14.5
ECG の解釈 I: リズム
心電図 (ECG) は、心臓の電気的活動を ECG 用紙またはモニター上にグラフで表します。
心電図の構成要素
正常洞調律 (NSR) における正常な ECG 波形の主な構成要素には、P 波、PR 間隔、QRS 群、ST セグメント、T 波、および場合によっては U 波が含まれます。
ECG 波形は…
心電図またはECGは、心臓の電気的活動を捕捉して分析し、その機能、リズム、および電気伝導システムを評価します。
心周期の各フェーズは、心臓モニターまたはECGグラフ用紙のストリップのディスプレイ上の特定の波形で表されます。
ECG波形の主要成分には、P波、PR間隔、QRS群、STセグメント、T波、場合によってはU波が含まれます。
P波は通常、高さが2.5mm以下、持続時間が0.11秒以下です。
PR 間隔は 0.12 秒から 0.20 秒まで変動します。
QRSコンプレックスは通常0.12秒未満続きます。
STセグメントは通常等電性です。
T波は、滑らかで正のたわみとして表示されます。QT間隔は心拍数によって異なります。
1分間のリズムストリップには、300個の大きなボックスと1500個の小さなボックスが含まれています。
RRインターバル内の小さなボックスを数え、1500をその数で割って、規則的なリズムで心拍数を決定します。
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Q1: What are the main components of a normal ECG waveform?
A normal ECG waveform includes the P wave, PR interval, QRS complex, ST segment, T wave, and sometimes a U wave. The P wave represents atrial depolarization, the PR interval shows conduction delay, the QRS complex reflects ventricular depolarization, the ST segment indicates early ventricular repolarization, and the T wave represents ventricular repolarization. These components together create the electrical signature of a normal heartbeat.
Q2: How do you measure the PR interval on an ECG?
The PR interval is measured from the beginning of the P wave to the start of the QRS complex and normally ranges from 0.12 to 0.20 seconds. This interval encompasses the P wave and the PR segment, representing the time for electrical impulses to travel from the atria through the atrioventricular node to the ventricles. Variations outside this range may indicate conduction abnormalities.
Q3: What does the QRS complex represent on an ECG?
The QRS complex represents ventricular depolarization and consists of three waves: the Q wave (negative deflection), R wave (positive deflection), and S wave (negative deflection). The entire complex normally lasts less than 0.12 seconds. This rapid electrical activity triggers ventricular muscle contraction, making it one of the most prominent features on an ECG strip.
Q4: How is heart rate calculated from an ECG strip?
To calculate heart rate from an ECG strip with regular rhythm, count the small boxes between two consecutive R waves and divide 1500 by that number to get beats per minute. For example, if there are 25 small boxes between R waves, the calculation is 1500 divided by 25, which equals 60 beats per minute. A one-minute rhythm strip contains 300 large boxes and 1500 small boxes.
Q5: What is the significance of the ST segment on an ECG?
The ST segment links the QRS complex to the T wave and is usually isoelectric, meaning it appears as a flat line on the ECG. It indicates the early phase of ventricular repolarization. Elevation or depression of the ST segment from its normal baseline can signal cardiac injury, ischemia, or other serious conditions requiring clinical attention.
Q6: What do the RR and PP intervals tell you about cardiac rhythm?
The RR interval, measured from one QRS complex to the next, determines ventricular rate and rhythm. The PP interval, measured from one P wave start to the next, measures atrial rate and rhythm. Regular intervals indicate normal sinus rhythm, while irregular intervals suggest arrhythmias. These measurements help identify abnormal heart rhythms that may require further evaluation with ecg interpretation of arrhythmias ii atrial junctional and ventricular arrhythmias.
Q7: What are the normal measurements for the P wave and T wave?
The P wave typically measures 2.5 millimeters or less in height and 0.11 seconds or less in duration, representing atrial depolarization. The T wave appears as a smooth, positive deflection following the QRS complex and represents ventricular repolarization. Both waves should display consistent morphology and timing across the ECG strip to indicate normal electrical conduction.