A focused collection of 39 calculators, scores, and clinical references.
Atrial Fibrillation (AF) Burden: Explanation and Clinical Context Atrial Fibrillation (AF) burden refers to the cumulative duration of AF episodes experienced by a patient per day, typically measured via continuous ECG monitoring or implantable devices. It is quantified in minutes/day and provides valuable prognostic information beyond AF presence alone. Studies show that higher AF burden is associated with increased
AFEQT Score (Atrial Fibrillation Effect on Quality of Life): Explanation and Clinical Context The AFEQT Score is a validated patient-reported outcome measure that assesses health-related quality of life in patients with atrial fibrillation (AF). It evaluates four domains: Symptoms, Daily Activities, Treatment Concern, and Overall Health. Each domain is scored from 0 to 100, where higher scores indicate better quality
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) Task Force Criteria (2010 Revised): Explanation and Clinical Context The ARVC Task Force Criteria (2010 revised) is a structured diagnostic tool used to improve diagnostic accuracy for ARVC, a genetic cardiomyopathy characterized by fibro-fatty replacement of the right ventricular myocardium, leading to arrhythmias and sudden cardiac death. The criteria are divid
Brugada Risk Score: Explanation and Clinical Context The Brugada Risk Score, developed by Brugada et al. in 2010, is a clinical tool designed to stratify the risk of sudden cardiac death (SCD) in patients with Brugada Syndrome. It incorporates key predictors: spontaneous Type 1 ECG pattern, history of syncope, family history of SCD, fragmented QRS, and early repolarization in inferolateral leads. Each variable is ass
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Chronotropic Index: Explanation and Clinical Context Chronotropic Index is a physiologic measure that reflects the ability of the heart to increase its rate during physical exertion. It evaluates the relationship between the actual heart rate achieved during exercise and the predicted heart rate reserve. This parameter is commonly used in exercise stress testing to assess whether the chronotropic response is appropri
DANISH Score (ICD Benefit Model): Explanation and Clinical Context The DANISH Score is derived from the DANISH trial (Køber et al., 2016) to estimate the potential benefit of implantable cardioverter-defibrillator (ICD) therapy in patients with non-ischemic systolic heart failure. It considers clinical variables such as age, sex, ischemic cardiomyopathy, left ventricular ejection fraction (LVEF), diabetes mellitus, a
Depolarization Abnormality Index (DAI): Explanation and Clinical Context DAI is a quantitative ECG measure designed to evaluate intraventricular conduction abnormalities and predict risk of adverse cardiac events. It is calculated by subtracting the intrinsicoid deflection in leads V5 or V6 from the total QRS duration and dividing by the QRS duration. A higher DAI indicates a greater conduction abnormality and potent
EHR–AF Recurrence Model: Explanation and Clinical Context The EHR–AF Recurrence Model is a predictive tool designed to assess the risk of atrial fibrillation recurrence following catheter ablation. It incorporates clinical parameters such as B-type natriuretic peptide (BNP), neutrophil-to-lymphocyte ratio (NLR), albumin levels, lymphocyte count, left atrial diameter (LAD), and the presence of non-paroxysmal atrial fi
EHRA Symptom Score (AF Severity Class): Explanation and Clinical Context The EHRA (European Heart Rhythm Association) symptom score is a standardized tool to quantify the severity of symptoms in patients with atrial fibrillation (AF). It categorizes patients based on the impact of AF-related symptoms on daily activities. The score ranges from EHRA I (asymptomatic) to EHRA IV (disabling symptoms), allowing clinicians
ESC 2022 ARVC Risk Score: Explanation and Clinical Context The ESC 2022 ARVC Risk Score is a validated tool to estimate the 5-year risk of ventricular arrhythmias in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC). It uses a combination of clinical variables including age, sex, history of syncope, presence of non-sustained ventricular tachycardia (NSVT), premature ventricular contractions (PVCs),
: Clinical Explanation and Context The estimated maximum heart rate is calculated using one of the simplest and most widely recognized formulas in cardiovascular physiology, which is the subtraction of age from the number two hundred twenty. This estimation represents the highest heart rate an individual can theoretically achieve during peak physical exertion. Although it does not directly measure the true maximal he
Fragmented QRS (fQRS) Index: Explanation and Clinical Context Fragmented QRS (fQRS) refers to additional R waves (R’) or notching in the nadir of the S wave in contiguous ECG leads, representing myocardial conduction delay due to fibrosis or scarring. The fQRS Index is calculated as the number of ECG leads showing fQRS divided by the total number of leads (usually 12-lead ECG), providing a quantitative measure of myo
Heart Rate Variability (HRV): SDNN and RMSSD: Explanation and Clinical Context Heart Rate Variability (HRV) is a non-invasive marker of autonomic nervous system function and cardiac health. SDNN (Standard Deviation of NN intervals) represents overall HRV and reflects both sympathetic and parasympathetic influences. RMSSD (Root Mean Square of Successive Differences) reflects short-term parasympathetic activity and is
JTc Interval: Explanation and Clinical Context The JTc interval represents the corrected JT interval, calculated as the QT interval minus QRS duration, adjusted for heart rate. It isolates ventricular repolarization from depolarization, offering a more precise assessment than QTc in patients with wide QRS complexes. Normal values are generally <330 ms for men and <340 ms for women. Prolonged JTc is associated with an
LF/HF Ratio (Autonomic Tone): Explanation and Clinical Context The LF/HF ratio is a key heart rate variability (HRV) parameter reflecting autonomic nervous system balance. LF (low frequency) power represents both sympathetic and parasympathetic activity, while HF (high frequency) power is primarily a marker of parasympathetic (vagal) activity. The LF/HF ratio quantifies the relative contribution of sympathetic vs par
MADIT II Risk Model: Explanation and Clinical Context The MADIT II Risk Score is a validated tool designed to estimate the 2-year mortality risk in patients with ischemic cardiomyopathy and severely reduced left ventricular ejection fraction (<30%). It uses easily obtainable clinical variables including age >70 years, NYHA functional class >I, presence of diabetes, QRS duration >120 ms, atrial fibrillation, BUN >26 m
MUSTT Score (VT Inducibility): Explanation and Clinical Context The MUSTT (Multicenter Unsustained Tachycardia Trial) Score is designed to estimate the risk of arrhythmic events and sudden cardiac death in patients with prior myocardial infarction, left ventricular dysfunction, and non-sustained ventricular tachycardia. It incorporates key clinical parameters: age, left ventricular ejection fraction, NYHA functional
NSVT Duration Index: Explanation and Clinical Context The NSVT Duration Index quantifies the burden of nonsustained ventricular tachycardia (NSVT) over a defined monitoring period. It is calculated as the total duration of NSVT episodes divided by the total duration of monitoring (in minutes). This index provides a standardized measure to assess arrhythmic risk in patients with cardiomyopathies, ischemic heart diseas
P-wave Axis Deviation Index: Explanation and Clinical Context The P-wave axis is calculated using the frontal plane ECG leads I and aVF to estimate atrial depolarization direction. A normal P-wave axis ranges from 30° to 75° in adults. Values outside this range indicate potential right or left atrial enlargement, atrial conduction abnormalities, or underlying structural heart disease. Abnormal P-wave axis has been as
P-wave Dispersion (PWD): Explanation and Clinical Context P-wave Dispersion is defined as the difference between the maximum and minimum P-wave durations measured on a standard 12-lead ECG. It reflects the heterogeneity of atrial conduction and has been widely studied as a predictor of atrial fibrillation (AF) in both structural heart disease and healthy populations. Increased PWD indicates inhomogeneous and disconti
PVC Burden Percentage: Explanation and Clinical Context PVC Burden Percentage represents the proportion of premature ventricular contractions (PVCs) relative to the total number of heartbeats over a 24-hour period as recorded by Holter monitoring or similar continuous ECG monitoring. A low PVC burden (<1%) is generally considered clinically insignificant, moderate burden (1–10%) may warrant follow-up in symptomatic p
QRS Duration Index: Explanation and Clinical Context The QRS Duration Index (QRSd Index) is a heart rate–corrected measure of ventricular depolarization duration, initially described by Brodie et al. in 1982. It is calculated by dividing the QRS duration (in milliseconds) by the square root of the RR interval (in seconds). This index accounts for heart rate variability when assessing intraventricular conduction and c
QRS-T Angle Index: Explanation and Clinical Context The QRS-T angle represents the spatial difference between the depolarization (QRS) and repolarization (T wave) vectors of the heart on a 12-lead ECG. A wider QRS-T angle is associated with abnormal ventricular repolarization and is a strong predictor of adverse cardiovascular events, including sudden cardiac death and all-cause mortality. Normal values are usually <
QRSD Ratio (Bundle Branch Differentiation): Explanation and Clinical Context The QRSD Ratio is a metric used to differentiate types of bundle branch conduction delays on ECG, especially in borderline QRS prolongation cases. It is calculated by dividing the QRS duration (ms) by the square root of the RR interval (ms), providing heart rate–corrected QRS assessment. A QRSD ratio <1.15 is typically considered normal, ind
QTc Bazett Formula: Explanation and Clinical Context The QT interval represents the time from the start of ventricular depolarization to the end of ventricular repolarization on an electrocardiogram (ECG). QT interval duration varies with heart rate, and QTc (corrected QT) is calculated to standardize QT for heart rate. Bazett's formula is the most widely used correction: QTc = QT / √RR, where QT is in milliseconds a
Comprehensive explanation and clinical context The QT interval measures ventricular depolarisation and repolarisation on the electrocardiogram. Correcting the QT interval for heart rate yields QTc. Several correction formulae exist. Bazett's formula divides QT by the square root of the RR interval in seconds. Fridericia's formula divides QT by the cube root of the RR interval. Framingham's formula adjusts QT by addin
QTc Fridericia Correction: Explanation and Clinical Context The Fridericia formula is used to correct the QT interval for heart rate: QTcF = QT / (RR^1/3), where RR is the interval between heartbeats in seconds. It provides a more accurate correction than Bazett's formula, especially at extreme heart rates. QTc prolongation is associated with increased risk of ventricular arrhythmias, including Torsades de Pointes, a
Rautaharju QT Correction Formula: Explanation and Clinical Context The Rautaharju QT correction formula is a regression-based method developed to correct the QT interval for heart rate more accurately than traditional formulas such as Bazett or Fridericia. It was derived from large population-based ECG studies to provide a less biased estimate of QTc across a wide range of heart rates. It uses the RR interval (in sec
Risk of Sudden Death in Brugada (RB Score): Explanation and Clinical Context The RB Score is a clinical scoring system designed to estimate the risk of sudden cardiac death in patients with Brugada Syndrome. It incorporates key risk factors: spontaneous Type 1 ECG, history of syncope, family history of sudden cardiac death, and inducible ventricular arrhythmias on electrophysiologic study. A total score of 0–5 points
Signal-Averaged ECG (SAECG) Abnormality Index: Explanation and Clinical Context SAECG is a specialized electrocardiographic technique used to detect subtle abnormalities in ventricular depolarization that are not visible on standard ECG. The SAECG Abnormality Index quantifies risk for ventricular arrhythmias by scoring three primary parameters: filtered QRS duration, low amplitude signal duration, and root mean squar
Spatial Angle Index (SAI QRST): Explanation and Clinical Context SAI QRST is a quantitative ECG-derived index that measures the spatial angle between the QRS complex and T wave vectors in three-dimensional space. It reflects the degree of heterogeneity in ventricular depolarization and repolarization. Higher values of SAI QRST indicate greater electrical instability and are associated with increased risk of ventricul
SCD-HeFT Risk Model: Explanation and Clinical Context The SCD-HeFT Risk Model estimates the 5-year risk of all-cause mortality in patients with heart failure with reduced ejection fraction (HFrEF) who are candidates for implantable cardioverter-defibrillator (ICD) therapy. The model uses clinical variables available at baseline, including age, NYHA functional class, left ventricular ejection fraction (LVEF), presence
Schwartz Score for Long QT Syndrome: Explanation and Clinical Context The Schwartz Score is a validated diagnostic tool to assess the probability of congenital Long QT Syndrome (LQTS). It incorporates electrocardiographic, clinical, and family history features including QTc interval, history of syncope, congenital deafness, and family history of sudden cardiac death or LQTS. Points are assigned based on QTc duration,
Shanghai Score for Brugada Syndrome: Explanation and Clinical Context The Shanghai Score is a diagnostic scoring system developed to assess the likelihood of Brugada Syndrome based on clinical, electrocardiographic, familial, and genetic criteria. It assigns weighted points to spontaneous Type 1 ECG, fever-induced or drug-provoked Type 1 ECG, documented ventricular arrhythmias, family history of sudden cardiac death,
Signal-Averaged QRS Duration: Explanation and Clinical Context Signal-Averaged QRS (SA-QRS) duration is a specialized ECG measurement designed to detect subtle conduction abnormalities that predispose patients to ventricular arrhythmias. It is typically performed using high-resolution ECG recordings and computer averaging to reduce noise. Normal SA-QRS duration is generally less than 114 ms. Values between 114–120 ms
T-wave Alternans (TWA): Explanation and Clinical Context T-wave Alternans (TWA) refers to beat-to-beat variations in the amplitude or morphology of the T-wave on the electrocardiogram, reflecting repolarization heterogeneity. Elevated microvolt-level TWA has been validated as a non-invasive marker for increased risk of ventricular arrhythmias and sudden cardiac death, particularly in patients with structural heart di
Tpeak-Tend Interval Index: Explanation and Clinical Context The Tpeak-Tend (Tpe) interval represents the time from the peak to the end of the T wave on the ECG and reflects transmural dispersion of repolarization. The Tpe Index, calculated as Tpe/QT ratio, normalizes the Tpe interval relative to the QT interval and provides a dimensionless measure of ventricular repolarization heterogeneity. Increased Tpe Index has b
Ventricular Late Potentials (VLP) Score: Explanation and Clinical Context Ventricular Late Potentials (VLP) detected on signal-averaged ECG represent delayed depolarization of the ventricular myocardium, typically seen after myocardial infarction. The VLP score uses three parameters: filtered QRS duration (fQRS), low-amplitude signal duration in the terminal 40 ms of QRS (LAS40), and root mean square voltage of the l