Cardiac Cycle

Cardiac Cycle

Definition

It is the cardiac events that occur from the beginning of one heart beat to the beginning of the next coordinated by the conducting system of the heart.

Consists of alternating contraction and relaxation of the myocardium

Cardiac Events

Cardica events during one cycle

The cycle is divided into two major phases

Systole :- The period of ventricular contraction -

Diastole :- The period of ventricular relaxation

The cycle is futher subdivided into several discrete phases :-

The phases and the duration are as follows:-

Total ventricular systole 0.3 sec

Isovolumic contraction 0.05 sec (0.015sec for RV)

Maximal ejection 0.1 sec

Reduced ejection 0.15 sec

Total ventricular diastole 0.5 sec

Isovolumic relaxation 0.1 sec

Rapid filling phase 0.1 sec

Slow filling 0.2 sec

Atrial systole 0.1 sec

GRAND TOTAL (Syst+Diast) = 0.8 sec

1 Beat = 0.8 sec (800 msec)

Systole = 0.3 sec

Diastole = 0.5 sec

Heart Sounds

Due to closure and after vibrations of AV Valves.

S1 is normally split (~0.04 sec) because mitral valve closure precedes tricuspid closure. (Heard in only 40% of normal individuals)

S1 heart sound

low pitch and relatively long-lasting

S1 is a relatively prolonged, low frequency sound, best heard at apex

S2 is heard when the semilunar vlaves close.

A2 is heard prior to P2 as Aortic valve closes prior to pulmonary valve (A2 aortic valve sound P2 pulmonary valve sound)

Normal split: Two components heard during inspiration and is single sound during expiration.

Common causes of wide split S2

RBBB

Sev PAH

ASD

Idiopathic dilatation of pul artery

Sev right heart failure

Moderate to severe PS

Severe MR

Causes of reverse split S2

LBBB

RV pacing

RV ectopy

Severe AS

Acute MI

WPW type B

Severe TR

Aneurysm of ascending aorta

Severe systemic hypertension

Causes of S3

Physiological: Childrens & young adults <40 yrs (nearly 25%)

(Not heard in normal infants & adult >40 yrs.)

Pathological:

Ventricular failure

Hyperkinetic state (anemia, thyrotoxicosis, beri-beri)

MR, TR

AR, PR

Systemic AV fistula

S4 (atrial or presystolic gallop) - atrial emptying after forcible atrial contraction. (late diastolic)

Caused by vibration of ventricular wall during rapid atrium emptying into non compliant ventricle

Causes of S4

Physiological;

>60yrs (Recordable, not audible)

Pathological;

All causes of concentric LV/RV hypertrophy

Coronary artery disease

Acute regurgitant lesions

An easily audible S4 at any age is generally abnormal.

In contrast to S3, which may mean ventricular failure, the presence of S4 does not indicates heart failure. It only signify "hardworking ventricle".

Gallop rhythm

A gallop rhythm is a grouping of three heart sounds that together sound like hoofs of a galloping horse.

For more on heart sounds scroll down . . . .

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Atrial Systole

Heart Sounds

S4 (atrial or presystolic gallop) - atrial emptying after forcible atrial contraction.

appears at 0.04 s after the P wave (late diastolic)

lasts 0.04-0.10 s

Caused by vibration of ventricular wall during rapid atrium emptying into non compliant ventricle

Causes of S4

Physiological;

>60yrs (Recordable, not audible)

Pathological;

All causes of concentric LV/RV hypertrophy

Coronary artery disease

Acute regurgitant lesions

An easily audible S4 at any age is generally abnormal.

Clinical Facts about S4

In contrast to S3, which may mean ventricular failure, the presence of S4 does not indicates heart failure. It only signify "hardworking ventricle".

The presence of S4 correlate with a gradient of at least 50mmHg across LVOT in suspected LVOT obstruction.

(This correlation is not applicable in HCM)

In setting of MI, an audible S4 indicates that at least 10% of myocardium is at jeopardy.

In presence of Shock, S4 indicates that hypovolemia is unlikely as PCWP will be >18mmHg.

S4 can be heard when RVEDP >12mmHg on Rt or LVEDP > 15mmHg on Lt side. If EDP is very high i.e. >25 mmHg, S4 may be absent b/c of insufficient atrial functions.

S1 is d/t closure and after vibrations of AV Valves. (M1 occurs with a definite albeit 20 msec delay after the LV-LA pressure crossover.)

S1 is normally split (~0.04 sec) because mitral valve closure precedes tricuspid closure.

(Heard in only 40% of normal individuals)

S1 heart sound

low pitch and relatively long-lasting

Some Clinical facts about S1

S1 is a relatively prolonged, low frequency sound, best heard at apex.

Normally split of S1 (~40%)is heard only at tricuspid area.(As tricuspid component is heard only here.)

If S1 is equal to or higher in intensity than S2 at base, S1 is considered accentuated.

Variable intensity of S1 and jugular venous pulse are highly specific and sensitive in the diagnosis of ventriculoatrial dissociation during VT, and is helpful in distinguishing it from supraventricular tachycardia with aberration.

Heart Sounds : S2 is heard when the semilunar vlaves close.

A2 is heard prior to P2 as Aortic valve closes prior to pulmonary valve

S2 heart sound

Appears in the terminal period of the T wave

lasts 0.08 - 0.12s

Some clinical facts about S2

Normal split: Two components heard during inspiration and is single sound during expiration.

(A2-P2 ~20- 50 msec in inspiration)

Clinically split is defined as wide, if it is heard well in standing position, in expiration (normally not heard as the split is 15 msec, which can not be heard by human ears)

Single S2: absence of audible split in either phase of respiration.

Fixed split: two components fails to move with respiration.

Reverse split: Inaudible split during inspiration and audible split during expiration. (recognized by wider split in expiration)

Common causes of wide split S2

RBBB

Sev PAH

ASD

Idiopathic dilatation of pul artery

Sev right heart failure

Moderate to severe PS

Severe MR

Normal variant

Common causes of wide fixed split S2

ASD

All causes of wide split with associated severe right ventricular failure.

Common causes of single S2

Truncus arteriosus

Pulmonary atresia

Aortic atresia

TGA

AS, PS

Single loud P2 in extreme PAH

Causes of reverse split S2

LBBB

RV pacing

RV ectopy

Severe AS

Acute MI

WPW type B

Severe TR

Aneurysm of ascending aorta

Severe systemic hypertension

Clinical facts about S3

In presence of HF, S3 correlates well with ventricular end diastolic pressure and is usually >25mmHg on left side.

Right sided S3 correlate well with rapid y descend in neck veins.

Normal A2-S3 interval is between 120-160 msec.

Correlates of S3

Gallop rhythm

A gallop rhythm is a grouping of three heart sounds that together sound like hoofs of a galloping horse.

Protodiastolic gallop or ventricular gallop or S3 gallop

addition of an S3 to the physiological S1 and S2 creates a three-sound sequence, S1-S2-S3.

Presystolic gallop rhythm or atrial gallop

addition of an S4 to the physiological S1 and S2 creates a three-sound sequence, S4-S1-S2.

(during tachycardia S4-S1 can fuse, producing a summation gallop )