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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Cardiology

Decoding Your Cardiac Tests: Reading the Signals

At a Glance

Hereditary cardiac conduction disease is evaluated with several complementary tests: ECGs measure electrical timing, monitors capture intermittent fast or slow rhythms, and EP studies assess the HV interval. Echocardiograms and cardiac MRI check for heart-muscle thickening, scarring, or enlargement.

Because Hereditary atrial tachyarrhythmia-infra-Hisian cardiac conduction disease involves two different electrical problems—fast rhythms in the top and slow signals in the bottom—your medical team uses a “toolkit” of tests to see the full picture. These tests help determine if your condition is purely electrical or if it is beginning to change the physical structure of your heart muscle [1][2].

The ECG: Your Electrical Blueprint

The Electrocardiogram (ECG or EKG) is the most common tool used to monitor your condition. It measures the timing of the electrical “spark” as it moves through your heart. Key numbers to watch include:

  • PR Interval: This measures how long it takes for the signal to travel from the top chambers (atria) to the bottom chambers (ventricles). In healthy adults, this is usually 120 to 200 milliseconds [3]. A longer PR interval (over 200 ms) indicates first-degree AV block, meaning the signal is being delayed [4].
  • QRS Duration: This measures how long it takes for the electricity to spread through the bottom chambers. A normal QRS is usually under 120 milliseconds [5]. If your QRS is “widened” (e.g., ≥120 ms), it means there is an intraventricular conduction delay, which can be a sign the infra-Hisian wiring is damaged, forcing the signal to take a slower route. (However, QRS widening can have other causes, and early infra-Hisian disease may not widen the QRS) [4][6].
  • Bundle Branch Block: This is a specific pattern on the ECG showing that conduction through one of the two main “highways” (the left or right bundle branch) is delayed or interrupted [6].

The EP Study: Measuring the “HV Interval”

If your ECG shows significant delays or if you have unexplained syncope, your doctor may suggest an Electrophysiology (EP) Study. This is an invasive procedure where thin wires are guided into the heart to measure internal signals directly [7].

The most critical measurement for your condition is the HV Interval. This measures the exact time it takes for a signal to jump from the “junction box” (Bundle of His) to the bottom muscle (Ventricles) [8].

  • Normal: Usually between 35 and 55 milliseconds [9].
  • The 70 ms Threshold: An HV interval of 70 milliseconds or longer is a marker of significant infra-Hisian disease [10]. However, this is not a universal stand-alone rule that mandates a pacemaker for every asymptomatic patient. The decision to pace based on the HV interval is highly context-specific, relying on symptoms, guideline recommendations, and other risk factors [11][10].

Catching “Ghost” Rhythms: Holter and Event Monitors

Because symptoms like racing (atrial tachyarrhythmia) or fainting (syncope) often come and go, a standard 10-second ECG might miss them.

  • Holter Monitors: You wear these for 24 to 48 hours to record every single heartbeat [12].
  • Event/Patch Monitors: These can be worn for up to 30 days. They are excellent for catching “silent” AFib or brief pauses in your heart rate that happen while you sleep [13].

Imaging: Checking the Heart’s Structure

Even if your condition is primarily electrical, some genes can cause the heart muscle itself to change over time.

  • Echocardiogram (Echo): This ultrasound uses sound waves to see the heart beating. It is the primary tool to look for hypertrophy (thickening of the heart walls), which is common in PRKAG2 mutations [14][15].
  • Cardiac MRI (CMR): This provides the most detailed “photograph” of your heart. It can detect fibrosis (microscopic scarring) that an Echo might miss [16]. In conditions like LMNA, an MRI can show if the heart is beginning to “dilate” (stretch and weaken) before you ever feel a symptom [17][18].

By tracking these tests, you and your doctor can decide exactly when it is time to move from observation to treatment.

Common questions in this guide

What does a long PR interval mean on my ECG?
A PR interval longer than 200 milliseconds means the electrical signal takes longer than usual to travel from the atria to the ventricles, a pattern called first-degree AV block. It shows delayed conduction but must be interpreted alongside the rest of your ECG and clinical picture.
Can a wide QRS prove that I have infra-Hisian disease?
A QRS duration of 120 milliseconds or more indicates a delay in electrical spread through the ventricles and can occur when conduction below the Bundle of His is affected. It does not prove infra-Hisian disease because QRS widening has other causes, and early disease can occur without a wide QRS.
Why would I need an EP study and an HV interval measurement?
An electrophysiology study uses thin wires to measure the heart’s internal electrical signals directly. The HV interval measures the time for a signal to travel from the Bundle of His to the ventricles; a value of 70 milliseconds or longer can indicate significant infra-Hisian disease, but treatment decisions also depend on symptoms and other risk factors.
How can a Holter or event monitor find problems an ECG misses?
A Holter monitor records every heartbeat for about 24 to 48 hours, while an event or patch monitor can record for up to 30 days. Longer monitoring can capture intermittent atrial tachyarrhythmias, silent atrial fibrillation, or pauses that are not present during a brief office ECG.
What can an echocardiogram or cardiac MRI show?
An echocardiogram checks the heart’s movement and can identify thickened heart muscle, including changes associated with PRKAG2 mutations. Cardiac MRI provides a more detailed view and can detect fibrosis or early enlargement and weakening of the heart, including changes associated with LMNA variants.

Get notified when new evidence is published on Hereditary atrial tachyarrhythmia-infra-Hisian cardiac conduction disease.

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References

References (18)
  1. 1

    Molecular and genetic insights into progressive cardiac conduction disease.

    Asatryan B, Medeiros-Domingo A

    Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology 2019; (21(8)):1145-1158 doi:10.1093/europace/euz109.

    PMID: 31087102
  2. 2

    Current Topics of Progressive Cardiac Conduction Disease.

    Sumitomo N, Mori H, Kumamoto T, et al.

    Journal of arrhythmia 2026; (42(3)):e70383 doi:10.1002/joa3.70383.

    PMID: 42368294
  3. 3

    Leucocyte telomere length and conduction system ageing.

    van Duijvenboden S, Nelson CP, Raisi-Estabragh Z, et al.

    Heart (British Cardiac Society) 2025; (111(7)):314-320 doi:10.1136/heartjnl-2024-324875.

    PMID: 39689933
  4. 4

    Cardiac Conduction Disorders as Markers of Cardiac Events in Myotonic Dystrophy Type 1.

    Itoh H, Hisamatsu T, Tamura T, et al.

    Journal of the American Heart Association 2020; (9(17)):e015709 doi:10.1161/JAHA.119.015709.

    PMID: 32812471
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    Relationships of Measured and Genetically Determined Height With the Cardiac Conduction System in Healthy Adults.

    Kofler T, Thériault S, Bossard M, et al.

    Circulation. Arrhythmia and electrophysiology 2017; (10(1)) doi:10.1161/CIRCEP.116.004735.

    PMID: 28039282
  6. 6

    Prevalence and clinical significance of electrocardiographic complete right bundle branch block in young individuals.

    MacLachlan H, Antonakaki D, Bhatia R, et al.

    European journal of preventive cardiology 2025; (32(12)):1054-1061 doi:10.1093/eurjpc/zwae082.

    PMID: 38412448
  7. 7

    A method for noninvasive beat-by-beat visualization of His bundle signals.

    Sengottuvel S, Shenbaga Devi S, Sasikala M, et al.

    Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc 2023; (28(5)):e13076 doi:10.1111/anec.13076.

    PMID: 37496182
  8. 8

    Noninvasive Determination of HV Interval Using Magnetocardiography.

    Senthilnathan S, Selvaraj RJ, Patel R, et al.

    Pacing and clinical electrophysiology : PACE 2017; (40(5)):568-577 doi:10.1111/pace.13067.

    PMID: 28247926
  9. 9

    High-density mapping of his-ventricular intervals: impact of recording site and sex-specific differences.

    Serban T, du Fay de Lavallaz J, Knecht S, et al.

    Journal of interventional cardiac electrophysiology : an international journal of arrhythmias and pacing 2026; (69(6)):1493-1501 doi:10.1007/s10840-026-02438-z.

    PMID: 42758258
  10. 10

    Electrocardiogram vs Electrophysiological Study and Major Conduction Delays in Myotonic Dystrophy Type 1.

    Clementy N, Labombarda F, Grolleau F, et al.

    JAMA cardiology 2025; (10(11)):1121-1129 doi:10.1001/jamacardio.2025.3055.

    PMID: 40991257
  11. 11

    Incidence and management of atrioventricular conduction disorders in new-onset left bundle branch block after TAVI: A prospective multicenter study.

    Massoullié G, Ploux S, Souteyrand G, et al.

    Heart rhythm 2023; (20(5)):699-706 doi:10.1016/j.hrthm.2023.01.013.

    PMID: 36646235
  12. 12

    aTrial arrhythmias in inhEriTed aRrhythmIa Syndromes: results from the TETRIS study.

    Conte G, Bergonti M, Probst V, et al.

    Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology 2024; (26(12)) doi:10.1093/europace/euae288.

    PMID: 39527076
  13. 13

    External prolonged electrocardiogram monitoring in unexplained syncope and palpitations: results of the SYNARR-Flash study.

    Locati ET, Moya A, Oliveira M, et al.

    Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology 2016; (18(8)):1265-72 doi:10.1093/europace/euv311.

    PMID: 26519025
  14. 14

    Familial Atrial Enlargement, Conduction Disorder and Symmetric Cardiac Hypertrophy Are Early Signs of PRKAG2 R302Q.

    Hu J, Tang B, Wang J, et al.

    Current medical science 2020; (40(3)):486-492 doi:10.1007/s11596-020-2207-z.

    PMID: 32681253
  15. 15

    Echocardiographic characteristics of PRKAG2 syndrome: a research using three-dimensional speckle tracking echocardiography compared with sarcomeric hypertrophic cardiomyopathy.

    Tang L, Li X, Zhou N, et al.

    Cardiovascular ultrasound 2022; (20(1)):14 doi:10.1186/s12947-022-00284-3.

    PMID: 35509080
  16. 16

    The Cardiovascular Magnetic Resonance Phenotype of Lamin Heart Disease.

    Topriceanu CC, Al-Farih M, Joy G, et al.

    JACC. Cardiovascular imaging 2025; (18(6)):644-660 doi:10.1016/j.jcmg.2025.01.004.

    PMID: 40372342
  17. 17

    Clinical Features of LMNA-Related Cardiomyopathy in 18 Patients and Characterization of Two Novel Variants.

    Ferradini V, Cosma J, Romeo F, et al.

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    PMID: 34768595
  18. 18

    Late gadolinium enhancement role in arrhythmic risk stratification of patients with LMNA cardiomyopathy: results from a long-term follow-up multicentre study.

    Peretto G, Barison A, Forleo C, et al.

    Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology 2020; (22(12)):1864-1872 doi:10.1093/europace/euaa171.

    PMID: 32995851

This page explains cardiac tests used to evaluate hereditary cardiac conduction disease for informational purposes only and does not constitute medical advice. Your cardiologist or electrophysiologist should interpret your results and recommend care for your situation.

Guide contents Hereditary atrial tachyarrhythmia-infra-Hisian cardiac conduction disease
Research & Literature
03 The Biology of Your Heart's Electrical Wiring 05 Standard of Care