Clinical Quiz on Prolonged P-R Interval

Electrophysiology (Abnormal Rhythms & Conduction Defects)

• This study covers abnormal heart rhythms and conduction defects
• Topics include tachycardia, bradycardia, sinus arrhythmia, AV nodal block, and more.
• A 20-year-old patient with a fever of 104°F, nausea, and vomiting, was diagnosed with malaria. The patient also experienced palpitations requiring an ECG.
• Palpitations are a feeling of heart sounds.
• Sinus tachycardia is when the heart rate is above 100 beats per minute(bpm).
• A normal heart rate is around 70-80 bpm.
• ECG is normal except for the intervals between QRS complexes. These intervals are around 150 bpm, instead of 72 bpm.
• Causes of tachycardia include increased body temperature (10 bpm increase per °F) and stimulation of the sympathetic nerves.

Causes of Tachycardia

• Increased body temperature (10 beats per minute for each degree Fahrenheit increase.)
• Stimulation by sympathetic nerves.
• Toxic heart conditions.

Hypertension and Bradycardia

• A 40-year-old woman with hypertension was prescribed beta-blockers.
• She started experiencing lethargy, dyspnea (difficulty breathing), and excessive sweating.
• An ECG assessment revealed bradycardia.
• Bradycardia is a slow heart rate, typically below 60 bpm.
• Bradycardia can occur in athletes
• Beta-blockers can cause bradycardia
• Vagal stimulation can decrease the heart rate.

Sinus Arrhythmia

• Heart rate increases and decreases by 5% during quiet respiration.
• Inspiration causes increased heart rate.
• Results from signals spilling over from the respiratory center to the vasomotor center.

AV Nodal Block

• Impulses from the sinoatrial (SA) node to the atrioventricular (AV) node might be blocked.
• Reasons include inflammation, ischemia, scarring/compression, and extreme vagal nerve stimulation.
• First-degree AV block: PR interval greater than 0.20 seconds.
• This type of block is typically associated with rheumatic fever and is common, especially during periods of swelling in the joints, and may be present when there is a high temperature from infections like strep throat (streptococcal throat infections)

Second-Degree AV Block

• Some impulses from the SA node reach the AV node but are delayed
• PR interval continues to extend until a QRS beat is missed
• two types of 2nd Degree block include Mobitz type 1 and type 2
• Mobitz type 1 block leads to progressive increases in the PR Interval and a drop in ventricular beats.
• Mobitz type 2 block is when an impulse from the AV node is dropped without increasing the PR interval.

Third-Degree AV Block (Complete Heart Block)

• Complete blockage of impulses from the SA to AV node
• Ventricles create their own pacemaker (usually 40 beats per minute)
• Atrial (atria) rate (100 bpm) is not synchronized with ventricular rate due to the disrupted conduction.
• Treatment often involves a pacemaker.

Stokes-Adams Syndrome

• In some cases with complete AV block, ventricles may pause momentarily before restarting.
• This temporary pause in conduction leads to a loss of blood supply to the brain, causing a brief period of unconsciousness.
• Ventricles escape: ventricles start to beat on their own.

Re-entry Phenomena (Circus Movements)

• Impulse repeatedly circulates through the heart, causing continuous stimulation and potentially irregular heart beats
• 3 causes of re-entry include: longer than normal pathways, decreases in velocity of conduction, and a shortened refractory period

Ventricular Fibrillation

• Irregular, rapid, and often chaotic contraction of the ventricles.
• No coordinated pumping action.
• Requires emergency intervention (defibrillation).

Atrial Fibrillation

• Irregular, rapid contraction of the atria, usually 350-600 bpm
• Atrial muscle is separated by fibrous tissue from ventricular muscle.
• Doesn't affect ventricle rhythm unless it is very rapid
• Reduction in the efficiency of overall heart pumping by ~20-30%.

Atrial Flutter

• Rapid, regular atrial contractions, often 200-300 bpm.
• Impulses that reach the ventricles are reduced because of the A-V node and A-V bundle refractory periods
• Typically results in a 2:1 (or 3:1) atrial-ventricular conduction ratio.

Angina Pectoris

• Chest pain due to reduced blood supply to the heart (myocardium).
• ST-segment elevations are common on an ECG during an angina attack.

Myocardial Infarction

• Heart attack, resulting in reduced blood flow to the heart muscle (myocardium), often from a blood clot.
• Common findings include prominent Q waves and elevated ST segments on an ECG.

Premature Contractions

• Contractions of the heart occur before the expected time.
• Ectopic foci may cause premature contractions, which are abnormal areas that start impulses spontaneously.

Different Types of Premature Contractions

• Atrial Premature Contractions (PACs).
• Ventricular Premature Contractions (PVCs).