Sick sinus syndrome

Japanese: 洞不全症候群 - どうふぜんしょうこうぐん（英語表記）Sick sinus syndrome

What is the disease?

Sick sinus syndrome is mainly Sinus node ( Procedure ) ( Right atrium ( Ushinbo ) This is a disease in which the function of the vein (a crescent-shaped structure at the border between the wall of the vein and the superior vena cava) is reduced, causing the pulse to slow, resulting in dysfunction of organs such as the brain, heart, and kidneys.

Electrocardiographically, it is classified into three groups as follows (Figure 23A, B, F).

Group 1: Persistent with unknown cause Sinus bradycardia ( Dojomyaku ) (50 beats per minute or less)

Group 2: Sinus arrest or Cave ( Dobo ) block

Group 3: Bradycardia-tachycardia syndrome (see below)

In either case, it is a syndrome in which a decrease in the amount of blood pumped from the heart causes circulatory disorders in major organs. When the number of P waves reflecting atrial excitation that appear at regular intervals on an electrocardiogram is small, it is called sinus bradycardia, and when the P waves suddenly stop appearing, it is called sinus arrest (or sinoatrial block).

What is the cause?

This is caused by a decrease in the sinus node's ability to produce impulses or by impaired sinus node-to-atrium conduction. Ischemic ( Traveler ) Heart disease, Cardiomyopathy ( New Year's Eve ) , Myocarditis ( Shinkinen ) , rheumatic heart disease, Collagen disease ( Public health center ) It is thought that it is easy to be complicated by other conditions, but in more than 90% of cases, the cause cannot be identified. Functional causes include increased vagus nerve tone, hyperkalemia, and drug administration ( β ( beta ) These include blockers, digitalis, and antiarrhythmic drugs.

How symptoms manifest

Normally, the heart beats about 60 to 100 times per minute, but the pulse rate is greatly affected by the situation the person is in. In sick sinus syndrome, the heart rate does not increase accordingly even when exercising or having a fever. There are also types in which the pulse suddenly stops and the heart stops functioning for a while.

The brain, a major organ, is prone to ischemic symptoms, such as dizziness, lightheadedness, slurred speech, near-fainting, and fainting. Other symptoms include congestive heart failure, Angina ( Public Notice ) , whole body Fatigue ( Health test ) , oliguria may also occur.

Testing and diagnosis

On the electrocardiogram, the number of waves (P waves) generated by excitation of the atria decreases. If the atria are not excited, electrical impulses are not transmitted to the ventricles, so the number of waves (QRS waves) on the electrocardiogram that indicate ventricular excitation also decreases. If the number of P waves is extremely low, impulses are naturally generated from stimulation centers located other than the sinus node. The electrical activity of the heart at this time is called escape rhythm.

However, people who have been engaged in long-term intense training such as long-distance running may be completely asymptomatic even if their heart rate is below 40 beats per minute. If bradycardia is observed on the electrocardiogram and coincident symptoms such as cerebral ischemia are revealed, the diagnosis of sick sinus syndrome is confirmed.

Treatment methods

Drugs that increase the frequency of spontaneous sinus node excitation are used. Anticholinergic drugs (atropine sulfate), β ( beta ) These include oral medications such as stimulants (isoproterenol) and intravenous medications. If bradycardia does not respond well to medications or symptoms worsen when medication is discontinued, a pacemaker may be indicated (Column).

What to do if you notice an illness

First, if you notice symptoms of cerebral ischemia, lie down (or squat) to prevent hitting your head if you faint. If possible, count your pulse.

If symptoms persist, immediately visit a hospital and undergo tests such as an electrocardiogram. If symptoms recur, see a cardiologist.

Hirao Kenzo

Figure 23. Various electrocardiogram waveforms
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Figure 23. Various electrocardiogram waveforms

Source: Houken “Sixth Edition Family Medicine Encyclopedia” Information about the Sixth Edition Family Medicine Encyclopedia

Japanese:

どんな病気か

　洞不全症候群とは、主に洞結節(どうけっせつ)（右心房(うしんぼう)の壁と上大静脈の境にある三日月状のもの）のはたらきが低下することによって脈が遅くなり、そのために脳、心臓、腎臓などの臓器の機能不全が現れる病気です。

　心電図的には以下のように3つの群に分類されます（図23A、B、F）。

　1群：原因不明の持続性洞徐脈(どうじょみゃく)（50拍／分以下）

　2群：洞停止または洞房(どうぼう)ブロック

　3群：徐脈頻脈(ひんみゃく)症候群（後述）

　いずれにしろ、心臓から送り出される血液量の低下によって主要臓器の循環障害が起こる症候群です。心電図上で、心房興奮を反映するP波が規則正しい間隔で現れる数が少ないものを洞徐脈、P波が突然現れなくなる場合を洞停止（あるいは洞房ブロック）といいます。

原因は何か

　洞結節の刺激を生み出す能力の低下、あるいは洞結節→心房間伝導の障害が原因です。虚血性(きょけつせい)心疾患、心筋症(しんきんしょう)、心筋炎(しんきんえん)、リウマチ性心疾患、膠原病(こうげんびょう)などに合併しやすいと考えられていますが、90％以上は原因が特定できません。機能的なものでは、洞結節の刺激の発生数を低下させる迷走神経の緊張亢進、高カリウム血症、薬剤投与（β(ベータ)遮断薬、ジギタリス）、抗不整脈薬などによるものがあります。

症状の現れ方

　通常、心臓は1分間に60～100回ほど脈を打ちますが、脈拍数は本人のおかれた状況に大きく左右されます。洞不全症候群では運動、発熱時などにも相応の心臓拍動数の上昇がみられません。また、突然脈が止まってしばらく心臓が活動しなくなるタイプもあります。

　主要臓器の脳には虚血症状が出やすく、めまい、立ちくらみ、ろれつが回らない、失神しそうになる、失神などがあります。その他、うっ血性心不全、狭心症(きょうしんしょう)、全身の倦怠感(けんたいかん)、乏尿なども起こりえます。

検査と診断

　心電図上で、心房の興奮によって生ずる波（P波）の出現が少なくなります。心房が興奮しないと電気刺激が心室に伝わらないため、心室興奮を表す心電図上の波（QRS波）も減ります。P波の発生が極端に少ないと、洞結節以外の場所にある刺激中枢から自然に刺激が発生します。この時の心臓の電気的活動を補充調律といいます。

　ただし、長期に長距離走などの激しいトレーニングを積んできた人では、心拍数が40／分以下であってもまったく無症状のことがあります。心電図上で徐脈があり、その時に一致して脳の虚血症状などの存在が明らかになれば、洞不全症候群の診断は確定します。