ECG Findings in

Life-Threatening Conditions

BY / DR. MOHAMED RAMZY YOUSEFER RESIDENT, QUALITY COORDINATOR QPSD MEEQAT GENERAL HOSPITAL

ECG Graph Paper• Runs at a paper speed of 25 mm/sec• Each small block of ECG paper is 1 mm2

• At a paper speed of 25 mm/s, one small block equals 0.04 s

• Five small blocks make up 1 large block which translates into 0.20 s (200 msec)

• Hence, there are 5 large blocks per second

• Voltage: 1 mm = 0.1 mV between each individual block vertically

Elements of the ECG:• P wave: Depolarization of both atria;

• Relationship between P and QRS helps distinguish various cardiac arrhythmias• Shape and duration of P may indicate atrial enlargement

• PR interval: from onset of P wave to onset of QRS• Normal duration = 0.12-2.0 sec (120-200 ms) (3-4

horizontal boxes)• Represents atria to ventricular conduction time (through

His bundle)• Prolonged PR interval may indicate a 1st degree heart

block•

• QRS complex: Ventricular depolarization• Larger than P wave because of greater muscle

mass of ventricles• Normal duration = 0.08-0.12 seconds• Its duration, amplitude, and morphology are

useful in diagnosing cardiac arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc.

• Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are abnormal and may represent MI

ST segment:• Connects the QRS complex and T wave• Duration of 0.08-0.12 sec (80-120 msec

T wave: • Represents repolarization or recovery of

ventricles• Interval from beginning of QRS to apex of T is

referred to as the absolute refractory period

QT Interval• Measured from beginning of QRS to the end of

the T wave• Normal QT is usually about 0.40 sec• QT interval varies based on heart rate

P

Q

R

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A 65-year-old woman presents to the ED with generalized fatigue and palpitations. She was started on an angiotensin-converting enzyme (ACE) inhibitor 2 months ago but has missed her follow-up appointments. What metabolic abnormality could be responsible for the life-threatening condition shown in her ECG tracing?

Life-Threatening Condition (I): Hyperkalemia. The tracing shows a regular rhythm at 75 bpm. A P wave is present in front of each QRS complex, indicating that the rhythm is sinus. A flattened P wave (black arrow), prolonged PR interval (blue bar), borderline widened QRS complexes (green bar), and -- more pathognomonic -- pointed, narrow, and tented tall T waves (red arrow) are all features of hyperkalemia. The patient's serum potassium when the tracing was recorded was 7.2 mEq/L.

An 83-year-old man with known ischemic cardiomyopathy has an out-of-hospital cardiac arrest. He is rushed to the ED by paramedics. What life-threatening condition is shown in his ECG tracing and what rhythm is he at risk of developing?

Life-Threatening Condition (II): Long QT Interval and T-Wave Alternans. The tracing shows a sinus rhythm at 60 bpm. The QT interval (black bar) is prolonged to 680 msec (normal: 300-440 msec), with a QTc also of 680 msec (normal: < 460 msec). The T-wave heights alternate (blue arrows), which is often a precursor to the more severe rhythm of torsade de pointes.

A 74-year-old man with mild dementia presents to the ED with worsening confusion. His medications include omeprazole, aspirin, simvastatin, and digitalis. He lives alone at his home and his daughter comes to visit once a week to lay out his weekly medications. What could be responsible for the life-threatening condition shown on his ECG tracing?

Life-Threatening Condition (III): Digitalis Toxicity. The tracing shows no P waves, with a baseline of irregular, fine undulations, reflecting atrial fibrillation. The QRS complex is narrow and occurs regularly sometimes (in the latter part of the middle strip) and in groups at other times. This tracing is an example of junctional tachycardia with variable conduction to the ventricle. Conducted and skipped QRS complexes are present in patterns of 2:1 (black asterisk), 3:2 (blue asterisk), or 4:3 (red asterisk). The tracing is highly suggestive of digitalis toxicity, especially in this clinical context.

A 25-year-old man arrives at the ED with a heavy cough after getting caught outside in a snowstorm while hiking. A routine ECG is performed. The concerned intern takes one look at it and rushes over to show you what he believes to be a serious problem. Do you agree with the intern's assessment of a life-threatening condition on the tracing?

Life-Threatening Condition (IV): Artifact Simulating a Run of Ventricular Tachycardia. At first glance, this ECG suggests a run of ventricular tachycardia. However, sharp deflections occur regularly at the same rate as the sinus rhythm seen at the beginning and at the end of the tracing (black bar). These deflections are undoubtedly QRS complexes of the sinus rhythm and provide an example of an artifact simulating ventricular tachycardia.

A 32-year-old woman comes to the ED complaining of light-headedness and sweating. She is 5'6" tall and weighs less than 100 lbs. An ECG is immediately obtained, which evolves while you are watching. What life-threatening condition is seen on the ECG tracing?

Life-Threatening Condition (V): Torsade de Pointes. Sinus rhythm is present at the beginning (blue box), but the QT interval of the sinus beats is long (black bar). This is followed by a wide QRS tachycardia at a rate of approximately 200 bpm (red box). The QRS morphology and axis continuously change, indicating torsade de pointes, which is life-threatening.