What are the characteristics of Normal Sinus Rhythm (NSR)? — Rate: 60–100 bpm. Regular rhythm. P wave before every QRS. PR interval: 0.12–0.20 sec. QRS: < 0.12 sec. This is the baseline against which all arrhythmias are compared.

What is Sinus Tachycardia? — NSR with heart rate > 100 bpm. Normal P waves, regular rhythm. Causes: fever, pain, anxiety, dehydration, anemia, hyperthyroidism. Treat the underlying cause.

What is Sinus Bradycardia? — NSR with heart rate < 60 bpm. Normal P waves, regular rhythm. Causes: athletes (normal), hypothyroidism, increased ICP, digoxin toxicity, beta-blockers. Treat if symptomatic (Atropine).

What is Sinus Arrhythmia? — Irregular rhythm caused by changes in breathing — heart rate increases with inspiration and decreases with expiration. Normal in children and young adults.

What are Premature Atrial Contractions (PACs)? — Early, abnormal P waves that interrupt the normal rhythm. Usually benign. Causes: caffeine, stress, alcohol, electrolyte imbalance. No treatment usually needed.

What is Atrial Fibrillation (A-Fib)? — Chaotic, disorganized atrial activity with no distinct P waves — replaced by irregular fibrillatory waves. Irregularly irregular ventricular rhythm. Rate: 350–600 atrial impulses/min. Major risk: thrombus formation and stroke. Treatment: rate control, anticoagulation.

What is Atrial Flutter? — Regular, rapid atrial activity at 250–350 bpm producing classic sawtooth (flutter) waves. Usually 2:1, 3:1, or 4:1 conduction to ventricles. Treatment: cardioversion, rate control, anticoagulation.

What is Supraventricular Tachycardia (SVT)? — Rapid heart rate 150–250 bpm originating above the ventricles. Narrow QRS, regular rhythm. Causes: stress, caffeine, WPW syndrome. Treatment: Valsalva maneuver, adenosine, cardioversion.

What is a First-Degree AV Block? — PR interval > 0.20 seconds (> 5 small squares). Every P wave is followed by a QRS. No dropped beats. Usually benign — monitor only. Causes: vagal tone, digoxin, inferior MI.

What is a Second-Degree AV Block Type I (Wenckebach/Mobitz I)? — Progressive lengthening of the PR interval until a QRS is dropped. Then the cycle repeats. Usually benign but monitor. Causes: inferior MI, increased vagal tone, digoxin toxicity.

What is a Second-Degree AV Block Type II (Mobitz II)? — Constant PR interval with sudden, unexpected dropped QRS beats (no progressive lengthening). More serious than Mobitz I. Risk of progressing to complete heart block. May require pacemaker.

What is a Third-Degree (Complete) AV Block? — Complete dissociation between P waves and QRS complexes — atria and ventricles beat independently. Life-threatening. Requires immediate transcutaneous pacing and likely permanent pacemaker.

What are Premature Ventricular Contractions (PVCs)? — Early, wide, bizarre-looking QRS complexes > 0.12 seconds with no preceding P wave. Causes: hypoxia, hypokalemia, caffeine, MI. Occasional PVCs are benign; frequent/multifocal PVCs require treatment.

What is Ventricular Tachycardia (V-Tach)? — 3 or more PVCs in a row at a rate > 100 bpm. Wide, bizarre QRS complexes. May be pulseless. With pulse: Amiodarone, cardioversion. Pulseless V-Tach: DEFIBRILLATE immediately + CPR.

What is Ventricular Fibrillation (V-Fib)? — Chaotic, disorganized ventricular activity — no identifiable P waves, QRS, or T waves. No cardiac output. IMMEDIATELY DEFIBRILLATE + CPR. This is a cardiac arrest rhythm.

What is Torsades de Pointes? — A form of polymorphic V-Tach with QRS complexes that appear to "twist" around the baseline. Associated with prolonged QT interval. Treatment: IV Magnesium sulfate, remove offending drugs.

What is Asystole? — Complete absence of electrical activity — a flat line on ECG. No cardiac output. CPR + Epinephrine. Note: Confirm in 2 leads — never shock asystole (defibrillation will not help).

What is Pulseless Electrical Activity (PEA)? — Organized electrical activity on ECG but no pulse (no mechanical cardiac output). CPR + Epinephrine + treat reversible causes (5 H's and 5 T's).

What are the 5 H's and 5 T's of cardiac arrest? — H's: Hypovolemia, Hypoxia, Hydrogen ion (acidosis), Hypo/Hyperkalemia, Hypothermia. T's: Tension pneumothorax, Tamponade, Toxins, Thrombosis (pulmonary), Thrombosis (coronary/MI).

What is a Left Bundle Branch Block (LBBB)? — Wide QRS > 0.12 seconds with a broad, notched R wave in lateral leads (I, aVL, V5, V6). The left ventricle is activated late. May indicate cardiac disease or MI.

What is the difference between cardioversion and defibrillation? — Cardioversion: Synchronized shock delivered during QRS complex. Used for unstable arrhythmias WITH a pulse (A-Fib, SVT, V-Tach with pulse). Defibrillation: Unsynchronized shock. Used for pulseless V-Tach and V-Fib.

What is the drug of choice for symptomatic bradycardia? — Atropine 0.5 mg IV (first-line). If atropine fails: transcutaneous pacing or dopamine/epinephrine infusion.

What is adenosine used for and how is it given? — Used to terminate SVT. Given as a rapid IV push (over 1–2 seconds) followed immediately by a 20 mL NS flush, in the largest vein available (antecubital). Causes brief asystole — warn the patient.

What nursing assessments are done before giving digoxin? — Check apical pulse for 1 full minute — hold if < 60 bpm. Check digoxin level (therapeutic 0.5–2 ng/mL). Monitor for toxicity: nausea, bradycardia, visual changes (yellow-green halos).

What is QT prolongation and why is it dangerous? — QT interval > 440ms (men) or > 460ms (women). Indicates slow ventricular repolarization. Dangerous because it predisposes to Torsades de Pointes and sudden cardiac death. Many drugs prolong QT (antipsychotics, antibiotics, antiemetics).