History and Physical Examination
History
Most patients with sinus node dysfunction (SND) present with one or more of the following nonspecific symptoms, primarily due to bradycardia, sinus pause, and sinus arrest:
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Fatigue
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Lightheadedness
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Palpitations
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Presyncope/syncope
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Dyspnea on exertion
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Chest discomfort
Symptoms are frequently intermittent with gradual progression in frequency and severity, although some patients may present with profound, persistent symptoms. Rarely, patients with SND may be asymptomatic and identified on routine electrocardiography (ECG) or ambulatory ECG monitoring.
Patients with symptomatic SND are usually older with frequent comorbid diseases; they often seek medical attention owing to symptoms of lightheadedness, presyncope, syncope and, in patients with alternating periods of bradycardia and tachycardia, palpitations and/or other symptoms associated with a rapid heart rate.
Patients with coexisting cardiac pathologies such as valvular or ischemic heart disease may notice increasing dyspnea on exertion or worsening chest discomfort related to a lower heart rate and the resulting reduction in cardiac output. Because symptoms may be variable in nature, nonspecific and, frequently, transient, it may be challenging at times to establish this symptom-rhythm relationship. Atrial arrhythmias appear to develop slowly over time, possibly the result of a progressive pathologic process that affects the sinoatrial (SA) node and the atrium. [29]
Prior to any testing beyond an ECG, a thorough clinical evaluation should be performed for potentially reversible causes, which include medication use (eg, beta blockers, calcium channel blockers, digoxin, antiarrhythmics), myocardial ischemia, systemic illness (eg, hypothyroidism), and autonomic imbalance.
Physical examination
The physical examination essentially demonstrates findings of the underlying condition(s). The universal feature, however, is bradycardia.
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This 12-lead electrocardiogram (ECG) is from an asymptomatic girl aged 10 years, which was brought to our attention because of the irregularity of the P-P intervals. This ECG shows sinus arrhythmia at a rate of 65-75 beats per minute. The P waves all originate from the sinus node (SN) because they have a positive axis (upright) in leads I, II, and aVF. The PR interval is 104ms, and the QRS is narrow at 86ms, with a normal axis of 64°. The corrected QT (QTc) interval measures 402ms. Therefore, this is a normal ECG.
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Below is an electrocardiogram (ECG) of a girl aged 2 years who was referred to the clinic by a pediatrician for evaluation of a heart murmur. This ECG shows atrial rhythm originating most likely from the lower left atrium (P waves are inverted in lead I and are positive in II and aVF, with a frontal axis of 124°). The PR interval measures 113 ms, and the QRS is narrow at 90 ms. Right ventricular (RV) conduction delay is shown and is best seen in the precordial leads V1 and V2. The QRS frontal axis shows right axis deviation (reference range for a child aged 2 years is 0-110°). The patient does not have RV hypertrophy by voltage criteria. The inverted T waves in V1 are a normal finding at this age. An echocardiogram showed a moderately sized atrial septal defect. Nonsinus atrial rhythm is not a synonym of sinus node dysfunction.
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This is a 12-lead electrocardiogram (ECG) from a boy aged 12 years with a history of syncope. This patient was healthy until 1 month earlier, when he started to experience episodes of lightheadedness. The ECG shows sinus arrhythmia (bradycardia) at a rate of 50-79 beats per minute, with a PR interval of 136 ms. Two junctional escape beats are present after a prolonged pause. The QRS is narrow at 85 ms, with a normal frontal axis of 70°. The corrected QT interval (QTc) is 411 ms. A later electrophysiologic study showed prolonged sinus node recovery time (SNRT) and sinoatrial conduction time (SACT). Because of the patient's symptoms and his sinus node (SN) dysfunction, he received an atrial pacemaker. If this 12-lead ECG had been recorded from an asymptomatic patient, the findings would be considered within normal limits and no further workup would be indicated. In this case, the lightheadedness and, ultimately, the syncope defined sick sinus syndrome, with the patient requiring pacemaker therapy.
