The last major wave component of the ECG is the T wave, which is usually larger than the P wave and rounded or slightly peaked. The QRS complex may have one, two, or three wave components, depending on the lead and your patient's condition.
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The QRS complex is variable in appearance and may have a different shape (or morphology) in different patients or even look different in various ECG leads in the same patient. A duration greater than 0.12 second usually indicates prolonged ventricular conduction caused by a bundle-branch block. The QRS complex normally has a duration of 0.06 to 0.1 second. (Remember that electrical activity precedes mechanical activity, and the ECG shows only electrical activity.) If you palpate a carotid or radial pulse while looking at a cardiac monitor, you should feel a pulse with each QRS complex on the monitor. Ventricular depolarization generates the QRS complex, the electrical equivalent of ventricular systole. The function of the Purkinje fibers is to rapidly stimulate ventricular muscle fibers, resulting in the next major event in the cardiac cycle: ventricular depolarization. These fibers form a complex network that mingles with ventricular myocardial cells. The bundle branches are high-speed conducting fibers that run down the intraventricular septum and transmit the cardiac impulse to the Purkinje fibers. A collection of cardiac conduction fibers, the bundle of His splits into the right and left bundle branches. The AV node receives the atrial impulse and (after a brief pause to let the ventricles fill) transmits it to the ventricles via the bundle of His.
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The wave of depolarization continues through the atria until it encounters the next important structure, the atrioventricular (AV) node. The P wave is the first part of the cardiac cycle and appears as a small, semicircular bump (see Tracing a normal ECG waveform). The SA node normally depolarizes at a rate of 60 to 100 times/minute, causing the atria to contract and propel blood into the ventricles.Ītrial depolarization produces the first element on the ECG waveform: the P wave. A normal heartbeat is initiated in the sinoatrial (SA) node, a specialized group of cells in the right atrium. The heart's internal conduction circuit initiates each heartbeat and coordinates all parts of the heart to contract at the proper time.
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In a future article, I'll discuss ECG abnormalities. In this article, I'll cover the basics of 12-lead ECG interpretation, focusing on a normal ECG. Smythe's 12-lead ECG is abnormal? Could you recognize signs that he's having a myocardial infarction (MI)? If you can independently interpret a 12-lead ECG, you can anticipate and prepare for the emergency care your patient may need. Following your facility's protocol, you administer supplemental oxygen at 2 to 4 L/minute via nasal cannula and page the healthcare provider on call, who orders stat serum cardiac biomarkers, a 12-lead ECG, and sublingual nitroglycerin.ĭo you know what to look for to determine whether Mr. You ask about associated signs and symptoms and factors that aggravate or relieve the pain. You take his vital signs and perform a chest pain assessment, which includes the onset, location, quality, intensity, duration, and any radiation of the discomfort. Smythe had a laparoscopic cholecystectomy earlier today.
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Responding to the call bell, you find George Smythe, 67, sitting up in bed and complaining of chest discomfort.