Prolongación del intervalo PR hasta que una P no se conduce. A longer PR may imply a block in conduction and a shorter interval indicates a vulnerability to arrhythmias.ġ3 BLOQUEO AV DE SEGUNDO GRADO MOBITZ I (FENOMENO DE WENCKEBACH) The PR interval should be 120 to 200 milliseconds, or 3 to 5 little squares. Rule 1 As described in Module 3, the PR interval is the time from initiation of depolarisation of the atria to initiation of the depolarisation of the ventricles. The 10 rules for a normal ECG For an ECG to be determined as normal, Chamberlain has described 10 rules which must be met.1 The next ten slides will outline these rules. All these changes imply myocardial infarction, and will be discussed in more detail over the next few slides.Ĭardiopatías: Isquémica Valvulopatías Miocardiopatías Enfermedad degenerativa Medicamentos: Metoprolol Digoxina Alteraciones en el K Hiperkalemia Rule 10 In leads I, II, and V2 to V6 the T wave must be upright.īloqueo AV de primer grado Bloqueo AV de segundo grado Bloqueo AV de segundo grado – Mobitz I (Fenómeno de Wenckebach) Bloqueo AV de segundo grado – Mobitz II Bloqueo AV completo It is important to recognise these features as they occur rather than in association with each other. A patient can present at any stage and a progression through the ECG changes will not be seen. Although these changes occur sequentially, it is very unlikely they will all be clearly observed by the paramedic or GP. Later still, the ST segment returns to normal, and at this point the T wave also decreases, eventually becoming deeply and symmetrically inverted. Later the R wave becomes reduced in size, or completely lost. Several hours later pathological Q waves begin to form, and tend to persist. Shortly after infarction there is an elevation of the ST segment seen over the area of damage, and opposite changes are seen in the opposite leads. In the early stages changes are also seen in the ST segment and the T wave, and these can be used to assist diagnosis of myocardial infarctions. The only diagnostic evidence of a completed myocardial infarction seen on the ECG are those in the QRS complexes. It is therefore very important to know the changes that occur in this situation. Retrazo ó interrupción de la conducción entre aurículas y los ventrículos Characteristic changes in AMI The 12-lead ECG is the most useful investigation for confirming the diagnosis of acute myocardial infarction, locating the site of the infarct and monitoring the progress. This type of infarction often results in bradycardia due to damage to the atrioventricular node. Inferior infarctions may occur due to occlusion of the right circumflex coronary arteries resulting in infarction of the inferior surface of the left ventricle, although damage can be made to the right ventricle and interventricular septum. Location of infarction and its relation to the ECG: inferior infarction ST elevation in leads II, III and aVF, and often ST depression in I, aVL, and precordial leads are signs of an inferior (lower) infarction. Using these rules and nomenclature all QRS complexes can be described, enabling more accurate diagnosis.ĥ Intervalo PR mide normalmente: 0.12 a 0.20 seg.ĮLECTROCARDIOGRAMA Intervalo PR mide normalmente: 0.12 a 0.20 seg. The first positive wave is labelled with r or R Any second positive wave is labelled r´ or R´ A negative wave which follows an R wave or r wave is labelled S or s A negative wave that precedes an R or r wave, is labelled a q or Q wave Any wave that is entirely negative is labelled qs or QS. This can be done using combinations of the letters q, r, s, Q, R, S, lower case letters denoting small waves and upper case larger waves. In order to be able to describe these complexes, a nomenclature for the waves is needed. The QRS complex is very important when diagnosing myocardial infarction. However, these waves can vary immensely in size, and arrangement. All sharp deflections resulting from electrical activation of the ventricles are called QRS complexes. ![]() The QRS complex of waves is the largest deflection of the ECG and is always spiky in shape. QRS waveform nomenclature The ECG consists of a small deflection called the P wave, arising from the atria, a more complicated deflection called the QRS complex due to ventricular depolarisation and a final T wave resulting from repolarisation of the ventricles. Segmento QRS: Despolarización de los ventrículos. Intervalo PR: Retardo del impulso en el nodo auriculoventricular. Onda P: Despolarización de las aurículas. José Antonio Espejel Santana Urgencias Médico Quirúrgicas Unidad Medica de Alta de Especialidad de Centro Médico “La Raza” MéxicoĢ MIOCARDIO Filamentos de actina y miocina Sarcolema Discos Intercalaresįunción de “sincitio” Sincitio atrial y ventricularĤ ELECTROCARDIOGRAMA Registro de la actividad eléctrica del corazón
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