ARRHYTHMIAS: KIN 500C - ADVANCED CONCEPTS IN CARDIOVASCULAR PHYSIOLOGY AND REHABILITATION

500C - Advanced Concepts in Cardiovascular Physiology and Rehabilitation
KIN 500C: ADVANCED CONCEPTS IN CARDIOVASCULAR PHYSIOLOGY AND REHABILITATION
Instructor:	Dr. Darren Warburton
Email:	darren.warburton@ubc.ca
Office:	Indigenous Health & Physical Activity Program, Seminar Room, Lower Mall Research Station
Office Hours:	Via Zoom
Class Schedule:	N/A
Important Course Pages

Draft - Currently in production.

Background

Arrhythmias are irregularities in the heart's rhythm caused by disruptions in the electrical impulses that regulate heartbeats. These disturbances can result in the heart beating too fast (tachycardia), too slow (bradycardia), or irregularly. Arrhythmias can originate in different parts of the heart, including the atria (supraventricular arrhythmias) or the ventricles (ventricular arrhythmias). While some arrhythmias are benign and may not cause noticeable symptoms, others can lead to serious complications such as stroke, heart failure, or sudden cardiac arrest.

The heart's electrical system relies on the sinoatrial (SA) node, known as the natural pacemaker, to generate electrical impulses that travel through the atrioventricular (AV) node and into the ventricles. Any disruption in this conduction system can lead to abnormal rhythms. Arrhythmias can be triggered by various factors, including structural heart disease, electrolyte imbalances, ischemia, genetic predisposition, and external influences such as medications or stimulants like caffeine and alcohol.

The clinical significance of an arrhythmia depends on factors such as its duration, frequency, and impact on cardiac output. Some arrhythmias, like premature atrial contractions (PACs) or premature ventricular contractions (PVCs), are common and typically harmless. However, others, such as atrial fibrillation (AF) or ventricular fibrillation (VF), require immediate medical attention due to their association with life-threatening complications. Treatment options range from lifestyle modifications and medications to advanced interventions like catheter ablation, pacemakers, or implantable cardioverter-defibrillators (ICDs).

Measurement of Arrythmias

The measurement and diagnosis of arrhythmias primarily rely on electrocardiography (ECG or EKG), which records the heart's electrical activity. A standard 12-lead ECG provides a snapshot of cardiac rhythms and helps identify abnormalities in impulse generation and conduction. Continuous monitoring methods, such as Holter monitors and event recorders, are used for detecting intermittent arrhythmias that may not be captured during a short ECG recording.

More advanced diagnostic tools include implantable loop recorders (ILRs), which are small devices implanted under the skin to monitor heart rhythms over extended periods. These are particularly useful for detecting arrhythmias that cause unexplained syncope (fainting) or infrequent palpitations. Wearable devices, including smartwatches with ECG capabilities, are emerging as accessible tools for detecting conditions like atrial fibrillation.

In clinical settings, electrophysiological (EP) studies may be conducted to map the electrical pathways of the heart and pinpoint the source of arrhythmias. This invasive procedure involves threading catheters with electrodes into the heart via blood vessels, allowing physicians to evaluate conduction abnormalities and determine appropriate treatment strategies. Together, these measurement techniques enable accurate diagnosis and guide personalized management of arrhythmias.

Electrocardiography (ECG/EKG)

Electrocardiography (ECG or EKG) is the primary tool used to measure and diagnose arrhythmias. A standard 12-lead ECG records the heart's electrical activity from multiple angles, providing a detailed assessment of rhythm abnormalities. It is particularly useful for detecting atrial and ventricular arrhythmias, conduction blocks, and ischemic changes. However, since arrhythmias can be transient, a single ECG recording may not always capture intermittent abnormalities, necessitating longer monitoring periods.

Holter Monitors and Ambulatory ECG

For patients experiencing occasional arrhythmias, ambulatory ECG monitoring devices like Holter monitors are commonly used. A Holter monitor is a portable ECG device that records continuous heart activity over 24 to 48 hours, or even up to several weeks in some cases. These devices are particularly useful for detecting arrhythmias that may not occur during a brief in-office ECG. Ambulatory event monitors, another variation, allow patients to activate the recording when they experience symptoms, providing targeted data collection.

Implantable Loop Recorders (ILRs)

For long-term arrhythmia detection, implantable loop recorders (ILRs) are used. These small devices are implanted under the skin and continuously monitor heart rhythms for months to years. ILRs are particularly valuable for diagnosing unexplained syncope (fainting), detecting silent atrial fibrillation, and identifying rare but serious arrhythmias that may not be caught by shorter-term monitoring. Data from ILRs can be transmitted wirelessly to healthcare providers for real-time assessment.

Wearable and Consumer Devices

Recent advancements in wearable technology have introduced consumer devices capable of detecting arrhythmias, such as smartwatches with ECG capabilities. These devices, while not as precise as medical-grade ECGs, can provide early detection of atrial fibrillation and other rhythm abnormalities, prompting individuals to seek further medical evaluation. Some wearable patches, like the Zio Patch, offer continuous ECG monitoring for up to two weeks, providing a convenient alternative to traditional Holter monitors.

Electrophysiology (EP) Studies

For a more detailed and invasive assessment, electrophysiology (EP) studies are performed in specialized cardiac labs. During an EP study, catheters with electrodes are inserted into the heart through blood vessels to map electrical activity and identify abnormal conduction pathways. This technique is particularly useful for evaluating complex arrhythmias, determining the risk of sudden cardiac death, and guiding catheter ablation therapy for conditions like supraventricular tachycardia (SVT) and ventricular tachycardia (VT).

Each of these measurement techniques plays a crucial role in diagnosing and managing arrhythmias, with the choice of method depending on the suspected arrhythmia type, symptom frequency, and patient risk factors.

Classifications of Arrhythmias

Arrhythmias, or irregular heart rhythms, are classified based on their origin within the heart, as well as the nature of the rhythm disturbances. These classifications help in understanding the mechanisms, diagnosing the condition, and determining appropriate treatments.

1. By Origin

Supraventricular Arrhythmias: These arrhythmias originate above the ventricles, typically in the atria or the atrioventricular (AV) node. They include conditions such as atrial fibrillation, atrial flutter, and supraventricular tachycardia (SVT). Supraventricular arrhythmias often involve abnormal electrical activity that disrupts the coordinated contraction of the atria, which can affect heart rate and efficiency.
Ventricular Arrhythmias: These arrhythmias arise from the ventricles and include conditions such as ventricular tachycardia, ventricular fibrillation, and premature ventricular contractions (PVCs). Ventricular arrhythmias can be life-threatening due to the potential for causing inadequate blood flow and leading to sudden cardiac arrest.

2. By Rhythm and Conduction

Tachyarrhythmias: These are fast heart rhythms with a rate exceeding 100 beats per minute (bpm). Tachyarrhythmias can be either supraventricular or ventricular in origin and include conditions such as atrial fibrillation (AF), atrial flutter, and ventricular tachycardia.
Bradyarrhythmias: These are slow heart rhythms with a rate less than 60 bpm. Bradyarrhythmias may arise from disturbances in the sinoatrial (SA) node or other conduction pathways, leading to conditions like sinus bradycardia, heart block, or sick sinus syndrome. In extreme cases, bradyarrhythmias can lead to syncope or reduced cardiac output.

3. By Mechanism

Reentrant Arrhythmias: These occur when an electrical impulse repeatedly travels through a part of the heart, re-entering previously excited tissue and causing a loop. This mechanism is responsible for many types of arrhythmias, such as atrial fibrillation, atrial flutter, and certain types of ventricular tachycardia.
Focal Arrhythmias: Focal arrhythmias are caused by ectopic pacemaker activity from a localized area of the heart, rather than the normal sinoatrial node. These arrhythmias include conditions like atrial or ventricular premature beats and ectopic atrial tachycardia.
Conduction Disorders: These involve abnormal conduction of electrical impulses through the heart, often due to damage to the heart's conduction system. Examples include atrioventricular (AV) block and bundle branch blocks, where the electrical signal is delayed or blocked between the atria and ventricles.

4. By Duration

Acute Arrhythmias: These are sudden-onset arrhythmias that can occur as a result of myocardial ischemia, electrolyte disturbances, or other acute cardiac conditions. They often require immediate medical intervention to prevent further complications.
Chronic Arrhythmias: Chronic arrhythmias persist over time and may require ongoing management. Atrial fibrillation is an example of a chronic arrhythmia that can lead to significant health issues, such as stroke or heart failure, if not properly controlled.

5. By Severity

Life-Threatening Arrhythmias: These include arrhythmias that can lead to severe consequences, including sudden cardiac arrest. Examples are ventricular fibrillation and certain types of ventricular tachycardia.
Non-Life-Threatening Arrhythmias: These arrhythmias may cause symptoms such as palpitations or dizziness but do not immediately threaten life. Many supraventricular arrhythmias, such as benign atrial premature beats, fall into this category.

Common Types of Arrhythmias

Arrhythmias can be classified into different categories based on their origin, heart rate effects, and underlying mechanisms. They may arise from the atria (supraventricular arrhythmias) or the ventricles (ventricular arrhythmias) and can cause the heart to beat too fast (tachycardia), too slow (bradycardia), or irregularly. Some arrhythmias, such as atrial fibrillation, are common and may increase the risk of stroke, while others, like ventricular fibrillation, are life-threatening and require immediate intervention.

The classification of arrhythmias is important for determining the appropriate diagnosis and treatment. While some irregular heart rhythms cause noticeable symptoms such as palpitations, dizziness, or fainting, others may be asymptomatic and only detected through medical testing. Various factors, including structural heart disease, electrolyte imbalances, medication side effects, and genetic predisposition, can contribute to arrhythmia development.

The following table provides an overview of the different common types of arrhythmias, their characteristics, and their clinical significance:


Arrhythmia	Clinical Description	ECG Characteristics	Clinical Presentation
Atrial Fibrillation	Irregular and often rapid heart rate originating from the atria, causing the atria to fibrillate rather than contract normally	No distinct P waves, irregularly irregular rhythm, rapid ventricular response	Palpitations, fatigue, dizziness, shortness of breath, risk of stroke
Ventricular Fibrillation	Ventricles quiver ineffectively, preventing blood from being pumped to the body	Chaotic, disorganized electrical activity, no identifiable QRS complexes, or P waves	Sudden collapse, no pulse, unresponsiveness, requires immediate defibrillation
Atrial Flutter	A rapid but regular atrial rhythm, often occurring due to a reentrant circuit in the right atrium	Sawtooth-shaped flutter waves, especially seen in lead II, regular ventricular rhythm	Palpitations, dizziness, fatigue, shortness of breath, risk of stroke
Supra-ventricular Tachycardia (SVT)	A general term for any arrhythmia that originates above the ventricles, usually characterized by a rapid heart rate	Regular, narrow QRS complexes, rapid heart rate (usually 150-250 bpm), absent or abnormal P waves	Palpitations, dizziness, lightheadedness, shortness of breath, chest pain
Ventricular Tachycardia	A fast heart rate originating from the ventricles, which can lead to hemodynamic instability or sudden cardiac arrest if untreated	Wide, bizarre QRS complexes, usually greater than 120 ms, often with a regular rhythm	Palpitations, dizziness, syncope, chest pain, lightheadedness, may lead to sudden cardiac arrest
Idiopathic Ventricular Rhythm	A rhythm originating from the ventricles without an underlying structural heart disease or known cause	Wide QRS complexes, but no clear cause identified	Often asymptomatic but may present with palpitations or dizziness
Sinus Arrhythmia	A normal variation in heart rate related to breathing (heart rate increases during inspiration and decreases during expiration)	Regular rhythm but varying P-P intervals with a normal sinus rhythm	Generally asymptomatic; no clinical concern in healthy individuals
1st Degree AV Block	A delay in the conduction of the electrical impulse from the atria to the ventricles	Prolonged PR interval (> 300 ms) but every P wave is followed by a QRS complex	Usually asymptomatic, may cause mild fatigue or dizziness if the block is severe
2nd Degree AV Block - Mobitz Type I	A progressive delay in conduction at the AV node leading to intermittent non-conducted P waves (dropped beats)	Progressive lengthening of the PR interval until one P wave is not followed by a QRS complex (dropped beat)	Often asymptomatic, but may cause dizziness or syncope in severe cases
2nd Degree AV Block - Mobitz Type II	A more serious form of 2nd degree block with intermittent non-conducted P waves, but without the progressive PR interval elongation seen in type I	Dropped beats (non-conducted P waves) without preceding PR interval elongation	May cause dizziness, syncope, or even sudden cardiac arrest in severe cases. Often requires a pacemaker
3rd Degree AV Block - Complete Heart Block	Complete failure of electrical communication between the atria and ventricles, causing atria and ventricles to beat independently	P waves and QRS complexes occur independently at different rates (atria and ventricles), with no relationship between them	Syncope, fatigue, dizziness, chest pain, and risk of sudden cardiac death
Right Bundle Branch Block	A delay or blockage in the electrical conduction through the right bundle branch, causing delayed right ventricular activation	Wide QRS complex (> 120 ms), an rSR’ pattern in V1, and a broad S wave in lead I and V6	Generally asymptomatic but may cause mild fatigue or dizziness
Left Bundle Branch Block	A delay or blockage in the electrical conduction through the left bundle branch, causing delayed left ventricular activation	Wide QRS complex (> 120 ms), broad and notched R wave in lead I and V6, deep S wave in V1	May cause fatigue, shortness of breath, or chest pain, especially in those with underlying heart disease
Right Ventricular Hypertrophy	Thickening of the right ventricular wall due to increased workload, often secondary to pulmonary disease or left heart failure	Right axis deviation, tall R waves in V1, deep S waves in V5/V6	Shortness of breath, fatigue, palpitations, or swelling in the legs
Left Ventricular Hypertrophy	Thickening of the left ventricular wall, often due to hypertension or aortic stenosis	Increased voltage of the QRS complexes, deep S waves in V1, and tall R waves in V5 or V6	Fatigue, shortness of breath, chest pain, or palpitations
Right Atrial Enlargement	Enlargement of one or both atria, usually due to chronic pressure or volume overload	Tall, peaked P waves (P pulmonale)	Fatigue, palpitations, shortness of breath, or symptoms of heart failure
Left Atrial Enlargement	Enlargement of one or both atria, usually due to chronic pressure or volume overload	Broad, notched P waves (P mitrale)	Fatigue, palpitations, shortness of breath, or symptoms of heart failure
Wolff Parkinson-White Disease	A congenital condition where an accessory pathway between the atria and ventricles causes a pre-excitation of the ventricles	Shortened PR interval, presence of a delta wave (slurred upstroke of the QRS complex), and a wide QRS complex	Palpitations, dizziness, syncope, risk of SVT or sudden cardiac arrest