Causes of an Absent Apex Beat

When a doctor examines the point at which the beating of the heart is most felt on the chest (referred to as the cardiac impulse), s/he can expect to find valuable clues to help in the diagnosis of diseases of the heart. Surprisingly, in some cases, this cardiac impulse is absent.

In this article:
What is the apex beat?
Causes of an absent apex beat
Understanding the apex beat
Classification of some common apex beat characters

What is the apex beat?

The Apex Beat (latin. ictus cordis), also called the Point of Maximum Impulse (PMI), is the furthermost point outwards (laterally) and downwards (inferiorly) from the sternum at which the cardiac pulsation can be felt by an examining hand. It is also known as the "apical impulse" or the "cardiac impulse".

Examination of the cardiac impulse can give valuable clues into the diagnosis of cardiac disease. In some cases, however, it is absent. An absent apical impulse may be due to physiological or pathological causes.

Causes of an absent apex beat

The mnemonic, DR MOPE, can be used as a prompt for the causes of an absent Apex Beat:
1). PHYSIOLOGICAL CAUSES

Dextrocardia. Though it will be absent at the 'usual' location on the left side, it will be present on the right side. NOTE: Some authorities do not accept this as a cause of 'absence' since it is present on the right side of the chest.
Apex behind a Rib. In this case it may not be palpable in an intercostal space. Just turning the patient to the left lateral position will reveal the apex beat, confirming this cause.

2). PATHOLOGICAL CAUSES

Moribund obesity and thick chest wall
Obstructive airway disease: Emphysema, Chronic bronchitis
Pericardial effusion, Constrictive Pericarditis, Pleural effusion (left sided)
Endomyocardial fibrosos

Understanding the apex beat

Like already described above, the apex beat is the outermost and lowermost point of maximal cardiac pulsation as measured from the sternum and felt by the examining hand.

This cardiac impulse come about as the result of the heart rotating, moving forward and striking against the chest wall during systole. It is not the apex of the heart but the point where the apex beat is felt.

IDENTIFICATION
The normal apex beat can be palpated in the precordium left 5th intercostal space, at the point of intersection with the left midclavicular line. In children the apex beat occurs in the fourth rib interspace medial to the nipple. The apex beat may also be found at abnormal locations; in many cases of dextrocardia, the apex beat may be felt on the right side.

INTERPRETATION
Lateral and/or inferior displacement of the apex beat usually indicates enlargement of the heart, called cardiomegaly. The apex beat may also be displaced by other conditions:

Pleural or pulmonary diseases
Deformities of the chest wall or the thoracic vertebra

Sometimes, the apex beat may not be palpable, either due to a thick chest wall, or conditions where the stroke volume is reduced; such as during ventricular tachycardia or shock.

Classification of some common apex beat characters

The character of the apex beat may provide vital diagnostic clues:

A forceful impulse indicates volume overload in the heart (as might occur in aortic regurgitation)
An uncoordinated (dyskinetic) apex beat involving a larger area than normal indicates ventricular dysfunction; such as an aneurysm following myocardial infarction

An algorithm for the classification of some common apex beat characters is shown in the image below.

Algorithm for classification of the apex beat characters - click to enlarge image.
(Credit: Shashikiranu via Wikimedia Commons)

References:
1). Longo DL, Kasper DL, Jameson JL, et al: Harrison's Principles of Internal Medicine, 18th ed.. Chap 227. Physical Examination of the Cardiovascular System. The McGraw-Hill Companies Inc.
2). Wikipedia, the Free Encyclopedia: Apex Beat. Accessed 10.07.12. Available here: https://en.wikipedia.org/wiki/Apex_beat