Electrocardiogram (Images)

20 Electrocardiogram Hung-Fat Tse Case 20.1 Leading question A 7l-year-old man with a history of diabetes and hypertension presents with sudden onset of chest discomfort. (See p. 296.) Questions I. Describe two ECG abnormalities. 2. What is the ECG diagnosis? 3. Name two investigations which help to confirm the diagnosis. Answers L. Convex ST segment elevation over lead IT, III, and aVF, and ST segment depression and T wave inversion over lead V1-V4. 2. Acute inferior myocardial infarction. 3. Chest X-ray, cardiac enzyme, radionuclide imaging, echocardiogram.

Case 20.1 Electrocardiogram 297 Description + The ECG abnormalities associated with acute myocardial infarction typically evolve in a relatively predictable phase. « The earliest ECG changes is marked peaking of the T wave— “hyperacute T wave’—over the site of myocardial infarction. If the myocardial ischemia persisted, the peaked T waves evolve into ST segment elevation. * Significant ST segment elevation is defined as = 1 mm (0.10 mV) in 2 or more limb leads or precordial leads V4-V6 or = 2 mm (0.20 mV) in two or more precordial leads V1-V3. The ST segment elevation of myocardial infarction is usually upwardly convex. * As the acute infarction continues to evolve, the ST segment elevation decreases and the T wave begins to invert. As the ST segment elevation subsides, the T wave usually becomes pro- gressively deeper. Discussion * In contrast to convex ST segment elevation during acute myo- cardial infarction, concave ST segment elevation is typically seen in the setting of pericarditis or normal variant early repo- larization abnormality. * The potential clues to differentiate these conditions with acute myocardial infarction includes: ~ The leads with ST segment elevation in acute infarction are more localized than the diffuse changes in pericarditis (all leads except aVR). ~ The presence of reciprocal ST depression over other leads during acute myocardial infarction as shown in this case. However, the ST segment changes over other leads can rep- resent coexisting myocardial ischemia over other sites. ~ The presence of PR segment depression during acute peri- carditis (rarely in acute myocardial infarction).

298 Problem-Based Medical Case Management Case 20.2 Case 20.2 Leading question A 56-year-old man with a history of on-and-off chest discomfort presents with ankle oedema and progressive shortness of breath.

Case 20.2 Electrocardiogram 299 Questions 1. Describe two ECG abnormalities. 2. What is the ECG diagnosis? 3. Name two investigations which help to confirm the diagnosis. Answers 1. Pathological Q wave over V1-V3, and left atrial abnormality. 2. Old anteroseptal myocardial infarction. 3. Chest X-ray, cardiac enzyme, echocardiogram, radionuclide imaging, cardiac catheterization, magnetic resonance imaging. Description + Abnormal Q waves usually develop in the first several hours to days after acute infarction following resolution of ST elevation. In the majority of cases, Q waves persist indefinitely (~85%). * Persistence of ST elevation with abnormal Q wave should raise the suspicion of ventricular aneurysm. * Q waves over lead III and aVR can be normal. * The presence of isoelectric ST segments and upright T waves suggest that the infarction is not acute (months to years). Discussion * Other than myocardial infarction, abnormal Q wave can be observed in the following conditions: ~ Wolff-Parkinson-White syndrome: negative delta-waves over inferior lead can mimic inferior myocardial infarction. ~ Left bundle branch block: QS pattern over V1-V4 together with 1-2 mm ST segment elevation mimic anteroseptal myocardial infarction. — Chronic obstructive airway obstruction: Q wave over infe- rior lead with poor R wave progression, P pulmonale, and low voltage QRS.

300 Problem-Based Medical Case Management Case 20.3 — Hypertrophic cardiomyopathy: septal hypertrophy with Q wave over I, aVL, V4-V6. — Pulmonary embolism: Q wave over lead III and aVF associ- ated with ST and T wave changes can mimic inferior myo- cardial infarction, but Q wave over lead II is rare. Case 20.3 Leading question A 26-year-old man presents with intermittent palpitation. 3 i J : ¥ ! Y i J L (SRS — AJ [ L }

Case 20.3 Electrocardiogram 301 Questions 1. Describe two ECG abnormalities. 2. What is the ECG diagnosis? 3. Name two abnormal cardiac arrhythmias that can be associated with this condition. Answers 1. Short PR interval, and presence of delta wave. 2. Wolff-Parkinson-White syndrome. 3. Atrial fibrillation, ventricular fibrillation, paroxysmal supraven- tricular tachycardia. Description * The presence of a short PR interval (< 0.12 s), wide QRS complex (> 0.1 s), delta wave (prolonged upstroke of QRS complex) with or without secondary ST and T wave changes indicative of Wolff-Parkinson-White syndrome. Discussion * Other causes of an RSR’ complex in V1 include: ~ Right ventricular hypertrophy: associated with right axis deviation, right atrial enlargement, R wave > 10 mm and ST depression and T wave inversion over V1-V3. — Posterior myocardial infarction: associated with inferior myocardial infarction. ~ Right bundle branch block: QRS duration > 120 ms, T wave inversion over V1-V2 and wide S wave in V5-V6.

302 Problem-Based Medical Case Management Case 20.4 Case 20.4 Leading question A 53-year-old woman complains of chest discomfort, shortness of breath, and palpitation.

Case 20.4 Electrocardiogram 303 Questions 1. Describe two ECG abnormalities. 2. What is the ECG diagnosis? 3. Name two appropriate investigations. 4, Name two drugs that can control the heart rate and relieve her symptoms. Answers 1. Narrow complex tachycardia (rate 150 bpm) and flutter wave. 2. Atrial flutter with 2:1 conduction. 3. Chest X-ray, electrolytes, cardiac enzymes, thyroid function test, echocardiogram. 4. Digoxin, diltiazem, verapamail, beta-blockers, and amiodarone. Description * Atrial flutter shows rapid regular atrial undulation (flutter waves) at a rate of 240-340 per minute. * Atrioventricular conduction ratio is usually fixed (2:1, 3:1 or > 4:1), but may be variable and mimic atrial fibrillation. Discussion * The response to carotid sinus massage or drugs (e.g., adeno- sine or ATP) which decrease atrioventricular conduction can unmark the atrial activity during atrial flutter. In contrast, these manoeuvers terminate other regular supraventricular tachycar- dias (atrioventricular nodal re-entry or atrioventricular re-entry tachycardias).

304 Problem-Based Medical Case Management Case 20.5 Case 20.5 Leading question A 57-year-old man with a history of hypertension presents with shortness of breath and palpitation. Sokol. 3.32 au 18 mn/mV aur Coeoem /oo ks 0TC 433 as 1 X I

Case 20.5 Electrocardiogram 305 Questions 1. Name two ECG diagnoses. 2. Suggest two appropriate investigations. 3. Name two drugs that can control the heart rate and relieve his symptoms. Answers 1. Atrial fibrillation and left ventricular hypertrophy. 2. Chest X-ray, electrolytes, cardiac enzymes, thyroid function test, echocardiogram. 3. Digoxin, diltiazem, verapamail, beta-blockers, and amiodarone. Description + Discrete P waves are absent during atrial fibrillation and atrial activity is totally irregular and manifest as fibrillatory rate wave with varying amplitudes, duration, and morphology. During atrial fibrillation, ventricular rhythm is irregularly irregular (unless the presence of complete heart block). * ECG diagnosis of left ventricular hypertrophy is based on the presence of left amplitude QRS complexes (S in V1 + Rin V5 or V6 > 35 mm or any R + S >45 mm). * Down-sloping ST depression and asymmetrical T wave inver- sion: “strain pattern” are present. Discussion * Atrial fibrillation may be mimicked by: - Mu;El/i,focal atrial tachycardia-atrial rate > 100 bpm with 3 or more different P wave morphologies, and PR, RR, and RP intervals vary. — Atrial flutter or atrial tachycardia with variable block—rapid and regular P wave or flutter wave is observed. * Digoxin toxicity may result in regularization of the RR inter- val due to complete heart block with junctional tachycardia.

306 Problem-Based Medical Case Management Case 20.6 It can be exacerbated by hypokalaemia, hypomagnesaemia, and hypercalcaemia. * ST segment depression and T wave inversion can also be observed with digoxin therapy and myocardial ischemia. Case 20.6 Leading question An 87-year-old man presents with syncope. 10nn/aV. VI-v2-V3 ) Rbythalil) | 10mn/ay

Case 20.6 Electrocardiogram 307 Questions 1. Name three ECG abnormalities. 2. What is the ECG diagnosis? 3. Suggest two appropriate investigations. 4. What is the immediate treatment for this patient? Answers 1. Right bundle branch block, left axis deviation, bradycardia, atrioventricular dissociation. . Complete heart block. 3. Chest X-ray, electrolytes, cardiac enzymes, thyroid function test. 4. Temporary external or transvenous cardiac pacing. ) Description * During complete heart block, the atrial and ventricular activities are independent of each other, unually described as atrioven- tricular dissociation. As a result, the PP and RR intervals are constant, but the PR interval varies. * Furthermore, the atrial rate is faster than the ventricular rate during complete heart block. Discussion * In the majority of cases, complete heart block is caused by degeneration of conduction system, and rarely due to congeni- tal heart block. * Potential reversible causes of complete heart block include hyperkalaemia, endocarditis, acute myocardial infarction, digoxin toxicity, and Lyme diseases.

308 Problem-Based Medical Case Management Case 20.7 Case 20.7 Leading question A 67-year-old man complains of sudden onset of shortness of breath and chest discomfort.

Case 20.7 Electrocardiogram 309 Questions . Name two ECG abnormalities. . What is the diagnosis? . Suggest two appropriate investigations to confirm the diagnosis. W oo — Answers 1. Sinus tachycardia and S1Q3T3. 2. Pulmonary embolism. 3. Chest X-ray, CT scan of thorax, ventilation-perfusion scan, and pulmonary angiogram. Description * During acute pulmonary embolism with acute cor pulmonale, changes appear in the frontal plane leads (I, IIT, aVF, V2-V3) that mimic acute inferior myocardial infarction. * Lead IIT is mainly involved with an increase in the size of Q wave, slight ST segment elevation, and shallow inversion of the T wave (Q3T3). * Other changes include increase size of S wave in lead I (S1), right axis deviation, right bundle branch block, and sinus tachycardia. Discussion * The presence of sinus tachycardia and findings consistent with right ventricular pressure overload as described above are sug- gestive of acute pulmonary embolism. *+ ECG abnormalities of pulmonary embolism are often transient. * Other causes of right ventricular overload include right ven- tricular hypertrophy with pulmonary hypertension and chronic obstructive airway diseases.

310 Problem-Based Medical Case Management Case 20.8 Case 20.8 Leading question A 67-year-old man presents with sudden collapse and physi- cal examination shows a rapid heart rate with a blood pressure 70/30 mmHg. 1 A gy { s/ 7 05 07 SE i Awun gy p Auju o1 Al g1

Case 20.8 Electrocardiogram 311 Questions |. What is the ECG diagnosis? . List three possible causes for this ECG abnormality. . Suggest two appropriate investigations. . What is the immediate treatment for this patient? FNIES) Answers 1. Wide complex tachycardia. 2. Ventricular tachycardia, supraventricular tachycardia with pre- existing right bundle branch block, supraventricular tachycardia with aberrant conduction and antidromic tachycardia through accessory pathway. . Chest X-ray, electrolytes, cardiac enzymes, echocardiogram. 4. External DC cardioversion. > Description * QRS morphology during wide complex tachycardia that favours ventricular tachycardia include atrioventricular dissociation, capture beats, fusion beats, > 140 ms for right bundle branch block pattern or > 160 ms for left bundle branch block pattern, when QRS deflections in the precordial leads are all positive or negative (concordance) and when the R wave is taller than the R’ wave in V1. Discussion * In contrast, ECG features suggestive of supraventricular tachy- cardia with aberrancy include QRS morphology similar to sinus rthythm or aberrantly conducted atrial premature beats, QRS deflection discordance in precordial lead. * All haemodynamic unstable wide complex tachycardia should be treated as ventricular tachycardia with DC cardioversion.

312 Problem-Based Medical Case Management Case 20.9 Case 20.9 Leading question A 52-year-old man presents with sudden onset of palpitation. 1 Ty | i 0000-00000 507 sasfus s2ipasds Aufwu gytisany Awfws 01qui

Case 20.9 Electrocardiogram 313 Questions I 2 3 4 5 . Name three ECG abnormalities. . What is the ECG diagnosis? . What are the possible mechanisms for this ECG diagnosis? . Suggest two appropriate investigations. . What is the immediate treatment for this patient? Answers 1. w o Narrow complex tachycardia, retrograde atrial activation, and ST and T wave abnormalities. . Supraventricular tachycardia. . Atrioventricular nodal re-entry tachycardia, atrioventricular re-entry tachycardia, and atrial tachycardia. . Chest X-ray, electrolytes, cardiac enzymes, thyroid function test. . Vagal manoeuvers, fast-acting atrioventricular nodal blocking agents, such as adenosine and verapamail. Description During supraventricular tachycardia, the heart rate is > 100 bpm, the QRS complex is regular and narrow, and the P wave is not easily identified. Retrograde atrial activation lead to inverted P waves in leads II, III, and aVE. ST and T wave abnormalities suggestive of myocardial ischemia are common during rapid tachycardia. Discussion Although the number and location of P wave may provide a cue to the diagnosis of the mechanisms of supraventricular tachy- cardia, it is difficult to distinguish them based solely on ECG: ~ Atrioventricular nodal re-entry tachycardia: P wave fused to or immediately after QRS complex.

314 ' Problem-Based Medical Case Management Case 20.10 — Atrioventricular re-entry tachycardia: P wave in the ST segment. — Atrial tachycardia: P wave > QRS complex. Case 20.10 Leading question A 67-year-old woman presents with syncope after taking medica- tions for “flu” symptoms. NN NN N o~ dd~ L~ i I I | s ! \J‘ e ! SN [N Tty o8 AT PA G I | % e ) -

Case 20.10 Electrocardiogram 315 Questions 1. Name three ECG abnormalities. 2. List three possible causes for this ECG abnormality. 3. Suggest two appropriate investigations. Answers 1. Sinus bradycardia, right bundle branch block, sinus arrhythmia, and prolonged QT interval. 2. The possible causes are: - Drugs: anti-arrhythmic agents, antibiotic (erythromycin, clarithromycin), antihistamine (terfenedine, diphenhy- dramine), and anti-pyschotic agents. - Electrolytes imbalance: hypokalaemia, hypocalcaemia, and hypomagnesaemia. - Congenital long QT syndrome. — Metabolic disorder: hypothyroidism and diabetes. — Neurologic disorder: ~stroke, trauma, subarachnoid haemorrhage. — TIschemic heart disease and bradycardia. 3. Electrolytes, cardiac enzymes, thyroid function test. Description * Normal QT interval varies inversely with heart rate. Therefore, measurement of QT interval needs to be corrected with heart rate: QTc = QT/YRR interval (in second). * During right bundle branch block, the QRS duration > 120 ms, RSR’ pattern with R’ taller than R wave, wide slurred S wave in lead V5-V6, and ST segment depression and T wave inversion over V1-V2. Discussion * Prolonged QT interval is associated with polymorphic ventricu- lar tachycardia—torsades de pointes.

316 Problem-Based Medical Case Management Case 20.10 * In contrast to left bundle branch block, right bundle branch block can occur in normal subjects, and does not interfere with ECG diagnosis of left ventricular hypertrophy or ST elevation myocardial infarction.