What to know about second degree heart block type 1 Health ConditionsHealth ConditionsAlzheimer's & DementiaAnxietyArthritisAsthma & AllergiesBreast CancerCancerCardiovascular HealthCOVID-19Dermatology & SkincareDiabetesEnvironment & SustainabilityExercise & FitnessEye HealthHeadache & MigraineHealth EquityHIV & AIDSHuman BiologyInflammatory Bowel DiseaseLeukemiaLGBTQIA+Men's HealthMental HealthMultiple Sclerosis (MS)NutritionParkinson's DiseasePsoriasisSexual HealthWomen's HealthDiscoverNewsLatest NewsOriginal SeriesMedical MythsHonest NutritionThrough My EyesNew Normal HealthPodcastsHow to understand chronic painWhat is behind vaccine hesitancy?The amazing story of hepatitis C, from discovery to cureNew directions in dementia researchCan psychedelics rewire a depressed, anxious brain?Why climate change matters for human healthToolsGeneral HealthDrugs A-ZHealth HubsHealth ToolsBMI Calculators and ChartsBlood Pressure Chart: Ranges and GuideBreast Cancer: Self-Examination GuideSleep CalculatorHealth ProductsAffordable Therapy OptionsBlood Pressure MonitorsDiabetic SuppliesFitness TrackersHome GymsGreen Cleaning ProductsHow to Shop for CBDQuizzesRA Myths vs FactsType 2 Diabetes: Managing Blood SugarAnkylosing Spondylitis Pain: Fact or FictionConnectAbout Medical News TodayWho We AreOur Editorial ProcessContent IntegrityConscious LanguageNewslettersSign UpFollow UsMedical News TodayHealth ConditionsDiscoverToolsConnectSubscribe What is second degree heart block type I Medically reviewed by Dr. Payal Kohli, M.D., FACC — By Zawn Villines on August 12, 2022Heart block, or atrioventricular (AV) block, means that the electrical signal in a person’s heart does not travel through it correctly. Second degree heart block type I means that the signal sometimes does not reach the ventricles, causing skipped beats. There are three subtypes of second-degree heart block. Type I is often benign and may not require treatment, whereas the others are more serious. Learn more about second degree heart block type I, including symptoms, causes, treatment, and how it differs from other types of second degree heart block. What is it Share on PinterestChristin-Marie Arold/EyeEm/Getty ImagesThe heart has a complex electrical system. In heart block, the electrical signal does not travel from the top part of the heart — the atria — to the bottom part of the heart — the ventricles. This affects heart rhythm. Doctors can determine the type of heart block by checking the rhythm and electrical activity of a person’s heart using an electrocardiogram (EKG). The “P wave” on the test shows when the atria contracts. The QRS complex — a combination of the Q, R, and S waves — shows when the ventricles contract. Second degree heart block is a missed heartbeat with either a sudden or progressive delay in how long it takes for the signal to move across the atria. Experts break this form of heart block into three subtypes: Second degree heart block Mobitz type I — also called Wenckebach heart block — second degree heart block Mobitz type II, and second degree high grade. Second degree Mobitz type I: The heart’s electrical signal gets weaker, and eventually, it cannot send an electrical impulse between the atria and ventricles, causing the heart to skip a beat. This form usually does not require treatment.Second degree Mobitz type II: Structural damage, such as that from a heart attack, causes heart cells to fail to conduct an electrical impulse. This can lead to unstable blood flow and worsening heart block.Second degree high grade: This is two or more blocked P waves in a row. However, some electrical impulses travel between the ventricles and atria, differentiating it from third degree heart block. Learn more about the types of heart block. Type I vs type II Second degree heart block type I is often harmless and does not require treatment. It sometimes occurs in athletes, individuals with very healthy hearts, and during sleep. In second degree heart block type II, issues with the heart’s electrical signal come on suddenly rather than intermittently. Rather than slowing the heart rate or causing skipped beats, it causes sudden changes in the rhythm below the atria. This increases the risk of dangerous heart rhythms, fainting, and sudden cardiac death. People with type II are also more likely to have symptoms such as fatigue, exercise intolerance, and dizziness or fainting. Second degree heart block type II may also progress to third degree heart block, which is a complete heart block. Symptoms Second degree heart block type I may not cause any symptoms at all. If it does, a person may experience:dizzinessfaintinga feeling of skipped heartbeats Causes Second degree heart block type I can occur in people with no heart disease, including trained athletes. However, second degree heart block type II usually occurs in people with an underlying condition that damages the heart. Examples include: cardiomyopathy from Lyme diseasestructural diseases of the heartheart tumorsinfections, such as acute rheumatic feverhypertension, or high blood pressurediabetesheart attackdeposition diseases, such as amyloidosis Some medications used to treat heart disease may also increase the risk of heart block. These include:beta-blockersdigoxincalcium channel blockersarrhythmia medications A 2019 study identified several risk factors for heart block, including: a prior heart attackolder agemale sexhigh blood pressurehigh fasting glucose or diabetescongestive heart failure However, these risk factors may be absent in people with second degree heart block type I. This type can occur in athletes and people with otherwise healthy hearts. Prevalence Experts do not know how common second degree heart block is due to no large population studies measuring the prevalence. No specific research has consistently found it to be more common in certain populations. Some smaller studies have found a higher risk of heart block in males, but this research is not definitive. Treatment People with second degree heart block type I are less likely to progress to complete heart block than those with second degree heart block type II. If they have no symptoms, they may not need treatment. However, if the condition causes a slow heartbeat or dangerously low blood pressure, a person may need medication, such as the drug atropine. In some cases, they may need a pacemaker. Heart-healthy lifestyle changes designed to reduce blood pressure and cardiovascular risk factors can also be helpful. If a person develops a heart block due to another disease, a doctor may prescribe additional treatments. Outlook The outlook for people with second degree heart block type I is good. People often have no symptoms, and this type of heart block does not typically progress to more severe forms of heart block. They may need no treatment at all. Summary Second degree heart block type I is often a benign condition that does not usually progress to more serious types of heart block. However, in some people, it may cause symptoms or indicate that a person has an underlying medical condition. People who have signs of heart disease or an irregular heart rhythm should seek medical care. Last medically reviewed on August 12, 2022Heart Disease 3 sourcescollapsedMedical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.Kashou, A. H., et al. (2022). Atrioventricular block.https://www.ncbi.nlm.nih.gov/books/NBK459147/Kerola, T., et al. (2019). Risk factors associated with atrioventricular heart block.https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2734061Mangi, M. A., et al. (2022). Atrioventricular block, second-degree.https://www.ncbi.nlm.nih.gov/books/NBK482359/FEEDBACK:Medically reviewed by Dr. Payal Kohli, M.D., FACC — By Zawn Villines on August 12, 2022 Latest newsWhat sets 'SuperAgers' apart? Their unusually large neuronsOmega-3 may provide a brain boost for people in midlifeSeasonal affective disorder (SAD): How to beat it this fall and winterCDC: Monkeypox in the US 'unlikely to be eliminated in the near future'Why are more women prone to Alzheimer's? New clues arise Related CoverageWhat is first-degree heart block? First-degree heart block is when the electrical signals that cause the heart to beat are partially blocked. Learn more here.READ MOREWhat is obstructive hypertrophic cardiomyopathy? Obstructive hypertrophic cardiomyopathy (HCM) is a thickening of the heart walls that causes a restriction in blood flow. Learn more about obstructive…READ MOREWhat is the life expectancy for someone with a leaking heart valve? Most people with a leaky heart valve who get surgery to repair or replace the leaky valve can expect to have a near-normal life expectancy. Learn more…READ MORE