ECG: "Zero Foundation" to an orderly reading

Home > Health

ECG: "Zero Foundation" to an orderly reading

2022-01-28 12:06:16 38 ℃

ECG: "Zero Foundation" to an orderly reading

Electrocardiogram, blood gas analysis, chest reading is three basic skills of internal medicine doctors. ECG is an important auxiliary examination method in clinical work. Its operational technology and reading skills should be mastered by doctors of various subjects. However, due to the many complicated heart electrophysiological knowledge, it has always been a difficult problem in medical learning.

This paper strives to start from the most basic electrocardiogram, which is intended to explain the concept, familiar with the meaning of each lead, and then understand the normal electrocardiogram, the base abnormality change, the disease is unique. This allows the reader to get started from the "zero basis" to understand simple ECG. The last list summarizes the characteristics of the diseases and proposes an electrocardiogram reading order.

I. Each wavelength meanings (starting from P, in accordance with alphabetical order, QRS T u)

1.P wave: atrium

[TA wave: the atrium is polar, usually, the living room transmission block is visible]

2.PR segment (real PQ segment): atrium is complement, atrial conduction

3.QRS wave group: ventricular except

The first upward wave is R wave (not the highest wave is R wave), and the left side of the R wave is Q wave, and the right side is an S wave. Two upward wave rows appear R '. If there is no direction, it is qs wave

More than 0.5mV (vertical 5 small) uppercase, less than 0.5mV lowercase

4.ST paragraph: ventricular early times slow

[J point: the intersection of the QRS wave group end and the ST segment]

5.T wave: ventricular advanced quadrant

6.u wave: generating mechanism is unknown

7.PR Interval: The process of atrium except for the ventricular

8.QT interval: the process of the ventricular except to the ventricular complex

["Inter-interval" includes "wave" and "segments"]

Second.

Limit lead:

Right arm (R), left arm (L), leg (f) composition I, II, III, AVR, AVL, AVF

[AVF is in the middle of II, III, so the image is between II, III]

2. Chest lead:

The order of "red-yellow green brown purple", constitutes V1 ~ V6

V1: Right edge of the sternum fourth intercostal (flat nipple) (right ventricle)

V2: left edge 4th ribs (right ventricle)

Midpoints of V3: V2 and V4 (room separated, nearby ventricle)

V4: Left bone midline and the fifth ribs intercostal (room separation, near left and right ventricles)

V5: Left armpit front line and V4 level (left ventricle)

V6: left axillary midline and V4 level (left ventricle)

V7: left irrigation and V4 level (back wall)

V8: left shoulder wiring and V4 level (back wall)

V9: Left nicker and V4 level (back wall)

The right side of V3R ~ V6R: V3 ~ V6 (used for pediatric right heart lesions)

3. Normal ECG

(1) according to the band

1.P wave:

Direction: The direction of the vector direction, before, in combination, the leading direction map, the AVR down, I, II, AVF, V4 ~ 6, and the rest can be. V1 can have two-way P-waves, first right atrium except, then left atrium

Time: <0.12s (3 small grid)

Amplitude: <0.3mv (3 small grid)

2.QRS wave group:

Direction: I, II main wave, AVR main wave, other limb leaders can be. V1, V2 main wave down (R / S <1), V3, V4 R / S wave vibration equal, V5, V6 main wave, up (R / S> 1). The R wave of V1 to 6 gradually increases, and the S wave gradually decreases.

Time: 0.06 ~ 0.10s (1.5 ~ 2.5 small)

Amplitude: R wave V1 <1.0mv (2 large grid), AVR <0.5mv (1 big grid), otherwise the right ventricular fat is large. R wave V5 <2.5mV (5 big grid), AVF <2.0mV (4 big grid), otherwise left ventricular fat. QRS wave group forward wave and negative direction wave vague absolute value is added to the limb lead in should be <0.5mV, and the chest is not necessarily <0.8mV, otherwise low voltage

3.ST paragraph: Lifting (equipotent line to ST upper edge), downward (equipotent line to ST) no more than 0.1mv (1 small grid), V1 ~ V3 is lifted slightly

[Some normal people can raise the J point, follow the tower T wave, called early compound poles, such as V2 ~ 4 above]

4.T wave:

Direction: I, II, V4 ~ 6, AVR down, the rest can be. If V1 is up, the remaining chest leads should be up

Amplitude: Up to 1.5mV at the chest promotion (3 big grid)

5.u wave:

Small amplitude wave (<1 small grid) in 0.04S (1 small grid) after t wave, the direction is consistent with T wave, V2, V3 is obvious

6.PR Interval:

Time 0.12S (3 small) ~ 0.20S (5 small)

7.QT interval:

Time 0.32S (8 small grid) ~ 0.44S (11 small grid), corrected QTC = QT / √RR

8.PP or RR interval:

0.6S (3 large grid) ~ 1.0s (5 big grid)

(2) Press the lead

I: Both is forward

II: Both are forward, each wave amplitude is greater than I, AVF

AVR: all reverse

V1: QRS main wave down, R wave V1 ~ V6 increments; there may be two-way P wave; T wave is forward, V2 ~ V6 T wave should be forward

V2: QRS main wave down, T wave may be high

V3: R wave is substantially equal to the S wave amplitude, T wave may be high, U wave significantly V4: R wave and S wave vagration substantially equal, P-wave, T wave forward

V5:

V6:

Fourth. Basic changes

(Time extension is mainly conducted block, amplitude increase is mainly equipment-quality fat)

1.P wave:

Direction: Retrograde P Wave: AVR up, II, III, AVF up, indicating ectopic pacing

Time:> 0.12s (3 small grid), left ventricle fertilizer, in-room conduction block

Amplitude:> 0.3mv (3 small), right heart room fertilizer

2.QRS wave group:

Time:> 0.12s (3 small grid), indoor conduction blocking (left and right branch convection block, indoor difference transfer, ventricular pacing)

amplitude:

R wave V1> 1.0mV (2 big grid), AVR> 0.5mV (1 big grid), right ventricular fat

R wave V5> 2.5mV (5 big grid), AVF> 2.0mV (4 big grid), left ventricle fat

QRS wave group forward wave and negative wave vane absolute value are added to the limb leader <0.5mV, the chest lead is <0.8mV, which is low voltage

Pathological Q wave: Time> 0.04S (1 small grid), amplitude> 1/4 R wave, indicate myocardial infarction and other

Electrical axis: Test Method, I, III lead, pointer pair pair (III on III) Electrical axis right numeral, back pair (III under III) Electrical axle

The electrical axis is biased to include the following meanings:

Duality hypertrophy: left ventricular hypertrophone left numeral, right chamber fat large electric axis right

Paramond: Left front branch block, left rear branch blocking electrical axis

Ventricular muscle necrosis: electrical axis is biased toward normal myocardial (reverse direction of lesionic myocardium)

Clock-to-turn: V3, V4 R / S wave amplitude equal, R / S of V1 ~ V6 gradually increase

When V1, V2 R / S wave amplitude is equal, for the reverse direction, the left ventricular hypertrophy (all graphic of the left ventricular)

When V5, V6 R / S wave amplitude is equal, it is a clock direction, and the right room is large (all graphs of the right chamber)

3.ST paragraph:

The ST segment is low, which is myocardial ischemia, myocardial injury, and hypotension, foreign yellow, pre-excitation syndrome.

The ST segment is raised and the bow is up, for myocardial infarction, variant angina, and room wall tumor.

The ST segment is raised and the bow is down, for acute heartbuitment

4.T wave:

Direction: T wave press: I, II, V4 ~ 6 T wave down, <0.5mv (1 big grid), 心 外 下 心心 心心

T wave depression: 0.5mV ~ 1.0mv (2 big grid)

T wave huge inverted:> 1.0mV (2 large grid), hypertrophic cardiomyopathy, non-ST segment elevation myocardial infarction, etc.

Amplitude: T wave low: <1/10 R wave, myocardial ischemia

T-wave high: high blood potassium, intimae myocardial ischemia, acute myocardial infarction

5.u wave:

Appeared in non-V2, V3 lead, low blood potassium

6.PR Interval:

PR Interpretation:> 0.20S (1 Big Gger), One Room Conduction Block

PR Inter-intermediation: <0.12S (3 small) pre-excitation syndrome, room junior rhythm

7.QT interval:

QT interval: male> 0.45s (11 grid), female> 0.46s (11 plus half), long QT syndrome, myocardial ischemia damage, ventricular hypertrophy, indoor conduction block, hypothermia, etc.

QT interference shorten: <0.39s (10 grid), short QT syndrome, high blood calcium, foreign yellow effect, etc.

V. ECG diagnosis and clinical significance

1. The atrium fertilizer:

Right heart fertilizer: Pionex Fa Luo Sanxia, ​​room separation, pulmonary heart disease

Left heart fertilizer: mitral stenosis, etc.

Double heart fertilizer: congenital heart disease, expanded myocardial disease

2. Room Features:

Right ventricular hypertrophy: pulmonary heart disease, mitral stenosis, pulmonary stenosis, arterial catheter is not closed, indoor separation

Left ventricle hypertrophy: high blood pressure, coronary heart disease, mitral valve close, the aortic valve disease, myocardial disease

Doublex ventricular fertilizer: mitral stenosis combined with unity, mitral valve combined with aortic valve disease, expandable myocardial disease, indoor separation

3. Myocardial ischemia:

Heart disease: coronary heart disease, coronary interlayer, coronaryitis, myocardial bridge, etc.

Non-heart disease: anemia, hypoxia, hyperthyroidism, pheochromocytoma

[Heartic mildinal muscle is less ischemia, left ventricular is easily ischemia, ischemia, left ventricular, and left ventricular.

4. Myocardial infarction:

ST segment elevated myocardial infarction: the coronary is completely blocked, the ST section is high

Non-ST-segment elevated myocardial infarction: coronary partial blockage, ST segment does not raise, troponin increase

Unstable angina: coronary partial blockage, ST segment does not raise, troponin does not rise

[Reverse damage is irreversible for 20 minutes after coronary thrombosis, 1/3 of the left ventricle wall; 3 ~ 6 hours of transmissive infarction]

5. Electrolyte disorders: low potaemia, high potammia

6. Drug effect: foreign yellow effect, foreign yellow poisoning

7. Pacemaker

8. Arrhythmia:

Sinus arrhythmia: sinus speed, sinus, sinus, sinus syndrome

Pre-contraction (premature beat): premature, early room, junction early

Room speed: Room Folding Tummy Tummy AVNRT, Room Refractive Tummy Tummy AVRT, Dougroup Folding Tummy Tummy, Housing Strong, Expressway

Room speed

Pool and trend: room, atrial fibrillation, chamber, vendor terror

Room Conduction Block: One degree, Second (Moh Type / Wen, Moi Type), three-degree indoor conduction block: right bundle support, left bundle support, multi-branch

Precision syndrome

Yi Bug, Yugang

6. Concise disease performance (only select the most specific performance)

1. The atrium fertilizer:

Right heart fertilizer:

P wave is higher than 0.25mV (2 sizes), see II, called "pulmonary P wave" (time prolong is covered by left atrium)

V1 can occur in two-way P wave

Left heart fertilizer: P wave time> 0.12s (3 small), see II, called "Mitral Paves"

Double heart fertilizer: Time amplitude> 3 small, V1 two-way P wave

2. Room Features:

Right ventricular hypertrophy: the right right navigation, the clock direction (V5, V6 R / S wave amplitude is equal)

Amplitude R Wave V1> 1.0MV (2 Big), AVR> 0.5mV (1 Big)

Left ventricle hypertrophy: the left navigation of the electric axis, the inverse direction (V1, V2 R / S wave amplitude is equal)

Amplitude R wave V5> 2.5mV (5 big grid), AVF> 2.0mV (4 big grid)

Different venue fertilizer: R wave V1, V5 amplitude increase

3. Myocardial ischemia:

Stable angina (intramiathyl myocardial ischemia): temporary ST segment pressure

Varizable angina (translucent myocardial ischemia, caused by coronary spasm): Temporary ST segment is high, then T-wave

4. Myocardial infarction:

Basic changes: ischemic damage to death

Ischemia: Cardiopathy, on the opposite side high T wave

Rebartenxer (transistor), this side T wave

QT interval extension

Damage: this ST section is high

Necomine: this pathological Q wave

Installivity change: progress / super acute phase (<6h), acute period (6h ~ 1 week)

Healing / Recent / subaracressive period (1 week to January), the old period (> Jan)

Progress period: T-wave high (ischemic) ST segment angle elevation (damage) and connected to T wave

Acute phase: pathological Q wave (necrosis), ST segment elevation (damaged), T wave press (transistor ischemia)

Healing period: pathological Q wave constant, ST segment elevation gradually falls, T wave is gradually

Duration: pathological Q wave does not change, the ST segment and T wave are normal, or T wave is low or continuous inverted

position:

Unstable angina: ST segment pressure

Non-ST-segment elevated myocardial infarction: ST segment pressure is low, more than 12 hours; can be accompanied by T wave; no pathological Q wave

5. Electrolyte disorders:

Hypokalemia:

U wave increase, or Tu fusion, double peak, see V2, V3 lead

The ST segment is low, T wave low or inverted

QT-U interpretation

Severe hypotellous potassium can be accompanied by multi-source rooms early, tip torsional ventricular speed

High blood potassium:

Potassium> 5.5mmol / L, QT interval is shortened, T-wave high

Potassium> 6.5mmol / L, QRS wave group is widened, PR Interpretation (> 1 large grid), R / S is small, ST segment pressure is low

Potassium> 7.0mmol / L, P wave increase, amplitude reduction

Potassium> 8.5mmol / L, P-wave disappears

Potassium> 10.0mmol / L, QRS wave group slow, larger, even integrated with T wave into sine wave

Hyperopa potassium can cause sinus, stop, venomibus

6. Drug effect:

Yan Gehuang effect: QT inter-time shortening, ST-T fish norm change

地 黄 中: Secondary Law / Triple Logn Lear, Early, Velocity, Vermark, Room Conduction Block, etc.

7. Pacemaker: A strike signal, a short (<1 small), linear signal vertical with baseline (staple)

7. The arrhythmia

Sinus arrhythmia

Sinus rhythm: excitement from the sinus knot: AVR down, I, II, AVF, V4 ~ 6 upward

Sinus speed: sinus rhythm, PP / RR interval <0.6s (3 big grid, 100 times), rare over 180 times / min

Dougo: sinus heart rhythm, PP / RR interval> 1.0S (5 big grid, 60 times), rare less than 40 times / min

Sinus arrhythmia: sinus rhythm, adjacent PP / RR interval Differences> 0.12s (3 small grid)

Sinus stop: no P wave, long PP interval and normal sinus PP interval non-integer multiple relationship;

Sneak syndrome: sinus disease has changed its functional reduction

Swicked doubts, PP / RR interval> 1.2s (6 big grid)

Sinus stop

Sinus blockage

Slow syndrome: sinus slow and chamber speed alternate

Double nodules: tired of the border area of ​​the room, sinus blocking + room block

2. Introduction

Housing premature beat:

P 'waves appear in advance, PR Interval> 0.12s (3 small) (the border of the room is still in no period)

QRS wave group forms normal

Incomplete repayment interval: two sinus P wave spacings before and after premature beats

[If the room early P 'wave is different, the interval is not equal, the excitement comes from different places, saying that multi-source housing is early, often a atrial fibrillation

Room premature beat:

QRS wave appears in advance,> 0.12s (3 small) (indoor conduction is slow)

The T wave direction is opposite to the main wave direction (a quarterly pump is starting)

Completely payment interval: two sinus P wave spacings before and after premature beat = normal twice PP interval (ventricular pacing does not affect sinus knot) [If the QRS wave group is different, the interval is not equal, then excited From different, it is called multi-source room early, easy to initiate ventricular velocity, ventricular fibrillation]

Broadlocking premature beat: happened in the room knot, His bunch

There is a QRS wave group in advance, the form is normal

Retrograde P 'waves before or after the QRS wave group, or overlap with QRS wave groups

Most of the complete compensation

3. Alternative tachycardial speed:

PP / RR Inter-interval 0.24S (6 small, 250 times) ~ 0.4S (2 large grid, 150 times), sudden ruling, absolute rules

QRS wave group is normal

The ST segment pressure can occur, T-wave is inserted (due to a relative ischemia)

4. Various tachycardia:

A series of rooms early (3 consecutive times), RR inter-room period 0.24S (6 small grid, 250 times) ~ 0.6s (3 big grid), law Qi or slightly uniform

QRS wave group is widely malformed,> 0.12s (3 small grid), T wave directions opposite to the main wave

Room separation: P-wave and QRS wave groups have no fixed relationship (sinus is slow in ventricular muscles, and can only control the atrial)

The ventricular seized: Normal QRS wave group appeared early, and with P wave (sinus excitement can avoid the ventricles of the ventricles, causing normal QRS wave group)

Room fusion wave: QRS wave group appeared early, with P-wave, morphology is in normal and ventricular QRS wave group (when the ventricular ectopic excitement is simultaneously excited)

[Tip Duty Torsional Variety: QT interval, QRS wave group continues to reverse its main wave direction (one type of ventricular speed)]

5. Pool and trend

Atrial founcing:

Pool wave (F wave): continuous large sawtooth, uniform power supply line, amplitude interval, II, III, AVF obvious

Frequency: 0.17S (4 small, 350 times) ~ 0.25s (6 small, 240 times)

Based on fixed room (2: 1 or 4: 1), ventricular rate rules

P-wave disappears, QRS wave group is normal

Heart fibrillation:

Biblibo (F wave): low amplitude baseline tremor, amplitude interval constantly changing

Frequency: 0.10s (2 half, 600 times) ~ 0.17s (4 small grid, 350 times)

Value rate is absolutely irregular

P-wave disappears, QRS wave group is normal

Vember Pusher:

The large amplitude wave of continuous rules, can not distinguish QRS wave group, ST segment and T wave

Frequency: 0.24S (6 small grid) ~ 0.30s (1 half large)

Vessel shaking: different shapes, size, low wavelet, extremely irregular low wave, amplitude is getting lower

6. Room Conduction Block:

One degree of block: PR Interval> 0.20S (1 big grid); QRS wave group is normal and accompanied by each P wave

Seconditude type I:

P wave laws have occurred, and the PR is gradually extended.

Until 1 P-wave leaks QRS wave group, the PR is shortened, and then gradually extended

Secondary type II:

The PR is constant, it can be normal or extended

A QRS wave group can be released after several P waves, forming 3: 2, 4: 3, 5: 4, etc.

[Type I blocking part in the room knot, Hipster, II blocking part in Pu Kechan]

Tri-level block:

Separation of complete housing room: P-wave and QRS wave groups are not related to each other

Atrial rate> Value rate, PP interval

QRS wave group is Yizhu heart rhythm, divided into boundaries (more stable), room sex (unstable, <40 times / min)

7. Indoor blocking:

[The normal state is removed from the left, then the left, then overall to the left (the left room is larger than the right room)]

[Depending on whether the qrs wave group is> 0.12s, it is divided into completeness and incomplete beam blocking]

Complete right beam block block:

QRS wave> 0.12s (3 small grid), normal, late wide

The QRS wave group of V1 is RSR 'or M type

[Erclock in the first room to remove the right, then remove the left ventricle to the left, and finally the heart and the right ventricle is slow to right]

Complete leaving hysteresis:

QRS wave> 0.12s (3 small), starting to change

V1 lead QRS wave group is RS or QS type

V5 lead QRS wave group of R wave sticks or poses

[The interval is extremely changed to the left, while the ventricular muscle is slowly removed from left to the left (right ventricle mask by the left ventricle)]

8. Precision syndrome:

Pre-shock (Δ wave): bypass bypassing the rapid excitement of the room, integration with QRS wave groups

PR Interval <0.12s (3 small) (the ventricular is excited in advance, ie pre-excite)

QRS wave group> 0.12s (3 small grid) (incorporated with Δ wave)

ST-T secondary changes, such as T-wave

Type A: left room - left ventricular pre-excision, QRS wave group main wave in the right chest lead V1, left chest lead V5

Type B: Right Rate - Right Room Precision, QRS Wave Square Wave in the right chest lead V1 down, left chest lead V5

9. Yi Bug, Yi Zhutong:

[Three consecutive three and above the low-level parent point control, the heart of Yizhu, less than 3 as Yi Zhu, is the compensation of the high-level starting point]

[Similar to the premature beat, but Yizhao appeared, early premature beats appeared in advance]

Housing life, Yugang rhythm:

P'R interval> 0.12s (3 small grid), each lead P 'wave direction and pacing position related frequency: 1.0s (5 big grid, 60 times) ~ 1.2s (6 big grid, 50 times)

QRS wave group is normal

The junction of Yi Zhu, Yizhu arrhythm:

P'R interval <0.12s (3 small) or RP 'interval <0.20S (1 big grid), P' wave may also hide in QRS wave group

Frequency: 1.5s (7 darner, 40 times) ~ 3.0s (15 big grid, 20 times), basic law

QRS wave group is normal

Room Yi Bug, Yi Zhutong:

Wide deformity QRS wave group, 0.12S (3 small) ~ 0.16s (4 small) (indoor conduction is slow)

Frequency: 1.0s (5 big grid, 60 times) ~ 1.5s (7 darner half, 40 times), the law appears

The T wave direction is opposite to the main wave direction (a quarterly pump is starting)

[If the frequency is> 40 times / min, "said accelerated room sex independent rhythm]

Eight. Summary of disease performance

Nine. ECG reading order

1. Electrical axis (I, III) and clock direction (V1V2, V3V4, V5V6)

Electrical axle left: look at R wave amplitude high (V5, AVF), counter-to-turn left ventricular hypertrophy

Electrical axis right: Look at the R wave amplitude (V1, AVR), the clock direction of the right chamber

2.P wave (II)

Amplitude high and right heart

Time long left heart fertilizer

Avantimetric high + time long breadth

3. Heart rate (PP interval, RR interval)

Fast: Dou Express, speed, ventricular speed, room fuse, room fuse

Slow: Dou, sinus, Yugang

Not Qi: Sinus arrhythmia is not good, premature beat

Sinus speed: sinus heart rate, 100 ~ 150 times / min, PP inter-line period 2 big, 3 big grid

Room speed: absolute rules, 150 ~ 250 times / min, RR interval 6 small ~ 2 big grid

House: P-wave 2: 1 or 4: 1, 240 ~ 350 times / min, PP inter-line period 4 small ~ 6 small grid

Atrial fibrillation: the ventricular rate is not in, 350 ~ 600 times / min, PP inter-time 2 small ~ 4 small grid

Velocity: QRS wave group wide malformation

Room, versal: It is easy to distinguish

Dougo: sinus heart rhythm, 40 ~ 60 times / min, PP inter-line period 5 large ~ 7 big half

Sneak syndrome: Is there a slow syndrome, a dual-node?

Housing life: PR Interval> 0.12s (3 small grid), 50 ~ 60 times / min, PP inter-line period 5 big grid ~ 6 big grid, QRS wave group is normal

Junctional Yi Zhu: PR Interval <0.12s (3 small grid), 20 ~ 40 times / min, RR interval 7 large half ~ 15 big grid, QRS wave group is normal

Room Yugo: QRS wave group wide malformation

Sinus arrhythmia: adjacent PP / RR interval Differences> 0.12S (3 small grid)

Early: PR Interval> 0.12S (3 small grid), incomplete compensation intermittent

Breakfall: PR Interval <0.12s (3 small grid), complete compensation

Early morning: QRS wave group wide malformation

4.PR interval

PR Interpretation: Room Conduction Block

PR Inter-time shortening: pre-excitation syndrome

One room blocking: P wave can be issued

Secondary type I block: PR Interpretation gradually extended gradually

Secondary II block: PR Inter-interval constant leakage constant

Three-degree room blocking: P wave can't be separated, the room separation

Preclass a type: normal heart rate, QRS wave group is widely malformed, on the main wave V1, V5

Precision B: Normal heart rate, QRS wave group is widely malformed, main wave V1, V5

5.QRS wave group

Wide deformity: ventricular (room breakfast, ventricular speed, chamber, ventricular Yutao), heart infarction, high blood potassium, pre-excitation syndrome

Pathological Q wave: ST segment elevated myocardial infarction Next positioning diagnosis

Wave group form (V1, V5): Brand block

low voltage

[High blood potassium: poor specificity]

Left branch block: V1 QS type, V5 R waffles or bustle, long time (> 3 small grid)

Right beam block: V1 RSR 'or M-type, long time (> 3 small grid)

6.ST segment and T wave

Only ST sections low: stable angina, unstable angina, non-ST segment elevation myocardial infarction

[Not easy to identify, need dynamic observation and other checks]

ST segment elevation: variability angina, ST segment elevated myocardial infarction

7. Others

U wave (V2, V3): low blood potassium (QT interval, ST segment pressure)

Fish hook: Yangdu Yellow effect (shortening QT interference)

Nail sample: pacemaker