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Last Updated: 2/15/2026

ECG Evaluation and Monitoring in Hypertrophic Cardiomyopathy

Baseline Electrocardiographic Abnormalities

  • In phenotypic HCM, the 12‑lead ECG is abnormal in the vast majority of patients, yet these abnormalities do not reliably correlate with the anatomic severity or pattern of ventricular hypertrophy on imaging. [American College of Cardiology] 1, 2, 3
  • The most frequent baseline finding is increased QRS voltage that meets standard left‑ventricular‑hypertrophy (LVH) criteria. [American College of Cardiology] 1, 2
  • ST‑segment depression with accompanying T‑wave abnormalities (secondary ST‑T changes) is commonly observed. [American College of Cardiology] 1, 4
  • Deep T‑wave inversions, especially in lateral and inferior leads, are characteristic. [American College of Cardiology] 1, 2, 3
  • Left atrial enlargement manifests as broad, notched P‑waves in lead II or biphasic P‑waves in V1. [American College of Cardiology] 1, 2, 4
  • A pseudo‑myocardial‑infarction pattern (loss of septal Q waves) may appear, particularly in younger individuals before echocardiographic wall thickening is evident. [American College of Cardiology] 3, 5, 6
  • Presence of a Wolff‑Parkinson‑White pattern should raise suspicion for HCM phenocopies such as glycogen‑storage diseases (e.g., Danon, PRKAG2) or Fabry disease. [American College of Cardiology] 1, 2, 3
  • Incomplete left‑bundle‑branch block can develop, often with a slurred R‑wave upstroke. [American Heart Association] 4

Post‑Event Electrocardiographic Findings

Arrhythmic Events

  • After a cardiac event, LVH with repolarization abnormalities is present in 75–95 % of HCM patients, and arrhythmias such as atrial fibrillation (AF), nonsustained ventricular tachycardia (NSVT), or conduction disturbances may become more pronounced or newly apparent. [American College of Cardiology] 1, 2, 3
  • Atrial fibrillation is detected in up to 50 % of HCM patients during extended monitoring and is a major adverse outcome associated with stroke risk. [American Heart Association] 2, 3, 6
  • Risk factors for AF in HCM include left‑atrial dilation, older age, longer disease duration, and NYHA functional class III–IV. [American College of Cardiology] 1, 2, 7
  • Annual extended ambulatory monitoring (>24 h) is recommended for high‑risk HCM patients to detect paroxysmal AF. [American College of Cardiology] 1, 6
  • NSVT on 24–48 h Holter monitoring identifies patients at significantly higher risk for sudden cardiac death. [American College of Cardiology] 1, 3, 5
  • NSVT occurring in patients younger than 35 years carries greater prognostic significance than in older patients. [American College of Cardiology] 1, 3, 7
  • Longer duration and faster rate of NSVT episodes are associated with a higher incidence of ICD‑treated arrhythmias. [American College of Cardiology] 1, 3, 7

Ischemic Events

  • Following myocardial ischemia or infarction, HCM patients may develop new ST‑segment changes beyond their baseline repolarization abnormalities. [American College of Cardiology] 1, 7
  • Evolution of Q waves or emergence of a pseudo‑infarction pattern can be observed after ischemic events. [American College of Cardiology] 3, 5, 6
  • Coronary angiography (CT or invasive) is recommended for HCM patients who present with symptoms or objective evidence of myocardial ischemia. [American College of Cardiology] 1, 2, 7
  • Immediate post‑event: obtain a 12‑lead ECG to document acute changes and compare with the patient’s baseline tracing. [American College of Cardiology] 1, 2, 3, 6
  • Symptomatic patients (e.g., palpitations, light‑headedness) should receive extended ECG monitoring or event recording until the symptoms are captured. [American College of Cardiology] 1, 2, 3, 6
  • Implantable loop recorders are advisable when symptoms are infrequent and not captured by external monitors. [American College of Cardiology] 1, 3
  • Serial follow‑up: repeat a 12‑lead ECG every 1–2 years to identify new conduction abnormalities or arrhythmias. [American College of Cardiology] 1, 2, 3, 6
  • Holter monitoring: perform 24–48 h Holter every 1–2 years in patients without an implantable cardioverter‑defibrillator (ICD) to reassess NSVT burden. [American College of Cardiology] 1, 3, 5
  • Extended ambulatory monitoring (>24 h) should be performed annually or every 1–2 years in patients at high risk for AF (left‑atrial dilation, advanced age, NYHA III–IV). [American College of Cardiology] 1, 2, 6

Clinical Pitfalls and Caveats

  • ECG abnormalities do not correlate with the severity or distribution of hypertrophy seen on imaging studies. [American College of Cardiology] 1, 2, 3
  • The optimal duration of ambulatory monitoring for NSVT detection is not yet established; longer monitoring periods increase the likelihood of identifying additional NSVT episodes. [American College of Cardiology] 1, 3, 7
  • Asymptomatic AF episodes, particularly brief ones, may not translate into adverse outcomes, although the clinical significance remains uncertain. [American Heart Association] 2, 3, 6
  • Clinical correlation of symptoms with monitor findings is essential, as HCM patients exhibit a broad spectrum of arrhythmias, most of which are not lethal. [American College of Cardiology] 1, 7

ECG Findings and Monitoring Recommendations in Hypertrophic Cardiomyopathy

Prevalence and General Characteristics

  • The 12‑lead electrocardiogram is abnormal in 75 %–95 % of patients with phenotypic hypertrophic cardiomyopathy (HCM), most commonly demonstrating left‑ventricular hypertrophy (LVH) with repolarization abnormalities; however, these ECG changes do not reliably correlate with the anatomic severity or pattern of hypertrophy. [American Heart Association] 8, 9, 10, 11

Voltage and Repolarization Abnormalities

  • Increased QRS voltage fulfills standard LVH criteria in the majority of phenotypic HCM cases. [American Heart Association; American College of Cardiology] 8, 11
  • ST‑segment depression frequently accompanies T‑wave abnormalities, producing a classic “strain pattern.” [American Heart Association] 8

Conduction and Atrial Findings

  • Left atrial enlargement is reflected by broad, notched P‑waves in lead II or biphasic P‑waves in V1. [American Heart Association; American College of Cardiology] 8, 10
  • Wolff‑Parkinson‑White (WPW) pattern on the ECG should raise suspicion for HCM phenocopies such as glycogen‑storage diseases (e.g., Danon, PRKAG2) or Fabry disease. [American Heart Association; American College of Cardiology] 8, 9, 10

Arrhythmia Detection and Prognostic Implications

  • Atrial fibrillation is identified in up to 50 % of HCM patients during extended monitoring and confers a significant risk of stroke. [American Heart Association] 8, 9, 12
  • Nonsustained ventricular tachycardia (NSVT) detected on 24–48 hour Holter monitoring identifies patients at higher risk for sudden cardiac death. [American College of Cardiology] 10, 11, 13
  • NSVT in patients younger than 35 years carries greater prognostic significance for sudden death than in older patients. [American College of Cardiology] 10, 11

Initial Evaluation

  • Obtain a baseline 12‑lead ECG in every individual with suspected or confirmed HCM. [American Heart Association; American College of Cardiology] 8, 10, 11
  • Perform 24–48 hour ambulatory ECG monitoring at baseline to detect NSVT for sudden‑death risk stratification. [American Heart Association; American College of Cardiology] 8, 10, 11

Serial Follow‑Up (Stable Patients)

  • Repeat 12‑lead ECG every 1–2 years to identify new conduction abnormalities or arrhythmias. [American Heart Association; American College of Cardiology] 8, 10, 11
  • Repeat 24–48 hour Holter monitoring every 1–2 years in patients without an implantable cardioverter‑defibrillator (ICD) to reassess NSVT burden. [American College of Cardiology] 10, 11
  • Conduct extended ambulatory monitoring (>24 hours) annually in patients at high risk for atrial fibrillation (e.g., left‑atrial dilation, advanced age, NYHA class III–IV). [American College of Cardiology] 10, 11

Symptomatic Patients

  • For patients who develop palpitations or light‑headedness, initiate extended ECG monitoring or event‑recording and continue until the symptoms are captured. [American Heart Association; American College of Cardiology] 8, 10, 11
  • Consider implantable loop recorders when symptoms are infrequent and not captured by external monitoring. [American Heart Association; American College of Cardiology] 8, 10

REFERENCES

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