Place of atrial fibrillation in the classification of arrhythmias
The electrocardiographic classification refers atrial fibrillation to the group of disorders of myocardial excitability function. Unlike automaticity or conductivity failures, this process is caused by the ectopic origin of impulses outside the sinus node.
In the structure of excitability pathology, three main directions are distinguished:
- Extrasystole: supraventricular (atrial, atrioventricular) and ventricular variants;
- Paroxysmal tachycardias: supraventricular and ventricular forms;
- Other paroxysmal states: episodes of atrial fibrillation (atrial fibrillation/flutter), as well as atrial flutter.
Episodes of atrial fibrillation often occur against the background of accessory conduction pathways. In particular, in Wolff-Parkinson-White (WPW) syndrome, excitation circulation via the re-entry mechanism through an accessory pathway can provoke not only supraventricular tachycardia but also paroxysms of atrial fibrillation.
ECG manifestations in heart defects and thyrotoxicosis
The electrocardiographic picture of atrial fibrillation is closely related to the primary disease that caused myocardial damage:
- Mitral stenosis.
- When sinus rhythm is preserved, P-mitrale (a sign of left atrial overload) and right ventricular hypertrophy (rsR' or qR types) are visualized.
- When rhythm breaks into atrial fibrillation, a coarse-wave form of atrial fibrillation is recorded on the tracing, combined with pronounced signs of right ventricular hypertrophy.
- Thyrotoxic heart.
- The initial stage is characterized by persistent sinus tachycardia (100–140 beats per minute), which does not disappear even during nighttime sleep.
- As myocardial dystrophy and chamber dilatation progress, atrial fibrillation occurs—initially as transient paroxysms, and then in a permanent form.
- On the ECG, atrial fibrillation is accompanied by changes in the terminal part of the ventricular complex: ST segment shifts and T wave inversion.
Diagnosis of fibrillation in hypertrophic cardiomyopathy
In hypertrophic cardiomyopathy (HCM), atrial fibrillation acts as a formidable marker of an unfavorable course. For its timely detection, a standard 12-lead electrocardiogram is often insufficient, which is why 24-hour Holter monitoring becomes crucial.
| Method of examination | Recorded pathology markers |
|---|---|
| Standard ECG | Left ventricular, left atrial, and interventricular septum hypertrophy (deep Q in I, aVL, V5–V6), left bundle branch block, ST depression, negative T |
| Holter monitoring | Episodes of atrial fibrillation, paroxysms of ventricular tachycardia, ventricular extrasystoles, QT interval prolongation |
Holter recording allows for the timely detection of asymptomatic fibrillation paroxysms, which, together with ventricular tachyarrhythmias, pose a direct threat of sudden cardiac death.
Excitability arrhythmia forms are easily systematized by increasing severity: "E-T-P" — Extrasystoles (single or runs), Paroxysmal tachycardias, and Paroxysms of atrial fibrillation/flutter.
Class and exam questions
How does the ECG in mitral stenosis during sinus rhythm differ from the picture in atrial fibrillation?
During sinus rhythm, the P-mitrale wave and right ventricular hypertrophy are determined. When atrial fibrillation occurs, the P wave disappears, replaced by a coarse-wave form of atrial fibrillation against the background of persisting signs of right ventricular hypertrophy.
How does atrial fibrillation develop in thyrotoxic heart syndrome?
It begins with persistent tachycardia at rest and during sleep, transitions into rare paroxysms of atrial fibrillation, and with the progression of dystrophy and chamber dilatation, transforms into a permanent form.
What diagnostic study is mandatory when latent atrial fibrillation is suspected in a patient with HCM?
Holter ECG monitoring is necessary as it allows documentation of atrial fibrillation paroxysms and assessment of the risk of sudden cardiac death.
What else to study on this topic
- Topical diagnosis and variants of atrioventricular extrasystoles on ECG
- Criteria for functional extrasystole and its differences from organic ones
- Electrocardiographic signs of Wolff-Parkinson-White (WPW) syndrome
- Echocardiographic criteria for asymmetric hypertrophy and SAM syndrome in HCM
- Auscultatory phenomenon of the "mitral stenosis melody" and percussion heart borders
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