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Sinus Rhythms Chapter 13 Normal Sinus Rhythm Autonomic Nervous System Sympathetic nerves Parasympathetic nerves (vagus nerve) Sympathetic Stimulation Increase in HR Palpitations pounding normal, premature beats, or ectopic (nonsinus) beats, Tachycardia HR exceeding 100 beats/min Increase SNS and/or decrease in PNS Elderly individuals rarely show HR greater than 140150 bpm HR above this range usually indicate non-sinus tachycardia (e.g. atrial fibrillation or a paroxysmal supraventricular tachycardia) Sinus Tachycardia • • • • • • • • • • P Wave - Visible before each QRS complex P-R Interval - Normal QRS Duration - Normal Rhythm - Regular Rate - More than 100 beats per minute Tachycardia Each QRS complex is preceded by a P wave With a very fast rate, the P wave may merge with the preceding T wave Tachycardia Anxiety, exertion, pain, Drugs: increase SNS or decrease vagal tone Fever Congestive heart failure Pulmonary embolism Acute MI Hyperthyrodism Pheochromocytoma Sinus Bradycardia Heart rate less than 60 bpm Sinus Bradycardia P Wave - Visible before each QRS complex P-R Interval - Normal QRS Duration - Normal Rhythm - Regular Rate - less than 60 beats per minute Usually benign and often caused by patients on beta blockers Sinus Bradycardia Normal variant Drugs: decrease SNS or increase vagal tone Hypothyroidism Hyperkalemia Sick sinus syndrome (Fig 13-5) Sleep apnea Carotid sinus hypersensitivity syndrome Vasovagal reactions Sinus Bradycardia Symptoms Moderate sinus bradycardia produces no symptoms If HR is very slow, lightheadedness and syncope Sinus Arrhythmia Beat to beat variation in HR Younger, healthy individuals Common cause: respiration Respiratory sinus arrhythmia Sinus Pauses/Sinus Arrest SA fails to stimulate the atria Sinus pause or sinus arrest (Fig. 13-5) Escape Beats Escape beat (Fig. 13-6) Atria, AV node or ventricles Sinus Pauses/Sinus Arrest Causes of sinus pause or arrest hypoxemia Ischemia or MI Hyperkalemia Drug toxicity Vagal hyperreactivity Sick sinus syndrome (Fig 13-5)
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