Premature contraction Notes

NOTES NOTES PREMATURE CONTRACTION GENERALLY, WHAT IS IT? PATHOLOGY & CAUSES ▪ Depolarizing potential from anywhere in heart other than sinoatrial (SA) node → contraction earlier than normal in cardiac cycle ▪ Triggered activity ▫ Cells triggered by preceding action potential after repolarization ▫ Cause: reperfusion therapy after myocardial infarction/digoxin toxicity ▪ Ectopic focus ▫ Cells irritated by electrolyte imbalances, drugs, ischemic damage → increased sympathetic activity → enhanced automaticity → early depolarization ▪ Reentrant loop ▫ Tissue unable to depolarize (e.g. scar tissue, amyloid) → no signal conduction → depolarizing wave obstructed → depolarizing wave circles tissue → abnormal electrical circuit CAUSES ▪ Often idiopathic ▪ Electrolyte imbalances (hypokalemia, hypercalcemia, hypomagnesemia) ▪ Recreational/prescription drugs (methamphetamines, cocaine, digoxin intoxication) ▪ Alcohol use ▪ Heart dilation: cardiomyopathies, cor pulmonale ▪ Heart scarring: after myocardial infarction, myocarditis COMPLICATIONS ▪ Rarely atrial/ventricular fibrillation SIGNS & SYMPTOMS ▪ Usually asymptomatic ▪ In case of frequent premature contractions: lightheadedness, palpitations DIAGNOSIS OTHER DIAGNOSTICS ▪ ECG ▪ Holter monitor ▪ ZIO patch TREATMENT ▪ See individual disorders OSMOSIS.ORG 117

PREMATURE ATRIAL CONTRACTION (PAC) osms.it/premature-atrial-contraction PATHOLOGY & CAUSES ▪ Contraction of atria earlier than normal in cardiac cycle ▪ Atrial bigeminy: premature atrial contraction consistently occurs after each normal cardiac cycle ▪ Atrial trigeminy: premature atrial contraction consistently occurs after every two normal cardiac cycles CAUSES ▪ Heart structural disorders, intoxication, electrolyte imbalances COMPLICATIONS ▪ Atrial fibrillation SIGNS & SYMPTOMS ▪ Usually asymptomatic ▪ In case of frequent premature contractions: lightheadedness, palpitations DIAGNOSIS OTHER DIAGNOSTICS ECG ▪ Early, abnormal P wave ▫ Ectopic focus in bottom of atria → negative P wave ▫ Ectopic focus closer to atrioventricular (AV) node → PR interval shorter ▫ P wave, T wave overlap 118 OSMOSIS.ORG ▪ Noncompensatory pause ▫ Premature impulse enters sinoatrial (SA) node → shortens cycle ▫ Distinct from compensatory pause: premature ventricular contraction → premature impulse does not reach SA node → if AV node still refractory, pauses → lengthens cycle ▪ Normal QRS ▫ Premature impulse reaches AV node in refractory → blocked premature atrial contraction → QRS nonexistent ▪ Ashman phenomenon ▫ R-R interval prolongs → increases refractory period of right bundle branch → abnormal conduction of subsequent impulse → right bundle branch block on ECG ▪ Holter monitor ▫ 24h, detect premature contractions TREATMENT ▪ Typically requires no treatment MEDICATIONS ▪ If symptomatic: beta blockers/calcium channel blockers ▪ Electrolyte replacement SURGERY ▪ If triggering atrial fibrillation: radiofrequency catheter ablation

Chapter 17 Premature Contraction Figure 17.1 Illustration depecting abnormal P wave in atrial bigeminy and trigeminy. Figure 17.2 Illustration comparing normal ECG tracing vs ECG tracing with premature atrial contraction. OSMOSIS.ORG 119

PREMATURE VENTRICULAR CONTRACTION (PVC) osms.it/premature-ventricular-contraction PATHOLOGY & CAUSES ▪ Contraction of ventricles earlier than normal in cardiac cycle ▪ Ectopic focus ▫ Latent pacemakers: AV node, bundle of His/Purkinje fibers take over SA node’s function of pacemaker ▫ Irritated cardiac muscle cells → early depolarization ▪ Triggered activity ▫ Ventricular repolarization → ventricle cells triggered by preceding action potential ▫ Cause: reperfusion therapy after myocardial infarction/digoxin toxicity ▪ Reentrant loop ▫ Tissue unable to depolarize (e.g. scar tissue, amyloid) → no signal conduction → depolarizing wave obstructed → depolarizing wave circles tissue → abnormal electrical circuit ▪ Ventricular bigeminy: premature ventricular contraction consistently comes after each normal cardiac cycle ▪ Ventricular trigeminy: premature ventricular contraction consistently comes after every two normal cardiac cycles CAUSES ▪ Heart structural disorders, intoxication, electrolyte imbalances 120 OSMOSIS.ORG RISK FACTORS ▪ Hypertension, smoking, exercise, stress, people of African descent (+30% risk), biological male COMPLICATIONS ▪ Ventricular tachycardia, ventricular fibrillation, increased risk for sudden cardiac death SIGNS & SYMPTOMS ▪ Can be asymptomatic ▪ Lightheadedness, palpitations DIAGNOSIS OTHER DIAGNOSTICS ECG ▪ Wide, bizarre QRS: signal goes through ventricular muscle, not normal conduction pathway → conduction is slower than normal ▪ Ectopic impulse in right ventricle ▫ Left bundle branch block pattern of QRS complex ▫ V1: large negative complex, dominating S wave ▪ Ectopic impulse in left ventricle ▫ Right bundle branch block pattern of QRS complex ▫ V1: large positive complex, dominating R wave

Chapter 17 Premature Contraction ▪ Abnormal ST segments: deviation from isoelectric baseline in opposite direction from QRS complex ▪ Inverted T waves in leads, QRS complex predominantly positive ▪ Nonexistent P wave: covered by wide QRS complex ▫ QRS followed by compensatory pause ▪ Ventricular fusion beat: premature QRS complex occurs during PR segment, combines with normal depolarization wave ▪ R-on-T phenomenon: premature QRS complex occurs at/near T wave apex ▪ Holter monitor TREATMENT ▪ Typically requires no treatment MEDICATIONS ▪ If symptomatic: venodilators, calcium channel blockers, administer beta blockers with caution SURGERY ▪ If triggering ventricular arrhythmias: radiofrequency catheter ablation to destroy ectopic focus/replacement if necessary OTHER INTERVENTIONS ▪ If mild, no exercise restrictions; if severe, reduced physical activity Figure 17.3 Illustration comparing premature ventricular contractions that occur during a P wave, during a PR segment, and during a T wave. Figure 17.4 Illustration comparing ventricular bigeminy and trigeminy. OSMOSIS.ORG 121