Pericardial effusion with decreased ventricular voltages

ECG 4A: This tracing shows a sinus rhythm; low-voltage QRS pattern (absence of QRS amplitude > 5 mm in limb leads); A cardiac ultrasound revealed a significant pericardial effusion (2.5 cm circumference) with probable perforation of the right ventricular lead; pericardial puncture and repositioning of the right ventricular lead;

ECG 4B: Tracing recorded after puncture; increase in QRS voltages (R wave exceeds 5 mm in  leads I and aVL);

Comments: Physiologically, the pericardial sac is filled with a serous liquid of small volume (between 15 and 50 ml). Various diseases can cause the occurrence of pericardial effusion (pathological increase in the volume of intrapericardial fluid) which can be serous, hematic, purulent or chylous. A sudden accumulation of fluid causes the intrapericardial pressure to increase rapidly and exponentially due to the low extensibility of the pericardium, which triggers the compression of the right cavities.  The absolute volume of intrapericardial fluid as well as the speed of its increase will dictate the extent of the clinical picture which can vary between a simple alteration of the general state (aspecific signs: fatigue, dyspnea, chest pain, etc) to a tamponade (pericardial effusion with diastolic collapse of the right heart chambers, systemic hypotension and shock). Cardiac ultrasound allows to highlight the effusion, estimate its volume and assess the hemodynamic repercussion by looking for signs of compression. A pericardial puncture (pericardiocentesis) allows to decompress the pericardial cavity (emergency treatment of the tamponade) and to collect liquid for diagnostic purposes (chemical, microbiological and histological analysis).

The rapid formation of a pericardial effusion leads to electrocardiographic changes, most often aspecific and directly related to the effusion, to a modification of the position of the cardiac cavities when the effusion is abundant and to an eventual constriction (tamponade).

• The most common observation is the presence of a reduction in the voltage of the P-waves, T-waves and QRS-complexes observed in a diffuse manner throughout all leads. This decrease in the voltage of QRS-complexes can also be observed in patients with hypothyroidism, emphysema, abundant pleural effusion, hemochromatosis, cardiac amyloidosis, with clinical presentation most often being fundamentally different. Low voltage, defined as the absence of limb leads with a QRS amplitude exceeding 5 mm and the absence of precordial leads with a QRS amplitude exceeding 10 mm, is proportional to the volume of the effusion and regresses after an evacuating puncture. The persistence of reduced voltages after puncture should evoke a recurrence or evolution toward a chronic pericardial constriction. Low voltage can also be observed in patients with pleural effusion, restrictive, infiltrative or ischemic heart disease with extensive sequela, emphysema, hypothyroidism or obesity.
• An electrical alternans can be observed with evidence of P-waves, T-waves and successive QRS-complexes of various amplitude or morphology.
• The presence of tachycardia is a sign of poor tolerance.
• Widespread disorders of atrial and ventricular repolarization can also be observed. A depression of the PQ interval has good diagnostic value for pericarditis. The abnormalities in ST-segment (slight depression) and T-wave (negative or flattened) patterns are most often discrete or absent.
• In the most severe cases, when the effusion leads to the occurrence of tamponade and a heart attack, it is frequent to observe an electromechanical dissociation, with persistence of a subnormal trace followed by a sudden sinus bradycardia and a subsequent agonal pattern.

Take-home message: The two main electrocardiographic signs observed during an abundant pericardial effusion are low voltage and electrical alternans.