Rate calculation

Common method: 300-150-100-75-60-50

Mathematical method: 300/# large boxes between R waves

Six-second method: # R-R intervals x10

Rhythm Guidelines:

1. Check the bottom rhythm strip for regularity, i.e. - regular, regularly irregular, and irregularly irregular.

2. Check for a P wave before each QRS, QRS after each P.

3. Check PR interval (for AV blocks) and QRS (for bundle branch blocks). Check for prolonged QT.

4. Recognize "patterns" such as atrial fibrillation, PVC's, PAC's, escape beats, ventricular tachycardia, paroxysmal atrial tachycardia, AV blocks and bundle branch blocks.

Lead I | Lead aVF | |

1. Normal axis (0 to +90 degrees) | Positive | Positive |

2. Left axis deviation (-30 to -90) Also check lead II. To be true left axis deviation, it should also be down in lead II. | Positive | Negative |

3. Right axis deviation (+90 to +180) | Negative | Positive |

4. Indeterminate axis (-90 to -180) | Negative | Negative |

Right axis deviation differential: RVH, left posterior fascicular block, lateral wall MI.

1. LVH -- left ventricular hypertrophy = S wave in V1 or V2 + R wave in V5 or V6 > 35mm or aVL R wave > 12mm.

2. RVH -- right ventricular hypertrophy = R wave > S wave in V1 and gets progressively smaller to left V1-V6 (normally, R wave increases from V1-V6).

3. Atrial hypertrophy (leads II and V1)

Ischemia | Represented by symmetrical T wave inversion (upside down). Look in leads I, II, V2-V6. |

Injury | Acute damage -- look for elevated ST segments. |

Infarct | "Pathologic" Q waves. To be significant, a Q wave must be at least one small square wide or one-third the entire QRS height. |

V1-V2 | anteroseptal wall | II, III, aVF | inferior wall |

V3-V4 | anterior wall | I, aVL | lateral wall |

V5-V6 | anterolateral wall | V1-V2 | posterior wall (reciprocal) |

Continue to the clinical cases.