I would like to finish this short book which deals with the bases of normal ECG and the clues of ECG diagnosis, with a short chapter devoted to the importance of taking into consideration the clinical context of each patient in interpreting the ECG. For this we will comment on two situations that the physician is faced with: (1) patients without any symptoms or physical signs of heart disease who present an abnormal ECG; and (2) a patient who has a normal (or nearly normal) ECG, but presents with serious heart disease that may be advanced. [A]

We will see how important it is in both cases to know that these situations exist, and that it is important to correlate the ECG with the clinical context of the patient.

18.1.  Abnormal ECG in a Patient with Normal History Taking and Physical Examination

On occasion, an abnormal ECG is recorded (bundle branch block or patterns suggesting chamber enlargement, ischemias, or necrosis, or different types of arrhythmias) in a patient who does not present any symptoms or is not aware that he has this abnormal ECG. The physical examination is also normal. In this situation, we feel that the most important measure to take is to follow the steps outlined below.

1. Do not trust in the automatic interpretation.
   All ECGs need a double-check by a physician.
   
   
2. Ensure that the ECG recording is correct.
   Many patterns compatible with partial RBBB (rSr’ in V1) and many other abnormal patterns are due to the erroneous placement of the electrodes (Chapter 3).
   
3. Complete the medical history again.
   Special emphasis must be placed on any symptoms the patients may not have evaluated correctly or not noticed, for example:
   
   
   
   
   1. High abdominal pain that may be the expression of an apparently silent diaphragmatic infarction, according to the Framingham study. This study showed that the appearance of a Q wave of necrosis from 1 year to the next in the ECG, was due to undiagnosed infarction, especially in diabetics.
      
   2. Episodes of arrhythmia, especially of atrial fibrillation (AF), or premature beats, or runs of paroxysmal tachycardia that were incorrectly diagnosed, and attributed to emotional palpitations (sinus), or were unnoticed by the patient. In these patients it is important to determine whether emotion or consumption of alcohol or energizing agents could be causing the ECG abnormalities. The presence of asymptomatic arrhythmia, especially if frequent, obliges us to rule out any associated heart disease.
      
   3. Erroneous evaluation of dyspnea, which may be due to heart failure or pulmonary embolism, but had been considered to be related with obesity, age, etc.
      
   4. Erroneous evaluation of syncope or presyncope as due to hypotension or neuromediated by vagal reflex when it may be the expression of a serious condition. We must ask patients about a family history of sudden death and inquire more about possible inherited heart disease. We must measure the QT interval carefully, and closely examine the entire ECG recording to rule out Brugada syndrome or any cardiomyopathy of genetic origin (see Chapter 17).
      
   5. It is necessary to complete the ‘bedside diagnosis’ with a good physical exam that encompasses inspection, palpation and auscultaton of the heart and the great vessels. This may provide some information, such as the presence of heart murmurs, which may be useful for the global approach of the problem.
      
   6. Finally it is necessary to follow the systematic method of interpretation explained in Chapter 4.
   
   
4. The cases with abnormal ECG that we have to study more carefully are the following:
   
   
   
   1. Presence of abnormal classical parameters: PR and QT intervals, ÂQRS axis, etc.
      
   2. Presence of Q wave of necrosis in asymptomatic patients. [B]
      Above all, it is important to remember that some deep Q waves may be normal. For example, in lead III a deep Q wave may simulate a myocardial infarction. However, these Q waves are benign and due to positional changes, especially in a horizontal and dextrorotated heart if they disappear with deep breathing (Fig. 4.22).
      As previously explained, the presence of a pathologic Q wave may be due to silent myocardial infarction. However, an abnormal Q wave in a patient without previous antecedents of ischemic heart disease may be a sign of other conditions that have remained asymptomatic, such as inherited cardiomyopathy (hypertrophic), systemic diseases with myocardial involvement (amyloidosis, sarcoidosis, etc.), previous myocarditis, neuromuscular disease, or any type of restrictive or hypertrophic cardiomyopathy that has not yet produced symptoms (Chapters 16 and 17).
      
   3. Presence of repolarization disturbances.
      Flat/slightly negative T waves seen in many leads may be a sign of previous pericarditis that went undetected or undiagnosed myocarditis. Naturally, they may be also seen as a residual pattern of ischemic heart disease. In these cases some specific lead patterns are usually located, and the T wave may be deeper and present a mirror pattern.
      The T wave changes (flat/slightly negative), may be also seen in many other circumstances (Fig. 9.29) and sporadically after consuming alcohol or certain foods, and hyperventilation (Fig. 4.25).
      ST changes may be due to multiple causes (Figs 9.20 and 9.28) apart from ischemic heart disease. In acute ischemic heart disease, ST changes occur especially in relation with angina. However they may remain as a residual pattern after the acute phase (see Chapter 9).
      
   4. Presence of voltage criteria for LVE. This may be seen in healthy patients, especially in thin young people without ST abnormalities, in the absence of anatomic LVH. However, in some cases especially in the presence of repolarization abnormalities, they may be the expression of undetected true LVH. [D]
      
   5. Presence of high R wave or r’ in V₁. This may be a sign of many types of heart disease, but it may also be seen as a normal variant (Table 6.1).
      
   6. Presence of advanced bundle branch block in asymptomatic patients. These cases must be studied in depth, especially if the patient is relatively young and the block in located in the left branch. Heart involvement, especially cardiomyopathy due to any etiology, must be ruled out. However, in at least 10% of LBBB patients and in a large number of RBBB patients, it is an isolated manifestation of an exclusive problem in the ventricular conduction system (Lenègre syndrome and Lev syndrome). Nevertheless, it is important to remember the patterns of right or left bundle branch block, that are markers of high risk (Chapter 16). [F]
      
   7. Presence of active arrhythmias (especially PVCs and/or passive arrhythmias (pauses and/or blocks).

In all these cases it is necessary to rule out the effect of some drugs that may trigger these ar­­rhythmias. It will probably be necessary to per­­form complementary tests such as Holter ECG, exercise testing and also echocardiography (imaging techniques).

18.2.  Normal ECG in Patients with Advanced Cardiovascular Disease

Although the ECG is very important in the diagnosis of heart disease, we must not forget that a normal, or apparently normal, ECG may be recorded just before sudden death (SD) of cardiovascular origin. The most common (not exhaustive) severe forms of cardiovascular disease that may be accompanied by a normal ECG are listed below.

1. Acute heart attack.
   In the presence of NSTE-ACS, the ECG may appear normal in a small number of cases (see Section 9.3.3.1.4 in Chapter 9). We must also remember that a peaked symmetrical T wave may be the only visible abnormality, especially in V1-V2 in the hyperacute phase of STE-ACS (see Section 9.2.3.1.2 in Chapter 9).
   
2. Pulmonary embolism.
   The cataclysm that is a severe pulmonary embolism may appear suddenly, especially in bedridden patients without evident heart disease and with a previous apparently normal ECG recording. The patient generally presents sinus tachycardia and other ECG abnormalities (Figs 15.3 and 15.4), but elderly patients with deteriorated sinus function and previously abnormal basal ECG, may not present sinus tachycardia, which makes the diagnosis more difficult.
   
3. Inherited heart diseases.
   The ECG may be slightly abnormal or poorly evaluated. This type of disease includes channelopathies (Brugada syndrome and long and short QT syndromes) and genetic cardiomyopathies (e.g. hypertrophy) (see Chapter 16).
   In hypertrophic cardiomyopathy the ECG may appear abnormal before the echocardiogram, but in 5% to 10% of cases the ECG may appear to be normal. The same may occur in arrhythmogenic RV dysplasia.
   In Brugada syndrome the ECG may vary abruptly from normality to type 1 or 2 pattern with certain triggers (e.g. fever, drugs). Furthermore, it may appear normal or nearly normal in the fourth intercostal space (IS) and it may be pathologic in the second IS.
   The limits of normality in the long and short QT syndromes may require additional tests.
   In patients with a family history of inherited channelopathy or cardiomyopathy, a careful analysis and additional tests are required before determining whether an ECG is normal or pathologic.
   
4. Aortic aneurism with dissection or rupture.
   The ECG may be normal or show LVH with strain in V5-V6 that may be confused in V1-V2 with an ST elevation of ACS (mirror pattern) (Fig. 15.2). In young people with normal ECG, a dissection/rupture of an aortic aneurism may be seen especially in case of bicuspid aortic valve.
   
5. Chronic ischemic patients with or without previous myocardial infarction. In many patients, including postinfarction patients or those who have undergone various bypasses, the ECG is normal or becomes normal over time (Fig. 9.42). Furthermore, rarely the Q wave of necrosis may remain undetected due to a second infarction (Fig. 9.43) or the association of bundle branch blocks..
   In these patients, a stress test is useful, as well as a Holter recording, if possible, to identify abnormalities in repolarization or arrhythmias, and an echocardiogram may be used to test contractility and ventricular function. In some cases a coronariography or magnetic resonance (Fig. 9.43) may solve the problem.
   
6. In some cases of valvular or congenital heart disease that may be severe but not advanced, the ECG may remain normal or show non-evident changes even over years.
   
7. Other heart diseases with normal ECG. In the first phase of heart failure especially of diastolic type, and also often in pericarditis, cardiomyopathies, cardiac tumors etc, a normal ECG may be recorded. [H]