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Practical Approach to a Patient with ECG Changes

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Practical Approach to a Patient with ECG Changes CHAPTER Practical Approach to a Patient with ECG Changes 17 Shirish MS Hiremath The ECG is the oldest cardiologic test, but even 100 years Acute or evolving changes in the ST– T waveforms and after its inception, it continues as the most commonly Q waves, when present, potentially allow the clinician used cardiologic test. to time the event, to identify the infarct-related artery, to estimate the amount of myocardium at risk as well as Historical milestones in ECG1 prognosis, and to determine therapeutic strategy. Various 1887: Augustus Desire Waller, recorded electric current algorithms predict the IRA in case of STEMI, though this preceding cardiac contraction. correlation is not valid in NSTEMI. 1903: Einthoven, developed string galvanometer. Coronary artery size and distribution of arterial segments, collateral vessels, location, extent and severity 1911: Sir Thomas Lewis published his pioneering work of coronary stenosis, and prior myocardial necrosis can on ECG all impact ECG manifestations of myocardial ischaemia. 1929: Dock, use of cathode ray oscilloscope for ECG Electrocardiographic evidence of myocardial ischaemia 1932: Wolferth CC and Wood CC, introduced chest leads in the distribution of a left circumflex artery is often overlooked and is best captured using posterior leads at 1942: Goldberger E, Introduced unipolar limb leads. the fifth intercostal space (V7 at the left posterior axillary ECG in emergency room: Despite the advent of expensive line, V8 at the left mid-scapular line, and V9 at the left and sophisticated alternatives, ECG dictates the timely paraspinal border). A cut-point of 0.05 mV ST elevation is diagnosis and management in acute coronary syndrome recommended in leads V7–V9; specificity is increased at a (ACS) and arrhythmias. cut-point ≥0.1 mV ST elevation and this cutpoint should be used in men, 40 years old. ST depression in leads V1–V3 In a suspected case of ACS, ECG should be acquired and may be suggestive of infero-basal myocardial ischaemia interpreted promptly (i.e. target within 10 min) after (posterior infarction), especially when the terminal T clinical presentation, and initial ECG is non-diagnostic wave is positive (ST elevation equivalent), however this is then serial ECG should be acquired (15-20 minute interval) non-specific. In patients with inferior and suspected right 3 to catch the dynamic changes. ventricular infarction, right pre-cordial leads V3R and V4R should be recorded, since ST elevation ≥0.05 mV (≥0.1 R mV in men , 30 years old) provides supportive criteria for the diagnosis (ref Fig---). Other ECG signs associated with acute myocardial ischaemia include cardiac arrhythmias, intraventricular and atrioventricular conduction delays, Isoelectric line: horizontal PR ST segment level between cardiac cycles and loss of precordial R wave amplitude. Coronary T wave artery size and distribution of arterial segments, collateral J vessels, location, extent and severity of coronary stenosis, P P QRS V= Vulnerable Table 1: ECG manifestations of acute myocardial ischaemia (in 1 period 2 absence of LVH and LBBB)4 ST elevation ST depression and T Phase 0 3 wave changes Phase 4 New ST elevation at the J New horizontal or down- QT point in two contiguous sloping ST depression leads with the cut-points: ≥0.05 mV in two Cell cytoplasm ≥0.1 mV in all leads other contiguous leads and/orT K+ K+ K+ Na+ K+ K+K+ Na+ than leads V2–V3 where inversion ≥0.1 mV in two – – – + + + + – – – – – the following cutpoints contiguous leads with + + + – – – – + + + + Cell membrane Na+ K+ apply: ≥0.2mVinmen≥4 prominent R wave or R/S Na+ Na+ K+ Na+ influx Efflux 0years;≥0.25mVinmen ratio >1. <40 years,or ≥0.15 mV in Fig. 1: The action potential, and the electrocardiogram2 women. 85 ST-segment elevation in V1, V2 and V3 ST-segment elevation in V1 (>2.5 mm) ST-segment depression (≤1 mm) or ST-segment depression (>1 mm) or right bundle-branch block with in II, III, and aVF ST-segment elevation in II, III, and aVF Q wave or both CHAPTER 17 Proximal left anterior Proximal left anterior Distal left anterior descending artery descending artery descending artery Sensitivity 12% Sensitivity 34% Sensitivity 66% Specificity 100% Specificity 98% Specificity 73% Positive predictive value 100% Positive predictive value 93% Positive predictive value 78% Negative predictive value 61% Negative predictive value 68% Negative predictive value 62% Fig. 2: Algorithm for identifying IRA in anterior wall MI5 ST ä ≥ 1 mm Inferior Wall AMI POS T – WAVE PROXIMAL OCCLUSION RCA (ST elevation II, III, aVF) LCx vs RCA NO ST ä : POS T – WAVE DISTAL OCCLUSION RCA ST segment elevation III > II NEG T – WAVE OCCLUSION CX Yes No ST segment Fig. 4: Value of ST-T changes in acute infero-posterior MI LCX or Distal RCA elevation VI poorly because of a low sensitivity of 10%, although the Yes No specificity was high at 82%. Using a criterion of twice the upper limit of normal value ST elevation V4R for serum troponin as the ‘gold standard’ for confirmation Proximal RCA and 11 RV Infarction of myocardial injury, the investigators in the Wong et al. Yes No study demonstrate a high specificity for the criteria. Acute pericarditis very closely resembles acute coronary Proximal RCA with Mid RCA, No RV involvement syndrome in terms of symptoms and the ECG changes. RV involvement The two classical ECG findings of acute pericarditis Fig. 3: Algorithm for identifying IRA in inferior wall MI6 are ST elevation (most sensitive and consistent) and PR depression (most specific). Characteristic ST-elevation of and prior myocardial necrosis can all impact ECG acute pericarditis is concave upwards and it is present in manifestations of myocardial ischaemia. the majority of the standard ECG leads, except in leads When the patient has LBBB on admission and recent AVR and V1 where the ST segment is always depressed. previous ECGs do not show LBBB, the patient is presumed This ST-elevation is often transient and are sometimes to have new-onset LBBB, which many investigators followed (after a variable time) by diffuse T-wave and current guidelines accept as the equivalent of inversions. electrocardiographic findings supportive of AMI.8,9 When Event ECG at the time of palpitation is of foremost the patient has LBBB on arrival and no preexisting ECG importance in diagnosis and management of arrhythmia. is available for comparison, then there are specific ECG For evaluation of arrhythmia, traditional step-wise criteria which could distinguish between patients with assessment of event-ECG should be followed i.e. rate, new injury or infarction and those without. Sgarbossa rhythm, axis, tachycardia cycle-length, QRS morphology, et al. proposed specific electrocardiographic criteria for p-wave morphology, p-QRS relationship. ECG during the diagnosis of AMI in the presence of LBBB applied asymptomatic period has equal importance in diagnosis to patients in GUTO-I trial.10 But this criteria performed i.e. p/QRS-morphology, QRS duration (QRSd), QT- 86 Table 2: Differential diagnosis of ST-elevation7 1. Ischemia/myocardial infarction Noninfarction, transmural ischemia (Prinzmetal’s angina, and probably Tako-Tsubo syndrome, which may also exactly simulate classical acute infarction) Acute myocardial infarction Postmyocardial infarction (ventricular aneurysm pattern) 2. Acute pericarditis 3. Normal variants (including “early repolarization” patterns) 4. Left ventricular hypertrophy/left bundle branch CARDIOLOGY block 5. Other (rarer) Acute pulmonary embolism Fig. 5: An electrocardiogram in acute pericarditis. Brugada patterns (right bundle branch block–like Narrow QRS tachycardia pattern with ST elevations in right precordial (QRS duration less than 120 ms) leads) Class 1C antiarrhythmic drugs Regular tachycardia? DC cardioversion Yes No Hypercalcemia Visible P waves? Atrial fibrillation Hyperkalemia Atrial tachycardia/flutter with No Yes variable AV conduction Hypothermia [J (Osborn) waves MAT 6. Nonischemic myocardial injury Atrial rate greater than ventricular rate? Myocarditis Tumor invading left ventricle Yes No Atrial flutter or Analyze RP Trauma to ventricles atrial interval tachycardia Table 3: Sgarbossa criteria for diagnosis of AMI in LBBB (score 10 ≥3 have high specificity) Short Long (RP shorter than PR) (RP longer than PR) ECG criteria Score 1. ST-segment elevation ≥1 mm and 5 concordant RP shorter than 70 ms RP longer than 70 ms Atrial tachycardia PJRT with QRS complex Atypical AVNRT 2. ST-segment depression ≥1 mm in lead V 1 3 AVNRT AVRT AVNRT V 2 V 3 Atrial Tachycardia 3. ST-segment elevation ≥5 mm and 2 12 discordant with QRS complex Fig. 6: Algorithm for diagnosis of a narrow QRS tachycardia can be done with intravenous beta-blocker, calcium interval, presence of pre-excitation, presence of channel blocker or adenosine. Long-term management pathological q-wave. largely depends on number of recurrences and underlying First step in assessment of tachycardia is QRSd, less structural heart disease. For tachycardia involving AV- than 120msec is defined as narrow-complex tachycardia junction (AVRT/AVNRT) electrophysiological study with (NCT) and ≥120msec is defined as broad complex radiofrequency ablation is highly effective, with more tachycardia (BCT). With few exceptions NCT is almost than 95% curing rate in long-term and very low risk of always supraventricular in origin therefore less likely to recurrence. be life-threatening. With few exceptions BCT is almost For atrial tachycardias (Afib, Aflutter and ATach), rate always ventricular in origin therefore more likely
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