ECGs for the Emergency Physician 1 Flashcards
**Sinus rhythm (SR), rate 60, normal ECG. **
SR is generally defined as having an atrial rate of 60–100/minute and a P-wave axis +15 to +75 degrees. Sinus beats can be identified by upright P-waves in leads I, II, III, and aVF; if the P-waves are inverted in any of these leads, it implies an ectopic atrial origin for the P-waves. The PR interval should be >0·20 seconds; a shorter PR interval suggests either an atrioventricular (AV) junctional origin or the presence of a pre-excitation syndrome (for example Wolff-Parkinson-White syndrome). The normal ECG often will demonstrate inverted T-waves in leads aVR and V1.
**SR with sinus arrhythmia, rate 66, benign early repolarization (BER). **
Sinus arrhythmia is defined as sinus rhythm with slight variation (>0·16 seconds) in the sinus cycles. This produces mild irregularity in the rhythm and usually occurs at lower heart rates (<70/minute). BER is a normal variant often found in young healthy adults, especially men. Patients will have ST-segment elevation in many leads, although not in aVR or V1. The absence of reciprocal ST-segment changes helps distinguish this entity from acute myocardial infarction. Acute pericarditis can be difficult to distinguish from BER. The presence of PR-segment depression in various leads favors the diagnosis of acute pericarditis; however, the distinction between these two entities often must be made based on the patient history and physicial examination: acute pericarditis is classically associated with pleuritic sharp chest pain that changes with body position, and these patients may have a pericardial friction rub heard during cardiac auscultation.
**SR, rate 91, with first degree AV block. **
The normal PR-interval is 0·12–0·20 seconds. This patient has a marked first degree AV block with a PR-interval of 0·32 seconds.
**Ectopic atrial rhythm, rate 82, otherwise normal ECG. **
P-waves in leads I, II, and aVF are inverted suggesting an ectopic origin of the atrial beats. The normal PR-interval (0·16 seconds) implies that the origin is in the atrium rather than in the AV junction.
**AV junctional rhythm, rate 50. **
AV junctional rhythms are usually associated with a rate of 40–60/minute and narrow QRS complexes (unless there is a conduction abnormality, for example bundle branch block). If an AV junctional rhythm has a rate 61–100/minute, it is referred to as an “accelerated AV junctional rhythm;” if the rate is >100/minute, it is referred to as an “AV junctional tachycardia.” In AV junctional rhythms, P-waves may be hidden or may precede or follow the QRS complex. When these “retrograde” P-waves precede the QRS, they will be associated with a short PR-interval (<0·12 seconds). This patient had recently started taking a calcium channel blocking medication for hypertension. When the medication was discontinued, SR returned and the ventricular rate increased.
Accelerated idioventricular rhythm (AIVR), rate 65.
Ventricular escape rhythms are usually associated with rates 20–40/minute. When a ventricular rhythm is 40–110/minute, it is referred to as an “accelerated ventricular rhythm” or “accelerated idioventricular rhythm.” When the rate exceeds 110/minute, “ventricular tachycardia” is diagnosed. This patient’s rhythm strip demonstrates evidence of AV dissociation, easily seen in the latter portion of the strip. AIVR is commonly seen in the setting of AMI, especially after the administration of thrombolytic agents. AIVR is thought to be a marker of reperfusion. This patient’s dysrhythmia resolved in minutes without therapy, typical of post-thrombolytic AIVR.
**SR, rate 100, right bundle branch block (RBBB). **
RBBB is typically associated with an rSR’ pattern in the right precordial leads, although a single, wide R-wave or a qR pattern may be seen instead. The S-wave in the lateral leads (I, aVL, V5, V6) is slightly wide, and the QRS duration is ≥0·12 seconds. If all the criteria are met except the QRS duration is ≤0·12 seconds, an incomplete RBBB is diagnosed. Leads V1−V3 often demonstrate ST-segment depression and inverted T-waves. Any ST-segment elevation should alert the healthcare provider to the possibility of AMI.
**SR, rate 80, first degree AV block, left bundle branch block (LBBB). **
LBBB is characterized by prolonged QRS duration ≥0·12 seconds, leftward QRS axis, a broad monophasic R-wave in leads I and V6, and a deep wide S-wave in lead V1 (often times without any R-wave). The ST-segments and the T-waves are directed in an opposite direction to the main QRS vector in all leads (the rule of “appropriate discordance”). This patient had a pre-existing LBBB and borderline first degree AV block. The increased dose of the beta-receptor blocking medication caused a significant increase in the PR-interval. See figure on p. 55.
**SR, rate 81, left anterior fascicular block (LAFB). **
LAFB is associated with a leftward QRS axis, a qR complex (small q-wave and large R-wave) or R-wave in leads I and aVL, rS complex (small r-wave and large S-wave) in lead III, and absence of other causes of leftward axis. The differential diagnosis of leftward axis includes the following: LAFB, LBBB, inferior myocardial infarction, left ventricular hypertrophy, ventricular ectopy, paced beats, and Wolff-Parkinson-White syndrome.
**SR, rate 85, RBBB, left posterior fascicular block (LPFB). The combination of a RBBB plus a fascicular block is also called a “bifascicular block.” **
LPFB is much less common than LAFB. It usually occurs concurrently with an RBBB rather than in isolation. The T-wave inversions in the inferior leads are commonly found with this type of bifascicular block. LPFB is associated with a rightward QRS axis, a qR complex (small q-wave and large R-wave) in lead III, and absence of other causes of rightward axis. The differential diagnosis of rightward axis includes the following: LPFB, lateral myocardial infarction, right ventricular hypertrophy, acute (for example pulmonary embolism) and chronic (for example emphysema) lung disease, ventricular ectopy, hyperkalemia, overdoses of sodium channel blocking drugs (for example cyclic antidepressants). Normal young or slender adults with a horizontally positioned heart can also demonstrate a rightward QRS axis on the ECG.
