responsible for generating the electrical activity that is recorded by the ECG. The ECG complex is made up of several components, including the P wave, QRS complex, and T wave, which correspond to different stages of the cardiac cycle.
Changes in ECG with Cardiac Pathologies
Certain cardiac pathologies can cause changes in the ECG, including:
- ST-segment elevation myocardial infarction (STEMI), which can cause changes in the ST segment and QRS complex 3
- Cardiogenic shock, which can cause changes in the ECG due to decreased cardiac output and perfusion 3
- Myocardial infarction, which can cause changes in the ECG due to damage to the heart muscle 4, 5
- Re-thrombosis, which can cause changes in the ECG due to the formation of new blood clots 6
Treatment and ECG Changes
Treatment of cardiac pathologies can also cause changes in the ECG, including:
- Fibrinolysis, which can cause changes in the ECG due to the breakdown of blood clots 3, 4, 5
- Percutaneous coronary intervention (PCI), which can cause changes in the ECG due to the restoration of blood flow to the heart muscle 3, 4, 6
- Aspirin and clopidogrel therapy, which can cause changes in the ECG due to the prevention of blood clot formation 4, 5, 6
Key Findings
Some key findings related to ECG changes and cardiac pathologies include:
- Clopidogrel pretreatment can reduce the incidence of cardiovascular death, MI, or stroke following PCI 4
- Aspirin combined with clopidogrel can effectively reduce the occurrence of re-thrombosis after PCI and improve the recovery of cardiac function after acute operation 6
- Fibrinolysis can cause changes in the ECG, including changes in the ST segment and QRS complex 3