Palpitations refer to the feeling of having an irregular or unusual heartbeat. They can be caused by various heart rhythm issues, both with and without underlying heart problems. To understand palpitations, it's important to consider factors like how often they happen, what triggers them, and any related symptoms such as chest pain, shortness of breath, dizziness, or fainting.
When evaluating palpitations, it's crucial to determine if the irregularity in the heartbeat is constant or intermittent. For instance, a "skipped beat" or a feeling of the heart "flip-flopping" might indicate a premature contraction, different from the irregular rhythm seen in conditions like atrial fibrillation or the fast yet regular rhythm of supraventricular tachycardia. If palpitations are accompanied by chest pain, shortness of breath, dizziness, or sweating, it suggests a significant impact on heart function and requires further assessment.
Typically, the evaluation starts with ambulatory electrocardiography (ECG), especially if structural heart issues or severe symptoms are present. Depending on the findings, more extensive testing may be necessary, particularly if there's suspected underlying heart disease.
Lightheadedness or fainting can result from various causes, such as heart rhythm problems, changes in cardiac output, vasomotor issues, or low blood pressure when standing up (orthostatic hypotension). Neurological conditions like migraines, transient ischemic attacks, or seizures can also lead to temporary loss of consciousness. Diagnosis often involves a careful history, physical examination, and ECG, which can help identify the cause.
Fainting due to a heart rhythm problem typically happens suddenly. Fainting during or right after physical activity might indicate conditions like aortic stenosis or hypertrophic obstructive cardiomyopathy. Additional testing may be needed to determine the exact cause, especially if the initial evaluation doesn't provide a clear diagnosis, particularly in patients with heart disease or abnormal ECG results. Continuous ambulatory ECG monitoring can help identify arrhythmias, and in some cases, specialized electrophysiological testing might be necessary. For individuals without evident heart disease, tilt testing can be useful to detect vasomotor issues causing fainting.
AMERICAN HEART ASSOCIATION/AMERICAN COLLEGE OF CARDIOLOGY GUIDELINES FOR USE OF DIAGNOSTIC TESTS IN PATIENTS WITH PALPITATIONS*
AMBULATORY ELECTROCARDIOGRAPHY:
- Class I:
- Palpitations, syncope, dizziness.
- Class II:
- Shortness of breath, chest pain, or fatigue (episodic and strongly suggestive of an arrhythmia if related to palpitations).
- Class III:
- Symptoms not reasonably expected to be caused by arrhythmia.
ELECTROPHYSIOLOGIC STUDY:
- Class I:
- Patients with palpitations and documented inappropriately rapid pulse rate when ECG fails to identify the cause.
- Patients with palpitations preceding a syncopal episode.
- Class II:
- Patients with clinically significant, sporadic palpitations suspected to be of cardiac origin.
- Studies aim to determine arrhythmia mechanisms, guide therapy, or assess prognosis.
- Class III:
- Patients with palpitations documented to have extracardiac causes (e.g., hyperthyroidism).
ECHOCARDIOGRAPHY:
- Class I:
- Arrhythmias with evidence of heart disease.
- Family history of genetic disorders associated with arrhythmias.
- Class II:
- Arrhythmias commonly associated with no evidence of heart disease.
- Atrial fibrillation or flutter.
- Class III:
- Palpitations without evidence of arrhythmias.
- Minor arrhythmias without evidence of heart disease.
1.Supraventricular Arrhythmias: This term refers to abnormal heart rhythms (arrhythmias) that originate in areas of the heart above the ventricles. The heart has four chambers: two upper chambers called atria and two lower chambers called ventricles. Supraventricular arrhythmias occur in the atria or in the specialized conduction system above the ventricles.
2.Bradyarrhythmias: These are slow heart rhythms. “Brady” means slow, so bradyarrhythmias are arrhythmias where the heart beats at a slower rate than normal.
3.Tachyarrhythmias: These are fast heart rhythms. “Tachy” means fast, so tachyarrhythmias are arrhythmias where the heart beats at a faster rate than normal.
4.His Bundle: The His bundle is a part of the heart’s electrical conduction system. It’s a bundle of specialized cells that help transmit electrical signals from the atria to the ventricles, allowing the heart to beat in a coordinated manner.
5.Supraventricular in Origin: When we say a rhythm is “supraventricular in origin,” it means that this abnormal heart rhythm starts in the areas of the heart located above the His bundle. In other words, it originates in the atria or in the specialized conduction pathways between the atria and ventricles.
So, in summary, supraventricular arrhythmias can be categorized into two main types: bradyarrhythmias (slow rhythms) and tachyarrhythmias (fast rhythms). Any abnormal rhythm that starts in the atria or above the His bundle is considered supraventricular. These arrhythmias are different from ventricular arrhythmias, which originate in the ventricles, the lower chambers of the heart.
1.Ventricular Arrhythmias: These are abnormal heart rhythms (arrhythmias) that originate in the ventricles, which are the lower chambers of the heart. The ventricles are responsible for pumping blood to the body.
2.His-Purkinje Tissue: This refers to specialized tissue in the heart that helps conduct electrical signals, allowing the heart to beat in a coordinated manner. It’s part of the heart’s natural electrical system.
3.Types of Ventricular Arrhythmias: Ventricular arrhythmias come in different forms:
•Premature Ventricular Contractions (PVCs): These are early, extra heartbeats that start in the ventricles.
•Nonsustained Ventricular Tachycardia (VT): This is when there are three or more rapid ventricular contractions in a row, but they don’t last very long.
•Sustained Ventricular Tachycardia (VT): This is a continuous, fast rhythm in the ventricles that lasts for more than 30 seconds and can lead to serious issues.
•Ventricular Fibrillation (VF): This is a life-threatening, extremely chaotic ventricular rhythm where the heart quivers rather than pumps effectively.
4.Definitions of VT: Ventricular tachycardia is defined as three or more consecutive ventricular contractions at a rate faster than 100 beats per minute. Sustained VT is when this rapid rhythm lasts for 30 seconds or longer. Sustained VT can cause severe problems, especially in people with underlying heart conditions.
5.Types of VT: VT can be further categorized:
•Monomorphic VT: This is a fast, wide-complex tachycardia where the QRS complexes (part of the ECG) all look the same from beat to beat.
•Polymorphic VT: In this type, the QRS complexes vary in shape and direction from beat to beat. Very fast polymorphic VT can be hard to distinguish from VF.
•Ventricular Fibrillation (VF): VF is a highly irregular, extremely fast ventricular rhythm where there is no effective pumping of blood. It’s a dire situation.
6.Torsades de Pointes and Bidirectional Polymorphic VT: These are specific subtypes of polymorphic VT, each with unique features.
7.Pleomorphic VT: This is when multiple episodes of monomorphic VT with different QRS configurations occur at different times in the same patient.
In summary, ventricular arrhythmias are abnormal rhythms originating in the heart’s ventricles. They can range from premature contractions to life-threatening rhythms like VF. VT can be categorized based on its characteristics, and certain types, especially sustained VT, can have serious consequences.
1.Prevalence of PVCs (Premature Ventricular Contractions): The occurrence of PVCs is influenced by how and how long heart activity is monitored. If monitoring spans 24 hours or more, PVCs can be observed in about 50% of seemingly healthy individuals. However, even if PVCs are symptomless, they might indicate more severe underlying heart issues.
2.Nonsustained VT (Ventricular Tachycardia): This is when there are rapid, abnormal heart rhythms that don’t last long. Up to 3% of people without known heart problems might experience nonsustained VT. The likelihood of PVCs and nonsustained VT increases not only with age but also with the presence and severity of heart disease. Therefore, finding nonsustained VT, even incidentally in a symptomless person, often leads to a cardiac evaluation to rule out underlying heart disease. In the late stages of a heart attack (myocardial infarction or MI), the prevalence of nonsustained VT can rise to 7-12%. It can be even higher, around 80%, in patients with heart failure due to dilated cardiomyopathy.
3.Idiopathic VT and VF (Ventricular Fibrillation): Idiopathic VT is a type of sustained VT that occurs without any identifiable heart disease. Idiopathic VF, on the other hand, is extremely rare. Ventricular arrhythmias, particularly VT and VF, are responsible for about 50% of all yearly cardiovascular deaths in the United States.
4.Underlying Heart Disease and Age: The type of heart disease associated with VT and VF varies with age. In individuals under 30 years old, genetic cardiomyopathies are the most common underlying conditions. In contrast, those over 40 years old are more likely to have acute heart attacks (MI) or chronic ischemic cardiomyopathies as the root causes of these arrhythmias. Interestingly, in about 13% of sudden cardiac deaths where there’s no clear heart disease found during autopsy, postmortem genetic analysis can reveal pathologic mutations in ion channels. These mutations, referred to as deleterious channelopathies, make individuals more susceptible to VT and VF.
On Epidemiology
In summary, ventricular arrhythmias like PVCs and VT can occur in healthy individuals but are more prevalent in older people and those with underlying heart disease. Nonsustained VT can be a sign of heart trouble and often prompts further evaluation. VT and VF are significant contributors to cardiovascular deaths, and the underlying heart disease varies with age. Some cases of sudden cardiac death may be linked to genetic mutations affecting ion channels in the heart.
This explains the different mechanisms and causes of ventricular arrhythmias, including ventricular tachycardia (VT) and ventricular fibrillation (VF). Here's an explanation:
**Classification of Ventricular Arrhythmias by Mechanism:**
Ventricular arrhythmias are classified into three main categories based on their underlying mechanisms: re-entrant, triggered, or automatic.
1. **Re-entrant Mechanism:** This type of arrhythmia occurs when there's an abnormal electrical circuit in the heart. Re-entry usually results from a combination of conduction block in one pathway and slow conduction in another, allowing the electrical signal to "loop" and continue circulating (re-entry). It's often seen in individuals with scarred heart tissue due to conditions like previous heart attacks, inflammation, or genetic factors.
2. **Triggered Mechanism:** Triggered arrhythmias result from abnormal electrical impulses that occur after the normal heartbeat. There are two types:
- **Early Afterdepolarizations:** These are oscillatory electrical signals that happen during the late phase of the heart's action potential due to delayed repolarization.
- **Delayed Afterdepolarizations:** These occur when there's an abnormal increase in intracellular calcium, leading to brief electrical signals after the heart's action potential ends.
3. **Automatic Mechanism:** This type arises from an accelerated pacemaker activity in the heart, where the heart's natural pacemaker cells start firing too rapidly.
**Underlying Causes of Ventricular Arrhythmias:**
The causes of ventricular arrhythmias can vary depending on the mechanism:
- **Re-entrant VT:** Often associated with heart conditions like heart attacks, inflammation, fibrofatty infiltration, genetic disorders (like hypertrophic cardiomyopathy), and scarring from previous surgeries.
- **Triggered VT:** Can occur in conditions like Brugada syndrome (abnormal conduction in the right ventricle) or idiopathic VT with a focal site of origin in specific heart areas.
- **Torsades de Pointes VT:** Results from early afterdepolarizations during prolonged heart action potential, often due to genetic long QT syndromes or medications that prolong QT intervals.
- **Bundle Branch Re-entry VT:** May occur in normal hearts as nonsustained beats but can become sustained in individuals with heart enlargement and slow conduction due to heart or conduction system diseases.
- **Accelerated Pacemaker Activity:** This can be triggered by various factors, including inflammation, excess digoxin levels, electrolyte imbalances, and more.
- **Bidirectional VT:** Caused by calcium overload in heart cells due to genetic mutations or digitalis toxicity.
- **Ventricular Fibrillation (VF):** VF is a chaotic, high-frequency electrical activity in the ventricles, often considered an end stage of severe electrophysiologic abnormalities. The exact mechanisms initiating VF are not fully understood, but it can be the result of various severe electrical disturbances.
In summary, ventricular arrhythmias can have different causes and mechanisms, and they may occur in individuals with various heart conditions or as a result of genetic factors, medication, or electrolyte imbalances. Ventricular fibrillation (VF) represents a particularly chaotic and life-threatening form of ventricular arrhythmia.