An electrocardiogram (EKG or ECG) is a non-invasive medical test that records the heart’s electrical activity. It helps healthcare professionals assess heart function and identify various conditions. The quick, painless procedure involves placing small electrode patches on the skin. The EKG machine translates these electrical signals into a visual wave pattern.
Understanding EKG Fundamentals
The heart generates its own electrical signals, coordinating contractions and relaxations to pump blood. An EKG detects these impulses through electrodes on the skin, which connect to a machine that amplifies and records the activity. These signals represent two primary processes: depolarization and repolarization. Depolarization is electrical activation leading to muscle contraction, while repolarization is electrical recovery allowing muscle relaxation. The EKG machine displays these events as waves, providing a detailed picture of the heart’s electrical rhythm and function.
Dissecting the EKG Waveform
An EKG tracing consists of distinct waves and segments, each representing a specific electrical event in the heart. The P wave is the first small upward deflection, signifying atrial depolarization. This electrical activity causes the atria to contract, pushing blood into the ventricles.
Following the P wave is the QRS complex, a sharp, larger deflection representing rapid ventricular depolarization. This complex signifies the electrical impulse spreading through the ventricles, prompting them to contract and pump blood. Atrial repolarization occurs during this time but is typically hidden by the larger QRS complex.
The T wave is a rounded wave that appears after the QRS complex, indicating ventricular repolarization. This allows the ventricular muscle to relax and refill with blood before the next beat. The complete cycle of P, QRS, and T waves represents one full heartbeat.
Beyond the individual waves, specific intervals and segments provide insights into the heart’s electrical conduction. The PR interval measures the time from the start of atrial depolarization to the beginning of ventricular depolarization. This interval reflects the time it takes for the electrical impulse to travel from the atria through the atrioventricular (AV) node to the ventricles. A normal PR interval typically ranges from 0.12 to 0.20 seconds.
The ST segment is the flat line between the end of the QRS complex and the beginning of the T wave. This segment represents the period when the entire ventricular muscle is depolarized. The QT interval measures the total time for ventricular depolarization and repolarization, extending from the start of the QRS complex to the end of the T wave. Its duration changes with heart rate, and its accurate measurement is important for assessing potential electrical abnormalities.
Calculating Heart Rate and Rhythm
Determining heart rate and rhythm from an EKG strip involves specific methods. For a regular heart rhythm, a common approach is to count the large squares between two consecutive R waves (the tall peak in the QRS complex) and divide 300 by that number. For instance, if there are four large squares between R waves, the heart rate would be approximately 75 beats per minute (300/4 = 75).
Another method for regular rhythms involves counting the number of small squares between two R waves and dividing 1500 by that count. Each small square typically represents 0.04 seconds, and five small squares make up one large square.
When the heart rhythm is irregular, a different method is used. Count the number of R waves within a 6-second strip (often marked on the EKG paper) and then multiply that number by 10 to estimate the heart rate in beats per minute. This provides an average rate over that period.
Assessing the rhythm involves observing the consistency of the R-R intervals, which is the distance between consecutive R waves. If these intervals are consistent, the rhythm is considered regular. If the intervals vary, the rhythm is irregular.
Identifying Common EKG Patterns
Normal sinus rhythm represents the heart’s typical electrical activity, originating from the sinoatrial node, the natural pacemaker. On an EKG, it is characterized by a regular rhythm with a heart rate between 60 and 100 beats per minute. Each QRS complex is preceded by a P wave, and the P waves are consistent in shape.
Bradycardia refers to a slower-than-normal heart rate, typically below 60 beats per minute in adults. On an EKG, sinus bradycardia appears as a regular rhythm where the P waves, QRS complexes, and T waves look normal, but are spaced further apart due to the slower rate.
Tachycardia indicates a faster-than-normal heart rate, generally above 100 beats per minute in adults. Sinus tachycardia shows a regular rhythm with normal-looking P, QRS, and T waves, but much closer together, reflecting the increased heart rate.
An irregular rhythm means heartbeats are not evenly spaced. This can range from slightly irregular, where there is a pattern to the irregularity, to completely irregular, where no discernible pattern exists. Identifying these patterns visually helps differentiate various cardiac behaviors.
Putting EKG Results in Context
An EKG provides valuable information about the heart’s electrical activity, but it is one diagnostic tool among many. A definitive interpretation requires a trained medical professional, such as a doctor or cardiologist. These experts consider EKG findings alongside a patient’s symptoms, medical history, and results from other diagnostic tests.
Self-interpreting EKG results without professional medical guidance can lead to misunderstandings. Healthcare providers undergo extensive training to accurately interpret the nuances of EKG tracings. The information presented here serves as a general understanding and should not replace consultation with a qualified healthcare provider for any health concerns.